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Re: Primary dummy-loading
Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-uswest-dot-net>" <R.E.Burnett-at-newcastle.ac.uk>
Hi Gary, all,
> I was wondering if anyone has come up with a way to dissipate the bulk
> of each primary bang in something less hazardous to my basement (and me
> and my scope) than streamers. I was thinking of either some kind of
> dummy load resistor in series with the primary ?
The answer is YES ! Connecting a resistance in series with the primary,
(or instead of the primary) works great to stop the sparks from the
toroid while making adjustments to the gap. It de'Q's the primary ;-)
I posted a message about using linear halogen lamps to achieve this in
1999, which I include again for reference:
* Hi all,
* For about the last month I have been dinking around with various
* sync and async rotaries, paying particular attention to
* charging efficiency. Some will remember a post several months
* ago asking about modifying a TC to produce no sparks so that
* measurements and fine adjustments could be made to the charging
* system without the noise and danger of a 3 foot arc buzzing
* around the toroid !
* It was generally agreed that removing the secondary is BAD. The
* problem is finding somewhere for the tank capacitor's energy to
* What I have done over the last few weeks, is replace my primary
* winding with a chain of 3 halogen filament lamps. The 1000W kind
* used for outdoor security flood-lights. I was originally hesitant
* to do this, because I feared that the filaments may "fuse" under
* the high peak discharge currents. However this idea seems to
* work well and provides many advantages to anyone wanting to study
* the charging behaviour or make fine adjustments to rotaries:-
* 1. There are no toroid sparks, hence less danger and less noise.
* (Also a far safer environment for using an oscilloscope.)
* 2. Peak currents are lower. The current when the spark gap fires
* is limited due to the resistance of the halogen lamps.
* This reduces wear and also dramatically reduced spark gap
* noise to a quiet buzz. (Even the safety gap made a quiet pop.)
* 3. Less RF interference. Since the capacitor now discharges into
* a resistive load, the energy is dissipated in an exponential
* type decay rather than the usual damped ringing. Therefore
* there is little RF generated and I found that television
* interference was almost eliminated completely.
* 4. Lamp brightness provides an indication of power throughput.
* Adjusting rotary phase for maximum brightness may be a good
* alternative for those without a scope and HV leads.
* 5. Charging behaviour is the same as with a normal TC. The
* substitution of the halogen lamps for the primary has little
* effect on the low frequency charging behaviour of the system.
* I just thought I would share this, as it has enabled me to
* carry out many hours of work on sync rotary charging without
* keeping the neighbours awake and messing with there TV's.
* I guess it would work just as well for static gap and async TCs.
* If anyone plans to try this please rate the series chain of lamps
* generously for the power you expect to process. I used three
* 1000W 240v lamps in series, and they lit dimly while running at
* 600 Watt. Also bare in mind what would happen if a lamp went
* open circuit ! (Dangerous charge left on capacitor !!! )
* - Richie
* - In sunny Newcastle.