Re: Vintage 10,000 volt DC 1ma supply for sale.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla729-at-cs-dot-com>

"Tesla list" <tesla-at-pupman-dot-com> wrote:

 >Original poster: "John Richardson by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <jprich-at-up-dot-net>
 >
 >
 >Hello,
 >To those of you who were at the Cheesehead Teslathon, you may remember how
 >long it took to charge Sam Barros' cap bank for the rail gun, and if I
 >remember correctly, that was with a 15/30 ma NST.  seems it was on the order
 >of fifteen minutes or so.  Just for perspective.
 >John Richardson> >

John, all,

It may also have taken a relatively long time because that the
power supply (15/30 NST in this case) had a voltage output that
only matched or SLIGHTLY exceeded the target charge voltage of
the capacitor. It takes a voltage source that can supply a volt-
age considerably higher than the target charge voltage of the
cap to charge it up in a timely manner, in addition to an ade-
quate current. I found that it took a very long time to fully
charge a 10 kV, 200 uFD cap bank with an app. 10 kVDC source
(15/30 NST center tapped at 7.5 kV  X 1.4) even with another
15/30 NST paralled to get 60 mA, it still took about the same
5 + minutes to charge. I changed the charging power supply to
(2) 7200 volt PTs in series for 14.4 X 1.4 (appr. 20 kVDC) and
found that I could fully charge the same 10 kV, 200 uFD cap in
about 15 to 20 seconds! Of course, very close monitoring of the
capacitor voltage is required when doing this to prevent pos-
sible catastrophic failure of the cap units due to overvoltage.
I'm sure a >10 kJoule capacitor failure could be quite literally
explosive! This is starting to get a little OT, but I just thought
the safety aspect of charging large multi-kJ cap banks should be
brought out since I know that some of us coilers also like to dab-
ble in the high energy discharge arena :-)The few joule caps of
our Tesla coils can explode pretty nicely from overheating due
mostly to overcurrent so I can only imagine the explosion potential
of a large multi-kJ cap or cap bank!

Safety first,
David Rieben