Oil Capacitor DC vs. AC Voltage Rating

[valveitude]

Can someone tell me how to determine the DC rating based on the AC rating of oil caps. I assumed it would be 1.414 the AC rating, but I've seen several caps listed with the DC being 2 or more times the AC. What gives?

Thanx,
Casey

 

[pedroskova]

If you're talking about ASC or GE motor run caps, 1.4x AC rating would be pretty conservative. I think a GE engineer told someone that the 440V motor runs were safe with 1000VDC. I wouldn't do that, but it's an indicator of sorts.

 

[Sherman]

If you're talking about ASC or GE motor run caps, 1.4x AC rating would be pretty conservative. I think a GE engineer told someone that the 440V motor runs were safe with 1000VDC. I wouldn't do that, but it's an indicator of sorts.

I was also told that doubling the AC voltage rating of ASC caps for DC was safe. However when I built a pair of power supplies using them I went with 1.4x as a maximum! 😉