Re: DC Resonance Charging Advice Sought

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

Original poster: "David Speck by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dave-at-davidspeckmd-dot-org>

Dave,
Your system sounds like an excellent application for a discharge relay.

I would suggest using a 100K ohm 100 or 200 watt resistor from the HV 
terminal which is automatically shorted to ground by a HV relay which is 
normally closed to ground.  Wire it so that the grounding relay coil is in 
parallel with the HV PS input.  The instant that the supply is shit off, 
the shorting relay also is deenergized and drops to dump the high voltage 
through a ballast resistor.  This would give a discharge time interval of 
0.7 seconds, and 6 intervals would only be 4.2 seconds.  The resistor would 
dissipate about 490 watts at the instant of relay closure, but this would 
rapidly decrease and it probably would not get detectably warm.

I know that others have objections to reliance upon discharge relays, as 
one can become complacent, and the single time that it fails to operate 
properly will be your last.  However, if you observe a reliable meter 
across your supply that goes from 7 kV to 0 when you shut it off, and you 
still short out the system with a shorting stick, I think you would be 
overall safer than waiting 35 minutes for a 50 meg resistor to bring the 
voltage down.

Nice, mechanically reliably grounding relays may be made quite easily with 
a rotary solenoid.  I have a 40 kV Candela laser cap charging supply that 
uses a small rotary solenoid to lift a grounded arm off of a terminal 
connected through the discharge resistor  to the HV side.  The whole thing 
is inside the HV module which is filled with transformer oil When the 
solenoid is de-energized, the rod falls onto the contact terminal by 
gravity and discharges the supply.  Very little machining skill is required 
to make one.  I can send you a photo of the unit inside my supply if you 
are interested.

Dave


> >
> > To be honest the DC supply scares me to death which is probably a good
> > thing. Obviously it is certain death to contact almost any part of it
>while
> > it is on with or without the caps. My main concern is to safe the caps
>after
> > operation to ensure inadvertent contact does not result in tragedy.
> >
> > I have bleeder resisters (two 100 megaohm 3 watt -at- 15KV in parallel) in
> > place on each cap that take the smoothing caps with a full charge to safe
> > values in about 35 minutes.
>
>This seems like a long time. Pretend your tesla coil was completely
>harmless. When making adjustments, you'd probably want to wait less than 35
>minutes after powering it off to make changes. Unless you're amazingly
>patient, it sounds like you might eventually get tired of waiting 35 minutes
>and start shorting the caps out yourself. The whole "safety" is then
>defeated. Utility company caps are designed to drop to 50 volts or less in 5
>minutes. I'm not sure if it's some NEMA standard, or who else uses it, but
>it sounds reasonable. Microwave ovens drop to safe voltages in just a few
>minutes as well.
>
>KEN
>
> > R*C=T  50,000,000 * .000,007 = 350
> > Estimated full discharge =6*T    6 * 350 = 2100 seconds
> > 2100 seconds / 60 = 35 minutes