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Electricians of NS I need your help

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Caveman.
Posts: 9067 - Karma: 330
I'm not sure how many people have any electrical knowledge but I stripped an old air conditioner so I could use the compressor for my vacuum press. I wired it with 120 volts coming from the wall straight to the compressor, the compressor wouldnt turn on but it was obviously drawing current because my shop light temporarily dimmed. Is this because I didn't wire the capacitor into it? + karma for any help

wiring schematic:Click for larger image
Mar 24 2008 10:38PM
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samskisalot
Posts: 711 - Karma: 12
i would say your assumption about the capacitor is probably correct.
Mar 24 2008 10:47PM
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Caveman.
Posts: 9067 - Karma: 330
the only thing that i am concerned about is the compressor says 115 VAC on it while the capacitor says something like 300 volts
Mar 24 2008 10:48PM
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samskisalot
Posts: 711 - Karma: 12
i dunno. i would personally go for the try it and see if it works method. good luck.
Mar 24 2008 10:51PM
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Caveman.
Posts: 9067 - Karma: 330
ya, i wonder what the worst that could happen would be
Mar 24 2008 10:53PM
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flyinghighagain
Posts: 1069 - Karma: 22
the capacitor might be the issue, does the compressor run on ac or dc power? cause that will also matter. most motors run on dc power because it gives constant power instead of alternating making the machine run smoother. The capacitor at 300 V should be fine but just remember to wire it the right way because if your wire the negative and positive ends wrong it could blow up, good luck
Mar 24 2008 10:56PM
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nopoles
Posts: 2216 - Karma: 883
It looks like your assumptoin is correct.

Capacitors build and hold charges, and because the changes are gradual based on the current flow, it's output is usually out of phase by 90 degrees from the source. It's purpose is probably to supply a second voltage spike, 90 degrees out of phase to push the middle piece.

It's common to use capacitors twice the size of what's needed to be safe.

~Paul
Mar 24 2008 10:56PM
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flyinghighagain
Posts: 1069 - Karma: 22
and i know Air condtioning unit run on 220V or 120V?
Mar 24 2008 10:59PM
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nopoles
Posts: 2216 - Karma: 883
Wikipedia's page on capacitors:

"Since the voltage across a capacitor is proportional to the integral of the current, as shown above, with sine waves in AC or signal circuits this results in a phase difference of 90 degrees"

Mar 24 2008 11:00PM
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samskisalot
Posts: 711 - Karma: 12
the capacitor could blow up, or shock you, cause they hold a charge. so just be careful, and you should be fine.
Mar 24 2008 11:01PM
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freestyler540
Posts: 13083 - Karma: 18,724
Correct, a capacitor not only builds charge, but also capacitors also help correct a power factor. A normal household will draw power at a factor of .9 to 1. There is a calculation you can use to find the correct capacitor size.

C=((Tan02-Tan01)Cos01 It)/(2pi f V)

02 is the corrected phase angle
01 is the original angle change
It is the current drawn from the pump
pi is 3.1415
f is the frequency (60hz)
V is your voltage (120V)

the answer will result in uFs (10^-6)

here is some etra help:
Power Factor= Power/(v I)=cos0

I hope this helps


Mar 25 2008 11:32AM
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Caveman.
Posts: 9067 - Karma: 330
thanks for the help guys, i got it wired and it works fine, no big explosions or anything. now i can press skis again!!

Click for larger image
Apr 3 2008 12:09AM
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