Re: A Variable Question.

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

No actual plans, but a fairly simple concept is a series PWM switch (or
"buck converter)...  You put a big bridge rectifier in series with the load,
and the FET across the bridge (that way, the current always flows the "same"
way through the FET). The drive waveform for the FET is a PWM generated by a
suitable circuit driven from an isolated supply (since the FET is
essentially floated at line potential).

The switching rate can be fairly low on this (10's of kHz), and IGBTs would
also work.  You might need a few small inductors/capacitors to make a filter
to reduce the hash.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, October 06, 2002 11:22 AM
Subject: A Variable Question.


> Original poster: "Ken Stevens by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<bluewaterdiver-at-earthlink-dot-net>
>
> I was musing over the cost of a descent variac.
>
> Anything worth while on E-Bay costs a small fortune to ship, and my
> local surplus store wants gold for even a tiny trashed unit.
>
> While I was crying in my milk, I cleaned out some boxes and found my
> stash of 150A Power HexFET's. I have several of these monsters that I
> used as R/C switches in my Battlebots endeavors.
>
> My question is does anyone have plans for or know of them for a FET
> based variable AC power supply? Basically an electronic variac!
>
> With 2 or 3 of these things in parallel you could conceivably create a
> 200A "variac".
>
> Any info on something like this hiding out there??
>
> As always, thanks,
>
> Ken Stevens
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Saturday, October 05, 2002 8:22 PM
> To: tesla-at-pupman-dot-com
> Subject: MOT Voltage Doubler--Again!
>
> Original poster: "Gregory Hunter by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>
>
> Dear List,
>
> I've gotten over my ill-tempered tiff with silicon,
> and rebuilt the twin MOT power supply with voltage
> doublers. I figured if some coilers can build an
> entire system from nothing but FETs and PWMs, then
> surely I can employ a simple rectifier string without
> blowing it. I don't usually give my coils or major
> components silly pet names, so I have simply dubbed
> this PSU the "Mark III", since it is my third
> iteration of the MOT doubler scheme. Have a gander at:
>
> http://hot-streamer-dot-com/greg/Mark III.htm
>
> Cheers,
>
> =====
> Gregory R. Hunter
>
> http://hot-streamer-dot-com/greg
>
>
>
>
>
>