Re: Blown Cap

Tesla List wrote:
> >> Subject: Re: Blown Cap
> >From jim.fosse-at-bdt-dot-comWed May 29 07:46:24 1996
> Date: Wed, 29 May 1996 05:55:14 GMT
> From: Jim Fosse <jim.fosse-at-bdt-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Blown Cap
> On Tue, 28 May 1996 22:30:00 -0600, Tesla List
> <tesla-at-poodle.pupman-dot-com>, you wrote:
> >> Subject: Re: Blown Cap
> >>From hullr-at-whitlock-dot-comTue May 28 22:10:12 1996
> >Date: Tue, 28 May 1996 09:51:45 -0700
> >
> >Also, the 60mil poly caps should never see more than about
> >9KVAC per cap.
> I understood that, and didn't move from 7.5kV to 15kV until I had
> build a 3 layer 0.030" cap. Then I tried 15kV on the single 0.060" cap
> - I wouldn't have been so down hearted if it had gone out with a bang
> instead of a whimper;(
> >Once you move on to
> >a pole pig or a non-shunted transformer and plan on 4 KW or more power
> >output, the homegrown rolled caps are going to be stressed to beyond
> >their limits.
> I'll have to check my lab notes (not bound yet so I cant call it a
> book) to see when I blew the 3 layer cap.
> >
> >The rolled amateur caps are for Neon Transformer systems and rather low
> >power use (under 3KW).  Most of the problems that I have seen occur are
> >when rotary gaps are used and the rep rate is taken up to levels beyond
> >500 bps.
> Oops,
>         I took out the second 3 layer 0.030" dialectric cap with a
> 15kV 60mA neon and a rotary gap at about 2500 bps (potentially).
>         jim


Good Grief!!!!!!!  2500 bps!!!!!  What were you using a .000006ufd cap!  
That's about the only one you'd recharge at that rate!  The very fastest 
we have ever dared to break at was 1000 BPS (NWL pulse caps) and that was 
.012ufd!  We only realized about 800BPS at that usage , too!  Most of our 
best work on two coil systems and even maggys are below 600 BPS.  
Everyone I have heard of, who consistently blew caps, used rotaries 
whizzing around at 5000 plus rpm with 10 or more points on the wheel.  If 
you use more than 10 points on a wheel the RPM should be below 2400 RPM. 
 For high speed rotaries 4-6 points is the absolute limit or you are 
probably missing 60% of your point presentations.  

The actual cap charge time is of little importance compared to the quench 
and deionization time.  It is real hard to use full transformer voltage 
and get more than 2-3 pops per half cycle.  Using 1/2 transformer 
voltage(by closing 10 tungsten static gaps to microscopic dimensions), we 
have had as many as 10 pops per half cycle at 50 watts input power (1200 
BPS) but this just can't be done with giant coil systems where long 
sparks are demanded.

NWL engineers, (my cap maker of choice), have had long engineer to 
engineer discussions with me and they say, unequivocally, that duty 
cycles drop to near zero on even the most high end pulse caps once the 
rep rate against AC power input exceeds 1000 BPS.  This is especially 
true if real large impulse RF currents are involved (as they always are 
in our kind of work).

Richard Hull, TCBOR