Re: High Power Dimmer, SS Relay ?inverter?

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

Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

Neilster,

I am planning an inverter system that will run up to 500W - I was going to
have the fets chopping the DC thru the transformer at 50Hz, but since its
just a simple 555 timing circuit with a varable resistor controlling the
resonance, then I can run it anywhere between about 1Hz and 1800Hz (the
saturating frequency of the xfmr core). If I use a line filter after it, and
a protection network (thx terry ;) after the NST then I could probably use
the inverter for TC use. With a scope I could get the frequency exact... It
would be interesting to see the effects of high frequency input  for TC
use!!!

On the subject does anyone have a design for a High Powered H-Bridge circuit
(about 50A) because I would prefer to use 'proper' AC rrather than square
DC....

Thanks,
Jason

Geek # 1139 Rank G-1
www.thegeekgroup-dot-org

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, July 07, 2001 4:01 AM
Subject: Re: High Power Dimmer, SS Relay ?inverter?


> 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
> >
> >
> >
>
>
>