Rating Motor Run Caps for Tube PS

cddeluca · 10th January 2010, 08:34 PM

Uber noob here. I can't seem to find a clear answer to what the voltage rating of a cap needs to be for a valve rectified, cap input power supply. I've seen motor run caps labeled 440 VAC, so am I correct in assuming that if the RMS input to the cap is below 440 V then I'm OK?

Thanks for any help.

RJM1 · 26th January 2010, 10:41 AM

I’m not sure if this answers your question, but. If you have a 440Vac motor run capacitor the peak voltage across the capacitor will be 440 Vrms * 1.414 = 622 Vdc and could safely be used in a DC power supply where the peak DC + AC is less than 622V.

cddeluca · 12th February 2010, 02:39 AM

thank you - i believe you did answer my question. it seems that if you look at caps from hobbyist suppliers they reference the peak voltage a cap will tolerate. However, on an apple-to-apples comparison it seems that a motor run cap rated "VAC" can be directly compared to a transformer secondary which is typically specified as VAC.

10th January 2010, 08:34 PM	#1
cddeluca diyAudio Member Join Date: May 2009	Rating Motor Run Caps for Tube PS Uber noob here. I can't seem to find a clear answer to what the voltage rating of a cap needs to be for a valve rectified, cap input power supply. I've seen motor run caps labeled 440 VAC, so am I correct in assuming that if the RMS input to the cap is below 440 V then I'm OK? Thanks for any help.

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26th January 2010, 10:41 AM	#2
RJM1 diyAudio Member Join Date: Jan 2010 Location: Titusville, Fl.	I’m not sure if this answers your question, but. If you have a 440Vac motor run capacitor the peak voltage across the capacitor will be 440 Vrms * 1.414 = 622 Vdc and could safely be used in a DC power supply where the peak DC + AC is less than 622V.

12th February 2010, 02:39 AM	#3
cddeluca diyAudio Member Join Date: May 2009	thank you - i believe you did answer my question. it seems that if you look at caps from hobbyist suppliers they reference the peak voltage a cap will tolerate. However, on an apple-to-apples comparison it seems that a motor run cap rated "VAC" can be directly compared to a transformer secondary which is typically specified as VAC.

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