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Re: help me put my coil on a diet; its capacitor appetite is expensive!
Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
Hi Nick,
OK, you are at 8.4KVA, Ipri =35a, Isec=0.58a, Cres=107nf, Cp=60nf,
and 120 BPS sync.
A spice simulation shows maximum firing voltage at 107KV and peak
voltage at 113 KV by timing the SRSG before peak. I will send you
the waves privately. You can destroy not only your caps but your pig
with this low of capacitance and running at 120 BPS sync. I'm not
kidding when I say that you need to go to a much larger Cp or go to a
much higher BPS. When you are dealing with inductive sources and
capacitive loads, there are resonances that can "suck" much more
current from the PIG than you are ballasted at. The capacitive
reactance subtracts from the inductive reactance and you can get a
very high resonant rise voltage across your capacitance. The easiest
way to see this is with a spice simulation of the circuit. If you
want to do 120BPS sync, you will need 300nf
Gerry R.
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, September 28, 2006 12:23 PM
Subject: Re: help me put my coil on a diet; its capacitor appetite is
expensive!
Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>
Hi Gerry (+ others of the list)
Thanks for the reply, and sorry also for taking so long myself. In
my case, the problem is that I seem not to be getting the digest
mail anymore (and I am not on the list directly either).
So I had to get this message from the pupman.com archive and paste
it into a new mail.
Re: the 100 A ballast-
Actually, I was probably confusing things when I said the ballast
was set to 100A. I meant the secondary (of the welder) was set to
100A which means the primary is closer to 35A. Also, my Cp is (now)
60nF, in the form of 6 strings of 15 x 942C20P15K. I am still
running 120 BPS sync. My pig's voltage output is 14400V. so I don't
think I am running it at 80KV... at least I hope not. I have a huge
MOV that I will be running in parallel with the pig, and a safety
gap in parallel as well. the MOV is a 27KV (and many KA) that is
about 2+ feet tall and at least 8 or 9 inches in diameter, contained
in a porcelain insulator. I figure the combination of those will
help protect the 30kv rating of the 942C's (which also handle
voltage reversals well, or so I hear) so this time around my caps
should at least last for a run or two before dying, I would hope.
I also think the caps were overvolted, but as I mentioed above,
probably not quite as badly as you might have thought from my
original statement. It did run for a few minutes without bursting
immediately into flames.... :)
Thanks!
NICK
---------------------------
Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx>Hi Nick,
Sorry about not answering before this. Your email got lost in a sea
of other email and I just now rediscovered it.
I will presume your 100amp ballast is with 240V so you are running
at 24KVA. If your Cp is 100nf and you are running at 120 BPS sync
and the timing of the SRSG is set normally, the voltage will be
43KV. However, if the timing is incorrectly set, the voltage could
go as high as 87KV. This is not a case where you adjust for maximum
voltage. I think it is very likely that the caps were overvolted.
Cres for a 25KVA PIG is 320nf so if you want to run at 120 BPS sync,
you will need a Cp of about 900 nf. Alternatively, you could go
async and shoot for a high BPS. With 100nf and 400BPS, some of the
firings will get to 39KV. I do think you need to have a larger Cp.
With 200nf and 400BPS, some of the firings will get to 24KV.
Hope this helps,Gerry R.