Battery Technology and Maintenance 101

Presented by: Andrew Sagl

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Agenda Types of Lead Acid Batteries Battery Applications Battery Failure Modes Battery Maintenance Maintaining VRLA Batteries Maintaining VLA Batteries Testing Parallel Strings

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Battery Types Primary Cells – These are non-

rechargeable batteries. These include the standard Alkaline battery and Lithium batteries.

Secondary Cells – These are the re-chargeable batteries. These include lead acid batteries, NiCD as well as Lithium Ion.

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Secondary Batteries Cyclic Batteries – These are

batteries that are used on a regular basis. The most common of these is auto-motive batteries or portable battery operated devices.

Standby Batteries – These are batteries that remain charged but are not used unless needed.

• Sub-stations (Relays)• Telecom (Communication)• Data Centers (UPS)

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Battery Types Lead-acid - can come in

several different chemistries, however regardless of chemistry they will all be either flooded cell (VLA) or sealed (VRLA) cells.

Flooded cells (VLA) – will vent hydrogen as they discharge. This will lead to water loss in the electrolyte. Therefore flooded cells need to have distilled water added to the electrolyte periodically.

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Battery Types Sealed cells - (Valve Regulated

Lead Acid VRLA) often referred to as “maintenance free batteries”, will recombine the hydrogen from the discharge reaction back into the electrolyte. This means the operator does not need to periodically add water.

However if they do overheat the internal hydrogen gas pressure will increase. If it gets too high the valve will vent the gas.

This will lead to water loss, which cannot be replaced.

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Battery Types VRLA oxygen recombination In VRLA batteries, oxygen

released from the positive plate travels to the negative plate where it combines with hydrogen to form water. It is because of this recombination that VRLA batteries remain moist and don’t have to be periodically filled with distilled water.

Not 100% efficient

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Battery Applications Batteries are not created

equally. Different Applications require

different battery designs. Plate design and surface

area are designed for specific applications.

Different applications can require different chemistry batteries.

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Battery Applications The more plate surface area

that is available the more capacity a battery will have and the more current it can deliver.

Batteries in cyclic applications will typically have less plates but they will be thicker.

Thicker plates allow them to better deal with the heat generated by repeated charge and discharge cycles.

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Battery Applications Lead antimony batteries will

be stronger. This helps deal with the heat generated from repeated charge / discharge cycles.

Antimony is not good for stand by applications because antimony batteries will suffer from antimony poising when left at float.

Lead Calcium batteries will deal with float applications better because they do not suffer from antimony poisoning.

Lead Calcium is not as strong as lead antimony so it does not deal with repeated charge and discharge cycles as well as lead antimony.

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Battery Applications Cyclic Batteries – These are batteries

that are used on a regular basis. The most common of these is auto-motive batteries or portable battery operated devices, such as forklifts and golf carts.

• Lead Antimony Design• Stronger plates good for the repeated heating effects of charge / discharge

cycling.• Not good on long periods of float, which cause antimony poisoning.

• Thicker Plates • More material to withstand corrosion

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Battery Applications SLI Batteries – (Starting Lighting

and Ignition) Batteries. These are a type of cyclic batteries used mainly in automotive applications.

• Lead Antimony Design• Stronger plates good for the repeated heating effects of charge / discharge cycling.• Not good on long periods of float, which cause antimony poisoning.

• Many Thinner Plates • Maximizes surface area in order to deliver high volumes of current in a small period of

time.• Only meant to be discharged a small amount. Not good for deep discharge cyclic

applications.

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Battery Applications Stationary Batteries – These are

batteries that remain charged but are not used unless needed.

• Sub-stations (Relays)• Telecom (Communication)• Data Centers (UPS)

• Lead Calcium Design• Good on long periods of float because NO antimony poisoning.• Not good for the repeated heating effects of charge / discharge cycling.

• Plate thickness dictated by capacity • More surface area = more capacity.• Thick plates = longer life span.

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Failure Modes

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Failure Modes Positive Grid Corrosion Normal failure mode in flooded lead-

acid (VLA) batteries Lead alloy turns to lead oxide. Plates grow Designed into batteries Acceleration due to:

• Overcharging• Excessive cycling• Excessive temperature

Increase in internal impedance

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Failure Modes Shedding Sloughing off of active material from plates into white lead sulfate. Small amount is normal Excessive build up can cause plate shorts Due to overcharging and / or excessive cycling. Only in flooded batteries.

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Failure Modes Sulfating Active plate material turns to lead

sulfate. Lead Sulfate = Inactive material Occurs in both Flooded and VRLA

batteries Natural process during discharge. Recharging reverses the process. Undercharging causes sulfate

crystals to form on the plate surfaces.

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Failure Modes Sulfating Sulfate crystals that harden over a

long period of time. These will not go back in solution

when proper voltage is applied. Decreases total active

material/capacity Result in a permanent loss of

capacity. Increase in internal impedance

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Failure Modes Shorts Shorts can occur in both Flooded and VRLA cells. Hard shorts are typically caused by paste lumps pushing through

the matte and shorting out to the adjacent (opposite polarity) plate. Soft shorts on the other hand, are caused by deep discharges. When the specific gravity of the acid gets too low, the lead will

dissolve into it. Since the liquid (and the dissolved lead) are immobilized by the glass matte, when the battery is recharged, the lead comes out of solution forming dendrites inside the matte.

In some cases, the lead dendrites short through the matte to the other plate.

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Failure Modes Dry out (Loss of Compression) VRLA batteries only (Most common failure mode) Dry-out is a phenomenon that occurs due to excessive heat, over

charging can cause elevated internal temperatures as well as high ambient (room) temperatures.

At elevated internal temperatures, the sealed cells will vent through the PRV.

When sufficient electrolyte is vented, the glass matte no longer is in contact with the plates, thus increasing the internal impedance and reducing battery capacity.

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Failure Modes Thermal Runaway Thermal run-away is when a battery internal components melt-down

in a self-sustaining reaction. Failure mode VRLA batteries Can end in complete and catastrophic failure Primarily due to oxygen recombination cycle Thermal run-away is relatively easy to avoid, simply by using

temperature-compensated chargers and properly ventilating the battery room/cabinet.

Temperature-compensated chargers reduce the charge current as the temperature increases.

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Failure Modes Thermal Runaway Flooded cell allows gas to escape VRLA recombines oxygen and

forms water Reaction produces heat Due to:

• Overcharging• High ambient• Low air flow• High float voltage

Heating is a function of the square of the current

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Failure Modes

Watts Lost = (Current)2 (Resistance)

Loose Connections

Frequent Problem all battery types

Easily found with resistance measurement

High resistance = elevated temperature = higher resistance

When serving load high temperatures can melt lead posts

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Battery Maintenance

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Battery Maintenance

No single test tells the whole story Determine condition Where condition is headed How fast Don’t find out during an outage that your battery failed Gather as much test data as possible

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Battery Maintenance Visual Inspection Float Voltage Float Current Ripple Current Specific Gravity Temperature Discharge Testing Ohmic Testing Strap Resistance

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Battery Maintenance Visual Inspection Check entire system Battery Electrolyte Level (Flooded Batteries) Ventilation system, floor & room clean Battery support system Check batteries for cracks, leaks and deformation Strap corrosion Record information

• Visual inspection will locate such things as cracks, leaks and corrosion can be found before they become catastrophic failures. However, visual inspection tells us nothing about the strings State of Charge (SOC), capacity or State of Health (SOH).

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Battery Maintenance Float Voltage Measure across each cell

Measure at posts

During float conditions• Not during discharge or

recharge

Compare float voltage to manufacturers recommendation

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Battery Maintenance Float Voltage Applied voltage to cell from charger Different voltages for different chemistries Low float voltage > not fully charging

• Can’t supply full capacity• Plate Sulfation

High float voltage > Over charging• cooks the battery• higher temperature• Grid corrosion• Thermal runaway• Dry-out

■ Float Voltage will tells us if something is wrong but it will not tells us anything about SOC, Capacity or SOH.

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Battery Maintenance Float Current Kirchhoff current law Measure anywhere in the string Usually low value Measure during float conditions Not during discharge or

recharge Increase in float current

precursor to Thermal Run-away VRLA

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Battery Maintenance Float Current Current through each cell

• Interaction between float voltage and internal resistance Supplied by charger Electrochemical process reversed

• Lead sulfate on plates converted to sulfuric acid and active material High float current precursor to thermal runaway

• Short circuits• Ground faults• High float voltages

■ Float Current will tells us if something is wrong but it will not tells us anything about SOC, Capacity or SOH.

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Battery Maintenance Ripple By-product of charging system Design, quality and age dictate Internal heating of battery and overcharging No more than 5A for every 100Ah

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Ripple Frequency When examining ripple

current we need to examine both the amplitude and the frequency of the ripple.

High frequency ripple above several hundred Hz has limited effects on lead acid batteries.

Low frequencies ripple can have significant effects.

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Ripple Frequency Low frequency ripple will

cyclically raise and lower the float voltage.

This can cyclically raise the float voltage above the maximum rating of the battery.

This can cyclically lower the float voltage below the open circuit voltage of the battery

This leads to repeated heating and sulfation of the battery.

Lowering its life span.

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Battery Maintenance

VolumeMassDensity

Specific Gravity Ratio of density of liquid with

respect to density of water How much sulfate is in

electrolyte – lead acid Gives SOC but not Capacity

or SOH. Density is temperature

dependent

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Battery Maintenance

Temperature Effects

50

60

70

80

90

100

110

120

47 62 77 92 107

Temperature (F)

Cap

acity

(%)

0

5

10

15

20

25

30

Bat

tery

Life

(yrs

.)

% Capacity Life (yrs.)

Temperature High temp = short life Low temp = low capacity possible damage 10 °C rise = ½ life

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Battery Maintenance

Partial Load Test

1.5

1.7

1.92.1

2.3

0 5 10 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240

Time (min)

Volts

per

Cel

l

Passes Better Failure

Discharge Testing Single absolute test Complexity & cost Acceptance Test

• Beginning of life based on design capacity

Performance Test• After two or three years when new then

every five years• Based on design capacity also

Service Test• As needed to determine if battery will

support existing load Discharge Testing is the only test that will

determine the capacity of the string, but not necessarily the SOH.

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Ohmic Testing

Ascending Impedance with Corresponding End Voltage

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

Impe

danc

e (m

Ohm

s) &

End

Vol

tage

Imp 0.27 0.27 0.27 0.56 0.61 0.63 0.65 0.68 0.71 0.72 0.74 0.75 0.79 0.8 0.82 0.84 0.89 0.9 0.91 0.94 0.96 1.17 1.19 2.1

End V 2.03 2.04 2.03 1.98 1.97 1.94 1.9 1.91 1.88 1.89 1.9 1.89 1.89 1.84 1.82 1.84 1.81 1.84 1.8 1.73 1.82 1.74 1.33 0.1

Cell # 11 15 16 3 18 22 13 24 10 14 23 20 5 9 6 4 21 8 1 12 2 17 7 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Provides SOH rather than just SOC As the battery ages and sulfates the impedance of the battery

will increase as the capacitance decreases.

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Ohmic Testing There are different types of ohmic tests.

Resistance – Measures only the resistive value of a battery, The battery also has capacitive and inductive values as well.

Conductance – (Actually Admittance) This is the reciprocal of impedance.

Impedance Testing – Measures the resistive, capacitive and inductive qualities of the battery.

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Ohmic Testing Impedance testing has a distinct advantage over resistive type testing. When

we look at a schematic representation of a battery there are more than just resistive components to that battery. There are also capacitive and inductive characteristics.

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Ohmic Testing AC impedance testing will detect signs of battery aging sooner than purely

resistive measurements. Batteries are NOT resisters. Batteries contain both an electrolyte liquid and solid plates. When liquids and solids meet they create a double layer effect. In essence

this is a capacitor. As a battery ages the capacitance of the double layer will change well before

the resistance of the plates. Resistive testing ignores the capacitive double layer effect.

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Ohmic Testing Ohmic testing is not an absolute test. The

measured value is not compared to a standard known good value to determine if the battery is good or bad.

(Ohmic testing is NOT a GO / NO GO Test) Ohmic testing is a relative test. The measured value is

compared to the previously measured value to see how much it has changed. The percentage change indicates how much the

battery chemistry has changed; which is an indicator of the batteries State Of Health. (SOH)

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Ohmic Testing Different instruments will measure

different values. Various ohmic test instruments

operate at different frequencies and currents.

Different test frequencies will provide different ohmic values for the same cell.

Some test currents are too low to get repeatable results on larger batteries.

𝑍=√𝑅2+𝑋 𝑐2

𝑋 𝑐=1

2𝜋 𝑓𝐶

Different frequency cause different reactive capacitance values which cause different

impedance values.

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Ohmic Testing Since you can get different measurements with different

models of instruments we can see that ohmic testing is a relative test NOT an absolute test.

We do not test against an absolute value. We test and compare that data to a previous test result.

Repeatability is the KEY parameter.

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Battery Maintenance Inter-cell Resistance If the torque not sufficient

this will cause a higher resistance causing a voltage drop that causes heat.

Measure across strap• Not on Strap• On Post

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Battery Maintenance When testing a strap with a DC low

resistance ohm meter the measurement must be taken in both directions.

This is because there is DC current already going through the strap from the charger.

One direction will be higher than the other. Therefore both directions must be measured and an average of both taken.

A low frequency AC measurement does not require dual measurements.

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Battery Maintenance Strap measurement are also

relative measurements just like battery measurements.

Different frequencies will give different values.

Different model duplex leads can give different values due to different current densities between the tips.

IEEE states that when a strap measurement deviates by 20% or more then that strap should be addressed.

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Maintaining VRLA Batteries

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Maintaining VRLA Batteries Failure Modes

• Dry out• Thermal Runaway• Sulfating• Soft shorts / deep discharge

Tests to Run • Inspection• Float Current• Ripple Current• Ohmic Testing• Inter-cell strap measurements

How often• Quarterly

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Performing an Ohmic Testing When performing battery ohmic measurements a certain test methodology

needs to be followed. This is because battery ohmic measurements are in micro-ohms.

Many factors can affect these measurements. For example, the following criteria will affect the reading taken to various degrees.

• Cell Type• Battery Charge• Temperature• Make and model of instrument being used.• Probe Type• String length and configuration.• Load• Charger• Where the measurement is taken on the battery.

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Ohmic Testing In order to maintain good

repeatability a certain test methodology must be performed.

• Battery string needs to be fully charged.

• The user must use the same make and model instrument

• The same probe type needs to be use from one test to another.

• The measurements need to be taken at the same point. (Posts are the preferable location)

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Ohmic Testing Establishing a Baseline A baseline is a reference value (starting value) used to

determine the amount a batteries chemistry has changed over time.

Baselines should NOT come from battery manufacturers• You do not know what equipment they used for testing.• The batteries they test are stand alone. • The battery is not in your string• The battery is not connected to your charger• The battery is green. Has not gone through formation.

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Ohmic Testing Test Data can be

analyzed in 3 ways.

Cell Average:

Ohmic values of each cell comprising the string are compared to the strings average ohmic value. This is useful in identifying weak cells within the bank. If the majority of cells in the bank are in poor

quality then the string average will be poor.This method will find poor cells but not

necessarily a weak string.

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Ohmic Testing Baseline Reference:

Comparison of ohmic values to baseline values.

Comparing the string average to the baseline helps establish the overall health of the string.

If all the cells have aged at the same rate then the cell average will look good, while

the entire string has aged.Comparing the values to an initial baseline value shows how much the sting has aged.

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Ohmic Testing Impedance Trending:

Trending of ohmic values and observing the percentage of change from one test period to the next test period is ideal for establishing an approximate rate of aging. This data is useful in forecasting future needs. If a battery is aging faster than expected then this could be an

indication of a possible issue. Wrong type of battery for application Environmental issues Maintenance issues Poor quality battery

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Maintaining VLA Batteries

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Maintaining VLA Batteries Failure Modes

• Positive Grid Corrosion• Shedding• Sulfating• Soft shorts / deep discharge

Tests to Run • Inspection• Float Current• Ripple Current • Ohmic Testing• Inter-cell strap measurements

How often• Bi Annual (6 Months)

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Maintaining VLA Batteries Large high capacity VLA batteries

have a larger plate surface area to support the higher capacity.

Since the batteries have more plate surface area the impedance of the cells is lower.

When performing ohmic testing the test current must be high enough to get repeatable results and overcome any signal to noise ratios.

Higher capacity batteries require higher test currents for repeatable results.

For example: If the battery under test is 500uΩ and the test current is only 100mA then the voltage drop across

the battery is only 50uV. A small amount of noise can cause non

repeatable results.

𝑉=0.1𝐴∗0.0005𝛺𝑉=𝐼 ∗𝑅

𝑉=0.005

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Parallel Strings VLA batteries typically fails in a

shorted mode. Due to plate corrosion. Current can still pass through the string.

VRLA batteries typically fail in an open mode. Dry-out. Current cannot pass through the string.

To increase reliability VRLA batteries are typically assembled in parallel string configurations.

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Parallel Strings When testing a series string the test

current only goes through the battery under test.

It is the only low resistance path for the test current.

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Parallel Strings When testing a parallel string the

test current goes through the battery under test as well as the parallel path.

The parallel path offers another low resistance path.

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Parallel Strings If the impedance of a battery

changes due to changes in the cell it will change the current draw through the parallel path.

This will change the current through the battery being tested.

This will lead to all the batteries showing altered impedance values.

Cannot locate the poor cell. Typically you must segment

the parallel string.

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Parallel Strings By using a CT to measure

the “escape” current in the parallel path the ohmic tester can determine the correct amount of current going through the battery being tested.

No false readings No segmentation required.

Questions or Comments?Email Nicole VanWert-Quinzi nicole.vanwert@Transcat.com

Transcat: 800-800-5001www.Transcat.com

For related product information, go to: www.Transcat.com/Megger