RE: DC Resonance Charging Advice Sought

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

At 05:01 PM 8/13/2003 -0600, you wrote:
>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.


Most relays of this type have some secondary contacts.. you put a set of 
those contacts in your safety interlock loop that prevents power from being 
applied.

A popular approach to this sort of thing is a spring closing switch with an 
electromagnet (Grainger catalog) to hold it open. You have to manually set 
the switch (i.e. you don't need a honking big solenoid to pull the armature 
all the way against the spring).  The sequence is "apply power to 
electromagnet" "move armature til it "clanks" against the electromagnet 
(which also closes an enable switch for the low voltage side of the power 
supply"


I really recommend you read the North Report (it's on hot-streamer-dot-com)... 
He's put a bunch of this kind of interlock design stuff in there.. it's a 
standard problem for high power transmitters.


>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