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Re: [TCML] Looking for Pole Pig Capacitors

Hey---
Without a de-Qing diode the voltage on the storage cap fluctuates in a sort of random manner above and below zero, and you can't get a full charge in a larger cap. With the diode the voltageclimbs to a max and stays there until the switch gap is triggered, then the sequence starts again, and if you want you can use a cap of any size. However, 40ish kV sounds hairy. With a full bridge rectifier on a 14.4 xfmr, you get about 20 kV, which with full reversal is still within the ratings of a 50 kV cap. With a resonant system, you need a storage cap about 5x the primary gap, although it doesn't need to be a pulse cap. With the full bridge, you only need the primary cap. 

---Carl






On 11/28/2011 1:12 PM, David Rieben wrote:

Travis,
Yea, the DC Res charging allows the versatility of a widely variable bps rate. I think you would also need a de-Q-ing diode between the storage cap and the primary cap as well. I have personally never built a DC Res charging power supply so you may do better seeking the advice of someone who has actual experience with this type of coil system. I know Roger Smith's big coil is a DC Res system. Maybe he could chip in on this? 

David Rieben

On Nov 28, 2011, at 10:52 AM, Travis Tabbal<travis@xxxxxxxxxx>  wrote:
Thanks for the great info. I wondered if I would be able to charge a .3uF 
with my 10kVA 14.4KV pig. LTR is an option, but I don't have a sync
motor... DC resonant looked interesting to me though. Other than needing a 
big cap rated for the transformer voltage, and diodes along with the
inductor, anything to look out for? I think one of my pigs can do 7.2Kv, so the DC resonant mode would kick it up to 14.4 if I'm reading properly. Does 
the DC filter cap see the inductive kick? I know the primary cap does.
Designing for 28kV sounds.... interesting... not sure I want to go there... 


On Sat, Nov 26, 2011 at 2:33 PM, drieben<drieben@xxxxxxx>  wrote:


Hi Travis,

No, I suppose there really isn't a reason, other
than that it would take a power supply of con-
siderable magnitude to be able to fully charge
a .3 uFd cap, at 14.4 kV (maybe more than the
typical residential, single phase electrical service could
reliably provide), especially with an ARSG churning
out several hundred breaks per second. This is
the typical way in which a classic SG driven, 14.4 kV
pole pig powered coil system is operated. If one was
so inclined to operate their pig powered system
LTR, with an SRSG at 120 BPS, or a DC resonant
charging power supply with a pole pig (ala - Roger Smith),
OR, if you are operating with a lower voltage output pole
pig, then a single unit of this persuation may be your ticket
to success ;^) Amir Mojarradi was looking for a suitable
capacitor in the 0.1 to 0.2 uFd range (and rightfully so
for the size and specs of his coil system, as his coil was
running great w/ 0.14 uFd), so that was the reason for
my suggestion as to the feasability of two of these units
in a series configuration.

Also, I would consider a 50 kV(DC) rating on a commercial
pulse cap to be on the very low end of the acceptable spec limit
for a suitable primary cap in a coil system driven by a 14,400
volt pole pig (especially with the high charge/discharge BPS
duty cycle of an ARSG). As Amir can now handily attest, a
35 kVDC rating is certainly NOT sufficient for a 14.4 kVAC
pole pig power supply! I have also personally experienced
a failure of a 0.1 uFd, 50 kV rated Hipotronics pulse cap
in my Green Monster Tesla coil system and I probably
only got 2-3 hours of total run time out of it before failure.
My GM coil also utilizes a 10 kVA, 240V/14.4 kV pig.
An autopsy revealed that the failure mode of the Hipotronics
cap was strickly dielectric breakdown, due to overvoltage -
NOT over current. The cap unit had no external signs of
internal failure - no case rupture or external bulging/swelling,
and the Hipotronics unit didn't get warm during operation.
I am currently using a 31885 Maxwell 0.1 uFd, 75 kVDC
rated Maxwell pulse cap and have had no more problems.
The 100 kV rating of two 50 kV rated units, in series, should
prove nearly bullet-proof for a 14.4 kV driven system. ;^)

Happy Sparkin',
David


----- Original Message ----- From: "Travis Tabbal"<travis@xxxxxxxxxx>
To: "Tesla Coil Mailing List"<tesla@xxxxxxxxxx>
Sent: Friday, November 25, 2011 9:45 PM
Subject: Re: [TCML] Looking for Pole Pig Capacitors
I've been considering one of those for a coil with similar power input. 
Any
reason .3uf wouldn't work with a properly tuned primary and top load?
On Nov 25, 2011 8:31 PM, "Roger Smith"<rwsmith@xxxxxxxxxxxxxx> wrote: 

On 11/25/2011 5:53 PM, Amir Mojarradi wrote:



Hello everyone!

I recently destroyed a 0.03 uFd  35kv Maxwell capacitor (#37667) of
which
I was using (4) in parallel to achieve 0.15 uFd at 35kv. I am running a 10kva 14.7kv pole pig powered coil with a 12in diameter, 57" winding 
length
secondary, and a 60in major/ 12in minor diameter toroid. The single
capacitor cracked in half and splashed oil for a good 8 feet.
Evidently, my
configuration was poorly designed to handle the ~ 15 kv input.
Apparently,
people have had this issue before and I was previously warned by David 
Rieben.
David suggested 2 of these Aerovox 0.305 uFd 50KV Capacitors in series, 
but that would be a bit pricey given the shipping for about152 lbs!
Yet, I
am considering them.
http://www.ebay.com/itm/****Aerovox-Tesla-50KV-High-**<http://www.ebay.com/itm/**Aerovox-Tesla-50KV-High-**> 
Voltage-Aerostor-Pulse-****Capacitor-/200679608603?pt=LH_****
DefaultDomain_0&hash=****item2eb96fd11b<http://www.**
ebay.com/itm/Aerovox-Tesla-**50KV-High-Voltage-Aerostor-**
Pulse-Capacitor-/200679608603?**pt=LH_DefaultDomain_0&hash=**
item2eb96fd11b<http://www.ebay.com/itm/Aerovox-Tesla-50KV-High-Voltage-Aerostor-Pulse-Capacitor-/200679608603?pt=LH_DefaultDomain_0&hash=item2eb96fd11b>
Is anyone willing to sell pole pig suitable capacitors, either single unit or several, for approximately a 0.15uFd 50KV + rated capacitor 
bank?
I'm a student and my budget is around $100-200 and I will of course pay 
for
shipping and handling; I live near Pasadena, California. Please let me 
know
if you have any comments or suggestions regarding possible capacitor 
choices; they will be greatly appreciated.

Thank you for your kindness,

Amir Mojarradi



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Those Aerovox capacitors sound like a good deal to me. Im tempted to
get a couple myself but if I made my coil any more powerful I would have 
to
take it outside to run it. Your set up sounds pretty awesome. Do you 
have any pictures?

Roger
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Travis, When I first built my big DC resonant charging Tesla coil I was using 7200 volt pole pig with a voltage double and I used a 5uF filter capacitor. The important thing about your filter capacitor is that it protects the diodes in your voltage doubler. If you have a little ripple in your supply voltage you wont notice it. One nice thing about about the voltage doubler is that you can regulate the output by changing the size of the shifter capacitor. Most people don't have variacs that can handle a pole pig system these days.
As for the voltage doubling effect at the primary capacitor, you don't have to worry about that. The same thing goes on with an AC system to some degree and remember the peak voltage of 14.5 KV transformer is 20.5 KV . I have upgraded from the 7.2 KV pole pig to a 19.5 KV pole pig that I am using with a full wave rectifier and a 1 uF filter capacitor and I haven't blown any capacitors yet and that's running it with 230V going directly to the pig with no ballasting ! I do believe I'm on thin ice though. I haven't put on a lot of run time running it this way.
As for the deQing diode , I would say you will probably want that . Some smaller DC resonant Tesla coils I have built didn't need them but my big one dose need it. I haven't done much running with low break rates. My big coil runs at about 400 breaks per second but on one of the first DC coils I ever built I got the longest sparks running at a real low break rate because I had a limited power supply . It was some kind of a MOT with voltage doubler arrangement. 

Roger
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