Re: BIG Xfmr - current limiting
>The three MOT's in series may be severely stressing the, core to
>secondary winding, insulation (depending on what the insulation looks
>like). There may be a work-around by submerging them in oil . . . or
>take your chances if they are cheap.
They were free (old microwaves from a dump) and, yes, I will run them under
>The idea of just putting a 4KW, five volt transformer, in series with
>the primaries of the MOTs, is not much of a current limiting solution.
>If it works, it would be more by accident, than by design. A shorted
>transformer is, just that: shorted. It won't go a long way towards
>limiting current, and won't provide any active current limiting.
>You may be able to do something like put a power rheostat on the 5 volt
>side for current adjustability, but a series variac would be a better
How does the series variac circuit work? Is it just a a variable inductor in
series with the MOT primaries?
>Ideally, what you want for ballast, is something that will actively
>regulate current. (act like a dead short when the current is light, and
>increase in impedance when the current tries to exceed some value . . .
>A shorted NST for instance, or a welding transformer, or other current
>regulating inductor, tungsten light bulbs, ballast tubes, etc.)
Why is a shorted nst different to a shorted xfmr of any other sort?
>It wouldn't be all that tricky to use a simple self-biasing transistor
>current limiter, on the low voltage side of a transformer. A five volt
>transformer would be pulling 800 amps, on the secondary, at 4 KW. That
>is too high for a cheap transistor current regulator. Use a 50 volt
>transformer, and it could be done with eight inexpensive transistors, a
>full wave bridge, and load resistors . . .
Yes but the 50V transformer would have to be BIG and the load resistors would
>The easiest way is to get a welding transformer, electric space heater,
>or wind an adjustable inductor.
Do just bung the space heater in series with the MOT primaries?
I'll need it!