PFC caps (was Re: Ballast Puzzle)

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

Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>" <broker-at-uwplatt.edu>

Scott,


>Yes, but I would have to then build a bigger control box.  I think the 
>infernal chanting of a few dozen self-proclaimed Geeks :) screaming "kill the 
>computer...kill the computer" somehow convinced me to ignore my common sense 
>and over-stress the system. Thank-you ma'am...may I have another.  I'll work 
>on the next ballast when I get around to designing the next RSG - I've got 
>plenty of watts, now I need to work on efficiency to get more sparks (20KW 
>should get me more than 10-foot arcs - nice hot thick white burning plasma 
>arcs such as they are). 

You seemed to also be enjoying the show :-)  Perhaps another set using 6AWG
would be capable of far more power with less heating?  I'm curious what the
resistance of your inductive coils are?  There's a TON of 
wire...


>Last week I borrowed a Fluke scopemeter (to stay isolated) and measured my 
>input voltage vs. current directly to see the phase difference.  Just running 
>a Jacob's ladder from the pig at 100A 220V, the phase difference was approx. 
>90 degrees.  My little stack of PFC caps didn't touch it (150uf).  The two 
>giant PFC (100KVAR at 2400KV) I got from The Geek Group had about the same 
>effect (none), so I took one apart (not easy to do) and measured the 
>capacitance of one stack (there were twelve inside).  The one cap was only 
>16uf, and there were bleeder resistors inside the box. 

A 20kVA JL is something I'd like to see....  I made one with a bank of 4
15/30s, and thought it was really cool :-)   Nice blue-white flame, not the
icky purple-blue one from the 12/30 I made for the physics department.

100kVAR -at- 2400VAC is only about 48uF.  I think I measured 50uF across one.
We had no real use for them either, since the trick to harnessing their
full potential is to run them on a step-up transformer.  If using a 10:1 
step up, the capacitance reflected to the 240V side is about 5000uF!  Big
enough to theoretically make Electrum and the 13M run with a leading PF!
One could make a variable PFC using this method by putting a 
variac in series with the PFC step-up transformer (or am I not thinking
properly?)  10:1 transformers are relatively common (2400Y/4160D -> 240)

I was wondering what the internal construction of those things is.  The
twelve caps were arranged 2 in series, 6 "strings" in parallel?  What value
bleeder resistor was used?  My cheap DMM couldn't handle the 
capacitance to make an accurate resistance measurement.

Good luck with your mods.


Mark Broker
The Geek Group's Chief Engineer