Re: PFCs

• To: tesla-at-pupman-dot-com
• Subject: Re: PFCs
• From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Fri, 22 Oct 1999 16:41:53 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Yes, they will work, but remember that motor start caps are designed for low
duty cycles (something like a few seconds in every hour).  The current
flowing through the cap will make it heat up.. In a motor start app, this is
short duration, so it doesn't get TOO hot.

You would want motor run caps, which are designed for 100% duty cycle (and
are correspondingly more expensive).

On the other hand, your motor start caps, if cheap enough, could be derated
to run continuously.  You'd need some combination of series and parallel to
get the right current ratings and capacitance (voltage will be no problem).

Or, odd thing, buy a power factor correction capacitor.

Typical motor run cap has a dissipation factor of 0.1% (GE 97F series).
Brand new, a 75 uF run cap (240VAC rating) will set you back about $30..
Surplus, a lot less. As you've noticed, motor start caps in the same size
run about $10.


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, October 22, 1999 5:18 AM
Subject: PFCs


>Original Poster: Grayson B Dietrich <electrofire-at-juno-dot-com>
>
>Hello All,
>
>I was wondering,
>
>Would a bank of paralleled motor-start caps be suitable as a power factor
>correction cap? I I calculated, if memory serves, something like 80uF or
>90uF for my 12kV 60mA NST. When powering my TC, it blows a 10 amp fuse no
>problem...   ...and I really wish it wouldn't. Since then I could safely
>fuse my variac with the fuse holder built into it.
>

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