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Old 8th June 2012, 01:47 AM   #1
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Default Motor run capacitor

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.
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Old 8th June 2012, 01:58 AM   #2
AJT is offline AJT  Philippines
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go ahead and use them, ripple frequencies are 100hz or 120hz, well within the cap spec...
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Old 8th June 2012, 02:19 AM   #3
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Thanks.

May I know what spec are you looking at?
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Old 8th June 2012, 02:27 AM   #4
AJT is offline AJT  Philippines
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http://www.galco.com/techdoc/gecp/27l801_cp.pdf
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Old 8th June 2012, 02:52 AM   #5
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I mean, which parameter are you looking at to know that?
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Old 8th June 2012, 04:05 AM   #6
AJT is offline AJT  Philippines
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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....

you line frequency is 50hz so ripple translates to 100hz, no cause for concern here....
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Old 14th June 2012, 02:22 PM   #7
fpitas is offline fpitas  United States
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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.
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Old 15th June 2012, 04:51 PM   #8
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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.
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Old 15th June 2012, 04:56 PM   #9
fpitas is offline fpitas  United States
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Quote:
Originally Posted by Navyblue View Post
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.
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Old 16th June 2012, 04:37 AM   #10
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Quote:
Originally Posted by fpitas View Post
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.
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