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Re: More about my capacitor (fwd)



---------- Forwarded message ----------
Date: Tue, 19 May 1998 06:44:53 -0500
From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: More about my capacitor (fwd)

> Date:          Tue, 19 May 1998 12:46:58 -0600 (MDT)
> To:            tesla-at-pupman-dot-com
> Subject:       More about my capacitor (fwd)
> From:          Tesla List <tesla-at-pupman-dot-com>

> 
> 
> ---------- Forwarded message ----------
> Date: Tue, 19 May 1998 09:26:15 +0300
> From: Marco Denicolai <marco-at-vistacom.fi>
> To: tesla-at-pupman-dot-com
> Subject: More about my capacitor
> 
> I got right now to know what dielectric was used in the capacitors below:
> it was polypropylene and paper, oil was I.P.B.P. Will they work with my
> TC (I use two of them in SERIES)?
> 
> ******************************************************************************
> I got some surplus Maxwell capacitors model 30561 0.1uF 25KV with following
> specs:
> 
> Capacitance: 0.1uF 25KV
> Rated peak current: 5 KA
> Max peak current: 25 KA
> Max ripple freq.: 10 KHz
> Max RMS current: 25 A RMS
> Max Dissipation factor: 0.3% -at- 120 Hz
> Inductance: 80 nH
> 
> They are enclosed in metal cans and have got ceramic terminals.
> Will they work with my Tesla Coil (frequency about 150 KHz) or will they 
> warm-up in 10 seconds and blow?
> ******************************************************************************
> 
> 
> 
> ________________________________________________________________________
> 
>  Marco Denicolai                   Vista Communication Instruments, Inc.
>  Hardware Development Manager      www.vistacom.fi   
> 
>  marco-at-vistacom.fi                 Kaisaniemenkatu 13 A
>  fax:    +358-9-622-5610           SF-00100 HELSINKI
>  phone:  +358-9-622-623-15         Finland
> 
>    Remember, Murphy was an optimist! I am not...
> ________________________________________________________________________


Marco,

The world of Tesla Coiling is one based on the premise of 
experimentation.  If you wish to know whether those Maxwell 
capacitors you described will work in a Tesla coil circuit for sure, 
my best advice is to try them!

I use Maxwell caps that are designed for little reversal and only 1 
Hz rep rate in fairly high power TC's with good results at 400 PPS 
break rate.  In this case I keep my run times to 30 second bursts only.
After about 5 or 6 firings of 30 seconds with actually less than 30 seconds
before each next fun-cycle, I find detectable warmness growing in the business 
region of the capacitors with my hand.  Knowing that the thermal TC 
of the case material is slow I shut down the fun once I get less than 
a 10 degree case temp increase.  I think these caps of mine use castor oil, 
kraft paper and polypropelene dielectric.  Limiting the run times 
(and internal temp rise) seems to be the key to making these fine 
Maxwells and any other cap for that matter _ survive_ in Tesla coil service 
after you have addressed the voltage rating by providing a hefty safety margine 
in the cap rating.  Run these surplus Maxwells at an absolute minimum at 3X the 
RMS of the system power transformer.  The ones I described getting 
warm are operating at just 12 kV RMS while they are each conservatively 
rated at 100 kVDC! (I have 3 x 0.04 uF in parallel for a total of 
0.12 uF).

I seriously believe that it is by the generous underrating of 
the stamped voltage rating of a capacitor that will allow less optimum designed 
units to tolerate Tesla coil service!  Having said that, recognize 
that depending on dielectric and construction, there are many surplus 
HV caps out there that just won't work at all at Tesla coil 
frequencies.

I believe you said your caps were rated with a 10 kHz ringing frequency rating 
as a maximum.  That ain't bad for (are these?) surplus capacitors 
being redirected to Tesla service.

The dissipation sound really high at 120 Hz, nevertheless I suggest you put 'em
in series and try them! Watts have you got to loose? : )

Robert W. Stephens
Director
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel: 1-519-925-1771   Fax: 
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