Original poster: Steve Conner <steve@xxxxxxxxxxxx>
> On my second DRSSTC i only use a very small
> electrolytic 1500uF at 350V. im just wondering if i
> would benefit in spark length by going upto 3000uF?
It depends on what bang energy you want to achieve. I
would guess you want your DC bus cap to hold at least
10 times the desired bang energy. Say about 6 joules
for a 30-40" spark, then you need at least 60 joules
which is a little over 1000uF at 330v.
If a 1000uF cap was at 330v before delivering a 6
joule bang, it will be at 311v afterwards which is
probably not too significant a drop. A 3300uF cap
(holding 180 joules) would drop from 330v to 325v when
it delivered 6 joules.
I used 3300uF on my mini coil but only because I had
some 3300uF @ 420V low ESR caps that I got cheap. If
they had been 1000uF I would probably have used that
instead. The bulk of the 3300uF capacitor caused some
problems in getting a compact layout with low
inductance.
I think the ESR and ESL are probably more important
than the capacitance. Bigger caps tend to have lower
ESR, but higher ESL. Multiple small caps connected in
parallel might be better, since paralleling reduces
both the ESR and the ESL. But again you have to be
careful how you wire them, or the inductance of the
bus work will just undo any benefit.
Steve Conner