Re: Power Factor Correction weirdness?

• To: tesla-at-pupman-dot-com
• Subject: Re: Power Factor Correction weirdness?
• From: Alan McIntyre <alan-at-fusion.pair-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Wed, 09 Feb 2000 18:41:44 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Adam wrote:
> Can someone explain what I'm seeing when I attempt to power factor correct
> my neons? I've got my DMM in series with the primary of a 12,000 60mA NST,
> and the secondary of the NST is shorted.  With no PFC caps, it reads 7.13
> Amps.  But when I start adding caps in parallel with the NST primary, the
> current reading drops dramatically-- more than I expected it to.  Here are
> the results:
>     PFC Caps    Ammeter Reading (amps)
> 
>     0                7.13
>     50 uF            4.96
>     100 uF           2.81
>     150 uF           1.14

Without running too many numbers through a calculator, I'm going to
guess here and say that your PFC's are bringing the power factor up
(with 150 uf I'd guess you're pretty close to pf=1).  A 150uf cap at 60
Hz and 120V should draw about 6.8A - which is close to the change in
current you've seen.  Since the current to the capacitors is 180 degrees
out of phase with the inductive portion of the NST current, it lowers
the total line current drawn.  If you go much higher than 150uf, I'll
bet you'd see current go back up.

Hope this makes sense,
Alan McIntyre
alan-at-norfolkgraphics-dot-com
http://norfolkgraphics-dot-com

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