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Re: no need to short cap?
Original poster: "Steve White by way of Terry Fritz <twftesla-at-qwest-dot-net>" <slwhite-at-zeus.ia-dot-net>
The cap is normally discharged when you turn it off because it is connected
as a dead short to your transformer (NST, pig, or MOT) secondary through the
TC primary circuit. That being said , I would still provide a means to
ensure that the cap(s) are discharged should that connection be broken for
some reason. Dielectric memory is real and that is why you normally see
large high voltage capacitors stored with the terminals wired together. Most
people seem to use bleeder resistors, but I do not trust them. They could
fail and you might not see it. Besides, the bleeder resistors on MMC arrays
are used mostly to ensure that the voltage is evenly distributed across the
string of series capacitors. The bleeding action is a secondary benefit. For
my pig-powered coil, I place a shorting bar across the cap terminals after I
turn it off. This provides visual indication to me that the caps are indeed
discharged and stay that way until I remove the shorting bar.
Steve: Coiling in Iowa
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Thursday, May 30, 2002 6:59 AM
Subject: RE: no need to short cap?
> Original poster: "Mike Wood by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi beans!
> you mean you checked by touching it? hey, cut that out!
> having said that, I've not worked with sw caps. But I'm still not sure
> should be prodding it to see if you get a shock. Energy stored inna cap
> 0.5 CV^2 (IIRC) and in tesla coil use, the V^2 is going to be quite big,
> even if your capacitance (I'm guessing maybe 6nF for your bottle cap) is
> Coilers building mmcs often include bleeder resistors across each cap to
> discharge them after powering down by converting the stored energy to
> I'd ideally choose bleeder resistors that discharge the caps rapidly
> to prevent any energy remaining by about the time I could walk over to the
> coil after shutting down, so if I need to adjust something I won't get a
> nasty surprise. I think caps without bleeder resistors can exhibit
> something called dielectric memory as well - which basically means that
> a cap that's been left disconnected and has just lurked unshorted in the
> shed for a while could bite the unwary.
> coil safe anyway!
> Wellington, NZ
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> I have alwas read, "be sure to short out your cap after you use it". Well,
> after runing my coil, i can touch my cap all i want and i get no shock.
> come? i am using a geek group SW cap with 6 bottes used.