OvervoltageProtection forAC GeneratorsThis simple project can preventexpensive Field Day equipmentdamage!By Jerry Paquette, WB810W

1966 Logans LaneWest Union, OH 45693

MOsthams look forward to the. challenges of Field Day: setting

up and operating around theclock under less-than-ideal conditions.Gathering such items as antennas, coax,tables, chairs and tents is easy. Hams arereluctant to loan transceivers and comput-ers, though, because of the possibility ofdamage by human error, such as coffee orsoda spills.

And then, there are the generators.Using portable generators, there is alwaysa possibility of damage to expensive equip-

ment as a result of generator failure, espe-cially from overvoltage.

A Field Day team operating in Class 3A(three transmitters plus a Novice/Techni-cian station) could very easily have over$5000 worth of equipment in use. If thegenerator supplying power to this equip-ment puts out too much voltage, you runthe risk of burning up power supplies orother electronic components. This articleaddresses the problem of increased volt-

age, not lower voltage or surges and spikeslasting for a few microseconds.

Using a portable generator overvoltageprotection device (PGOVPD) 120-V circuitand ground-fault circuit interrupter (GFCI)is good insurance. This overvoltage pro-tection device must be used in conjunctionwith a GFCI at each station!

Circuit DescriptionRefer to Figure 1 for this description.

Except as indicated, decimal values ofcapacitance ore in microfarads ( ",F);others ore in picofarads (pF);resistances ore in ohms' k=l 000NC= No connection

D1 770.. .. ..••..., v v

GROUND-FAULT Ul

CIRCUIT INTERRUP1ER 72312>

1 k > <-10 k V+ U2I HOT HOT > >

Une Load 4 1 MOC3011l

~INV IMP NC ~NC

T1 ccw~~6SET VREF....•• >- + ? VOLTAGE 5 f-LoNC20 Vac 120 Vac ....•• >-12.6 V .~~

NON-INVINP ':l....•• >- ac 100 I'F > Rl i: f--uNC

25 V 10 k ~, ......~

1 NEUTRAL NEUTRAL CW 11 2 4

lLine Load FREO I..••••

OSl ~, < COMP V- Vz DS2

< 2.7 k

~~ + 13 7 9

2.2 ",F ; r: 0.01; ...12 k <

25 V 2W <<;

I GROUNDI

Figure 1-Schematic of the Field Day equipment overvoltage-protection circuit. This circuit must be used in conjunction with a ground-fault circuit interrupter (GFCI). A separate GFCI must be installed at each station. Resistors are '/4-W,5% tolerance, unless otherwisespecified.01-200 PIV, 1 A diode; 1N4003 or

equivalent.OS1, OS2-Small LEDs.

R1-1 O-kn board-mounted, multiturnpotentiometer.

T1-12.6-V ac transformer (see text).U1-723 adjustable voltage regulator IC.

U2-Optoisolator with triac output; IsocomMOC3011, MOC302.1or MOC3041,orequivalent.

(Allparts available from Digi-Key,1-800-344-4539; FAX:218-681-3380).

June 1994 43

RI places an intentional fault on the loadside of the GFCI. With the value resistorused, the fault is limited to 100 mA. (Thenormal tripping threshold of a GFCI is5 mA.) This current forces the GFCI to tripin just a few milliseconds. This circuit willnot function at all without the use of aGFCI. A GFCI must be used at each sta-tion. If a single GFCI were used at the gen-erator, rather than one at each location,premature tripping could occur. Severalhundred feet of extension cords could haveenough leakage to trip the GFCI.

You can see that the GFCl has separatelines (inputs) and loads (outputs). GFCIinput terminals must be connected to thegenerator output. The GFCI ground mustbe tied to the ground of the generator. Theload (computers, radios, etc.) will plug intothe GFCI or are wired to the load side of theGFCI. Likewise, this over-voltage protec-tion device must be connected to the loadside of the GFCI via a standard 3-conduc-tor plug and can be mounted in a separatebox.

T1 can be any 120 to 12.6 V trans-former capable of delivering 100 mA ormore. Mounting of this transformer variesdepending on the type used. All remainingcomponents mount on a circuit board. D1

What's a GFCI?Article 100 of the National

Electrical Code, published by theNational Fire Protection Association(NFPA) says: The ground;fault circuitinterrupter is "A device intended forthe protection of personnel thatfunctions to deenergize a circuit orportion thereof within an establishedperiod of time when a currenttoground exceeds some predeterminedvalue that is less than that requiredto-operate the overcurrent protectivedevice of the supply circuit." TheGFGI can be purchased from anyelectrical supply house or mosthardware stores that carry electricalequipment and usually costs .about$10.

the board-mounted! potentiometer, hasonly three leads, but there are four pads onthe circuit board, to accommodate differ-ent styles of pots. The 2.2-llF capacitor pro- .vides a slight delay, to prevent false trip-ping when the circuit is powered up. The0.0 l-llF capacitor from pin 13 of the 723 tothe negative supply bus should always beused. When the pin 5 voltage goes higherthan the reference voltage at pins 4 and 6,pin 11 goes low, turning on the externalLED and the LED inside the optical cou-pler. LED current is limited by the 1-k re-sistor. The optical coupler turns on thetriac, which places a lO-mA fault betweenthe hot wire and ground of the GFCI.

/' AdjustmentAdjustment is simple. You'll need a

'variable ac transformer (Powerstat orVariac). Turn Rl fully cIockwiseand usethe variable transformer to adjust input to130 V ac. Turn the pot counterclockwiseuntil the GFCI trips.

1PC-boardtemplates are available from ARRL.Senda self-addressed,stampedenvelopeto:Technical Department Secretary, 225 MainStreet, Newington, CT 06111-1494. Ask forthe Overvoltage Protection template fromJune 1994 QST. IQ5'fx-1

New Books

rectifies the ac from TI; the 100-~ capaci-tor filters the de. This voltage provides thepower to the'723 voltage regulator.

Two fixed resistors and a potentiometerform the voltage-divider network supply-ing voltage to the LM723 input, pin 5. RI,

JUST WHEN TOM HAD JEAN CONVINCED THAT IDS FRIENDS WERE NORMAL,HE TOOK HER TO A HAMFEST!

By Tom Irwin, AA@METhe Grandpa Press, 1023 Kirkwood Ave,Iowa City, IA 52240; tel 319-337-9986.First edition, 1994. 103 pp, B& W cartoons.8>6112 inches. Retail price $8.95, plus $2s/h. ISBN 0-9640636-0-3.Reviewed By Brian Battles WS10QST Features Editor

Horrifying as it may sound, there arepeople who consider ham radio a hobby.They think the purpose of becoming a li-censed radio amateur, and building andoperating radios is to have fun in their sparetime. They see it as a recreational pursuit!For such fools, jokes and gag cartoons relat-ing to the noble Amateur Radio service areappropriate, although "serious" hams knowbetter. Keep them away from Just when Tomhad convinced Jean that his friends werenormal.i.By Tom Irwin, AA@ME.

Tom, who lives in Iowa City, Iowa, wasborn in 1936 and has been a ham since 1957(until his nonrenewable one-year Noviceticket expired; he was relicensed asWD0BNO in the early 1970s), and he's beendrawing since childhood. After earning -a-journalism degree, and several years ofcartooning for newspapers and magazines,he's turned his sights on the solemn subjectof Amateur Radio.

Over the years, a relatively few "regulars"AA n~

have represented the field of ham cartoon-ing. QST often presented the work of BandelLinn, K4PP, in the 1960s and '70s; HarryHick (ex-lESS) drew gags and covers frombefore WW I to the 1960s. More recently,Jim Massara, N2EST, did cartoons and amus-ing illustrations for- QST and ARRL books,and today Bob Beasley, K6BJH, is probablythe most widely published ham cartoonist,producing gag panels for the ARRL,WorldRadio and other publications. There'sa frustrating scarcity of hams who are profes-sional cartoonists. Although someone occa-sionally mails in a random, awkward sketch,we QST editors wish more pros would sendus high-quality original work for possiblepublication. The few submissions we see aregenerally doodles by radio amateurs whoaren't professional artists. It's refreshing tofind a ham who has a sense of humor and candraw. Also, unlike others who shall remainnameless, Tom doesn'r make an embarrass-ing attempt to copy the unique style of thelate, legendary Phil "Gil" (WICJD)Gildersleeve, WI CJD, whose classics were aQST trademark and a de facto standard forham cartoons for five decades. *

Tom brings a rare breath of fresh air in the

*Although it went out of print a year or two ago,the ARRL published an anthology of PhilGildersleeve's best work in a paperback calledGil: A Collection of Classic Cartoons from QST.

ham book marketplace. This collection of100 Amateur Radio-related cartoons offershearty chuckles, and even a guffaw or two.Veteran hams.newcomers, and long-suffer-ing nonham spouses and family memberswill get a charge out of many of the single-panel gags. Is Tom the next Bob Beasley orGil? Probably not; although the cartoons areclever and neat, his artwork doesn't haveBob's crisp, clean lines or Gil's quaint,artistic style. Tom's material is less formaland sometimes weak in composition, but ithas an appeal that places it several notchesabove much of the work you might find in atypical local club newsletter. Tom's tech-nique reminds me ofthe simple, hasty-look-ing drawings done by humorist JamesThurber during the 1930s through the '60sfor the New Yorker and his many books.

There's no doubt that few hams will beable to resist photocopying Tom's cartoonsto hang on their ham shack walls next to theirFCC licenses, DXCC certificates and QSLcards. This paperback is sure to disrupt theproceedings at many ham club meetings asit's passed around during the treasurer'sreport or reading of the minutes. But that'sokay because sometimes we need a goodreason to laugh at our chosen avocation-andourselves. At 11 cents a cartoon, Just whenTom had Jean convinced that hisfriends werenormal...looks like a good value. ~