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Double checking myself 110V/240V equipment switch

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large_ghostman

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I havnt actually looked at the moment, but lets say you have something like a boat anchor Logic analyzer, probably a Toroid transformer inside.

On the back is a switch to choose your line Voltage from 100V /240V depending on your country, am I correct in thinking this simply switches the input from one set of wingdings to say a center set?

All I am thinking is I need 110V, Because I have to mess with this anyway I dont really want to make things harder than needed. So if I am correct then I could take the power board from some dead boat anchor, use the 240V windings and simply use the..............No wouldnt work would it??

Wrong side of the trans former :S thought it was too easy. Bah, back to the drawing board! Although I guess i could go the other way and power the secondary side and then tap off the 110V winding??

Sorry kinda thinking out loud, I got some old logic analyzers etc that I am pretty sure have toroid power boards in, i am looking for a simple way to drop my 240V to 110V, from there I can mess with the switching frequency etc. Its that or a Variac and they are not cheap in the UK!!
 

Les Jones

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Hi LG,
The primary is probably two 110 (ish) volt windings. They would be connected in parallel for 110 volt operation and in series for 240 operation. If this is the case you could use it as an auto transformer to get about 120 volts but you could not get an isolated 120 volts. You could also use one of the secondary windings to add or subtract from the 120 volts. You would be in the same positionregarding isolation as using a variac as they are auto transformers.

Les.
 

large_ghostman

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Thx Les i wasnt sure, i dont need isolated, i have 240V and need 110V, from that i need to vary speed and drop further on some parts. Not sure i got a suitable transformer yet, I was checking my sanity!! I got a vague memory of a non working HP logic analyzer power board, i think its got a toroid transformer on it, but cant remember, i dont need the entire power board as its huge with roughly 12 different voltages on. But its old enough to be before SMPS became the only thing in town.

I looked at USA variacs and they are good value, here they are twice the price! but then again twice the Voltage :D. Thx for double checking me, sometimes i get myself in a knot.
 

unclejed613

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in the past, i've used boat anchor filament transformers to make an isolation transformer. if for instance you had a 220v:12V/10A filament transformer, and a 120V:12V/10A filament transformer you could connect the 12V windings together and you would have a 220:120V isolation transformer. of course that's assuming the load is less than [email protected] there will also be some thermal and copper losses, but that's the basic idea. you could probably do the same thing with output transformers from UPS supplies and get better results, since UPS supplies are often in the 500-1kw range.
 
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