Took a cheap ebay variac and disconnected the mains socket, voltage dial, and added test lead jacks. So I can prototype PSUs without having to have a gazillion different transformers on hand. Waiting to receive a green jack for earth. Will probably also remove the mains jack altogether and 3D print a couple of covers for the holes.
If your intent is to drive another transformer with that, fair enough. Just be mindful that it is an autotransformer, so the secondary is tied to the primary side, unlike a proper transformer that maintains isolation from mains voltage. Of course, for that, there was no need to remove those parts, so... *cringe*
mnem
*toddles off to ded*
I was wondering the same thing. Bson, are you sure the primary and secondary are totally isolated from each other? Your intention is a great idea but only if you are truly isolated from the mains. Otherwise you could be in for a world of hurt.
Yeah, I know for a fact that unit is NOT isolated. I've had a few of them apart.
I have a 90VA & a 300VA 1:2 line transformer I use for this purpose with my AMSCO VARIAC. If I want low voltage AC for prototyping, I use it backwards and I can get stable output down to about 6VAC @ 1.5A; lower at less current. If I need line voltage, I turn it forward and crank the VARIAC down; I can still get full 300-350VA output with the VARIAC at 50%. The problem with this approach is that you have to
be EXTRA CAREFUL... a lot of these step-up/step-down transformers are ALSO autotransformers, and so defeat the purpose of using them for isolation in the first place.med6753 - That's the way you could do it back when there were plenty of cheap transformers available. I used to wire identical back-to-back tube type power transformers with 500 vac hv windings to make isolation transformers. If the added voltage drop was a problem I'd wire the filament windings in series adding to compensate.
If you just needed voltage correction without isolation you could use a low voltage transformer with its secondary in series with the line to boost or buck the line voltage (see drawing). This allowed a relatively small transformer to correct a relatively large output current. The output current rating was equal to the low voltage secondary rating. Some of the line conditioners sold today use this scheme with sensing circuits and relays to automatically correct for line variations over a wide range.
For even more fun, I'll wire a dim bulb tester in series with the above contraption for quick & dirty current limiting. I keep 7W, 15W, 40W, 60W & 100W incandescent bulbs and one of those light blub "Y" adapters to come up with "best guess" current limiting.
And then there's THIS little suicide box... Essentially a dim-bulb tester with a bridge rectifier on the outputs. Good for quick SMPS proto work and desulfating lead-acid batteries. Provided you can put it behind a locked door to keep little fingers away.
Hmmm... I can make some of the room I need for my LAMBDAs by adding a simple DPDT to the output of this as a bypass...
then I can get rid of my big dim-bulb tester...
mnem
Don't get me thinking... that's a dangerous thing.