I am taking over a project, and what we have seems to work, although we are
switching to programmable DC supplies for some of our furnaces.

We are feeding 220VAC feeds through a Research Inc. (Minneapolis)
programmable triac phase angle controller to a 220V variac then to a 220V
power transformer which steps down to 16 volts at 500 amps.  We are running
furnace heaters and usually are running under 200 amps of current.

> Should we be using phase angle control into inductive loads (variac &
> transformer)?  Are there any problems running this way.  Obviously if we
> are turning on the sine wave part way through its cycle, there will be a
> lot of high frequency component being fed from the controller, but I am
> not really sure what the effect of this is.
>
> I understand phase angle control - in fact I have even built a few, for
> example to control lighting in our church using a 555 starting its delay
> from zero crossover, but it seems to me that a power control that would
> drop out individual cycles of the power - the more percentage of complete
> cycles you drop out, the less power you transfer to the load - would be
> better because then you could always use zero crossover switching.  It
> wouldn't be useful for lighting, because you would see the flicker, but
> should work fine for heating and work O.K. in our case of going through a
> variac/transformer.
>
> Pardon the dumb questions, but its the only way to learn.  The above could
> obviously be done with a PIC, but would it work?  What am I missing?  Is
> there something commercial I could buy?
>
> Mike
>
> Mike Montaigne
> Neutron Program for Materials Research
> Steacie Institute for Molecular Sciences
> National Research Council
> c/o Atomic Energy of Canada Ltd.
> Station 18, Chalk River
> Ontario, K0J 1J0, Canada
> Email: montaignem@aecl.ca
> Phone: (613) 584-3311 Ex:4005
> Fax:      (613) 584-4040
>

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