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Re: [TCML] DC Resonant Coil Questions

Hi David,

Your component values look to be in the right ballpark for a target break rate of 350 BPS, and you should be able to push it to over 450 BPS. However, it looks like there's a "gotcha" in your system as currently proposed.

An ideal DC resonant system will apply 2X your DC supply voltage to your tank cap. Real world resonant charging systems typically develop 1.7 - 1.95X supply voltage depending on the "stiffness" of the supply, storage cap size, whether you're using single or multi-phase power, and the DC resistance of your charging reactor. At 280 volts input, the no-load output voltage for your FWB supply will be ~23.7 kVDC, and your tank cap can be initially charged to 40-45 kVDC! This will severely stress your charging reactor, tank caps, and rotary gap. You may want to limit your HV DC supply voltage to perhaps 12 kVDC prevent potentially damaging critical system components.

Good luck and best wishes,

Bert Hickman
Stoneridge Engineering, LLC
Alternative email: berthickman1@xxxxxxxxx
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

David Rieben wrote:
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

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 _______________________________________________ Tesla
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