Re: PFC questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Malcolm Watts <m.j.watts-at-massey.ac.nz> 

Hi Dave,
          The PFC cap is not in the right place to do the job it's
supposed to be doing. It should be directly across the mains, not
coming after the welder. If the cap is positioned this way, the
resonant rise will disappear as the cap is now slugged by the
impedance of the mains supply.

Malcolm

On 3 May 2004, at 8:17, Tesla list wrote:

 > 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
 >
 >
 >