From here:
http://www.galco.com/techdoc/gecp/27l801_cp.pdf
It says:
"This capacitor series is designed specifically for the motor run applications where the capacitors are used in conjunction with permanent split capacitor type motors. They may be used on either 50 or 60‑Hertz systems but should not be used at higher frequencies or in applications where higher frequency harmonics are present. For those types of applications the General Purpose AC Capacitors should be used."
Apparently it is not uncommon for people to use motor run capacitor for audio. Should attention be paid to the above with regards to motor run capacitor in general? Or does that just apply for this particular line? The problem is I already got some of those for DC filtering and only found the datasheet after I ordered.
http://www.galco.com/techdoc/gecp/27l801_cp.pdf
It says:
"This capacitor series is designed specifically for the motor run applications where the capacitors are used in conjunction with permanent split capacitor type motors. They may be used on either 50 or 60‑Hertz systems but should not be used at higher frequencies or in applications where higher frequency harmonics are present. For those types of applications the General Purpose AC Capacitors should be used."
Apparently it is not uncommon for people to use motor run capacitor for audio. Should attention be paid to the above with regards to motor run capacitor in general? Or does that just apply for this particular line? The problem is I already got some of those for DC filtering and only found the datasheet after I ordered.
I'm using 120uF GE motor-runs for horn capacitors, so I dragged one into the lab and measured it on the Agilent Impedance Analyzer. It had almost unmeasurable DF, and had about 27nH series inductance. Up to 2MHz it was looking more or less like a perfect cap. Now, the Galco may or may not be as good, but I bet it's plenty good enough for bypass use.
What I ordered from eBay was said to be GE 120uF 150VAC (I haven't receive it). So glad to know that.
I couldn't find any datasheet, that was the closest I found and I thought the GEM is GE. They have similar model numbers though.
Sounds like the same cap (and maybe the same seller). The part number on mine is 27L781.
I imagine almost any motor-run cap is good for audio, since to my knowledge they're all very low loss polypropylene. They're designed to withstand huge surge currents, so the ESR has to be very low.
No, they are designed to run om mains supply and fail safe, so they often use evapourated metal film rather than foil, with fairly high ESR, so that a pin hole blows open. The dielectric is good, but there is a relatively high ohmic loss.
Still a much better dielectric than any electrolytic though.
Yes, they are film rather than foil, but they are also rather large physically, so there's plenty of surface area. I'll agree a foil cap of that size would beat these on ESR.
Yes, they are made for the low markup "industrial" market, not the "boutique audiophile" one and therefore affordable. The performance should be fine for a crossover or valve amp supply filter.
At least in the States, only the motor-start seem to be electrolytic. All the motor-runs that I found datasheets for were polypropylene.
As you noted, the rating for that cap is stated as volts RMS in the data sheet. I was looking at a Temco data sheet and they didn't specify a rating. I called and asked. They rate theirs peak to peak! In their video they even suggest using a 600v cap in a 440v service. Kind of shocking...
The take home here is that one should not assume to operate all motor run caps at 1.41 times name plate voltage until you read the data sheet.
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