# capacitor

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• 01-09-2013, 06:20 PM
Jesjen829
capacitor
Can you tell if a capacitor is failing from output voltage alone?
• 01-09-2013, 06:25 PM
wdshea
i always just check the mF against the rating... you can discharge a cap by setting your meter to VAC and stick it across its terminals.
• 01-09-2013, 06:45 PM
kdean1
No. Use a meter with a microfarad scale to measure its capacitance. Lacking that discharge it first by shorting across the terminals, then use the resistance scale. Hold the probes on the terminals and the resistance should rise as the capacitor stores the charge. Also test for continuity from the terminals to the capacitor case. There should be no continuity.
• 01-09-2013, 07:02 PM
wdshea
cant you damage a cap by shorting across the terminals? thats why i suggest the "voltage test" across the terminals...
• 01-09-2013, 08:50 PM
Core_d
The proper way to discharge a capacitor is with a resistor i forget what ohm rating but i think one off an old start cap will work. And from what ive been taught capacitors dont increase voltage they help smooth out the voltage drop in AC cycles witch is why their not needed for three phase. So no i dont think its possible to check with voltage
• 01-09-2013, 08:51 PM
Ductfisher
I always use a mfd setting on my meter. After discharging of course.
• 01-09-2013, 09:04 PM
hvac wiz 79
Quote:

Originally Posted by Core_d
The proper way to discharge a capacitor is with a resistor i forget what ohm rating but i think one off an old start cap will work

I just use my tongue. Beats drinking energy drinks

Sent from my SGH-T999 using Tapatalk 2
• 01-09-2013, 09:13 PM
SBKold
The capacitor has no "output voltage " you would be reading back emf voltage of motor and that alone does not tell
You mfd. However there is a formula to use two parameters and determine mfd of said capacitor.
• 01-09-2013, 09:13 PM
Mr Bill
Quote:

Originally Posted by hvac wiz 79
I just use my tongue. Beats drinking energy drinks.

+1...beats a cup of coffee in the morning anytime. :grin2:
• 01-09-2013, 09:20 PM
rundawg
Quote:

Originally Posted by Core_d
The proper way to discharge a capacitor is with a resistor i forget what ohm rating but i think one off an old start cap will work.

That would be a 15,000 ohm, 2 watt resistor. Here is what I use - see attachment.
• 01-10-2013, 08:01 AM
Jesjen829
I always check voltage to them then I wondered the other day why I was doing this. So basically that number tells me nodda, right?
• 01-10-2013, 08:15 AM
timebuilder
Quote:

Originally Posted by Jesjen829
I always check voltage to them then I wondered the other day why I was doing this. So basically that number tells me nodda, right?

The ressssst....of the story is this:

You use that voltage AND a current reading to calculate a value that tells you if the capacitor can supply the correct value of microfarads while under its normal load.

As for myself, I remove the cap wires and use my meter to measure uF directly.
• 01-11-2013, 12:19 AM
Core_d
[QUOTE=timebuilder;14958021]The ressssst....of the story is this:

You use that voltage AND a current reading to calculate a value that tells you if the capacitor can supply the correct value of microfarads while under its normal load.

Any chance i could get a solid formula on this? Ide like to mess around with this.
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