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Old 08-05-2008, 04:01 PM   #1
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Has anyone put a scope across the run/start capacitors of a 60 Hz motor and seen whether the caps see voltage or current at 60 Hz, assuming the motor is running at constant speed?

If so, are the waveforms sinusoidal?

I'm wondering what effect the motor back emf has on these caps.

Thanks.

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Old 08-05-2008, 08:04 PM   #2
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Man...you kinda got "issues" with capacitors...dont cha.

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Old 08-05-2008, 09:08 PM   #3
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Originally Posted by 8 Ball View Post
Man...you kinda got "issues" with capacitors...dont cha.
Here's my current issue with caps.
[Get it? Current?]


I think ya' can measure a compressa' motor cap in place wit' da' the motor runnin'; no C meedah, no removin' from da' circuit.

Ya' measure da' V across da' cap and da' I through da' cap wit' ya' clampon ammeter an' den, at 60 Hoitz, C in mikes is equal ta' 2650xI/V.

So for a 25 uf motor cap, you could measure V = 200v and I = 1.9A.
But if the current isn't a sine wave I don't know if this will work.

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Old 08-06-2008, 05:49 AM   #4
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LMAO!!...now me gots it!!
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Old 08-06-2008, 09:12 AM   #5
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Yes for a singe phase motor the waveform would be sinusoidal, and you should be able to see the change in the phase angle of the curve, between voltage and amperage, and the time it takes to change, as it limits the current to the motor.

Geek!!

Last edited by 8 Ball; 08-06-2008 at 10:00 AM.
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Old 08-06-2008, 11:11 AM   #6
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SINUSOIDAL???? Isn't that an old Phil Collins song?
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Old 08-06-2008, 01:30 PM   #7
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Originally Posted by statman View Post
SINUSOIDAL???? Isn't that an old Phil Collins song?
Nah, it's got more to do with this
http://www.youtube.com/watch?v=4qoymGCDYzU&feature=related

So, Mr. Ball, my idea is a valid in-circuit test for a motor capacitor?

I looked into
http://www.google.com/search?hl=en&q=define%3A+geek
and I'm not admitting anything until I talk to my attorney. I will say, though, that I don't do Carnivals.

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Old 08-06-2008, 06:10 PM   #8
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HEY STATSMAN!!! Where ya been...eh!!

Is Phil Collins Canadian too!?

I dont see why it would not be a valid test, although I cant picture setting up a scope at a customers house, or on a roof to test an $8.00 part.

I know you must have your reasons, and good luck. Telecommunications?

Last edited by 8 Ball; 08-06-2008 at 09:50 PM.
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Old 08-07-2008, 09:16 AM   #9
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Quote:
Originally Posted by 8 Ball View Post
HEY STATSMAN!!! Where ya been...eh!!

Is Phil Collins Canadian too!?

I dont see why it would not be a valid test, although I cant picture setting up a scope at a customers house, or on a roof to test an $8.00 part.

I know you must have your reasons, and good luck. Telecommunications?
No, no, no scope. That was only to confirm a sine wave.
All you need is the formula, a DVM and a clamp on ammeter to check motor capacitors in circuit.
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Old 08-07-2008, 06:53 PM   #10
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OK now I understand. Have you had a chance to apply it?

Last edited by 8 Ball; 08-07-2008 at 07:08 PM.
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Old 08-08-2008, 09:24 AM   #11
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OK now I understand. Have you had a chance to apply it?
Not yet. Too many honey-doos.

I'm hoping some HVAC guy on this forum with a clamp-on ammeter will do the lab work on this idea. The test should take 3 minutes. If the V I values don't match the capacitor's marked value on a known-good compressor, it's back to the drawing board.
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Old 08-10-2008, 07:31 AM   #12
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Will I get a prize?!

If not, can I volunteer someone else...eh!

That post that started..."if your REALLY comfortable working around electricity"... haunts me, at times like this.

Last edited by 8 Ball; 08-10-2008 at 07:43 AM.
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Old 08-10-2008, 09:17 AM   #13
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Originally Posted by 8 Ball View Post
Will I get a prize?!
Well, you'd contribute to the advancement of science, and so on, blah, blah. . .


No, hold on. . .I just found your prize.
http://www.youtube.com/watch?v=QXLqM...eature=related

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