New Battery Testing Guide en LR

8/2/2019 New Battery Testing Guide en LR

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Batterytesting guide

Wh bckup bis ndd B ps Filu mods Minnnc philosophis Pcicl b sing Fqunl skd qusions Mgg poducs ovviw


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Battery teStING GUIDe 3

ContentsWhy backup batteries are needed ................ 4

Wh s b ssms .......................................4Wh bis il ................................................... 4

Battery types .................................................. 5

Ld-cid ovviw ................................................5

Nickl-Cdmium Ovviw ..................................... 5

B consucion nd nomnclu ..................... 6

Conguions ....................................................... 6

Singl pos bis .................................................... 6

Mulipl pos bis ................................................ 6

Failure modes ................................................. 7Ld-cid (foodd) ilu mods ..........................7

Ld-cid (VrLa) ilu mods .............................. 7

Nickl-Cdmium ilu mods ..............................8

Maintenance philosophies ............................ 9

How o minin h b ..................................... 9

Sndds nd common pcics ........................... 9

Ieee 450...................................................................... 9

Inspcions .............................................................. 9

Cpci s (dischg s) should b don ........... 9

Ieee 1188.................................................................. 10

Inspcions ............................................................ 10

Cpci s (cpci s) should b don ........... 10

B plcmn cii ................................... 10

Ieee 1106.................................................................. 10

Inspcions ............................................................ 10

Cpci s (dischg s) should b don ......... 10

Summ bs w o s nd vlu oub ................................................................. 10

ts invls ............................................................. 10

evluion ................................................................. 10

Practical battery testing .............................. 11

Cpci s ........................................................... 11

B sing mix Ieee commnddpcics ..............................................................11

Pocdu o cpci s o vnd ld cidb ................................................................. 12

Impdnc s ....................................................... 13

Impdnc ho ................................................13

Incll conncion sisnc ................................... 14

tsing nd lcicl phs ........................................ 15Volg ..................................................................... 15

Spcic gvi ......................................................... 15

Flo cun ............................................................. 16

rippl cun ........................................................... 16

tmpu .............................................................. 16

D nlsis ........................................................... 17

Locing gound uls on DC ssms wihouscionlizing .......................................................... 18

Ovviw .............................................................18

Cun s mhods ........................................... 18

a b s mhod ...........................................18

Frequently asked questions ........................ 19B chnolog summ .................................. 19

Megger products overview ......................... 20

Impdnc s quipmn ...................................... 20

BIte 3 ................................................................20

BIte 2 nd BIte2P ............................................. 21Poaciv b dbs mngmn sow ...... 21

BIte ccssois ....................................................... 21

Cpci sing ...................................................... 23

tOrKeL 820/840/860 ..........................................23

tOrKeL ccssois ................................................... 23

Gound ul cing quipmn .............................. 24

B Gound Ful tc (BGFt).......................24

B Gound-ul Loco (BGL) ......................24

Digil Low rsisnc Ohmms (DLrO) ndMicohmms (MOM) .......................................... 26

DLrO 247000 sis ........................................... 26

DLrO10 nd DLrO10X ........................................26

MJLNer 200 nd MJLNer 600 ........................27

MOM200a nd MOM600a ................................. 27

MOM690 ............................................................27

Mulims ............................................................ 28MMC850 Muli-conduco aC DigilClmpm ........................................................28

Mulims .........................................................28

Insulion rsisnc ts equipmn ....................... 29

MIt400 sis insulion sisnc ss ............ 29


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4 Battery teStING GUIDe

Why backupbatteries are

neededBatteries are used to ensure that critical electrical equipmentis always on. There are so many places where batteries areused it is nearly impossible to list them all. Some of theapplications for batteries include:

elcic gning sions nd subsions o pocionnd conol o swichs nd ls

tlphon ssms o suppo phon svic, spcillmgnc svics

Indusil pplicions o pocion nd conol

Bck up o compus, spcill nncil dnd inomion

Lss ciicl businss inomion ssms

Without battery back-up hospitals would have to close theirdoors until power is restored. But even so, there are patientson life support systems that require absolute 100% electricpower. For those patients, as it was once said, failure is notan option.

Just look around to see how much electricity we use andthen to see how important batteries have become in our ev-eryday lives. The many blackouts of 2003 around the worldshow how critical electrical systems have become to sustainour basic needs. Batteries are used extensively and withoutthem many of the services that we take for granted wouldfail and cause innumerable problems.

Why test battery systemsThere are three main reasons to test battery systems:

to insu h suppod quipmn is dqul bckd-up

to pvn unxpcd ilus b cking h bshlh

to own/pdic dh

And, there are three basic questions that battery users ask:

Wh h cpci nd h condiion o h bnow?

Whn will i nd o b plcd?

Wh cn b don o impov / no duc is li?

Batteries are complex chemical mechanisms. They havenumerous components from grids, active material, posts,jar and cover, etc. any one of which can fail. As with allmanufacturing processes, no matter how well they are made,there is still some amount of black art to batteries (and allchemical processes).

A battery is two dissimilar metallic materials in an elec-trolyte. In fact, you can put a penny and a nickel in halfof a grapefruit and you now have a battery. Obviously, anindustrial battery is more sophisticated than a grapefruitbattery. Nonetheless, a battery, to work the way it is sup-

posed to work must be maintained properly. A good batterymaintenance program may prevent, or at least, reduce thecosts and damage to critical equipment due to an AC mainsoutage.

Even thought there are many applications for batteries,they are installed for only two reasons:

to poc nd suppo ciicl quipmn duingn aC oug

to poc vnu sms du o h loss o svic

The following discussion about failure modes focuses onthe mechanisms and types of failure and how it is possibleto nd weak cells. Below is a section containing a moredetailed discussion about testing methods and their prosand cons.

Why batteries ailIn order for us to understand why batteries fail, unfortu-nately a little bit of chemistry is needed. There are two mainbattery chemistries used today lead-acid and nickel-cad-mium. Other chemistries are coming, like lithium, which isprevalent in portable battery systems, but not stationary, yet.

Volta invented the primary (non-rechargeable) battery in

1800. Plant invented the lead-acid battery in 1859 andin 1881 Faure rst pasted lead-acid plates. With rene-ments over the decades, it has become a critically importantback-up power source. The renements include improvedalloys, grid designs, jar and cover materials and improvedjar-to-cover and post seals. Arguably, the most revolutionarydevelopment was the valve-regulated development. Manysimilar improvements in nickel-cadmium chemistry havebeen developed over the years.


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Battery typesThere are several main types of battery technologies withsubtypes:

Ld-cid

Floodd (w): ld-clcium, ld-nimon

Vlv rguld Ld-cid, VrLa (sld): ld-clcium,ld-nimon-slnium

absobd Glss M (aGM)

Gl

Fl pl

tubul pl

Nickl-cdmium

Floodd

Sld

Pock pl

Fl pl

Lead-acid overviewThe basic lead-acid chemical reaction in a sulphuric acidelectrolyte, where the sulphate of the acid is part of thereaction, is:

PbO2

+ Pb + 2H2SO4 2PbSO

4+ 2H

2+ 12 O

2

The acid is depleted upon discharge and regenerated uponrecharge. Hydrogen and oxygen form during discharge andoat charging (because oat charging is counteracting self-discharge). In ooded batteries, they escape and water mustbe periodically added. In valve-regulated, lead-acid (sealed)batteries, the hydrogen and oxygen gases recombine to formwater. Additionally, in VRLA batteries, the acid is immo-bilized by an absorbed glass matte (AGM) or in a gel. Thematte is much like the bre-glass insulation used in houses.

It traps the hydrogen and oxygen formed during dischargeand allows them to migrate so that they react back to formwater. This is why VRLA never need water added compared

to ooded (wet, vented) lead-acid batteries.A battery has alternating positive and negative plates separated bymicro-porous rubber in ooded lead-acid, absorbed glass mattein VRLA, gelled acid in VRLA gel batteries or plastic sheeting inNiCd. All of the like-polarity plates are welded together and to theappropriate post. In the case of VRLA cells, some compression ofthe plate-matte-plate sandwich is exerted to maintain good contactbetween them. There is also a self-resealing, pressure relief valve

(PRV) to vent gases when over-pressurization occurs.

Nickel-Cadmium OverviewNickel-Cadmium chemistry is similar in some respectsto lead-acid in that there are two dissimilar metals in anelectrolyte. The basic reaction in a potassium hydroxide

(alkaline) electrolyte is:2 NiOOH + Cd +2 H

2O Ni(OH)

2+ Cd(OH)

2

However, in NiCd batteries the potassium hydroxide (KOH) doesnot enter the reaction like sulphuric acid does in lead-acid batteries.The construction is similar to lead-acid in that there are alternat-ing positive and negative plates submerged in an electrolyte. Rarely

seen, but available, are sealed NiCd batteries.


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Figure 1 Battery construction diagram

Battery construction andnomenclatureNow that we know everything there is to know about battery

chemistry, except for Tafel curves, ion diffusion, Randlesequivalent cells, etc., lets move on to battery construction. Abattery must have several components to work properly: a jarto hold everything and a cover, electrolyte (sulphuric acid orpotassium hydroxide solution), negative and positive plates,top connections welding all like-polarity plates together andthen posts that are also connected to the top connections ofthe like-polarity plates.

All batteries have one more negative plate than positive plate.That is because the positive plate is the working plate and ifthere isnt a negative plate on the outside of the last positiveplate, the whole outer side of last positive plate will not have

anything with which to react and create electricity. Hence,there is always an odd number of plates in a battery, e.g., a100A33 battery is comprised of 33 plates with 16 positiveplates and 17 negative plates. In this example, each positiveplate is rated at 100 Ah. Multiply 16 by 100 and the capacityat the 8-hour rate is found, namely, 1600 Ah. Europe uses alittle different calculation than the US standards.

In batteries that have higher capacities, there are frequentlyfour or six posts. This is to avoid overheating of the cur-rent-carrying components of the battery during high currentdraws or lengthy discharges. A lead-acid battery is a series ofplates connected to top lead connected to posts. If the top

lead, posts and intercell connectors are not sufciently largeenough to safely carry the electrons, then overheating may oc-

cur (i2R heating) and damage the battery or in the worst cases,damage installed electronics due to smoke or re.

To prevent plates from touching each other and shortingthe battery, there is a separator between each of the plates.

Figure 1 is a diagram of a four-post battery from the toplooking through the cover. It does not show the separators.

CongurationsBatteries come in various congurations themselves. Add tothat the many ways that they can be arranged, the numberof possible congurations is endless. Of course, voltageplays the biggest part in a battery conguration. Batterieshave multiple posts for higher current draws. The more cur-rent needed from a battery, the bigger the connections mustbe. That includes posts, intercell connectors and buss barsand cables.

Single post batteriesSmaller battery systems are usually the simplest batterysystems and are the easiest to maintain. They usually havesingle post batteries connected with solid intercell connec-tors. Frequently, they are quite accessible but because theyare small and can be installed in a cubby hole occasionally,they may be quite inaccessible for testing and maintenance.

Multiple post batteriesBatteries with multiple posts per polarity start to becomeinteresting quickly. They are usually larger and frequently aremore critical.


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Failure modesLead-acid (fooded) ailure

modes Posiiv gid coosion Sdimn (shdding) build-up

top ld coosion

Pl sulphion

Hd shos (ps lumps)

Each battery type has many failure modes, some of whichare more prevalent than others. In ooded lead-acid batter-ies, the predominant failure modes are listed above. Someof them manifest themselves with use such as sediment

build-up due to excessive cycling. Others occur naturallysuch as positive grid growth (oxidation). It is just a matterof time before the battery fails. Maintenance and environ-mental conditions can increase or decrease the risks ofpremature battery failure.

Positive grid corrosion is the expected failure mode ofooded lead-acid batteries. The grids are lead alloys (lead-

calcium, lead-antimony, lead-antimony-selenium) that con-vert to lead oxide over time. Since the lead oxide is a biggercrystal than lead metal alloy, the plate grows. The growthrate has been well characterized and is taken into accountwhen designing batteries. In many battery data sheets, there

is a specication for clearance at the bottom of the jar toallow for plate growth in accordance with its rated lifetime,for example, 20 years.

At the designed end-of-life, the plates will have grown suf-ciently to pop the tops off of the batteries. But excessivecycling, temperature and over-charging can also increase thespeed of positive grid corrosion. Impedance will increaseover time corresponding to the increase in electrical resis-tance of the grids to carry the current. Impedance will alsoincrease as capacity decreases as depicted in the graph ingure 2.

Sediment build-up (shedding) is a function of the amount

of cycling a battery endures. This is more often seen in UPSbatteries but can be seen elsewhere. Shedding is the slough-ing off of active material from the plates, converting towhite lead sulphate. Sediment build-up is the second reasonbattery manufacturers have space at the bottom of the jarsto allow for a certain amount of sediment before it builds-up to the point of shorting across the bottom of the platesrendering the battery useless. The oat voltage will drop andthe amount of the voltage drop depends upon how hard theshort is. Shedding, in reasonable amounts, is normal.

Some battery designs have wrapped plates such that thesediment is held against the plate and is not allowed to drop

to the bottom. Therefore, sediment does not build-up inwrapped plate designs. The most common application ofwrapped plates is UPS batteries.

Corrosion of the top lead, which is the connection betweenthe plates and the posts is hard to detect even with a visualinspection since it occurs near the top of the battery and ishidden by the cover. The battery will surely fail due to thehigh current draw when the AC mains drop off. The heat

build-up when discharging will most likely melt the crackopen and then the entire string drops off-line, resulting in acatastrophic failure.

Plate sulphation is an electrical path problem. A thoroughvisual inspection can sometimes nd traces of plate sulpha-tion. Sulphation is the process of converting active platematerial to inactive white lead sulphate. Sulphation is dueto low charger voltage settings or incomplete recharge afteran outage. Sulphates form when the voltage is not set highenough. Sulphation will lead to higher impedance and alower capacity.

Lead-acid (VRLA) ailure modes D-ou (Loss-o-Compssion)

Pl Sulphion (s bov)

So nd Hd Shos

Pos lkg

thml un-w

Posiiv gid coosion (s bov)

Dry-out is a phenomenon that occurs due to excessive heat(lack of proper ventilation), over charging, which can cause

elevated internal temperatures, high ambient (room) tem-peratures, etc. At elevated internal temperatures, the sealedcells will vent through the PRV. When sufcient electrolyteis vented, the glass matte no longer is in contact with theplates, thus increasing the internal impedance and reducingbattery capacity. In some cases, the PRV can be removedand distilled water added (but only in worst case scenariosand by an authorized service company since removing thePRV may void the warranty). This failure mode is easilydetected by impedance and is one of the more commonfailure modes of VRLA batteries.

Soft (a.k.a. dendritic shorts) and Hard shorts occur for a

number of reasons. Hard sorts are typically caused by pastelumps pushing through the matte and shorting out to theadjacent (opposite polarity) plate. Soft shorts, on the otherhand, are caused by deep discharges. When the specic

gravity of the acid gets too low, the lead will dissolve intoit. Since the liquid (and the dissolved lead) are immobilizedby the glass matte, when the battery is recharged, the leadcomes out of solution forming threads of thin lead metal,known as dendrites inside the matte. In some cases, the leaddendrites short through the matte to the other plate. Theoat voltage may drop slightly but impedance can nd thisfailure mode easily but is a decrease in impedance, not thetypical increase as in dry-out. See gure 2, Abnormal Cell.

Thermal run-away occurs when a batterys internal compo-nents melt-down in a self-sustaining reaction. Normally, thisphenomenon can be predicted by as much as four months


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Figure 2 Changes in impedance as a result o battery capacity

or in as little as two weeks. The impedance will increase inadvance of thermal run-away as does oat current. Thermalrun-away is relatively easy to avoid, simply by using tem-perature-compensated chargers and properly ventilating thebattery room/cabinet. Temperature-compensated chargers

reduce the charge current as the temperature increases.Remember that heating is a function of the square of thecurrent. Even though thermal run-away may be avoided bytemperature-compensation chargers, the underlying cause isstill present.

Nickel-Cadmium ailure modesNiCd batteries seem to be more robust than lead-acid. They are

more expensive to purchase but the cost of ownership is similar

to lead-acid, especially if maintenance costs are used in the cost

equation. Also, the risks of catastrophic failure are considerably

lower than for VRLAs.

The failure modes of NiCd are much more limited than lead-acid. Some of the more important modes are:

Gdul loss o cpci

Cbonion

Floing cs

Ccling

Ion poisoning o posiiv pls

Gradual loss of capacity occurs from the normal agingprocess. It is irreversible but is not catastrophic, not unlikegrid growth in lead-acid.

Carbonation is gradual and is reversible. Carbonation iscaused by the absorption of carbon dioxide from the airinto the potassium hydroxide electrolyte which is why it isa gradual process. Without proper maintenance, carbon-ation can cause the load to not be supported, which can be

catastrophic to supported equipment. It can be reversed byexchanging the electrolyte.

Floating effects are the gradual loss of capacity due to longperiods on oat without being cycled. This can also cause

a catastrophic failure of the supported load. However,through routine maintenance, this can be avoided. Floatingeffects are reversible by deep-cycling the battery once ortwice.

NiCd batteries, with their thicker plates, are not well-suitedfor cycling applications. Shorter duration batteries gener-ally have thinner plates to discharge faster due to a higher

surface area. Thinner plates means more plates for a givenjar size and capacity, and more surface area. Thicker plates(in the same jar size) have less surface area.

Iron poisoning is caused by corroding plates and is irrevers-ible.


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MaintenancephilosophiesThere are different philosophies and ambition levels formaintaining and testing batteries. Some examples:

1. Just replace batteries when they fail or die. Minimum orno maintenance and testing.Obviously, not testing batteries at all is the least costlywith considering only maintenance costs but the risksare great. The consequences must be considered whenevaluating the cost-risk analysis since the risks are as-sociated with the equipment being supported. Batter-ies have a limited lifetime and they can fail earlier thanexpected. Time between outages is usually long andif outages are the only occasions the battery shows its

capability risk is high that reduced or no back-up isavailable when needed. Having batteries as back-up ofimportant installations without any idea of their currenthealth spoils the whole idea of a reliable system.

2. Replace after a certain time. Minimum or no mainte-nance and testing.This might also be a risky approach. Batteries can failearlier than expected. Also it is waste of capital if thebatteries are replaced earlier than needed. Properlymaintained batteries can live longer than the predeter-mined replacement time.

3. A serious maintenance and testing program in order to

ensure the batteries are in good condition, prolong theirlife and to nd the optimal time for replacement .A maintenance program including inspection, imped-ance and capacity testing is the way to track the batterysstate of health. Degradation and faults will be foundbefore they become serious and surprises can beavoided. Maintenance costs are higher but this is whatyou have to pay for to get the reliability you want foryour back-up system.

The best testing scheme is the balance between maintenancecosts and risks of losing the battery and the supportedequipment. For example, in some transmission substations,

there is upwards of $10 million per hour owing throughthem. What is the cost of not maintaining battery systemsin those substations? A $3000 battery is fairly insignicantcompared to the millions of dollars in lost revenues. Eachcompany is different and must individually weigh the cost-risk of battery maintenance.

How to maintain thebattery

Standards and commonpracticesThere are a number of standards and company practices forbattery testing. Usually they comprise inspections (observa-tions, actions and measurements done under normal oatcondition) and capacity tests. Most well-known are theIEEE standards:

Ieee 450 o foodd ld-cid

Ieee 1188 o sld ld-cid

Ieee 1106 o nickl-cdmium

IEEE 450IEEE 450, IEEE Recommended Practice for Mainte-nance, Testing and Replacement of Vented Lead-acid Bat-teries for Stationary Applications describes the frequencyand type of measurements that need to be taken to validatethe condition of the battery. The standard covers Inspec-tions, Capacity test, Corrective actions, Battery replacementcriteria etc.

Inspections

Monhl inspcion includ ppnc ndmsumns o sing volg, ippl volg, ippl

cun, chg oupu cun nd volg, mbinmpu, volg nd lcol mpu piloclls, b fo chging cun o spcic gvi pilo clls, uninnionl b gounds c.

Qul inspcions includ sm msumns smonhl inspcion nd in ddiion volg o ch cll,b fo chging cun o spcic gvi o 10%o h clls o fo cun, nd lcol mpu(10% o clls).

Onc qul inspcion should b xnddwih msumn o fo chging cun o spcicgvi o ll clls, mpu o ch cll, cll-o-cll

nd minl conncion sisnc pomd on hni sing.

Capacity test (discharge test) should be done

a h insllion (ccpnc s)

Wihin h s wo s o svic

Piodicll. Invls should no b g hn 25% oh xpcd svic li.


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annull whn h b shows signs o dgdion ohs chd 85% o h xpcd svic li. Dgdionis indicd whn h b cpci dops mo hn10% om is cpci on h pvious cpci s o isblow 90% o mnucus ing. I h b hs

chd 85% o svic li, dlivs 100% o g oh mnucu's d cpci nd hs no signs odgdion i cn b sd wo- Invls unil ishows signs o dgdions.

IEEE 1188IEEE 1188, IEEE Recommended Practice for Main-tenance, Testing and Replacement of Valve-RegulatedLead-Acid Batteries for Stationary Applications denes therecommended tests and frequency.

Inspections

Monhl inspcion includ b minl fo volg,chg oupu cun nd volg, mbin mpu,visul inspcion nd DC fo cun p sing.

Qul sm msumns s o monhl inspcionshll b don nd ddiionll cll/uni impdnc vlu,mpu o ngiv minl o ch cll nd volgo ch cll. Fo pplicions wih dischg o onhou o lss, sisnc o 10% o h incll conncionsshll b msud.

annull bov msumns should b kn nd inddiion Cll-o-cll nd minl conncion sisnco ni b nd aC ippl cun nd/o volg

imposd on h b.

Capacity test (capacity test) should be done

a h insllion (ccpnc s)

Piodicll. Invls should no b g hn 25% oh xpcd svic li o wo s, whichv is lss.

Wh impdnc vlus hs chngd signicnlbwn dings o phsicll chngs hs occud

annull whn h b shows signs o dgdion ohs chd 85% o h xpcd svic li. Dgdionis indicd whn h b cpci dops mo hn

10% om is cpci on h pvious cpci s o isblow 90% o mnucus ing.

Battery replacement criteriaBoth IEEE 450 and IEEE 1188 recommend replacing thebattery if its capacity is below 80% of manufacturers rating.Maximum time for replacement is one year. Physical char-acteristics such as plate condition or abnormally high celltemperatures are often determinants for complete battery orindividual cell replacements.

IEEE 1106IEEE 1106, IEEE Recommended Practice for Installation,

Maintenance, Testing and Replacement of Vented Nickel-Cad-mium Batteries for Stationary Applications.

Inspections

Inspcion ls onc p qu includ bminl fo volg, ppnc, chg oupu cunnd volg, pilo-cll lcol mpu.

Smi-nnull gnl inspcion nd msumn ovolg o ch cll shll b don.

Capacity test (discharge test) should be done

Wihin h s wo s o svic

a 5- invls unil h b shows signs oxcssiv cpci loss.

annull xcssiv cpci loss

Summary best way to test andevaluate your battery

Test intervals1. Make a capacity test when the battery is new as part of

the acceptance test.

2. Make an impedance test at the same time to establishbaseline values for the battery.

3. Repeat the above within 2 years for warranty purpose.

4. Make an impedance test every year on ooded cells andquarterly on VRLA cells.

5. Make capacity tests at least for every 25% of expectedservice life.

6. Make capacity test annually when the battery hasreached 85% of expected service life or if the capacityhas dropped more than 10% since the previous test or isbelow 90% of the manufacturers rating.

7. Make a capacity test if the Impedance value has changedsignicantly.

8. Follow a given practice (preferably from the IEEEstandard) for all temperature, voltage, gravity measure-ments etc. and ll in a report. This will be a great helpfor trending and for fault tracing.

Evaluation

1. Replace cell if the impedance is more than 50% abovebaseline. Make a capacity test if 20-50% of baseline.

2. Replace battery if capacity test shows less than 80% of

rated capacity.


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Practical batterytestingThe Battery testing matrix below may help guide even themost skilled battery testing technician and will help simplifythe recommended practices.

The following is a description of some of the tests or main-tenance parameters.

Battery testing matrix IEEE recommended practicesInstrument

Parameter

Bite3 Bite2 DLROs MOM/Mjlner

DCMs BMM80 M5091 BGFT BGL DMA35 TORKEL Visual

Capacity

Internal ohmic value

Intercell connectionresistance

Voltage of each

cell / pilot cell

Spec. grav. and temp.of each cell / pilot cell

Corrosion at Terminals

DC Float Current

Unintentional BatteryGrounds

Battery ripple current

Charger AC ripple.Current and Voltage

Cycling of Ni / Cdbatteries

Structural integrity ofrack / cabinet

Capacity testCapacity test is the only way to get an accurate value on theactual capacity of the battery. While used regularly it can beused for tracking the batterys health and actual capacity and

estimating remaining life of the battery. When the battery isnew its capacity might be slightly lower than specied. Thisis normal.

There are rated capacity values available from the manufac-turer. All batteries have tables telling the discharge currentfor a specied time and down to a specic end of dischargevoltage. Table below is an example from a battery manufac-

turer

EndVolt./Cell

Model8 hAh

Ratings

Nominal rates at 25 C (77 F)Amperes (includes connector voltage drop

1 h 2 h 3 h 4 h 5 h 6 h 8 h 10 h

1.75

DCU/DU-9 100 52 34 26 21 18 15 12 10

DCU/DU-11 120 66 41 30 25 21 18 15 13DCU/DU-13 150 78 50 38 31 27 23 19 16

Common test times are 5 or 8 hours and common end o dis-charge voltage or a lead acid cell is 1.75 or 1.80 V.

During the test it is measured how much capacity (currentx time expressed in Ah) the battery can deliver before theterminal voltage drops to the end of discharge voltage xnumber of cells. The current shall be maintained at a con-stant value. It is recommended to select a test time that isapproximately the same as the batterys duty cycle. Commontest times are 5 or 8 hours and common end of dischargevoltage for a lead acid cell is 1.75 or 1.80 V. It is recom-

mended to use the same testing time during the batterys


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Figure 3 I the battery reaches the end o discharge at 80%(8 h) or beore o the specied 10 h it is shall be replaced.

Figure 4 Replacement o battery is recommended when thecapacity is 80% o rated.

lifetime. This will improve accuracy when trending howbatterys capacity changes.

If the battery reaches the end of discharge voltage at thesame time as the specied test time the batterys actual

capacity is 100% of the rated capacity. If it reaches the endof discharge at 80% (8 h) or before of the specied 10 h itis shall be replaced. See gure 3.

Procedure or capacity test ovented lead acid battery1. Verify that the battery has had an equalizing charge if

specied by the manufacturer

2. Check all battery connections and ensure all resistancereadings are correct

3. Record specic gravity of every cell

4. Record the oat voltage of every cell5. Record the temperature of every sixth cell in order to

get an average temperature

6. Record the battery terminal oat voltage

7. Disconnect the charger from the battery

8. Start the discharge. The discharge current should becorrected for the temperature obtained at point 5 (not ifcapacity is corrected afterwards) and maintained duringthe entire test.

9. Record the voltage of every cell and the battery terminalvoltage in the beginning of the discharge test

10. Record the voltage of every cell and the battery terminalvoltage one or several times at specied intervals whenthe test is running

11. Maintain the discharge until the battery terminal voltagehas decreased to the specied end of discharge voltage(for instance 1.75 x number of cells)

12. Record the voltage of every cell and the battery terminalvoltage at the end of the test. The cell voltages at theend of the test have special importance since weak cellsare indicated here.

13. Calculate the actual battery capacity

It is important to measure the individual cell voltages. Thishas to be made a couple of times during the test. Mostimportant is to measure the cells at the end of the dischargetest in order to nd the weak cells.

It is also very important that the time OR the current duringa discharge test is adjusted for the temperature of the bat-tery. A cold battery will give less Ah than a warm. Tempera-ture correction factors and methods are described in theIEEE standards.

Manufacturers can also specify their batteries at constantpower discharge. This is used where the load has voltageregulators. Then the current will increase when the volt-age drops. Procedure for testing these batteries is the samebut the load equipment must be able to discharge with aconstant power.

Batteries can also be tested at a shorter time than their duty

cycle, for instance at 1 hour. Then the current rate has to beincreased. Advantage is that less capacity is drained fromthe battery (valid for lead-acid) and it requires less time torecharge it. Also less man-hour is needed for the test. Con-tact your battery manufacturer for more information. Athigher rates it is more important to supervise the batterystemperature.

Between load tests, impedance measurement is an excellent

tool for assessing the condition of batteries. Furthermore, it is

recommended that an impedance test be performed just prior to

any load test to improve the correlation between capacity and

impedance.


13/32


Figure 5 Ascending impedance with corresponding end voltage

Impedance testImpedance, an internal ohmic test, is resistance in AC terms.With regard to DC battery systems, impedance indicatesthe condition of batteries. Since it tests the condition of

the entire electrical path of a battery from terminal plate toterminal plate, impedance can nd weaknesses in cells andintercell connectors easily and reliably.

Basically, impedance test is determined by applying an ACcurrent signal, measuring the AC voltage drop across thecell or intercell connector and calculating the impedanceusing Ohms Law. In practice, not only is the AC voltagedrop measured but so is the AC current. The AC currentis measured because of other AC currents in a battery thatare additive (subtractive). Other AC currents are presentfrom the charger system. The test is performed by applyingan AC test signal to the terminal plates. Then measure both

the total AC current in the string and the voltage drop ofeach unit in the string by measuring each cell and intercellconnector consecutively until the entire string is measured.The impedance is calculated, displayed and stored. As thecells age, the internal impedance increases as depicted ingure 2. By measuring impedance, the condition of eachcell in the string can be measured and trended to determinewhen to replace a cell or the string which helps in planningfor budgetary needs.

The impedance test is a true four-wire, Kelvin-type mea-surement that provides excellent reliability and highly repro-ducible data on which to base sound decisions with regard

to battery maintenance and replacement. Impedance is ableto nd weak cells so that proactive maintenance can beperformed. After all, the battery is a cost but it is supporting

a critical load or revenue stream. If a single cell goes openthen the entire string goes off line and the load is no longersupported. Therefore, it is important to nd the weak cellsbefore they cause a major failure.

The graph in gure 5 shows the effect of decreasing capac-ity on impedance. There is a strong correlation betweenimpedance and capacity so that weak cells are ably andreliably found in sufcient time to take remedial action. Thegraph shows the reorganized impedance data in ascendingorder with each cells corresponding load test end voltage.(Impedance in milliohms coincidentally is the same scale asthe voltage, 0 to 2.5). This view, that is ascending imped-ance/descending voltage, groups the weak cells on the rightside of the graph to nd them easily.

Impedance theoryA battery is not simply resistive. There is also a capacitiveterm. After all, a battery is a capacitor, a storage device, andresistors cannot store electricity. gure 6 shows an electrical

circuit, known as the Randles Equivalent Circuit, that de-picts a battery in simple terms. There are those who wouldhave people believe that the capacitive term is not necessaryand that the resistance is the only part that needs measuring.

Impedance measures both the DC resistance (the realcomponent in impedance) and the reactance (the imagi-nary components in impedance). Only by measuring bothcan the capacitive term start to be understood. The otherargument used against impedance is that frequency is avariable in the reactance part of the impedance equation.That is true except that since Megger uses a xed frequency,namely 50 or 60 Hz depending upon geography, it is always


14/32


10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2 2 23

micro-ohms

Figure 7 Intercell connection resistance bar graphFigure 6 Randles equivalent circuit

the same. This variable, 2, now becomes a constant and,therefore, frequency does not affect the nal result in any

way. The only parts that affect the nal result are the partsthat vary within the battery, namely resistance and capaci-tance, which paint the whole capacity/condition picture.

In the diagram shown in gure 6, Rm is the metallic re-sistance, Re is the electrolyte resistance, Rct is the chargetransfer resistance, Wi is the Warburg impedance and Cdl isthe capacitance of the double layer. Rm includes all of themetallic components one post to the other post, i.e., post,top lead and grids and to a certain degree, the paste. Reis the resistance of the electrolyte which doesnt vary thatmuch on a bulk basis. But at the microscopic level in thepores of the paste, it can be signicant. Rct is the resistanceof the exchange of ions from the acid to the paste. If thepaste is sulphated, then Rct increases or if that portion ofthe paste is not mechanically (electrically) attached to the

grid so that electrons cannot ow out of the cell. Warburgimpedance is essentially insignicant and is a function ofthe specic gravity. Cdl is what probably makes the mostimportant contribution to battery capacity. By only measur-ing DC resistance, capacitance, an important part of thecell, is ignored. Impedance measures both DC resistanceand capacitance.

A battery is complex and has more than one electrochemi-cal process occurring at any given time, e.g., ion diffusion,charge transfer, etc. The capacity decreases during a dis-charge due to the conversion of active material and deple-tion of the acid. Also, as the plates sulphate, the resistance

of the charge transfer increases since the sulphate is lessconductive than the active material. (See discussion aboutthe differences between the thickness of the plates in long-duration versus short-duration batteries.)

Intercell connection resistanceIntercell connection resistance is the other half of the bat-tery. A battery is comprised of cells connected in a seriespath. If any one component fails the entire series connec-tion fails. Many times batteries fail, not because of weakcells, but due to weak intercell connections, especially onlead posts which can cold-ow. Generally, hardware should

be tightened to the low end of the torque scale that is rec-ommended by the battery manufacturer. But torque wrench-es are a mechanical means to verify low electrical resistance.It is far better to actually perform an electrical test using anappropriate instrument. It is a low electrical resistance that

is desired. This test should be performed before the batteryis commissioned. Proper intercell connections are necessaryto ensure that discharge rates can be met. The instrumentof choice is a DLRO or a MOM which can easily verifythat all connections have been made properly. It can even

nd minor errors before the battery is commissioned, pre-venting possible causes of failure or damage to supportedequipment.

Testing intercell connection resistance performs two func-tions:

Vlids incll conncion sisnc

Finds possibl goss os wih op ld innl o h cll

By following IEEE Recommended Practices, intercell con-nection resistance can be validated. Those recommendedpractices specify that the variation of intercell connectionresistance be less than ten percent. This translates into 7micro-ohms on a 70-micro-ohm intercell connection resis-tance. This method can even nd a washer stuck betweenthe post and the intercell connector whereas torquing willnot. They also specify that ten percent of the intercell con-nectors be measured quarterly and all intercell connectorsannually.

In multiple post batteries, it is possible to nd those raregross errors in a cells top lead. (See multiple post bat-tery diagram in gure 1). On multiple-post cells, measure

straight across both connections, then measure diagonallyto check for balance in the cell and connections. Measur-ing only straight across does not adequately test for eitherintercell connection resistance or for gross top lead defects.This is due to the parallel circuits for the current.

The graph in gure 7 shows the data obtained from an ac-tual 24-cell telephone (CO) battery The peak at connector#12 (cell 12 to 13) is an intertier cable connection. Con-nector #3 was out of specication and it was determinedthat one of the two bolts was not properly torqued. It wasretorqued and retested. It came within ten percent of thestring average after retorquing.

The negative plates (odd-numbered plates #1 through 15)are all connected through negative top lead which is con-

nected to both negative posts. Positive plates (even-num-bered) are connected to each other through positive toplead which is connected to both positive posts. There aretwo intercell connectors between neg post 1 and pos post 1and between neg post 2 and pos post 2.


15/32


The higher the current draw the more critical is the propersizing of current-carrying components both internal to thecell and external. UPS batteries are usually designed fora high rate discharge lasting typically only 15-20 minutes.However, a telecommunications CO battery may have only

a 500 Amp draw but can discharge for up to eight hours. Soeither combination can have disastrous effects due to im-properly sized and maintained cells and intercell connectors.

Testing and electrical pathsIn order to properly test a multiple post cell, one must un-derstand its construction. Based on the diagram in gure 1,

it can be seen that there are two parallel paths for the testcurrent to travel. If the test leads are placed on neg post 1and pos post 1, the two parallel paths are (1) directly fromneg post 1 to pos post 1 through their intercell connectorsand (2) neg post 1 down to the top lead, up to neg post 2

and across the intercell connectors to pos post 2 down tothe pos top lead and back up to pos post 1.The two pathsare parallel circuits and hence indistinguishable. If one boltis loose, there isnt any way to determine that since the testcurrent will follow the path of least resistance. The bet-ter method to measure intercell connection resistance is tomeasure diagonally from neg post 1 to pos post 2 and againfrom neg post 2 to pos post 1. Compare the two readingsfor highest condence. Admittedly, diagonal measurements

are still parallel but the comparison becomes more interest-ing due to the increased inuence of top lead and loosehardware. Diagonal measurements do not allow for a directconnection from post to post. In the case of six-post cells,measure diagonally across the farthest posts in both direc-tions.

VoltageFloat voltage has traditionally been the mainstay of anytesting procedure. What is voltage? Voltage is the difference,electrically speaking, between the lead and the lead oxideon the plates or between the nickel and the cadmium. Thecharger is the item that keeps them charged. The sum of allof the cell voltages must be equal to the charger setting (ex-cept for cable losses.) This implies then that voltage merelyindicates the state-of-charge (SOC) of the cells. There is

no indication of a cells state-of-health (SOH). A normalcell voltage doesnt indicate anything except that the cell isfully charged. An abnormal cell voltage, however, does tellyou something about the condition of the cell. A low cellvoltage can indicate a shorted cell but only when the volt-age nally drops to about 2.03. If a cell is low then othercells must be higher in voltage due to the charger setting.Remember that the sum of all cell voltages must equal thecharger setting. Those cells that are higher are counteract-ing the low cell and generally speaking the higher cells are inbetter condition because they can tolerate the higher volt-age. But those cells are being overcharged which over-heats

them and accelerates grid corrosion and water losses.Lets say for the moment that the low voltage cell is not yetat 2.03, it is at 2.13 V. At 2.13 V it is not low enough to aga concern but it is degrading. It may or may not be able to

support the load when an outage occurs. Impedance is ableto nd that weak cell sooner than voltage. In this case, im-pedance will decrease since it is an impending short circuit.

A similar example can be found in VRLA when it comes to

dry-out or loss-of-compression. Voltage will not nd thiscondition until it is far later in the batterys life, until it is toolate. Impedance nds this condition much earlier so thatremedial action can be performed.

So dont confuse fully charged with full capacity.

As said above, cell voltage divergence can be caused by anumber of factors and one way to solve this problem couldbe to make an equalization charge. In an equalization chargeprocedure, the entire battery is charged at a higher (thannormal) voltage for several hours to balance the voltage inall the cells. The procedure can lead to heating and possiblywater loss. It is recommended to follow the manufacturers

procedure to avoid damaging the battery.

Specic gravitySpecic gravity is the measure of the sulphate in the acid of

a lead-acid battery. It is also the measure of the potassiumhydroxide electrolyte in nickel-cadmium battery but sincethe potassium hydroxide electrolyte isnt used in the chemi-cal reaction, it is not necessary to measure it periodically.

Specic gravity traditionally has not provided much valuein determining impending battery failure. In fact, it changesvery little after the initial 3 to 6 months of a batterys life.This initial change is due to the completion of the forma-

tion process, which converts inactive paste material intoactive material by reacting with the sulphuric acid. A lowspecic gravity may mean that the charger voltage is set toolow causing plate sulphation to occur.

In a lead-acid battery the sulphate is a closed system in thatthe sulphate must be either on the plates or in the acid.If the battery is fully charged then the sulphate must bein the acid. If the battery is discharged, the sulphate is onthe plates. The end result is that specic gravity is a mirrorimage of voltage and thus state-of-charge. Specic grav-ity readings should be taken when things are amiss in thebattery to obtain as much information about the battery as

possible.Different battery applications and geographies have varyingspecic gravities to accommodate rates, temperature, etc.Following is a table that describes some applications andtheir specic gravities.

Specifc gravities and their applications

Specifc gravity Percent acid Application

1.170 25 topicl sion

1.215 30 Sndd sion

1.250 35 UPS/high

1.280 38 auomoiv

1.300 40 VrLa sion

1.320 42 Moiv pow

1.400 50 topdo


16/32


Figure 8 Constant-voltage Constant-current charge character-istics

Float currentAnother leg of the Ohms Law triangle is current. Thecharger voltage is used to keep a battery charged but voltageis really the vehicle to get current into the battery (or outof it during discharge). It is current that converts the leadsulphate back to active material on the grids.

There are two types of DC current on a battery: rechargecurrent which is the current applied to recharge a batteryafter a discharge and oat current which is the current used

to maintain a battery in a fully charged state. If there is adifference between the charger setting and the batterys

voltage, that difference will cause a current to ow. Whenthe battery is fully charged [1], the only current owing isthe oat current which counteracts the self-discharge ofthe battery (


17/32


perature, battery life is halved, battery life can start to bemanaged. The increased temperature causes faster positivegrid corrosion as well as other failure modes. By holding alead-acid battery at a temperature of 95 F (35 C) insteadof the designed 77 F (25 C), a 20-year battery will last

only ten years, a ten-year battery only ve years and so on.Increase the temperature by another 18 F to 113 F (45 C),a 20-year battery will last only ve years!

A battery is rarely held at a certain temperature for its entirelife. A more realistic scenario is for a battery to heat duringthe day and cool down at night with higher average tem-peratures in the summer and lower average temperaturesin winter. It is unfortunate but cooling the battery off tobelow 77 F (25 C) will not gain back the life that was lost.Once the positive grid corrodes, it cannot be convertedback again. Furthermore, positive grid corrosion occurs atall temperatures, it is merely a matter of speed of the cor-

rosion rate. The end result is to control, as best as possible(back to cost versus risk), the temperature of the batteries inthe network.

IEEE 450, Annex H offers a method for calculating theimpact of high temperatures on a lead acid battery.

Data analysisThe essence of any testing methodology is how to interpretthe data to make some sense of it all. The same is true ofbattery testing. If the data are to be hand-written and led

or if a printout from an instrument is reviewed then led,then there is no useful analysis except if there is an emer-gency at that very moment. The real value in battery testinglies in the trending of data to determine if problems areimminent or a little farther out. Trending of battery data,especially impedance and capacity, is an excellent tool forbudgetary planning. By watching the batteries degrade overtime, a decision can be made as to when to replace a battery.With trending, emergency replacements decrease dramati-cally.

The rst time a batterys impedance is tested can cause con-cern because there is no baseline. In these cases, it is good

to compare each cell against every other cell in the string.Weak cells stand out. It is these cells which require furtherinvestigation. The table below provides a guideline depend-ing upon the length of time batteries have been tested.

Single Test Trending

% Dviionom Singavg

Clls %Chng omLs ts

Clls %ChngOvll

Ld-cid,Floodd

5 2 20

Ld-cid, VrLa,aGM

10 3 50

Ld-cid, VrLa,Gl 10 3 50

NiCd, Floodd 15 10 100

NiCd, Sld 15 5 80


18/32


Locating ground aultson DC systems withoutsectionalizing

OverviewThe main objective of a battery system is to provide stand-by and emergency power to operate industrial, consumer,commercial or protective devices. Some of these devicesinclude emergency lighting units, uninterruptible powersupplies, continuous process systems, operating controls,switchgear components and protective relays.

In emergency situations, it is essential that these devices bein proper operating condition. Failure of a DC system orthe battery can result in operational failure of the devicesconnected to that system. System failure can lead to loss ofrevenue, damage to equipment and/or injured personnel.

It is a common situation for a oating DC system to de-velop grounds within it. When a battery system is partiallyor completely grounded, a short circuit is formed across thebattery and consequently may cause the protective device tofail to operate when needed.

Current test methodsTraditionally utilities and industrial complexes have goneto great lengths to nd ground faults within their batterysystems. However, locating these battery grounds proves to

be a very elusive and time-consuming process. The currentground-fault location method involves sectionalizing, orinterruption, of DC branches to isolate the ground fault.Sectionalizing disables the system protection and has beenknown to cause inadvertent line and generator tripping. Forthis reason, many utilities have banned sectionalizing. Untilmore recently, though, this had been the only method avail-able to locate ground faults.

A better test methodDevelopments have led to a better test method; injecting alow-frequency AC signal and using that AC signal to locatethe ground in the DC system. This method can be per-formed without sectionalizing the DC system and it reducesthe fault locating time from days to hours. Furthermore, itallows for system protection to be present at all times.

The AC injection method measures single or multipleground faults by rst injecting a low-frequency, 20 Hz AC

signal between the station ground and the battery system.Second, the resulting current is then measured by us-ing a clamp-on sensing current transformer. From this,the resistance value can be calculated using the in-phasecomponent of the circulating current, thus rejecting theeffect of capacitive loads. Therefore, if the signal is injectedat the battery terminal and the clamp-on CT is connectedto the outgoing lead, the instrument will measure the totalground resistance present on the battery system. If the CTis clamped on a feeder, then the instrument will measure the

ground resistance on that feeder. Faults can be traced easilyregardless of the number of distribution panels or circuitsbecause the tracer is merely following the strength of theAC signal. System integrity is maintained because it is an on-line AC test and is designed to prevent system trips.

After injection of a low-frequency AC waveform, a resistivefault on a branch of the battery system will be indicated bya low-resistance value. For example, if the total resistanceof a battery system showed 10 k, this would indicate aresistive fault on the battery system. The resistive fault canbe located by clamping on each individual circuit until aresistive value of 10 k is found.

It is easy to see that this method can be adapted in a straightforward manner to locate multiple faults by using the theoryof parallel paths. For example, if the total system resistanceindicates 1 k and an individual branch indicates 10 k

resistive fault, the user would know that the system has asecond fault because the total system resistance and thebranch resistance do not match. By using the AC injectionmethod, ground faults on ungrounded DC systems is easy,straight-forward and safe.


19/32


Frequently askedquestionsWhat does foat voltage o a cell tell me?

Float voltage indicates that the charger is working, thatis, state-of-charge. It does not indicate the state-of-health(condition) of the cell. It indicates that the cell is fullycharged, but dont confuse fully charged with full capac-ity. There have been many times that the oat voltage is

within acceptable limits and the battery fails. A low oatvoltage may indicate that there is a short in the cell. Thisis evident by a oat voltage at about 2.06 or below forlead-acid (if the charger is set for 2.17 V per cell)

In some cases, a cell oats considerably higher than theaverage. This may be caused by the high oat voltage cell

compensating for another cell that is weak and is oat-ing low. It is possible that one cell oats much higher tocompensate for several cells oating a little low. The totalof all cells voltages must equal the charger setting.

What are the recommended maintenance practices or thedierent types o batteries?

IEEE Recommended (Maintenance) Practices cover thethree main types of batteries: Flooded Lead-acid (IEEE450), Valve-Regulated Lead-acid (IEEE 1188) and Nickel-Cadmium (IEEE 1106). Generally speaking, maintenanceis essential to ensure adequate back-up time. There arediffering levels of maintenance and varying maintenanceintervals depending upon the battery type, site criticalityand site conditions. For example, if a site has an elevatedambient temperature, then the batteries will age morequickly implying more frequent maintenance visits andmore frequent battery replacements.

How important is intercell connection resistance?

Our experience has found that many battery failures aredue to loose intercell connections that heat up and meltopen rather than from cell failure. Whether a cell is weakor an intercell connector is loose, one bad apple doesspoil the whole bushel.

When lead acid batteries are frequently cycled, the negativeterminal may cold ow, thus loosening the connection.

The proper sequence of measuring multiple post batter-ies is critical. Not all instruments provide valid intercellconnection resistances due to their method of testing.Megger instruments provide valid data.

What are some common ailure modes?

Failure mode depends upon the type of battery, the siteconditions, application and other parameters. Please referthe summary on pages 7-8 or to the Battery FailureModes, which can be found on the Megger website.

Look under the Battery Test Equipment product section.In the upper right-hand column under Documents clickfor Application Guides, Articles and FAQs.

How oten should impedance readings be taken?

The frequency of impedance readings varies with batterytype, site conditions and previous maintenance practices.IEEE 1188 Recommended Practices suggests that a base-line shall be taken six months after battery has been inoperation and then semi-annual quarterly. With that said,Megger recommends that VRLA batteries are measuredquarterly due to their unpredictable nature and semi-an-nually for NiCd and ooded lead-acid. Impedance read-ing should also be taken prior to every capacity test.

At what point should I stop changing cells and replace theentire battery?

In shorter strings (less than 40 cells/jars), the entireshould be replaced when three to ve units have beenreplaced. In longer strings, a similar percentage that isreplaced is the criterion.

How can I predict when I need to change a cell?

Even though there is not a perfect mathematical cor-relation between battery capacity and impedance (orany other battery test except a load test), the amount ofincrease in impedance is a strong indicator of batteryhealth. Megger has found that a 20 percent increase in im-pedance for ooded lead-acid generally correlates to 80%battery capacity. In VRLA, that increase is closer to 50%from the batterys initial impedance or from the manufac-turers baseline values.

Will capacity testing destroy my battery?

The battery system is designed to provide back-up powerduring all outages that appear during its lifetime. Per-forming a capacity test is nothing else than simulating oneoutage but in a controlled way. Batteries can normally bedeep discharged (discharged to manufacturers end-ofdischarge voltage) 100 - 1000 times depending on typeof battery. Using a few of these cycles has no real impacton the batterys lifetime. On the other hand there is noreason to test more frequently than recommended by thestandards.

Can I make a discharge test while my battery is still connectedto the load (on-line)?

Yes it is possible to do. Megger has test equipment thatautomatically senses and regulate the discharge currenteven when the batteries are connected to the ordinaryload. Most users choose to make a 80% discharge testwhen on-line in order to still have some backup time atthe end of the test.

Battery technology summary

As you can see, there is a lot to a battery. It is a complex

electro-chemical device. There is much more information

available that goes further into the details of Tafel curves

and depolarization but that is beyond this scope. Essential-

ly, batteries need maintenance and care to get the most of

them which is the main reason people spend so much on

batteries to support far more expensive equipment and

to ensure continuous revenue streams.


20/32


Megger productsoverviewMegger offers solutions to ensure system performance withits comprehensive line of Battery Test Equipment, LowResistance Ohmmeters and Micro-ohmmeters, InsulationTesters, and Multimeters.

An overview of the various products available is describedbelow. For more information on these and many other Meg-ger products, please contact us at (800) 723-2861,(214) 333-3201. Visit our web site www.megger.com for themost up-to-date news, product and service information.

Impedance test equip-mentRegardless of whether you are testing ooded lead-acid,

VRLA or Ni-Cd cells, Megger has the right equipment foryour battery maintenance requirements. The products andassociated accessories provides meaningful data on bat-tery health without signicant expense or any reduction in

remaining battery capacity.

Interruption in service can cause disaster to supportedequipment and facilities. Consequently, a dependable backuppower system is critical so that when AC mains fail, costlyservice interruptions can be avoided. The battery impedancetest helps to identify weak cells before they cause problems.

Taking the battery off-line for testing is time consuming andadds risk to the process. This process is unnecessary with

the on-line testing capabilities of the Megger family of bat-tery test products. The highly repeatable instruments helpreduce downtime.

BITE 3

Dmins h condiion o ld-cid bis up o2000 ah

On-lin sing wih Pss/Wning/Fil clculions

Msus impdnc, incll conncion sisnc, cllvolg

Windows Ce Oping Ssm wih mo hn 16 MB ommo

Msus fo nd ippl cuns

The BITE 3 is a compact, battery-operated, instrument withpowerful on-board data analysis tools. It is the rst of itskind instrument in that the ProActiv can download all pre-vious data to provide the best in on-site data analysis like noother instrument of its kind. The menus are easy to navi-gate with a bright, backlit LCD. The data display includes

the normal numeric arrangement but adds two graphicaldisplays to help analyze weak cells.


21/32


BITE 2 and BITE2P

Dmins h condiion o ld-cid nd nickl-cdmiumbis up o 7000 ah

On-bod Pss/Wning/Fil indicions

On-lin sing

robus, libl insumns

Buil-in pin (BIte 2P)

The BITE 2 and BITE2P Battery Impedance Test Equip-ment work by applying a test current across the batterystring while on-line, then measuring the impedance, cellvoltage and intercell connection resistance. They alsomeasure ripple current which indicates the condition of thecharger. The instruments help evaluate the condition of theentire string from terminal plate to terminal plate and eventhe charger.

ProActiv battery database managementsotware

Ognizs nd mngs b d

Poms nding nlsis

assiss h us o mng mulipl bis

Pins bsic pos

The rst of its kind, ProActiv is a new, powerful, easy to use

battery database management software designed to analyzeeach individual battery in a battery system.

Battery testing is crucial to ensure a battery system providesstandby and emergency power to operate devices suchas emergency lighting, UPS systems, operating controls,switchgear components, protective relays and continuousprocess systems. Failure of a battery system within environ-

ments such as utilities, hospitals or manufacturing plants canresult in operational failure of the devices connected to it.ProActiv assists the user to avoid battery failures, budget forfuture battery string and cell replacements, and plan batterychange outs in an orderly manner.

ProActiv utilizes a standard MS Access database format. Itallows the user to organize and manage battery data such asvoltages, impedance, intercell connection resistance, ripplecurrent, specic gravity, IR thermographs and more.

BITE accessories enhncs h cpbiliis o h BIte lin

Full lin o ccssois

Dsignd o uniqu siuions

G o non-sndd insllions

Megger offers a complete line of accessories to enhance thecapabilities of the BITE product line. Many are shown inthe Data Sheet link above, but there are many others includ-ing extension cables, calibration shunts, etc. Even thoughwe have many accessories, we are continually evaluatingadditional products as interest arises.

ropCt is fxibl,highl ccu cunnsmi o msuingcun fow in lgb ssms. I comsin wo lnghs: 24 in.(60 cm) nd 36 in. (90 cm)o 8 in. (20 cm) nd12 in. (30 cm) dims,spcivl. I is dsigndspcicll o h BIte 2,BIte2P nd eBIte.

Mini-Cts o msuingcun in smll gugwis nd singl cblid in bundl.

th Cun tnsomki o h BIte 3 is omsuing h cunin nois b ssmsnd o msu scpcun in plll bsings. Compiiv

insumns do nomsu cun nd hn,m povid onousinnl ohmic vlus.


22/32


Lighd Pob exnsionscn b mound on hcivs nd pobs oh BIte 3, BIte 2 nd

BIte 2P. th idlo msuing bisin cbins nd hd-o-ch plcs. Wih hspob xnsions, bisndn b kn o lino msu hm l im nd cos svingdvic.

th BIte 3 oslniv ld ss omsuing eLUs nd

oh smll bpplicions, spdminl bis ndbis wih hnsss.th cili msuingh impdnc o bssms wih diculccss.

Digil Hdommsus spcic gvind mpu o chcll nd i clculs mpu-djusdspcic gvi o svim ll in hnd-hlddvic. I cn so up o256 clls p sing in upo igh sings. No ndo wo bou pllxo hnd wiing d onshs, c. I is much shn bulb hdomsnd wihou n spilldcid o cln up.


23/32


Capacity testing

TORKEL 820/840/860

Bis cn b sd in svic

Uni djuss o includ lod cuns in h s pms

Us djusbl lm nd shudown poins o voidxcssiv dischg

Batteries in power plants and transformer substations mustprovide the equipment they serve with standby power in theevent of a power failure. Unfortunately, however, the capac-ity of such batteries can drop signicantly for a number ofreasons before their calculated life expectancy is reached.This is why it is so important to check batteries at regularintervals, and the only reliable way of measuring batterycapacity is to conduct a discharge test.

The TORKEL instruments are used for discharge testing.Tests can be conducted at constant current, constant power,constant resistance or in accordance with a pre-selected loadprole. For extra discharge capacity there are auxiliary loadunits available.

TORKEL 820 can discharge batteries ranging from 12 to48 volts with currents up to 270 A

TORKEL 840 is used for battery systems ranging from12 to 250 V.

TORKEL 860 is designed for users who travel fromplace to place to maintain battery systems having differ-

ent voltages. It features excellent discharging capacity plusa broad voltage range and outstanding portability. TheTORKEL 860 is used for systems ranging from 12 to 480 V.

TORKEL accessories

tOrKeL Win is sowo po uncions ndmo conol o tOrKeL.

tXL830/850/870 xlod unis o povidinghigh lod cuns.togh, tOrKeL nd h

tXL x lods om ssm h cn dischgbis wih cuns upo svl ka.


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BGFT

BGL

BGFT

Ground ault tracingequipmentThere are two ground fault locating instruments from which

to choose, the Battery Ground Fault Tracer (BGFT) andthe Battery Ground-Fault Locator (BGL). The BGFT hassuperior noise elimination while the BGL has an automaticbridge to differentiate between high capacitance and lowresistance. Here is a brief description of each instrument.

Battery Ground Fault Tracer(BGFT) esil locs gound uls in ungounddDC b ssms

Ops in high lcicl nois nvionmn

Simplis ul cing b idniing ul chcisic(sisiv nd cpciiv) mgniuds

The Battery Ground-Fault Tracer is an economical, manu-ally balanced instrument that identies, tracks and locates

ground faults in ungrounded DC battery systems - on-line.It is particularly effective in high electrical noise environ-ments, as the strength of the test current can be adjustedup to 80W. The BGFT is particularly useful in any industrywhere supply of power for operating measurement, com-munication and control equipment is critical.

The Battery Ground-Fault Tracer accelerates fault locationby eliminating trial-and-error procedures and because faultscan be located without going off-line. It is line operated andhas a manual bridge. The manual bridge is used to differen-tiate between true, resistive faults and phantom, capacitivefaults by using a feedback cable to null the capacitance. Butthe manual bridge is not required in order to trace faults.

The BGFT works by converting line frequency to 20 Hz. Itthen pushes the AC signal through some coupling capaci-tors to prevent transients on the DC buss and applies theAC signal into the DC system while on-line. Using thehand-held tracer, follow the signals with the highest readingsuntil the fault is found.

Battery Ground-ault Locator(BGL) Gound uls in ungoundd DC b ssms sil locd

Fus n uomic bidg

B opd

Simplis ul cing b idniing ul chcisic(sisiv nd cpciiv) mgniuds

The Battery Ground-Fault Locator was developed to detect,

track and locate ground faults on battery systems, withoutresorting to sectionalizing! The BGL tracks and locatesground faults on live or dead battery systems. To save hoursof unnecessary troubleshooting, the BGL readily differ-


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entiates between the resistive fault currents and capacitivecharging currents. This feature allows the instrument todetect and track leakage paths, even in the presence ofsurge-suppression capacitors.

The BGL works by ltering and applying an AC signal tothe DC buss on-line. The low level output of the BGLallows it to be battery-operated but is more sensitive tosystem noise. It has a built-in automatic bridge to differenti-ate between real (resistive) and phantom (capacitive) faultsso only the real faults are traced. The BGL is moved frompanel to panel to continue the tracing process until the faultis found. Since it has an automatic bridge it is very easy totrace faults and as such is better designed for the noviceuser.


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DLRO247001

DLRO10X

Digital Low ResistanceOhmmeters (DLRO) andMicrohmmeters (MOM)Many times batteries fail not because of weak cells but dueto weak intercell connections. Torquing is a mechanicalmethod to ensure that the electrical path resistances is verylow. But it does not truly indicate the quality of the electri-cal path resistance. The only true method is to measure eachintercell connection resistance.

Megger has several DLROs and MOMs that are appropriatefor intercell connection resistance. The portability of the in-struments allows effortless mobility around battery strings.

The instruments are built into strong, lightweight cases thatare equally at home in the eld or in the laboratory. They

are light and small enough to be taken into areas which werepreviously too small to gain access.

DLRO 247000 series rsoluion o 0.1 on 599.9 ng

Sndd inccuc o 0.25%

Lg, digil LeD dou

The 247000 Series of DLROs are a family of highly accu-rate instruments that provide a simple, practical and reliablemeans of making low-resistance tests in the eld. They alsoare ideal for production quality control. They operate on the

four-wire measurement principle, thus eliminating lead andcontact resistances. With basic accuracies of 0.25% andresolution down to 0.1 , they are nonetheless designed to

be rugged and portable for use at the job site. A variety ofoptional test leads and calibration resistance standards areoffered for use with them.

DLRO10 and DLRO10X accu suls in und h sconds

Fus pocd o 600 V

auomicll dcs coninui in ponil nd

cun conncions

alph-numic kpd o ning s nos (DLrO10X)

Us congubl high nd low limis (DLrO10X)

Pin oupu nd mmo (DLrO10X)

The DLRO10 and DLRO10X are fully automatic instru-ments, selecting the most suitable test current, up to 10 ADC to measure resistance from 0.1 to 2000 on one of

seven ranges.

For users who desire more control over the measurementprocess, DLRO10X uses a menu system to allow manual

selection of the test current. DLRO10X also adds real-timedownload of results and on-board storage for later down-load to a PC.


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MOM690

MJLNER 200

MOM600A

MJLNER 200 and MJLNER 600 tu DC ippl cun

Inccuc 0.3

two displs LeD nd LCD o visibili in ll condiions Low wigh, 8.8 kg (19.4 lbs) nd 13.8 kg (30.4 lbs)

Full uomic sing

MJLNER is designed to measure the resistance of circuitbreaker contacts, bus-bar joints, contact elements in bus-bars and other high-current links. The product has been de-signed with safety, ease of use and versatility in mind. Thereare two models, one 200 A output current and one 600 A.

With MJLNER it is possible to make measurements ac-cording to the DualGround method. This means that thetest object will be grounded on both sides throughout the

test giving a safer, faster and easier workow.

MOM200A and MOM600A rsoluion 1 on 1999 ng

Sndd inccuc o 1%

MOM200A/600A are ideal for nding poor connectionssince they can put out 100 A for extended periods. Its rangeextending up to 20 milliohms makes it ideal for measuringmany different types of connections.

MOM690 rsoluion 1 on 200 m ng

Sndd inccuc o 1%

MOMWin sow

aC oupu

In addition to high current capacity, MOM690 featuresmicroprocessor-based measurement, storage and reporting.The built-in software enables you to carry out an individualtest or an entire series of tests and store the results.

With the optional MOMWin software you can also ex-port the test results to a PC for further analysis and report-

ing. Ranges are set automatically, resistances are measuredcontinually and test results can be automatically captured ata preset test current.


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MMC850

M8037

Multimeters

MMC850 Multi-conductor ACDigital Clampmeter Singl o mulipl conduco msumn

Fl o ound scion cbls

Bckli displ

Cbl cnlizing clmp

The MMC850 offers a unique solution to current measure-ment in multiconductor cables without the need to splitcables. The MMC850 is simply clamped to a multi-conduc-tor cable and the current owing is then read.

MultimetersMegger multimeters compliment the solution to measuringand maintaining battery strings and cells. All instrumentsundergo rigorous testing throughout the their design andmanufacture and are suitable for use in eld service applica-tions. All are CE marked and designed to National and In-ternational Safety Standard, EN61010-1. They include suchfeatures as large digital displays, automatic power down,water and dust resistance. There are three series of Meggermultimeters, the M8000, M7000 and AVO300 dependingupon needs and features wanted.


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MIT410

Insulation ResistanceTest EquipmentBatteries are supposed to be well insulated from adjacent

equipment and metallic objects. The insulation providesseveral benets: 1) keeps the charge in the battery ratherthan letting it leak, 2) provides for normal oat current, and3) reduces energy losses. If a battery is leaking electrolyte,then there may be a path to ground. When a path exists, thecurrent needed to keep the battery fully charged increases.It also shortens the length of back-up time of the batterydepending upon the severity of the leak. An insulation resis-tance test can identify whether there are leaks. The insula-tion resistance is measured across one of the terminals ofthe battery to some ground, presumably the battery rack ortray. It is a very easy test to perform and provides for a lotof condence in the overall state of electrical insulation.

This test applies a DC voltage, say 500 Vdc, between thebuss, off-line and the rack. Then measures the DC leakagecurrent to calculate resistance in M or G. The higher theresistance is the better. This test is recommended at instal-lation and whenever a leak may be suspected (from tell-talesigns such as salt build-up.)

Megger offers the MIT400 Series insulation and continu-ity testers designed for electrical testing by power utilities,industrials, telecommunication companies, commercial/domestic electricians and anyone with unique test volt-age requirements. The wide range of features also makes

the MIT400 Series ideal for maintenance technicians andengineers.

These instruments are available from as low as 50 V to ashigh as 1 kV. For analytical applications, multiple test volt-ages are desired.

MIT400 series insulationresistance testers Choic o 4 modls o commcil nd pln pplicions:MIt Modls 400, 410, 420 nd 430

Choic o 3 modls o lcom pplicions: MIt Modls

480, 481 nd 485

Spcil applicions modl o hos who nd uniqu s volg, MIt Modl 40X os viblinsulion s volg om 10 V o 100 V pplicions in1 V spspoviding soluion o pcicll n unusulmsumn quimn ou m hv.

The series consists of eight instruments

MIt400 250 V, 500 V nd 1000 V

MIt410 50 V, 100 V, 250 V, 500 V nd 1000 V plus PInd Dar

MIt420 Sm s Modl 410 plus sul sog nddownlod

MIt430 Sm s Modl 420 plus Bluooh downlod

MIt480 50 V, 100 V

MIt481 50 V, 100 V, 250 V, 500 V, 1000 V plus PI, Darnd sul sog

MIt485 Sm s Modl 481, plus Bluooh downlod

MIt40X 10 V o 100 V in 1 V sps


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New Battery Testing Guide en LR

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