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Re: DC power


 Te> The recent posting from Wes B. (copied below) is very interesting.  Is
 Te> there anyone out there running a large Tesla coil (in the 2 kva range)
 Te> on DC power? 
 Te> "Subject: Capacitor Charge Rate

 Te> Ed;

 Te> I'm glad my note on the subject made some sense. I wrote it in a hurry
 Te> and gushed out a lot of different items, and was concerned after
 Te> sending it that it might have seemed a bit incoherent. If you were able
 Te> to get out the information I was trying to put in, then that's just
 Te> great. 
 Te> As far as using rectifiers to always charge the cap in the same
 Te> direction goes, I don't think that the cost of the rectifiers should be
 Te> a problem. Commercial high voltage rectifiers tend to be made by
 Te> stacking lower voltage rectifiers in series, with each rectifier
 Te> shunted with a very large resistor. The idea is to make the resistors
 Te> small enough so that the inverse voltage is distributed equally among
 Te> each diode, but large enough so that the reverse leakage is acceptable.
 Te> With 1KV 1A rectifiers selling for ten cents each, it shouldn't have to
 Te> cost a fortune to roll our own. The problem as I see it is controlling
 Te> the kickback from the tank circuit. 
 Te> While the power transformers seem to be tough enough to handle a lot
 Te> of kickback-related punishment, it only takes one nearly-instantaneous
 Te> glitch of overvoltage to waste a semiconductor device. This means that
 Te> kickback prevention really will need to be designed rather than
 Te> estimated. I think that this problem is quite solvable, and it's one of
 Te> the items I'm working on, but it's going to take a lot of time at the
 Te> rate I'm going. Still, adequate kickback prevention can be based
 Te> entirely on passive filter design, which has been around a long time.
 Te> It should be theoretically possible to limit the kickback voltage seen
 Te> by the transformer to whatever level you want, and the difference
 Te> between the line frequency and the frequency of the kickback waveform
 Te> is so great that it should be practical to be able to limit the
 Te> kickback into insignificance. After this is done, rectifiers will be
 Te> more practical in the circuit, and a lot more efficiency should be
 Te> possible. 
 Te> Wes B."

 Te> Thanks, Ed Sonderman

 MG> There is a way to solve this problem. First, if your high voltage diode
 string is built out of lets say, 20- 1kv diodes in series, then connect a
 .05 ufd 1kv disk capacitor accrossed EACH DIODE. This will allow the diode
 to be bypassed for the high frequency kick-back and allow the 60 hz to be
 rectified normally. Also, putting the diodes on the transformer side of the
 filter/safety gap circuitry should help. If your using HV rectifier modules
 then simply connect enough capacitors in series across the module so the
 reverse breakdown of the rectifier module isn't compromised. Also, to be
 on the safe side, if your building your own HV string, match the 
 BACK RESISTANCE of all the diodes in a string to insure the reverse voltage
 (60hz) divides evenly between all the diodes in the string.

                                Mark Graalman
                                mark.graalman-at-mediccom.norden1-dot-com


... Alias, Mark the spark
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