Hi

I have a colleague that built a crude variable 480v drive conditioner out of a 120 to 480-volt transformer, a light dimmer, and a light bulb for current limiting. He told me that the output was reaching a maximum of 380 volts. I told him that the light dimmer is not an equivalent to a variac, in that it chops up the AC waveform to limit the voltage. After getting rid of the dimmer and running the transformer's input on my variac, he asked me if there is a smaller version that he could fit in his enclosure. I told him that variacs don't get much smaller than 2 or 3 amps. I thought about using a rheostat but rheostats limit current and not voltage.

With that said, I came here to see if anyone else had a good idea on how to control voltage while keeping the 60Hz line frequency untouched. Does anyone have any ideas?

Best Regards,
Joe M

 

You need to supply a lot more info. What is the required power level? And what is he trying to do with this?
For low powered applications, a 60hz oscillator driving an audio amp running into a transformer works well.

 

You need to supply a lot more info. What is the required power level? And what is he trying to do with this?
For low powered applications, a 60hz oscillator driving an audio amp running into a transformer works well.

The max current will be around 2 amps on the output side, therefore about 7-8 amps on the 120 volt side. We need to variate the 120 volt side. This is used to slowly condition drive capacitors.

 

It sounds like exact control is not needed.
How about a transformer with switched output taps? It will need to be a fairly large and probably expensive one.
Or you could use a number of smaller isolation transformers and connect their secondaries in series as required

 

It sounds like exact control is not needed.
How about a transformer with switched output taps? It will need to be a fairly large and probably expensive one.
Or you could use a number of smaller isolation transformers and connect their secondaries in series as required

I thought about that as well, but he wants a variable output. It seems that everywhere I look, every dimmer or variable AC power supply (other than a variac, of course), uses triacs or some sort of time-controlled voltage regulation...