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RE: What size PFC ...
The problem you show is different from the one I showed. The problem I
solved was for a 50% to 90% PF correction. Your problem is for a 100%
correction and a different no cap power factor. I will use your amperes.
The 11.16 amps at 120 volts = 1339.2 VA
The 7.5 amps at 120 volts = 900 VA
The power factor is 900/1339.2 = .672 = 67.2% power factor
The power factor angle is arc cos(.672) = 47.78 degrees
The VARs to correct to 100% = 900 * tan(47.78) = 991.8
The PFC capacitance = 991.8/(6.283 * 60 * 120^2) = 182.7 uf
You would need 182.7 uf to correct your NST to 100% power factor.
Actually your NST is operating at 1339.2 Var without a cap. However, the 900
VA is only a guess for the 100% power factor operation because of other
unknowns. You can confirm this only by test with a 182.7 uf cap. Even this
cap might give a leading power factor.
As you can see this problem is complicated and can be done in several ways.
Try this on MicroSim. You should get the same answer.
From: Terry Fritz [mailto:twftesla-at-uswest-dot-net]
Sent: Sunday, September 03, 2000 2:57 PM
To: John H. Couture
Subject: RE: What size PFC ...
At 12:42 PM 9/2/00 -0700, you wrote:
>The rearranged equation is still incorrect when used with active volt amps.
>The equation is correct only when used with reactive volt amps. To convert
>active to reactive amps you need to use complex numbers or trig functions.
>prefer to use trig functions as I show in my post to the Tesla List 7-14-96
>"PFC for Neons". Can it be that long ago?
>Note that using your "close enough" equation will always give you a leading
>power factor which is worst that a lagging power factor. It would be
>interesting to see what a model by microSim would show.
>To properly meter the TC load you need at least 4 meters, volts, amps,
>watts, power factor. The power factor meter is required to tell you if the
>load is leading or lagging. A VAR meter would help and save you having to
>the necessary calculations.
>Bart I am glad to hear that you are researching the problem. As Terry
>pointed out there may be other issues and your work may shed more light on
I pulled up your old post:
PFC for Neons
· To: Tesla List
· Subject: PFC for Neons
· From: "John H. Couture"
· Date: Sun, 14 Jul 1996 17:55:23 GMT
Uncorrected neon transformers are usually 50% power factor. To correct them
for 90% power factor add a capacitor calculated as follows:
For 120 volts c uf = .079 V A
For 240 volts c uf = .020 V A
V = neon secondary volts A = neon secondary amps
The factors K1 = sin(arccos(LPF)-sin(arccos(HPF))
K1 = .43 for 50% to 90% power factor
For 120 volts K2 = (.43 x 10^6)/(6.283 F V) F = 60 Hz
K2 = (.43 x 10^6)/(377 x 120^2) = .079
For 240 volts K2 = .0198 or .02
Example: Neon 15000 volts 60 ma 120 volts 60 Hz
C = .079 x 15000 x .06 = 71.1 uf
sniped efficiency text...
So your saying I should have a 71.1 uF cap instead of my present 200uF on
my 15/60 coil...
Let's look at the RMS current draw of my 15/60 coil with various PFC caps
Cap size AC line current Notes
0uF 11.16 ARMS No PFC cap
71.1uF 9.19 ARMS John's equation
165.8uF 7.75 Arms "Terry's" equation
200uF 7.72 ARMS The "real" best PFC cap size