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Re: Maxwell Pulse Capacitors

Original poster: "Steve White by way of Terry Fritz <twftesla-at-uswest-dot-net>" <slwhite-at-zeus.ia-dot-net>

Here is my limited experience with buying these used. I bought a couple of
0.03 uf Maxwells over E-Bay to connect in parallel. These seem to be quite
common on E-Bay. The add claimed they were from an X-ray machine. I checked
the part numbers on the General Atomics web site before I bought. The part
number (37667) was not shown in the list, but it was in the 37xxx series
which seems to indicate that it is one of the PD types which have a
100,000,000 pulse discharge cycle lifetime. The distinguishing external
features of these PD caps seem to be the terminals on opposite sides of the
cap. If these were indeed from an X-ray machine, perhaps these particular
caps were over-specified since I agree that an X-ray machine can certainly
get by with a low duty cycle cap. The add may have been wrong and they were
used on some different equipment such as a laser. The moral of the story is
to check the part numbers of what you want to buy before buying. Don't just
blindly buy a cap just because it has a high voltage rating and a
capacitance in the range that you need.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, May 06, 2001 8:17 PM
Subject: Re: Maxwell Pulse Capacitors

> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> In a message dated 5/6/01 8:14:45 PM Central Daylight Time,
> writes:
> Steve White writes:
> >
> > More preferable to me are used caps taken from X-ray machines.
> > How many X-rays can be taken in a day. 100? Even if the X-ray machine
> > used for 10 years, there would still be a lot of life left in the cap.
> Bert Hickman writes:
> < Most low duty cycle applications  such as
> < defibrillators, X-Ray filter cap, Marx generators, HV DC power supply
> < filters, and industrial pulsed welders typically (but not always!) use
> < Mylar caps.
> Hi Steve, Bert, all,
> I've gotta go with Bert on this one. Although x-ray caps are exposed
> to a very low duty cycle in normal operation, they are usually of a
> Mylar dielectric, since they are designed strictly for filtering service.
> I've torn into an x-ray filter cap before and it is NOT of the extended
> end foil construction and the terminations are quite wimpy. Obviously,
> it wouldn't hold up well in Tesla service.
> But again, Steve has also got a point in that one dosen't know how
> much use a used cap has seen when they get it.  However, most caps
> that are designed for lasers are designed for the rapid charge/discharge
> duty which would render them more suitable for Tesla duty. So, I believe
> the laser Maxwell caps are more likely to have the polypropylene dielec-
> tric, which has very low RF dissapation, which is what we want :-)
> Sparkin' in Memphis,
> David Rieben