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Re: Maxwell Pulse Capacitors

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>


For proprietary reasons, Maxwell does not readily disclose the dielectric
systems used inside their capacitors. However, if you can locate a spec
sheet for your capacitor, you can usually "decipher" which dielectric
system is being used. Another clue is that the specified design life - high
rep rate caps typically have lifetimes quoted in 10^8 or 10^9 "shots" (a
full charge-discharge cycle). Compare this to Maxwell's Type C High Energy
caps, where design life is only 10^3 or 10^4 shots.     

Look for capacitors rated for "high rep rate" (typically 400-1000 PPS).
These capacitors have a low loss dielectric system that uses, among other
things, polypropylene film. On the other hand, Maxwell's "low rep rate" (1
PPS) energy discharge caps use Mylar film (older energy storage "monsters"
even use Kraft Paper). These are not recommended for Tesla Coil duty. 

Sometimes the relative size of the capacitors also is a clue. Since Mylar
has a higher dielectric constant, a Mylar cap of the same capacity and
voltage rating may be significantly smaller in physical size than one with
identical ratings using a polypropylene dielectric system. However, you
must be careful to compare capacitors of about the same "age" since
capacitor vendors have been able to increasingly pack higher energy density
into smaller packages.  

Polypropylene capacitors are commonly found in high rep rate medical
lasers, excimer lasers, some types of high power pulsed industrial lasers,
induction heating equipment (in tank circuits or HF Power Factor
Correction), ultrasonic power oscillators, RADAR Pulse Forming Networks,
and in stroboscopic equipment.  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.  

Good luck, and happy hunting!

-- Bert --
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com 

Tesla list wrote:
> Original poster: "Yurtle Turtle by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <yurtle_t-at-yahoo-dot-com>
> Does anyone know where information can be found on
> which Maxwell capacitors are suitable for tesla coil
> applications? I searched www.ga-dot-com, but couldn't find
> an explicit list of model numbers and dielectrics
> used.
> Are there any rules of thumb, such as caps from lasers
> are or aren't suitable for AC RF application? Or the
> single ended plastic case caps are better or worse
> than the PD series caps.
> thanks
> Adam
> =====
> Adam Minchey
> yurtle_t-at-yahoo-dot-com
> www.geocities-dot-com/yurtle_t/index.htm
> _

Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com