Re: High Power Dimmer, SS Relay ?inverter?

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

Original poster: "Lynn Massie-Southerland by way of Terry Fritz <twftesla-at-qwest-dot-net>" <owlster-at-worldnet.att-dot-net>

Hi to all

Has any one given any thought to using an inverter instead of a variac? I
work a lot with Toshiba AC drives, which are just DC square wave inverters.
The beauty of these things is they typically can be ramped between 0-400 Hz.
And to boot they are darn tough with built in OL protection.
I have just thought their could be some possibilities here.

 Neilster
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, July 06, 2001 9:21 PM
Subject: Re: High Power Dimmer, SS Relay


> Original poster: "Metlicka Marc by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <mystuffs-at-orwell-dot-net>
>
> dave,
> this sounds very much like the VECTROL INC. phase proportioning scr
> power controller that i have? it will be interesting to see what if any
> differences or similarities are involved, since VECTROL is no longer in
> business (from what i can tell) any info to keep it alive will be
> useful.
> we'll look forward to the sch.
> marc m.
>
> Tesla list wrote:
> >
> > Original poster: "David Sharpe by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>
> >
> > Terry, All
> >
> > There has been an ongoing discuss of using dimmers and/or motor speed
> > controls for transformer voltage adjustment in lieu of a variac.  A
recent
> > circuit was shown in EDN magazine (3/15/2001) using two SCR's in a
> > "phase-leg" configuration, with PUT's (programmable unijunction
> > transistors) providing necessary triggering.  The circuit was unique in
that
> > it would work for incandescent as well as inductive loads, can be
> > optically isolated, and can operate as a phase control as well as a true
> on/off
> > SS relay.  If current and voltage feedback are provided, and an
integration
> > capacitor is placed across primary of powering transformer, a
> quasi-adjustable
> > voltage AC active ballast system with high speed (<8ms) shutdown is
> technically
> > possible.  The mentioned circuit would provide about 80% of requirements
> > as listed above.  The cost of all components would be _significantly_
less
> > then an equivalent VARIAC, with enhanced circuit protection, in a much
> smaller
> > more serviceable package.
> >
> > I much prefer SCR's over triacs in high power (read Tesla Coil)
applications
> > because:
> > 1. surge ratings are at least 10X better.
> > 2. far more robust then a triac
> > 3. higher temperature ratings
> > 4. isolated devices (even in a "phase leg" or doubler configuration) are
> > available
> > 5. voltage ratings of 1.4kV are available in isolated case, if you go
hockey
> >     puck case (and a deep pocketbook), devices to 15kV -at- 1kA+ are
> >     commercially available.  Does require more expensive heat sink,
cooling
> >     and HV insulation considerations at HIGH POWER (>50kW).
> > 6. If input voltage ratings are held constant, SCR's are cheaper at same
> > current
> >
> >     level as compared to Triacs.
> >
> > I have schematic, will sketch up circuit in Excel and shoot to Terry to
> post on
> > web site...  Cost of all parts minus SCR is probably about $50-$70 for a
> > 240 VAC
> >
> > unit to control up to 20A.  Predominate cost above that will be heat
sinks,
> > cooling
> > fan(s) and SCR's.  120 VAC service requires 400V SCR's,  240 VAC
requires
> > 800V devices, and 480 VAC apps (for us HIGH POWER junkies) would
> > need 1.2kV devices.  The circuit as shown is designed for currents of up
to
> > 100-200A according to author, but appropriate SCR(s) are up to designer
to
> > select.  I would not exceed 50% Irms rating at full power for reliablity
and
> > robustness.
> >
> > Regards
> >
> > Dave Sharpe, TCBOR
> > Chesterfield, VA. USA
>
>
>