RE: DC Resonance Charging Advice Sought

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

Original poster: "Dave Kyle by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dave-at-kyleusa-dot-com>

I am now definitely going to add some sort of spring loaded shorting switch
with a suitable resistor to instantly discharge the smoothing caps. I think
I can construct something that will be easier to use and more reliable than
a shorting stick. This will permit service on the system immediately
following operation.

I already have a 7KV Sodium hexafluoride relay which I could use as you
suggest. My concern with an automatic relay is that if for any reason it
remained closed when the power supply was energized it would be very bad. I
need to give this subject some more thought; perhaps a manually operated
momentary relay would be the ticket.

I really appreciate the design feedback as they definitely result in
improvements I might not have implemented even over time. It is safe to say
I would never have gotten this far this fast had it not been for this list.

Dave

=========================================
Dave Kyle
Austin, TX USA
Email: dave-at-kyleusa-dot-com


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, August 12, 2003 11:33 PM
To: tesla-at-pupman-dot-com
Subject: Re: DC Resonance Charging Advice Sought

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