Re: SCR/Triac pig controller? (fwd)
---------- Forwarded message ----------
Date: Tue, 19 May 1998 02:56:38 -0600
From: "D.C. Cox" <DR.RESONANCE-at-next-wave-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: SCR/Triac pig controller? (fwd)
We worked on this problem for a while back in the mid-70's. The simple
triac system just doesn't work properly because of transients (very rich in
TC work as opposed to HV DC x-ray applications). We did finally come up
with a good working circuit using separate antiparallel SCR's which were
triggered a completely independent pulse generator source with a lot of
line and isolation filtering with xmfrs, etc. This worked quite well, but
in some of our commercial science museum applications people actually stand
atop some of the smaller coils and when this xsistor type controller fails
everything goes to full conduction which could present huge legal problems,
so hence, we still use the tried and true variac system. When the wire
burns up or brush dies it just quits and does not go into full conduction.
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: SCR/Triac pig controller? (fwd)
> Date: Wednesday, May 13, 1998 10:13 PM
> ---------- Forwarded message ----------
> Date: Wed, 13 May 1998 19:12:02 PDT
> From: Bill the arcstarter <arcstarter-at-hotmail-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: SCR/Triac pig controller?
> Seems like one problem with powering the larger coils is the scavenging
> (and paralleling?) of enough variacs to handle the 7+ KVA which might be
> So why can't I just build a large phase-controlled scr/triac controller
> and run my pig off this huge "Light-Dimmer"??
> I understand the design of the scr drive circuitry is slightly
> complicated since the load is inductive (need snubbers, etc), but that
> doesn't seem insurmountable. I'd also need some good solid
> filtering/emi/efi construction techniques to minimize hf/rf getting into
> the gates or control lines, etc...
> The output voltage of our 60KVA x-ray transformers are controlled by
> phase controlled scrs/GTOs etc. (that's what made me think about it)
> Ya-ya. I know solid state and tesla coiling don't usually mix well -
> but I think in this case the benefits would be worth the effort.
> I'm presently using a bank of four scrs on the output of my (previously
> AC-only) welder. This gives me 180 amps DC in conjunction with my hf
> arc stabilizer- with no ill effects (ie - no uncommanded triggering of
> the scrs). Granted - I had to do a few HF bypassing tricks on the gates
> and I'm not doing phase control - just using it as a huge switchable
> full-wave bridge...
> If someone would tell me why this won't work as a pig controller before
> I go to the trouble of trying it - I'd really appreciate knowing!!
> Heck - maybe I'll go buy those ignitrons I saw up at the scrapyard...
> That'd take care of it.
> -Bill the arcstarter
> Starting arcs in Cinci, OH
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