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Re: PFC questions
Original poster: John Keith <jskeith-at-interaccess-dot-com>
David,
It seems to me that the location of the PFC caps is a bit odd. I beleive
the caps are usually placed across the 240V line before the ballast. The
purpose of the caps is to reduce current draw by counteracting the lagging
effect of the inductive ballast, which they can't do if they are placed
after the ballast.
The rise in voltage is likely being caused by resonance between the caps
and the ballast and/or the pig. This is actually increasing the current draw
and may burn out the caps. Try moving the caps and see if that helps.
Regards,
John Keith
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, May 03, 2004 9:17 AM
Subject: PFC questions
> Original poster: DRIEBEN-at-midsouth.rr-dot-com
>
> Hello coilers,
>
> I have some questions regarding using PFC caps w/ the primary of a pole
pig.
> I have a 14,400 volt, 15 kVA distribution transformer that I am currently
> just driving a Jacob's ladder with. The ballasting is provided by the
> guts of a 225 amp Lincoln arc welder that has been submerged in SAE 30
> non-detergent motor oil as well as (2) seriesed MOTs w/ their secondaries
> shorted. The MOTs are also submerged in motor oil. The rotory current
> selector switch of the arc welder is mounted where it's accessable so
> as to have some control over the current to the pig. Today, I had a
> little spare time so I decided to measure the input to the LV terminals
> of the pig as well as the output of the HV bushings. Also, I have 200
> uFD of PFC cap in parallel w/ the LV input lugs to the pig. I noticed
> that when I run the pig w/ PFC caps in place, the LV input and HV output
> of the pig increases. Here is a chart of the input/output measurements
> of the pig (the voltage regulation is provided by (2) seriesed 1156
> style 120/140 volt -at- 50 amp powerstats set up for 0 - 280 volts output)
>
> First with 200 uFD PFC without PFC
>
> Vin Vout Vin Vout
>
> 100 6400 100 6570
> 150 9550 150 9760
> 200 12,750 200 12,980
> 240 15,400 240 15,650
> 250 16,000 250 16,350
> 270 17,650 (variac dial at 73) 270 17,840 (variac dial
> 280 18,450 (variac dial at 76) is maxed out at 100)
> 300 20,340 (variac dial at 82)
>
> The arc welder current selector switch is set at 175 amps, I believe
> (don't have the marked dial guage anymore) and is paralleled with the
> two MOTs. MOTs are pretty beefy but don't know what kind of microwave
> oven that they come out of. Oh yeah, the HV output was obviously mea-
> sured open circuit with no load. The voltage measurements were made
> with a standard Sperry DVM (low voltage) and the HV measurements were
> made with a Radio Shack 10Mohm impedance DVM that is taken through
> an ebay special 40 kV (28 kVAC) HV probe. BTW, the variac's maxed
> output (measured at the ballasted input to the LV lugs of the pig)
> will reach nearly 320 volts with the 200 uFD primary PFC. Without
> the PFC cap, this same voltage point only reaches 270 volts with
> the variac(s) maxed out.
>
> My question is how much PFC capacitance would I need for this setup
> if I were going to use it to power a big Tesla coil? I suppose it's
> no surprise that the voltage increases with the PFC caps in place
> as there is probably resonance rise involved.
>
> Another problem is that this setup will trip out a 60 amp breaker
> in about 30 to 45 seconds if i run the Jacob's ladder. The 200 uFD
> PFC seems to reduce the current draw a little but I figure that I
> would probably need more capacitance to optimally reduce the current
> draw. Would a further increase in PFC capacitance cause a dangerous
> resonant rise in the voltage? I know the pig started humming loudly
> with the PFC caps in place when the input voltage starts to exceed
> 290 volts.
>
> I'm sorry for such a long post but I was just a little curious about
> these observations.
>
> Thanks,
> David Rieben
>
>