Motor Starting CondenserReplacements

E`CellC refrigerators with

c7n"e r-'ttrf;ngrooters have

been use or severalyears Meny instances Their con-densers are now worn out. Most servicing jobs disclose defec-tive condensers. But what replacements to get and where toget them-that's been the hitch until now.

Many AEROVOX jobbers have begun to stock AEROVOX motor -starting condensers. Also, AEROVOX has just issued a specialIndustrial Condenser Replacements Catalog listing electrolyticand oil condensers employed by the standard types of condenser -start motors. This data gives you the precise facts you need for

satisfactory replacement. Meanwhile your jobber can supplythe precise unit called for.

Just state that you are interested inWrite for Data servicing electric refrigerators andother motor -driven appliances using condensers, and we shallsend latest bulletins. And if your jobber does not stock the unitsyou call for, let us know.

AEROVOX CORPORATION70 WASHINGTON STREET, BROOKLYN, N. Y.

Soles Offices in All Principal Cities

,12eadgilLI Tat:, r:ewo,f.

papers are herebygiven permission toreprint in whole orin part, with propercredit to the Aeroves

e erovoy h

con-tents of this issue ofth A Researc

:eh:, .,j,i e,)v,ciorrkzetle.,

porafion. It is pub-lahed to bring tothe Radio Experi-menter and Engineerauthoritative, firsthand information oncondensers and resis-tances for radio work.

VOL. 8, NO. 9 SEPTEMBER, 1936Pk per peer to U.S.A.eoe par year in cam.

Methods of Testing Low -VoltageHigh -Capacity Condensers

By the Engineering Department, Aerovox Corporation

THE methods of measuring the ca-pacity and power factor of low -ca-

pacity condensers are sufficiently wellknown but they are not suitable forthe high capacity types. This articledescribes two ways of measuring thecapacity and series resistance of lowvoltage high capacity condensers(from 100 to 10000 microfarads).

The first method, illustrated in Fig-ure 1, employs the least amount ofequipment. It rests on the principleof measuring the impedance of thecondenser at a known frequency bythe voltmeter-arnmeter method. As-suming for the moment that the con-denser does not have any resistance,it will be seen that the reactance ofthe condenser is equal to E/I, thesevalues to be read simultaneously withthe switch S closed. Then the capacitycan be found from the relation

C '1,,c00i000 MICROFARADS(1)

or, expressing C directly in terms ofE and I,

Ca 1,0020,fg MICROFARADS iS)

In these expressions, E and I are involts and amperes.

Of course, no condenser has zeropower factor and therefore, the aboveequation is somewhat in error but theerror is never more than 2 or 3 per-cent so that it may not outweigh theadvantage of this simpler method.Also, the error is in such a direction

CONDENSER UNDER TEST

"rc

)

AMPS "three voltmeter method" of

towing mop.way. First close the swtich Sand read the values of E and I whichwill here be denoted by E, and I,.Then open switch S and again readthe voltmeter and ammeter whichgives the quantities E, and L. The de-sired quantities, Co and Rx, can thenbe obtained from the readings by theexpressions:

(W-Rx 2 OHMS

(3)

1,000,000o,000(4)

P11 -f\/

This is equivalent to the so-called

MICROFARADS

POWER PACK

as to make the condenser appearsmaller than it really is.

Accurate determination of the capa-city and of the series resistance ofthe condenser under test can be foundwith the circuit of Figure 1 in the fol-

ing resistance and reactance. If 5./I.= Z. and E,/I, = Zs, the relation of

AEROVOX PRODUCTS ARE BUILT BETTERPrinted in U. 8. Copyright 1936 bp Aerovon Corporation

the various impedance vectors is as inFigure 2. The triangle having thesides Z,, Z, and R is completely knownsince the three sides are given. Theangle a can then be figured out by therule of cosines (this is the phaseangle) and the values of Az and Zxfollow immediately.

All the above might seem rathercomplicated but the measurements areeasily taken and the chart of Figure 4avoids all calculations.

CIRCUIT DETAILSThe power supply for the measure-

ment should consist of a variabletransformer or some variable sourceof voltage. In the making of the chart60 cycle ex. has been assumed. Thecondenser must be given a polarizingvoltage which is larger than L4 timesthe ac. voltage to be applied. If thepolarizing supply is a power pad, itmust be bypassed by a condenser, C,which should be a condenser of aboutthe same capacity as the condenserundertest,test, or at least 200 cold, Theresistor R should be of a value to begiven in a table below and should beable to stand the current.

The a.c. voltmeter is to be con-nected in series with another con-denser, C,, which should be an oil orwax condenser. This is to keep thevoltmeter from being affected by thepolarizing voltage. The proper size ofC. depends on the re of thevoltmeter. If it is a hisistancegh-resietancerectifier type, the value of C, can prob-ably be about 1 or 2 mfd. paper typefora 10,000 ohm instrument. Its rangeshould be 0-10 volts.

The a.c. ammeter employed can bea movable iron type or a thermo-couple type. It has some extra currentflowing through it which is not de-sired; the voltmeter current and thed.c. leakage of the condenser. If thevoltmeter is of the high -resistancetype, its current is so small as to benegligible. However, it is easy to cor-rect for it if one would care to go tothe trouble. In order to avoid theleakage current one might employ

Range inmicrofarads

340- 10001000- 34003400-10000

thermal meters which add the d.c. anda.c. straight and make a correction. Itis also possible to employ a meter witha current transformer or to substitutea voltmeter in seri. with a condenseracross a resistor but the error is prob-ably not large enough to warrant theseprecautions.

CONDENSER UNDER aEST,oral, i

MAKING THE MEASUREMENTMake the polarizing voltage about

IS volts, connect the unknown con-denser, close switch S and adjust theun supply until the uc. voltmetershows 8 volts. Read the a.c. ammeter;this is the value to be 'mown as I..With an applied potential of 8 volts,there is 3 ma. per miorofarad, so thecapacity is known immediately. (ac-cording to equation 2).

Next open the switch S, readjust thea.c. supply to 8 volts and again readthe ammeter. This is L; the chart ofFigure 4 shows the value of Rx forany combination I, and I,. The chartis direct reading for the range 1000-

3400 microfarads, when R equals I

ohm and the ammeter range is 0-10amps. For other ranges, the TableI shows the required value of A,the recommended ammeter range andthe factors where one must multiplythe values of the chart so as to snakeit cover that range.

The second method is illustrated inFigure 3. In additon to the metersemployed in Figure 1 it also requiresa wattmeter and then the resistanceand switch are not necessary. One setof readings is sufficient to find boththe capacity and the resistance of theunknown condenser.

The wattmeter must be a "lowPower -factor" wattmeter, its currentcoil should be able to carry a largercurrent than the wattmeter rangewould indicate. The voltmeter coilcan be connected to the same terminalof condenser C. as the other volt-meter; in this way only one condenseris required, When all three readingshave been taken, Cu and Rx are foundfrom the following equations.

Rx=÷ OHMS

C 1,000,000

2-f*-D-G4Y

(5)

(6)MICROFARADS

Due to the fact that wattmeterswith low ranges are not available, itwill be necessary to employ a higherapplied voltage -for the low ranges.The recommended ranges with the re-quired meter ranges are shown inTable II.

TABLE 1Range M R Ammeter In Fig. 4, multiply or divide

nlicrofarads range L and I, Rx100-340 10 ohms 0-1 amp divide by 10 multiply by 10340-1000 3.0 ohms 0-3 amps divide by 3 multiply by 3

1000-3400 1 ohm 0-10 amps direct reading direct reading3400-10000 0.33 ohm 0-30 amps multiply by 3 divide by 3

TABLE IIAmmeter range Wattmeter range Volts

applied0- 3 amps 0-20 240-10 amps 0-20 8

0-30 amps 0-50 8

10.4

10.2

10.0

9.8

9.6

9.4

9.2

9.0

8.8

8.6

8.4

8.2

38.0

7.8Od 7.6

7.45)

7.2

7.0

6.8

2 6.6

g 6.4O 6.2

6.0

2 5.8

15 5.60

5.4

< 5.25.0

4.8

4.6

4.4

4.2

4.0

3.8

3.6

3.4

3.2

3.0

2.824 2.6 2.8 3D 3 2 34 38 3.6 4.0 4 44 48 48 50 52 ,5,4 56 68 6D 62 64 66 68 70

12 AMPERES CURRENT WITH S OPEN)

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