Bert,
Thanks for the info. I reviewed what you and David Speck said in answer to Tim's inquiry about the 31xxx series GA/Maxwells that are only rated at 1 PPS and it seems that you are suggesting that most of these are not very suitable for Tesla use, and I would tend to mostly agree. However, I have acquired (4) each used surplus 31885 cat # .1 uFd, 75 kV rated Maxwells (4"x 6"x 19" single ended plastic case) several years ago, via eBay (one is currently being used as the main tank cap for my Green Monster coil - the other 3 are "spares"), and this cap seems darn-near indestructable for running my coil at 300 to 400 PPS with 14,400 volts from an overdriven 10 kVA rated pig, that's typically processing about 75 amps with about 200 to 220 volts input from the control variacs. I have never been able to detect any significant warmth after even a several minute run under these conditions. And I have come back a few minutes later to feel and see if some of the internal "warmth" finally reached the surface of the outer casing. Have you been able to gather any info about these 31885 cat # Maxwells?
Thanks,David
On Wednesday, October 21, 2015 6:07 PM, Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx> wrote:
Hi Dave,
It's a mixed bag with the 35xxx series as well, and many caps in this
series are excellent for TC use. The Maxwell spec sheets for many in
this series have NO stated PPS rating. For these, the Max. Dissipation
Factor (MDF) or Design Life (# of charge discharge cycles, with 90%
survival) can provide some useful hints as to their suitability for TC
use. Mylar caps will have a higher factor (0.5% or higher) while
polypropylene typically run 0.1 - 0.3% at 120 Hz. Design life for caps
rated for high PPS will also have a long Design Life (millions or even
billions of shots).
For example, the popular 35174 (0.06 uF at 40 kV) is rated for 100 PPS,
has a an MDF of 0.3%, and a design life of 100 million shots - very
suitable. A similarly packaged 35282 (0.06 uF at 50 kV) is rated for 1
PPS, has an MDF of 0.5%, and a shot life of only 100,000. Some caps in
this series have shot lifetimes of only 30,000, and you never know how
many are left on YOUR surplus cap.
Over the years I've accumulated a number of spec sheets, so I may be
able to provide you with more information if you can provide me with
series numbers. However, in all cases, a call to the GAEP capacitor
engineers is really the best bet.
Best wishes,
Bert
--
Bert Hickman
Stoneridge Engineering, LLC
http://www.capturedlightning.com
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David Rieben wrote:
> Hi Bert, What can you tell us about the "Tesla suitability" of the
> GA/Maxwell 35xxx series pulse capacitors? I have seen these come up
> on eBay from time to time but don't recall anyone bringing their use
> up in this forum. David
>
>
> On Tuesday, October 20, 2015 7:20 PM, Bert Hickman
> <bert@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
>
> Hi Tim,
>
> Most of Maxwell's 31xxx series caps are only rated for 1 Pulse Per
> Second (PPS). A few exceptions models 31393, 31662, 31677, 31687,
> 31892, and 31981(all 100 PPS) and 31583(400 PPS). Maxwell's specs for
> the Model 31190 0.08 uF 100 kV cap (currently listed on eBay) show
> that the cap is indeed only rated for 1 PPS.
>
> Although not explicitly stated, the polymer film dielectric used in
> this cap may be Mylar (PET) and not (the more desirable)
> Polypropylene. A call to General Atomics Energy Products (the current
> owner of the old Maxwell line of products) would be strongly advised
> before buying this capacitor. If the cap uses Mylar, it may work for
> short run times in TC use, but you'll need to be very careful not to
> overheat (and destroy) it. There may be better choices, such as an
> MMC.
>
> Best wishes,
>
> Bert
>
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