Re: SCR/Triac pig controller? (fwd)

---------- Forwarded message ----------
Date: Fri, 15 May 1998 17:22:22 +0300
From: Harri Suomalainen <haba-at-cc.hut.fi>
To: tesla-at-pupman-dot-com
Subject: Re: SCR/Triac pig controller? (fwd)

>From: Bill the arcstarter <arcstarter-at-hotmail-dot-com>
> So why can't I just build a large phase-controlled scr/triac controller 
>and run my pig off this huge "Light-Dimmer"??

You can (in theory at least :) but it is a complicated task.

> 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 basic problem is that once the spark gap fires the load is like
a short circuit. This will kill the controller.

A proper approach would be to detect the overload and then commute
the tryristor/GTO/whatever off before current has got too large. This will
need some inductance to limit current risetime. Current cannot rise too
high before the output has been "turned off". Not an easy task.

Further complications would be stuff like imbalance in the transformer
core which might saturate it if this is not handled with. Some other
exist too.

> 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)

It can be done but you do not get away the inductors as a current limiter
totally. If you want to just control the average power task might be

> 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.

On the other hand variacs are very reliable and hard to break. Blowing up
expencive scr's does cost a lot too!

Harri Suomalainen     mailto:haba-at-cc.hut.fi

We have phone numbers, why'd we need IP-numbers? - a person in a bus