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Substitute value for motor start capacitor?

My greenhouse fogger (think of an upward-facing fan sucking water out of a reservior and blowing it in the air) failed recently, and I found that the capacitor attached to the motor had exploded, melting much of the specifications printed on the side. The only markings legible specify 250V AC, 50/60Hz, 25-70 degrees C, -5+10%, Capacitor.

So I contacted the distributor of the fogger, and he says the manufacturer specified the the capacitor as follows:

250VAC/12 micro F(U)/SH-M60HZ

The distributor has none of these in stock, so I tried to find a local source. I've found a number of sources for motor start capacitors (I'm assuming it's a motor start capacitor based on the 250VAC rating), but they all start at 21 mf.

QUESTION: Is it OK to substitute the 21 mf capacitor for the the 12 mf called out by the manufacturer? What will be the effect on the motor?

Thanks, A.D.

BTW, the (melted) capacitor is black plastic encased, measuring 1.125" x

2.375" x .625", with one white and one red lead.
Reply to
Augie Dawg
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Connect two 21mf/250V capacitors in series - this will give a total capacitance of 10.5mf, which may be ok.

woodglass...

Reply to
woodglass

I don't know anything practical about motor start or motor run capacitors or what size they should be, but I would just interject to say that mF would mean mili Farad (0.001 F) in general lingo, where a micro Farad is 0.000001 F. Micro is abbreviated with a greek letter 'mu', pronounced like the beginning of the word "mule" and written like a lower case 'y' except mirrored left-to-right. Micro is also sometimes abbreviated as a 'u' (e.g. uF for micro Farad), or, as I understand, 'mm' (e.g. mmF for mili-mili-Farad which would sort of be equivalent to micro Farad).

If the original capacitor was 12 micro Farad and someone offers a 21mF (or two paralleled 21mF) capacitor(s), make sure they are micro Farad and not mili Farad.

For what it's worth.

j
Reply to
operator jay

from experience only i have found that cap size is less important than cap voltage wire it up and listen to how it sounds on startup it may take a while longer

Reply to
PCK

Your comments are obviously spot-on....chalk my error up to not having used my undergraduate EE training for over 30 years! All values are indeed microfarads....a millifarad capacitor would pack quite a punch for a sub-horsepower motor!

A.D.

Reply to
Augie Dawg

2 capacitors of identical values connected in parallel results in a capacitance equal to 2x the value of a single capacitor.

So, connecting two 21mF capacitors in parallel will result in an overall capacitance of 42mF

2 capacitors of identical values connected in series results in a capacitance equal to 0.5x the value of a single capacitor.

So, connecting two 21mF capacitors in serieswill result in an overall capacitance of 10.5mF

woodglass...

Reply to
woodglass

thank you

Reply to
operator jay

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