Capacitor AC and DC voltage rating?

I have some AC capacitors and was curious to how to convert the AC rating to a DC rating. I have heard you can operate AC capacitors at 300% of their rating with DC, but I am not sure if this is true.

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lemonie7 years ago
What have you actually got? (Type, capacity)

L
workinprogress37 (author)  lemonie7 years ago
I believe it is a motor start or run capacitor from a washing machine. It is rated at 110 VAC and the capacitance wasn't specified but I measured it as 182 uF.
gmoon7 years ago
For those caps that specify both VAC and VDC, the VDC rating is usually 4 or 5 times the VAC ratings. So 3X is probably OK.

It's best to find the proper specs for the cap in question.

But even film caps intended in AC applications (such as coupling) are usually rated first and more prominently for VDC. So if you plan to convert the rating, be sure you know which one is the "base" rating.
Re-design gmoon7 years ago
Would you show me a cap that has both ratings?  I've never seen that and I might just be missing it.
gmoon Re-design7 years ago
Sure--it's usual to see this in full specs for polyester, propylene and other film caps.

I have the Allied catalog in my lap, and the "Cornell Dubilier" PVC Poly caps are rated: "100 to 1000 VDC (70-200 VAC)".

The "Illinois" MWR Series Polyester caps likewise are rated:
> Working voltage: 50 to 1,000 VDC
> Voltage, Alternating Current: 30 to 250 VAC

This film cap link (Illinois) might be helpful, it displays both ratings...

Anything above 600 VDC will work as a coupling cap in a typical tube amp, so that's all I generally care about...
Re-design gmoon7 years ago
Thanks, I love learning something that I didn't know!