# parallelling motor capacitors



## Electron_Sam78 (Feb 26, 2010)

Tomorrow I will have to parallel some capacitors together temporarily until we get the right replacement in. I haven't done a whole lot of work with capacitors over the years so I'd like to run this by the members here. We have a 65uf, 240VAC cap. (this is a factory cap. on a commercial gate opener motor, 1/2 HP, 120V). I have spare motor run caps. with ratings of 3uf, 370VAC + a 30uf, 440VAC + a 32uf, 400VAC. All parallelled I would have a 65 uf circuit, with a maximum safe operating voltage of 370 VAC correct? Would this setup work or do all the parallelled caps need to be around the same capacitance? Also, from what I've researched the voltage rating only determines maximum safe operating voltage. You can go lower but not higher and circuit voltage doesn't change capacitance. Is that correct? ​


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## A Little Short (Nov 11, 2010)

Electron_Sam78 said:


> Tomorrow I will have to parallel some capacitors together temporarily until we get the right replacement in. I haven't done a whole lot of work with capacitors over the years so I'd like to run this by the members here. We have a 65uf, 240VAC cap. (this is a factory cap. on a commercial gate opener motor, 1/2 HP, 120V). I have spare motor run caps. with ratings of 3uf, 370VAC + a 30uf, 440VAC + a 32uf, 400VAC. All parallelled I would have a 65 uf circuit, with a maximum safe operating voltage of 370 VAC correct? Would this setup work or do all the parallelled caps need to be around the same capacitance? Also, from what I've researched the voltage rating only determines maximum safe operating voltage. You can go lower but not higher and circuit voltage doesn't change capacitance. Is that correct? ​


That is correct, and I guess you already know (since you said 370V) that when you have caps with different voltage ratings paralled, the voltage for them all will only be the lowest of the caps.


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## Dennis Alwon (May 9, 2009)

I agree also. The capacitance will only be as high as the lowest capacitor. Hence a 370V and 440V unit will only put out 370V. The MF is, as you stated, additive when paralleled.


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## Roadhouse (Oct 16, 2010)

Grainger.


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## Electron_Sam78 (Feb 26, 2010)

Dennis Alwon said:


> I agree also. The capacitance will only be as high as the lowest capacitor. Hence a 370V and 440V unit will only put out 370V. The MF is, as you stated, additive when paralleled.


But it will only "output" 370V if the circuit supplies that voltage to the capacitors correct? Capacitors don't output a voltage other than what the circuit is designed to apply to the capacitors right? Just clarifying here. Like I said I'm rusty with capacitor theory


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## Dennis Alwon (May 9, 2009)

Electron_Sam78 said:


> But it will only "output" 370V if the circuit supplies that voltage to the capacitors correct? Capacitors don't output a voltage other than what the circuit is designed to apply to the capacitors right? Just clarifying here. Like I said I'm rusty with capacitor theory


........................


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## Dennis Alwon (May 9, 2009)

Dennis Alwon said:


> A 120V capacitor can put out 370V.


Sorry I should have said can tolerate 370V


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## Electron_Sam78 (Feb 26, 2010)

np just trying to eliminate confusion :thumbup:


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## GPM (Jun 17, 2012)

Capacitors do not add in serial, they add in parallel. So two caps of 100 uf in parallel is 200 uf. The voltage rating is what has been said - the lowest one is the highest you can go.


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