Yes, it was great to finally meet you and to see your "toys" first hand, up
close and personal ;^) Maybe I could return the favor and show you some of
my toys (which aren't quite as many as yours) if you ever come down toward
my neck of the woods.
Yes, I was wondering about my choke coil being able to withstand the the
harsh and aggressive HV transients and spikes developed by large SG driven
Telsa coils. I have thought of possibly immersing my currently used choke in
transformer oil (I have a fair amount of that) inside some type of leak
proof vessel, whose walls have good dielectric integrity (which I DON'T
currently have), OR just using the HV side of one of my spare pole pigs,
while leaving the LV terminals vacant. Of course, that would add a WHOLE LOT
more mass to my already massive system :^/
So I take it that the de-Q-ing diodes need to be quite robust for this
purpose? Should my current HV diode sticks not work out, I was thinking of
the viability of an appropriate number of those stackable Unitrode diode
"hockey pucks" that you see on eBay from time to time, too, although they do
tend to be rather pricey. As far as that goes, how about a bunch of those
PRHVP2A-20 in a series/parallel configuration? Do you think that say 16 of
these arranged in 4 strings of 4 for 80 kV @ 8 amps could be sufficient for
the d-Q-ing needs?
As far as the rectifier diodes, I have seen the PRHVP2A-20 diodes pretty
cheap on eBay as well, usually from China or Hong Kong sellers and often
with free shipping, so I'd expect a significant wait time on delivery. So do
you use just one each of these for each of the legs of your FWB rectifier,
or do you use multiple units in series and possibly parallel too, to upgrade
their standoff for your 19.2 kV pig? And I forgot to ask while there at your
place, what kind of current are you pulling from the 240 volt mains when you
fire off your bid DC res coil?
Thanks and happy sparkin' at your T'thon this upcoming Saturday,
David
----- Original Message -----
From: "Roger Smith" <rwsmith@xxxxxxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, August 10, 2016 9:30 AM
Subject: Re: [TCML] DC Resonant Coil Questions
On 8/10/2016 7:45 AM, 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 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. ;^)
Hi Dave, I very much enjoyed are get-together last weekend. I just had
a few more things to mention about DC res coils. 1. The Charging Choke,
in my experience the inductance isn't to critical but it has to withstand
a lot of high voltage abuse just like a pole transformer dose in an AC
coil system. I wound my choke by hand and applied many layers of
packaging tape in between each winding.
2. The de-Q-ing diode, In some of my smaller DC res coils I have
gotten by with not having a de-Q-ing diode at all so I would say depending
on your charging choke, you may not need it. Building a vacuum tube
de-Q-ing diode like I did is a lot of work and expense.
3. Rectifier diodes, I have been having good luck with the PRHVP2A-20
(2 amps at 20kv) and they can be gotten on Ebay for as little as $2.08
each!
Best regards, Roger
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