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Re: MMC Survivability

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Gerry,

Yes, it might be ok. But it is still riding the edge. Running the spice model would be ideal for the situation as this will at least give a model to go by (sure beats trial and error). When it comes to pigs in common STR mode, Cp is a good thing to spice up if one is thinking of using MMC's. The voltage capability of an MMC string becomes important as we near resonance, so the further we are away the better (in either direction). What is nice about high kva transformers is STR is still significant energy which helps the MMC compete with professional pulse caps in that range from a cost standpoint. However, to get a seriously robust MMC from a voltage standoff rating, pulse caps are a less expensive upfront cost (replacement cost is always on the side MMC's). I think for pig MMC's, we still need a larger value MMC cap to get the cost down. The 0.15uF's are just too low (I would really like to see a 0.5uF MMC available). 5kva is still in range of MMC's, so Jim just needs to decide what he is comfortable with.

Take care,

Tesla list wrote:

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Bart,

If biased at 5KVA, Cres should be 64nf. If Jim was running at 120BPS, his output voltage would be very high. Since he is at 200BPS, I think this value will be OK. My simulations (since I'm sorta in the same boat with my 5KVA pig) shows that with 240 BPS, I can go down to 75nf and still keep the voltage reasonably under control. I'm planning to go as high as 130nf to test 120 BPS so I will monitor my voltage rise. To be on the safe side, Jim could do a spice on his charging ckt with 200BPS and see what the voltage rise is. I could even do that if he wants.

Gerry R.

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Jim,

I suspect it will perform great! The voltage
standoff capability is low, but these are MMC's.
If you are running in a healthy LTR mode, you
would be fine. However, 0.1uF is not a healthy
LTR mode for your pig. It's kind of near the
static gap LTR value. I suspect you'll be using
an RSG of some type. You will be on the ragged
edge of "ok" and "slightly possible to overvolt a
cap" (which I have done with MMC's). Considering
the "costs" your looking at, another $100 could be good insurance.

If you were me however, you wouldn't spend the
extra cash. You would try to get away with the
minimum caps required. After all, when a cap
blows, it won't be a $500 nightmare. It will be a
$3 setback. That's what is nice about MMC's. If
you do this right, you won't need a professional
pulse cap, but doing it right doesn't have to be
perfect the 1st time round. At little costs, you
can simply add caps to the strings as necessary.
I eventually ended up with an 18 string cap bank,
but only after blowing up a 15 string (only 1 cap
died, so no big deal. And that is the coolness of MMC's)!

BTW, I run both MMC and Professional Polystyrene
pulse caps. They both perform well. I can't
really see a difference between the two from a
performance basis. But when it comes to cost,
MMC's are always the winner. Not always up front
cost, but certainly maintenance cost.

Take care,

Tesla list wrote:

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

Hello all,

I'm building a 12" coil powered by a 5KVA 14.4kv (pushed a bit). I had hoped to buy one of Dr R's Maxwell super caps but the buy won't go through until next spring.

What do you think the survivability of 10 rows (.1uf) of CD942C .15uf, 2000kv x 15 strings and a 200 BPS ASRG will be, since I have that many?

Thanks, I suspect it would be on the edge.

Jim Mora