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Old 16th June 2012, 11:53 AM   #11
fpitas is offline fpitas  United States
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Quote:
Originally Posted by davidsrsb View Post
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.
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Old 16th June 2012, 03:39 PM   #12
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by davidsrsb View Post
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.
Why use these as bypass over poly's ...?
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Old 16th June 2012, 04:44 PM   #13
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Originally Posted by a.wayne View Post
Why use these as bypass over poly's ...?
They tend to be quite a bit cheaper than "regular" film caps?
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Old 16th June 2012, 04:45 PM   #14
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Originally Posted by fpitas View Post
Sounds like the same cap (and maybe the same seller). The part number on mine is 27L781.
Yup, I guess we got the same cap from the same seller.
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Old 17th June 2012, 11:18 AM   #15
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Originally Posted by Navyblue View Post
They tend to be quite a bit cheaper than "regular" film caps?
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.
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Old 17th June 2012, 12:42 PM   #16
AndrewT is offline AndrewT  Scotland
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Motor run capacitors come in both plastic film type and electrolytic type.
The electrolytic are generally much smaller than the film type of the same value. And much cheaper.
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Old 17th June 2012, 12:44 PM   #17
fpitas is offline fpitas  United States
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Quote:
Originally Posted by AndrewT View Post
Motor run capacitors come in both plastic film type and electrolytic type.
The electrolytic are generally much smaller than the film type of the same value. And much cheaper.
At least in the States, only the motor-start seem to be electrolytic. All the motor-runs that I found datasheets for were polypropylene.
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Old 19th November 2012, 07:16 PM   #18
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Originally Posted by Tony View Post
voltage ratings for one, the ac voltage translates to about x1.4 dc, so if you have a 220vac cap, you are good to go for 308volts dc....
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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