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Variacs and isolation trafos

F

firestorm

pfm Member
I've been collecting bits and bobs through the years, but never had the space to use them till fairly recently. Some these bits are a variac and isolation transformer.

I've inspected the variac, looks like it has two adjustments, the big knob with a pointer and the plate beneath that which you can turn as well, it has a carbon brush.

Can any one tell me what that supposed to do?

I need to work out an enclosure for it, any ideas? The thing weighs about 6Kg, there are three screw hole on the bottom.


https://ibb.co/jJ00d2w
 
The large knob is usually to adjust the voltage. The other adjustment seems to be for the frequency (Hz).
This tool is very useful to verify things in a defective or re-worked amplifier as you can set it at a very low voltage instead of starting it at full voltage so it will be safer for the components.
The frequency adjustment should be set at 50 Hz or 60 Hz depending on where you leave.
As for a casing, I would not brother with this as most of the people I know are using bare as shown on your pictures. Keep it away from children though !
 
The big knob adjusts the voltage output. The pointer bit if adjustable in position but seemingly does nothing electrical is probably to allow you to go back to a previously set voltage ie lets say you have set it to a measured 200V out, then set the indicator pointer to the same point so you know that where the pointer is will be 200V.
The big knob should move the carbon brush around the winding, hence the output comes from the carbon brush.
8A is a usefully large Variac:)
 
Gervais Cote said:
The large knob is usually to adjust the voltage. The other adjustment seems to be for the frequency (Hz).
This tool is very useful to verify things in a defective or re-worked amplifier as you can set it at a very low voltage instead of starting it at full voltage so it will be safer for the components.
The frequency adjustment should be set at 50 Hz or 60 Hz depending on where you leave.
As for a casing, I would not brother with this as most of the people I know are using bare as shown on your pictures. Keep it away from children though !
Click to expand...

The frequency is whatever you put in.... 400Hz max is likely quoted as it's the frequency used in aircraft AC electrical systems, although usually 3 phase.
 
I built an Armageddon clone with a variac rather than a transformer some years ago. Has been powering the LP12 ever since. There was (is?) some discussion about the 'best' voltage for an LP12 motor. I still don't know, I just set it down as low as it would go whilst working. For a while I would turn it up bit when starting up...but don't bother anymore..
 
Arkless Electronics said:
The big knob adjusts the voltage output. The pointer bit if adjustable in position but seemingly does nothing electrical is probably to allow you to go back to a previously set voltage ie lets say you have set it to a measured 200V out, then set the indicator pointer to the same point so you know that where the pointer is will be 200V.
The big knob should move the carbon brush around the winding, hence the output comes from the carbon brush.
8A is a usefully large Variac:)
Click to expand...

The plate which is movable, with a carbon brush which traverses across the surface. I was thinking the pointer is the coarse AC Vout and the movable plate is a fine adjustment.
Most variacs seem to be 1, 2 or 5 amps. Not that many are 8A, though I believe I need to derate the output a lot at lower Vout.
 
I wired it up, but found the voltage wasn't changing. Upon closer inspection the plate is slightly warped and the knob isn't turning the thick plate. I've released the tension by adjusting it and it now turns a lot better. I'll see if I can flatten the plate. I'm surprised the spindle isn't slotted.
 
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