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Re: [TCML] GE Pulse Cap

Hello Kurt,

I can add a data point for the Maxwell 37667. I have been using 6 of them connected in series-parallel for 45 nF at 70 KV. My SGTC uses a 14.4 KV pole pig at 4.8 KVA. I have been using these at 240 PPS for a total run time of about 4 hours so far with no problem.

I actually had one problem during development. My original bus bars for the capacitor bank were too close together and I got a few flash-overs. One of the flash-overs cracked the case of one of the capacitors due to mechanical shock. I then re-designed the array to provide more separation between the bus bars to eliminate the flash-overs. Since that re-design I have had no problems with them.

Steve White
Cedar Rapids, Iowa

----- Original Message -----
From: "Kurt Schraner" <k.schraner@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, December 28, 2018 9:23:54 AM
Subject: Re: [TCML] GE Pulse Cap

Hi David, Jim, ...

concur with you David, about use of Maxwell pulse caps that are only rated at 1 pps: in my "Black & White" Coil are 2 series'ed Maxwell 31235, which are doing their service, some 3+ netto-hours in coil-operating, and for which results a caplife-time guess of about 473 hours, using the Maxwell/Jim Lux method. (Data of the 31235 see: http://www.ga.com/series-s-ss-high-voltage-1-pps-capacitors . (Total C measured is 0.162 uF and Vdc is 100+100 = 200kV).

Jim Lux had made available a method for cap live 
estimation before. In 2012, on this list. Please see in the archives:

http://www.pupman.com/listarchives/2012/Feb/msg00042.html
http://www.pupman.com/listarchives/2012/Feb/msg00044.html


https://www.pupman.com/listarchives/2012/May/msg00177.html


The method allows to estimate cap live, in respect of the 2 parameters 
"discharge voltage" and "voltage reversal". I've made an excel out of it, in 
order to evaluate my own Maxwell caps.  Jim has given me permission to give 
this excel to interested coilers. So, I can send it, if someone likes to try 
it. Please mail me offlist on k.schraner@xxxxxxxxxxx, if you want one. The 
excel is easy for Maxwells, for which you have a datasheet with all needed 
input-data.

In 2012 I purchased 6 of the 37667 on Ebay, owning 8 then. Those were combined 
for a sort of "Maxwell-MMC" with i.e. 60nF/70kVDC. And I'm not so much 
afraid of short live, if it's not for a bad history of those caps. Those caps are
buildt into the "Sirius" TC of Andreas Saile, working without problems.

Kurt Schraner
Basel, Switzerland

-----Ursprüngliche Nachricht-----
Von: Tesla <tesla-bounces@xxxxxxxxxx> Im Auftrag von jimlux
Gesendet: Freitag, 28. Dezember 2018 05:16
An: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Betreff: Re: [TCML] GE Pulse Cap

On 12/27/18 5:58 PM, David Rieben wrote:
> Hi Bob,
> 
> Yes, I seem to recall seeing that particular GE pulse cap on eBay before. It is probably the older style paper and oil dielectric system, hence its relatively large physical size for its voltage/capacitance rating. It would probably work fine for a mid-sized coil.
> 
> Actually, I’ve heard that the Maxwell 31393 capacitor, unlike most of its 31xxx series counterparts, actually has a several hundred pps rating instead of only 1 pps.
> OTOH, I have had much success even using Maxwell pulse caps that are only rated at 1 pps, assuming that their voltage rating is sufficient. Remember, pulse capacitor shot lifespan goes up more than exponentially with any descent in their operational voltage from their rated voltage. So if you have a 75 or 100 kV rated pulse cap that you are only running at only 15 kV (about 22 kV peak), then your capacitor’s shot lifespan will likely be many, many times what it’s rated shot life is for its rated voltage.
>


It is perhaps a good thing to point to this:
http://home.earthlink.net/~jimlux/hv/caplife.htm

life goes as the 7.5 power  (this is for polypropylene dielectric, it changes for others, but not hugely)

So a 50% reduction in voltage is a factor of 181 in life.

So a 1pps, with a 10,000 shot life, running on a rotary gap at 120 bps would last for about 15,000 seconds of run time.

As noted above, if you have a 100kV cap and you're running it at 22kV, the life increase is more than 85,000...
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