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canuck4
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Join Date: Jun 2008
Posts: 5

Capacitor testing

06/16/2008 1:03 AM

How do I test a capacitor? This is of a small compressor tag says pulls 13.5amps The printing on the capacitor is as follows CBB60 120uF + - 5% 250V AC 50/60 Hz Thanks
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Nagarajan.Suresh
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Join Date: Jun 2008
Location: Chennai
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#1

Re: Capacitor testing

06/16/2008 1:08 AM

Hi,

Use a capacitance meter which will directly give the capacitance value in micro farad/ farad.

N.Suresh

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Epsilon
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Join Date: Oct 2007
Posts: 11
#2
In reply to #1

Re: Capacitor testing

06/16/2008 7:25 AM

N. Suresh, "Use a capacitance meter which will directly give the capacitance value in micro farad/ farad." Thats correct but it should be mentioned that + - 5% means that the value on the capacitance meter should be within 114uF to 126uF reading.
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Nagarajan.Suresh
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#3
In reply to #2

Re: Capacitor testing

06/16/2008 7:28 AM

Hi,

The Original balue will be indiacted by the meter. It may +or - 5% or less.

N.Suresh

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olivinak
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Join Date: Aug 2007
Location: Heilonjang China. 2 blocks from you
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#4
In reply to #3

Re: Capacitor testing

06/16/2008 4:58 PM

There are some multimetres that have the provission like some fluke metres,it will give you the direct reading on your capacitor but take not if thehvalue is lower than the actual value,then make sure that if its low it should be within the -5% on the data as indicateed on the capacitor,below -5% it will not do the exact work it's surposed to do.

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#6
In reply to #1

Re: Capacitor testing

06/16/2008 11:40 PM

hi frnd

u informations r very useful to me.My question is

how we measure the ratio test in power transformer (pls explain with calculations)

my mail id ktva361_eee@yahoo.co.in

by

k.t.venkatraman
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Nagarajan.Suresh
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Location: Chennai
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#11
In reply to #6

Re: Capacitor testing

06/18/2008 7:50 AM

Hi,

Apply 415 V to the HV Side . Check volatge RY, YB, BR . Check the voltage for ry, yb, & br on the LV side. LV Side ry/RY, yb/YB, br/BR. The ratio obatined will be recoded. This is the ratio test.

N.Suresh

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bubbapebi
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#8
In reply to #1

Re: Capacitor testing

06/17/2008 4:46 AM

Please remember to remove the capacitor from the circuit and discharge it before you test it. A functional motor-starting capacitor can store enough of a charge to wallop your capacitance meter.
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Gadget Guy
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Location: Los Angeles, California
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#5

Re: Capacitor testing

06/16/2008 11:03 PM

Capacitor Meters are nice, but expensive. If you do not have one available try these old fashioned tests. First, remember that capacitors can store electricty, so use a Voltmeter to drain the static charge to earth (Ground) if you remove it. METHOD ONE-AMPERAGE TEST: With the capacitor in the circuit, use an Ammeter. The amps should be high for about one second, then low if the compressor starts. METHOD TWO-INSPECTION: Remove the capacitor and looks for signs of heat or expansion. METHOD THREE-SUBSTITUTE: Replace the capacitor with a good capacitor. METHOD FOUR-RESISTANCE TEST: With the capacitor removed from the circuit, place the terminals of an an analog (Needle type) Ohmmeter on the capacitor terminals. The needle should show low resistance for about one second, then high resistance over the next five seconds. Every meter is slightly different, so try this also on a known good capacitor. METHOD FIVE-TEST THE OTHER COMPONENTS: This size capacitor sounds like a Start Capacitor (Is it in a round plastic case?). It is typically disconnected from the circuit after 1-2 seconds. Is to motor good? Is the disconnect device good?
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Randall
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#7

Re: Capacitor testing

06/17/2008 3:24 AM

Here's a reasonable multimeter with a 200 µF (3% accuracy) range for £25 in the UK

http://cpc.farnell.com/jsp/displayProduct.jsp?sku=IN05245&CMP=KNC-GUK-CPC-GEN-SKU

Or $70 in the US

http://www.industrydepot.com/DigitalMultimeter01.htm

Of course: that's still too much for a one off job, but if you do this sort of thing regularly it could be a good investment.

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#9

Re: Capacitor testing

06/17/2008 6:50 AM

It has been my experience that motor starting capacitors are generally good or bad and don't usually degrade in value. So a simple check of whether one is good or bad is as follows:

1. As already stated, ensure the capacitor is discharged - if it's bad, it will be.

2. Disconnect all conductorss from it.

3. Using an ohmmeter, select a high range and connect the meter leads to the capacitor. A good capacitor will start out reading a very low value of resistance that will continualy increase in value as the capacitor charges. At some point, the capacitor will be charged as fully as the meter source can accomplish and the resistance reading will stabilize somewhere in the megohm to infinity range.

4. A bad capacitor will either read a steady very low resistance value if shorted (punctured dielectric) or a steady high to infinite resistance if internally open.
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umpradhan
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Join Date: May 2008
Posts: 50
#10

Re: Capacitor testing

06/18/2008 6:10 AM

Dear Sir,

The basic use of capacitor installation in the agricuture field or in engineering workshop etc. is for the power factor imorovement.

Ones the capacitor is installed of good and serviceable quality, the power factor of the system where it is installed should improve.

In past we have tested numerous types of capacitors normally being installed for electric motors of 7.5 HP and above as it was mandatory for the consumer of a state electricity board that at the consumer's premises where there is an electrical motor above 7.5 HP, the proper size of the capacitor is a must.

The capacitor testing will be conveyed to you shortly.

Regards,

Ulhas Pradhan
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Users who posted comments:

Anonymous Poster (1); bubbapebi (1); Epsilon (1); Gadget Guy (1); Nagarajan.Suresh (3); olivinak (1); Randall (1); umpradhan (1)

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