The AM Forum

I'd like to use oil capacitors in a power supply, and I'm willing to buy new ones.

But most of what I can find are motor-run capacitors and are rated in AC voltage.

For example, 440 vac oil capacitors are common and not too pricey.

Would those work as filters in a power supply intended to deliver 700 VDC?

(remembering of course, that with no load such a power supply might have a voltage of 800 or so if load is removed).

It seems like AC caps for motor apps would have to be pretty tolerant of transient peaks, and of course, the peak voltage of a 440vac line would be 1.4 times the RMS voltage.

I think we had a thread that touched on this a while back, but I can't seem to find it.

here is a source of oil capacitors that they say are good for 600-800 VDC:

http://angela.com/angelaascpolypropyleneandoilcapacitors.aspx

has anybody tried these caps?

This was originally posted here on an AM FONE thread that was eliminated (went Poof!) because we turned into AOM (angry old men) when the topic was whether to replace caps or not to...

Jim
WD5JKO

Try these:


http://amfone.net/Amforum/index.php?action=search2

or

http://www.highenergycorp.com/oil/oil-filled.html

RF Parts have some http://www.rfparts.com/caps_oil.html

With RF Parts, make sure they test them for capacitance value before shipping. I have ordered a number of caps and other parts from them but they were either out of tolerance or marked incorrectly.


Phil - AC0OB

Actually, that was my thread which went "poof".

Anyway, if you look at pictures in the Angela web page, you will see that those caps are ASC products and the only voltage rating on the cans is 370vac.

Allied carries ASC caps and has the ones on the Angela site as well as similar caps rated at 440vac.

This is what prompted me to post this thread since if the 370vac units will handle 600-800 then the 440vac units should be even safer at those voltages.

Allied seems a bit cheaper for the same caps vs. Angela.

Datasheets accessible from the Allied site also show 660vac versions, but Allied doesn't carry most of those.

I guess I check Newark or Mouser.

660 would be better if they aren't too much more money.

I may have answered my own question as I found some ratings info on the Web that state both a 440vac and a 1000vdc rating on the same cap. Specifically Cornell Dubilier caps.

Likewise they put a 1500vdc rating on the 660vac versions.

An AC rating on a non-polarized cap would still be subject to Vpk=Vrms*1.414

I have always played it safe and used AC caps at 1.414 x RMS voltage. I would not go higher unless the cap was clearly labeled with a DC voltage rating.