15uF Air Conditioner caps?

[Pdavis68]

I didn't even notice the others were 450VAC vs VDC, so they'll easily cover any voltage I'm going to hit in a tube amp. Nice!

The 15uFs seem like a much better deal. 750uF for $15 vs. 1000uF for $34. I ordered a set.

[tedmich]

check these as well
Lot of 50 Motor Start Capacitors CBB60 SH 20uF 240VAC | eBay
50 metalized PP film run caps (mistakenly listed as start caps which are usually electrolytics) for $0.68 each. They are not small but at 240VAC rating they should handle more than 500VDC

The translation of a VAC rating to a VDC rating is not a simple equation, a conservative rule of thumb is 2X, but its really specific for each cap design. For example the Vishay MKP series of PP film caps includes both VAC and VDC ratings:

and the VDC rating is about 3x VAC

[Leo_Gnardo]

A run cap often acts to help start a motor, but is not really called a "start" cap. They call them run caps but usually a motor will not start without it, or if it does it will start very slowly and build speed, rather than jump to action like you would see on an AC system

True 'nuff. What you want is a cap that's rated for 100% duty cycle. Heck at that price might well be a huge bargain. Over at Audio Asylum there's a bunch of inmates who love to use 'em. Search mostly the Vacuum Tube DIY and SE (single-ended) headings. You can search & read to your heart's content & spinning brain cells besides, without having to join.

[mort]

Mort says this is a start and run cap, so I'm assuming that qualifies. At $15 for 50 caps, it might be worth giving it a shot.

A run cap often acts to help start a motor, but is not really called a "start" cap. They call them run caps but usually a motor will not start without it, or if it does it will start very slowly and build speed, rather than jump to action like you would see on an AC system

[mort]

Well pucker my pituitary, learn something new all the time. And here I thought I had this question nailed but it looks like I am yet again the student. Thanks for the info.

[Pdavis68]

Mort says this is a start and run cap, so I'm assuming that qualifies. At $15 for 50 caps, it might be worth giving it a shot.

[Leo_Gnardo]

If you're going to experiment with this sort of cap, you want "run" caps not "start" caps. Oil caps have been the standard for many decades and they can last a very long time. In recent years film caps have started to take over the market. Yes they CAN be used for filtering DC, non polarized it doesn't matter which terminal is plus or minus, one less mistake you can make, what's wrong with that. Used in early hi fi & theater amps, who would argue with Western Electric, RCA, Altec, Marantz? Not so often used in guitar amps, especially commercial ones with a projected life of 5 or so years. In fact... never. FWIW Carr has been using film filter caps in their amps at least as far back as 2000. I guess Mr. Carr is in a "built to last" frame of mind. Like most of us.

If you select proper motor run caps & run them within their limits, they should work flawlessly for decades.

[Pdavis68]

I was looking for the + or -. I assumed it was polarized and you just couldn't see the + or - from the photo angles. Thanks for pointing that out. Oh well, would have been nice.

[mort]

That one is a start/run cap that stays in the circuit and aids in both the starting of a motor and also the correct running current of the motor. Some compressors rely on a start cap as well that has a potential relay that removes the high powered start cap from the circuit after start up.

[Jazz P Bass]

My thoughts are that the capacitor is a "Start" capacitor.



They are meant for intermittent duty. A centrifugal clutch kicks the capacitor out of circuit after the motor starts up.

In addition, it appears to be a nonpolarized unit.

[mort]

Those types of caps aren't polarized, so they couldn't be used as filters, and I don't think that size is used in amps anyway, plus they would be giant compared to electronics caps. Probably wouldn't work in an audio circuit anyway. But I do AC work for a living and on the face of it that is a stellar deal.

[Pdavis68]

I came across this auction on e-bay. Seems like a fantastic deal, if these would be usable in tube amps:

New 50 Piece Lot of 450V 15uF Capacitor 450VAC | eBay

Does it really matter if its original function was for AC motors (I assume that's what they're for as the comapny, Digital Tech, appears to specialize in capacitors for AC motors).

This isn't for amps for sell, just personal stuff. Fifty 450V, 15uF caps for $15 seems like a pretty exceptional deal.