Re: High Power Dimmer, SS Relay

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

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