Hi all,
I (along with my daughter and her husband) had a chance to visit Roger Smith (in Ohio) and get the personalized grand tour of his nice sized pole barn high voltage lab this past Saturday, August 6. Of course, the highlight of the visit was his huge, pole pig powered DC resonant Tesla coil! Of course looking at Roger's DC res setup got the wheels to turning in my head about how I could possibly convert my Green Monster to run DC res instead of asynch with raw and unfiltered AC strait from my pole pig.
My "junkbox" collection of parts has rendered enough for me to throw together a DC resonant setup without spending a fortune on new stuff, with numerous HV rectifier, a storage cap and a 5 H choke. I had a number of HV diodes pulled from x-ray transformers, including (8) of those 6" long x 5/8" dia. cylindrical, fuse styled ones, as opposed to the more common diode "sticks". I am using all 8 of these fused styled diodes for the FWB for the raw AC output from my 14.4 kV pole transformer, as this type of x-ray tranny diode seems more rob8ust than their stick style counterparts. With their 100 kVp+ rating, there should be plenty of overhead as far as potential goes, and I have paralleled 2 at each of the (4) diode positions of the FWB rectifier to beef up the current rating.
I am currently using (8) paralleled of the more typical diode "sticks" from an x-ray transformer for the D-Q-ing diodes between the choke and the Tesla coil circuit's input and they still tend to warm up pretty quickly in inital power up of the circuit, where the DC output is simply shorted through the 5 H inductive choke to look for the visible spark. Of course, with their 150 kVp rating, operational circuit voltage levels are not likely to be an issue, but current certainly can be! I figure that the .1 uFd tank capacitor of my Tesla coil circuit, firing at ~350 BPS will also load the output of my DC res in a similar fashion, but hopefully to a somewhat less extent that dead shorting the output of the DC res circuit through the 5 H choke.
I have a 5 Henry, 1.25 amp DC rated choke that was originally used for the output of a 2200 volt plate transformer that I was going to use for the choke. I do have some concerns as to its insulational standoff integrity for the ~15 kV voltage levels that my circuit will employ, but it seems to hold up ok in inital full potential testing of the circuit by running my pole pig all the way up to 16.8 kV by imputting 280 volts into its primary.
I am using a utility primary line power factor capacitor for the storage cap that is rated for 7960 line voltage, 150 KVAR, at 60 hz. Its measured capacitance is about 6.5 uFd. These caps seems nearly bullet proof, even at DC voltages of several times their AC line voltage rating and this one is also rated at 95 kV biL (basic impulse level), so I feel as though this capacitor will serve my purpose.
Anywho, I have slapped all of the above mentioned components on a 15 x 20 polyethylene cutting board - ($9 @ Sam's Club - and besides picking up some extra 1/4" bolts and nut hardware, that's all that I have spent out of pocket upon this endeavor so far), - tested them at the full voltage from one of my spare 14.4 kV pole pigs and I have reviewed Richie Burnett's website on DC resonant circuits for driving Tesla coils and my setup seems to be at least a start in the right direction. Of course, the real test will be when I actually try firing my coil through the newly assmbled DC res. circuit.
Any input (as to any possible fatal flaws in my design) from you more experienced DC res coilers would be most appreciated. ;^)
Thanks,
David
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