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Radio Editors ofmagazines and news-papers are herebygiven permission toreprint in whole orin part, with propercredit to the AerovoxCorporation, the con-tents of this issue ofthe Aerovox Research

Worker.

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The Aerovox Re-search Worker is a

monthly house organof the Aerovox Corporation. It is pub-lished to bring tothe Radio Experi-menter and Engineerauthoritative, f i r s thand information oncondensers and resis-tances for radio work.

.0111111

VOL. 10, NO. 2 FEBRUARY, 1938 50c per year in U.S.A.60c per year in Canada

Practical Methods of Testing CondensersPART 2

By the Engineering Department, Aerovox Corporation

THE capacity of low voltage high -capacity electrolytic condensers

can conveniently be found by the volt-meter -ammeter method, mentioned inlast month's Research Worker. When

is required to find the power factoror the equivalent series resistance aswell as the capacitance, the systemcan be expanded to find these quanti-ties in two ways. One method em-ploys a voltmeter, ammeter and watt-meter. The diagram of connectionsof these three instruments, togetherwith a variable source of supply isshown in Figure 1. The power trans-former is chosen so as to deliver analternating voltage of desired fre-quency within the rating of the con-denser. If the condenser is of thepolarized type, a d.c. power pack mustbe connected in series with the a.c.

CONDENSER UNDER TEST,,WATTS

Fig. 1

The magnitude of the d.c. voltage shallthen be at least as large as the peakvoltage of the transformer. C, is to

by-pass the power pack and should beas large a condenser as possible be-cause the alternating voltage dividesacross C, and the unknown, the largervoltage appearing across the smaller

C. be an oil or waxpaper condenser. Its size should bechosen so as to provide a reactancewhich is small compared to the resist-ance of the voltmeter. The wattmeterhas to be of a special kind since thecurrent is going to be so much out ofphase with the voltage that an unusu-ally heavy current will flow. Such"low power factor wattmeters" areavailable.

Readings are made on all three in-struments simultaneously; the desiredquantities are then given by the equa-tions:

Ca:-7citance

1000,000Cx

27fV(-92- (#7)2M ICROFARADS

Equivalent series resistance

R x = -1-T OHMS

Power factor - 100 WE I percent

A simplified formula for the capa-city, neglecting the equivalent seriesresistance. is

1,000,000 IC- MICROFARADS27 -FE

In all the foregoing equations theunits are volts, amperes, watts andcycles per second.

For the special case of 110 voltmotor -starting condensers, which aretested without the d.c. power pack,the chart of Figure 2 permits therapid determination of capacitanceand power factor when the three meterreadings have been made. It will alsoshow the capacity from voltmeter andammeter reading alone.

The use of the chart is as follows.It is assumed that all measurementsare taken at 110 volts, 60 cycles. Then,reading the current, find the value ofthe current on the bottom scale,marked "amperes", follow the verticalline upwards until it intersects theline A or B marked "mfds" and followthe horizontal line to the right read-ing the capacity at the right. Thecapacity can also he found directlyabove the corresponding current onthe line C -C.

To find the power factor from thewattmeter and ammeter readings, drawa horizontal line from the power scaleat the left and vertical line from theampere scale at the bottom. Readthe power factor at the intersection ofthe two lines. The capacitance isfound from the ammeter reading asbefore.

Example: To find the capacity whenthe ammeter shows 2 amperes. At 2on the current scale, follow the verti-cal line upwards to its intersection"X" with the line marked "mfds. scaleA", then follow the horizontal line to-wards the right and read the capacityon the right hand scale -48 mfds. Thesame can also be found at Y on theC -C scale.

AEROVOX PRODUCTS ARE BUILT BETTERPrinted in U. S. A. Copyright 1938 by Aerovox Corporation

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Fig. 3

measuring voltage and current, givingus E, and I,. Then the switch isopened and another set of readingstaken, to be known as E, and I,. It isoften more convenient to readjust thevoltage so as to make E, equal to E,.

CONDENSER UNDER TEST

VOLTSD.C.

VOLTSA.G.

POWER PACK

AMPSA.C.

Fig. 4

The magnitude of the capacitance andequivalent series resistance are nowgiven by the equations:

4,000,000Cx- M ICROFARA DS

27rf V (a) 2-Rx2

(12E2

) 2_ (I;)2 - R2

Rx 2ROHMS

The power factor is a function ofthe angle a in Figure 3, being equalto the cosine of this angle

P F = cos a 100 I, RxE percent

In all of the above equations theunits are volts, amperes, ohms andcycles per second.

In order to obtain the best accuracyof measurement the value of R shouldbe approximately equal to the valueof Rx. Keeping the value of E and Rconstant for a series of measurementsit is very simple to make a set ofcurves for the different values of Rxin a coordinate system where I, is theabscissa and I, the ordinate. A capa-city scale can be drawn directly op-posite the I, scale. Such curves andfurther information on this methodare found in the Research Worker ofSeptember 1936.

More precise methods of the deter-mination of Cx and Rx of large con-

AEROVOY(U SETTER

CONDENSERS AND RESISTORS

densers require special bridges whichwill be discussed in later installments.MEASUREMENT OF LEAKAGELeakage of electrolytic condensers

is simply measured by means of amilliammeter in series with the con-denser while it is placed across apower supply of the desired voltage.The necessary precautions have to betaken for safeguarding the instrument.It should be a multi -range instrumentif possible and it should be set on itshighest range or be short circuitedwhile the condenser is charging. Inaddition, a limiting resistor can beplaced in series with the circuit whichwill hold the current to a safe maxi-mum if the condenser were shortedduring the test.

The leakage to be expected is afunction of the capacity. A good 8mfd. condenser of 450 volt ratingmay have a leakage of 1 or 2 ma. Ifthe condenser has not been in use forsome time, the initial leakage will bevery much higher than this but it willgradually come down while the con-denser is being tested on a higherpotential than it has been subjectedto in service.

Measuring the leakage or insulationresistance of wax impregnated papercondensers requires a much more sen-sitive instrument since the resistancemay be up to 50,000 megohms orhigher. again depending on the capa-city. One of the simplest and mostreliable methods is to place the con-denser across some 300 volts of B -battery in series with a limiting re-sistor of 1 megohm and a multi -rangemicroammeter having a low range of0-1 microampere.

Again taking the necessary precau-tions, the meter must be fused and setto its highest range or shorted whilethe condenser is charging. It is cus-tomary to allow three minutes for thecharging process. Then the metermay be switched to lower and lowerranges until the leakage current canbe read. The insulation resistance isthen easily found by Ohm's Law.

A variation of the above method isshown in Figure 5. This circuit isp-obably preferred by those who donot possess a sensitive micro -ammeter.The condenser is placed in series witha high resistance of the order of 1 to5 megohms. The leakage through thecondenesr will then cause a voltagedrop across this resistance and thevoltage drop is measured with a vac-uum -tube voltmeter.

Fig. 5

In Figure 5, the condenser is shownin series with a battery (preferably250-300 volts). First the condensershould be charged by setting theswitch on a. R, is a limiting resistorwhich protects the battery in case thecondenser were shorted. An indicatingmeter in series with R, can be addedif desired.

When the condenser has beencharged, the switch is moved to c andthe voltage drop across R is read onthe vacuum tube voltmeter. If thisvoltage drop is called e and the con-denser charging battery has a voltageE, the insulation resistance is

E Rmegohms

when R is expressed in megohms.Changing the value of R permits the

use of several ranges.The vacuum -tube voltmeter shown

can consist of a battery -operated type30 tube, biased as an amplifier. Thesteady current can be bucked out witha battery or by another suitablemeans. The voltmeter can be cali-brated on d.c. There is no reason whyan a.c. operated supply could not beused for the voltmeter. A 55 or 85tube would perhaps be best since agrid cap is desirable.

Taking the condenser charging volt-age from a power pack is not recom-mended unless the unit is unusuallywell regulated. Any little variation involtage will cause charges and dis-charges of the condenser which resultin violent movements of the meter sothe result cannot be read. See theMay 1936 issue of the ResearchWorker for further information onthis subject.

New ThordarsonTransmitter Guide

Once again Thordarson comes forthwith a mighty important contributionto practical "ham" literature in theform of its new No. 344-C Thordar-son Transmitter Guide. This new edi-tion contains 48 pages as against 32for the previous edition.

Six engineers of the Thordarson or-ganization, who are likewise activeamateurs, compiled the constructionaldata ranging from 5 and 10 watt trans-mitters, beginners' and portable trans-mitters, all the way up to ambitious500 and 1000 watt transmitters, to-gether with a mass of mighty import-ant technical data. There is data onmodulation principles, calculations forClass A, B and C circuits, drivingpower and driver transformer ratios,overloading of modulator tubes, biassupply circuits, oscilloscope founda-tion unit, revised FCC regulations, anda lot more. A copy of this guide maybe obtained from your local jobberhandling Thordarson products, or dir-ect from Thordarson Electric Mfg.Co., 500 W. Huron St., Chicago, Ill.,for 15 cents.

Page 3

TYPES Cap.Mfd.

D.C.W.V.*Container

Size (In.)List

Price

PRS 50 4 150 9,'16x1-11/16 $ .40PRS 50 8 150 9 '16 x 1-11 /16 .45PRS 50 12 150 11/16x1-11/16 .50PRS 50 16 150 11/16x 1-11/16 .55PRS 50 24 150 II '16x2-3 /16 .60PRS 50 30 150 11/16x2-3/16 .65PRS 50 40 150 13 /16 x 2-3/16 .70

PRS 250 4 250 9 /16 x 1-11 /16 .45PRS 250 8 250 II/16x 1-11/16 .5UPRS 250 12 250 13/16 x 1-11/16 .65PRS 250 16 250 13 16 x 2-3 '16 .75

PRS 350 4 350 9 16 x 2-3 16 .50PRS 350 8 350 13/16x I-11 16 .55PRS 350 12 350 13 /16 x 2-3 16 .70PRS 350 16 350 13 '16 x 2-3 16 .80

PRS 450 4 450 13/16x 1-11 /16 .55PRS 450 8 450 15/16x 1-11/16 .60PRS 450 12 450 15/16 x2-3/16 .75PRS 450 16 450 1-1/16x 2-3/16 .90

CA tolerance of plus or minus I / 32" should be considered for all sizes

Small...Smaller ..

Smallest!And nour';you have the

DANDEETUBULAR METAL - CAN

ELECTROLYTIC* A brand new electrolytic . . . metal -can her-

metically -sealed type . . . with insulating heavy -paper jacket.

Size reduced fo smallest proportions consistentwith full rated capacity and voltage. Posi-tively no cheating.

Special rubber-bakelite end washers take spun -perfect hermetic seal.

Leak -proof, seepage -proof, corrosion -proof.

Paper jacket spun over metal rims, therebyeliminating all danger of "shorts" when tinnedpigtail leads are bent close to unit.

Ideal for midget AC -DC set repairs, for by-passfunctions, and for other average -duty work.These units are not, however, intended to re-place standard sized electrolytics for heavy-dutyservice.

Note sturdy con-struction of DAN-DEE. Paper jacketpartly removed toshow metal can. Her-metically sealed. Redand black end discsindicate polarity.31/2- tinned pigtailleads for connectionsand support.

Ask your jobber . .Insist on seeing these new tiny Aerovox electrolytics.And if you handle service work, always be sure tokeep an assortment on hand. You can't beat themfor AC -DC set repairs.

AEROVOX CORPORATION70 WASHINGTON STREET, BROOKLYN, N. Y.

Soles Offices in All Principal Cities