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Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
I've always had it in my head that you could make a slightly more mechanical variac by winding a transformer with several secondaries of different sizes (1 turn, 2 turns, 4 turns 8 turns). Using some relays you could set an number of voltages buy seriesing several of them together. If you can get your transformer to have 1V per turn even better. The coil might look like a mess but there isn't any reason you couldn't do it. I might make the low turn coils have a little heavier gauge wire.
Registered Member #2727
Joined: Tue Mar 09 2010, 02:39PM
Location: Montevideo - Uruguay
Posts: 33
A toroidal variac is a clasical design. You can do a linear variac, doing a transformer with long legs and winding it with only one layer of enamel wire.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Nik wrote ...
I've always had it in my head that you could make a slightly more mechanical variac by winding a transformer with several secondaries of different sizes (1 turn, 2 turns, 4 turns 8 turns). Using some relays you could set an number of voltages buy seriesing several of them together. If you can get your transformer to have 1V per turn even better. The coil might look like a mess but there isn't any reason you couldn't do it. I might make the low turn coils have a little heavier gauge wire.
I like that, Nik. You can switch voltages in known steps, without having to rotate the shaft. (I think that's what Slo-Syn motors were invented for).
But it's no longer an autotransformer. The binary-weighted voltage windings need to be isolated. You can get integer volts from 1 to 127 with 7 windings: 1, 2, 4, 8, 16, 32, and 64 volts.
I've thought about doing the same thing with ternary-weighted voltage windings. You can get integer volts from 1 to 121 with 5 windings: 1, 3, 9, 27, 81 volts if each can be switched 3 ways: bypass, series boosting, or series bucking. Though I think that needs twice as many SPDT switches per stage.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
If your brush is spring loaded (ie, use the brush carrier that you get the brush from) it gives more leeway as far as mechanical construction goes.
A transformer with multiple secondaries is also a good idea, as would be several small transformers on separate cores, with the option to switch them in and out in series or parallel.
Several MOT's with re-wound secondaries, or similar, could be used, you could even have one with separate, single turn, windings, for example, to give integer volt output, or whatever. (I'd probably go for increments of ~5V or so)
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
If there were a way to softly transition from one voltage to another with my "switching supply" ;) I would have tried it before now. Ramping it up would occur in very defined steps and would not be as smooth as a real variac.
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I want to make a variac
