15uF Air Conditioner caps?

[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.

[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.

[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]

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.

[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.

[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]

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.

[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.

[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

[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.

[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

[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.

[km6xz]

Non-polarized caps will work fine except where space is limited. Not sure where the notion that filters need to be polarized but a capacitance by one type is the same capacitance as from another. There are differences. For example motor caps have a lot higher inductive reactance than electrolytics of the same value of capacitance so you would not want then in high frequency circuits but you are talking about 120 hz, which would be fine. The larger ones use oil as the dielectric between the plates(rolls) which lasts for decades or more. High quality oil caps would last hundreds of years and would only deteriorate if the oil was contaminated or there was a leak. The problem with oil caps include size, cost and limited off the shelf values. Otherwise they are some of the best capacitors made.
Here, we can get oil caps in all sorts of sizes since they were commonly used in both military and consumer products for everything from filtering to coupling and bypassing functions. Another interesting cap found here in industrial surplus is Teflon Capacitors.

[tedmich]

Those 15uF caps are quite cheap! They are not small (about 1.5" dia x 3" long) and are probably CBB60 series PP film that will last almost forever. They cost 26X more elsewhere (!) http://www.amazon.com/CBB60-450VAC-P.../dp/B00E1GM2YG

The Ebay supplier linked to Senate testimony about fake electronic components from China, and this sobering video:

[eschertron]

Those 15uF caps are quite cheap! They are not small (about 1.5" dia x 3" long) and are probably CBB60 series PP film that will last almost forever. They cost 26X more elsewhere (!) http://www.amazon.com/CBB60-450VAC-P.../dp/B00E1GM2YG

The Ebay supplier linked to Senate testimony about fake electronic components from China, and this sobering video:

It looks like a video of a recycling center?