This is a long thought to make a short point...
Variacs are AC transformers that can vary their AC output. They are another significant monetary investment for an electronics lab. So, a work-around may be needed, at times, as I do not have one.
I am working on an AC converter for a friend's camper. It keeps the batteries charged up. It is an all-in-one device, having an on-board AC transformer on the same board as the regulator section.
The converter is blowing fuses, so I can not have the unit on long enough to find the short. This would be the perfect time to employ a variac... To use it to inject a low value of AC and look for a component that is heating up. But, as said, I do not have one.
So, what is the work-around. Well, I need a low value of AC voltage at low amps. Having this definition in mind, it occurred to me that this device is just a common transformer. Duh...
If I had a variac, I would be setting it at about 5 volts and maybe 1 amp. 5 volts should be enough to drive the transistors of various types. 1 amp x 5 volts = 5 watts; that's enough to create discernible warmth, without melting things.
So, the short point... A simple, low value transformer may be a perfectly acceptable substitute for a variac, correct? As I have tons of them, the price is certainly right...
Cautions...
- Great care is needed, if you intend to use an oscilloscope to look at the primary side of the circuit. See Dave's video on blowing up your scope and google isolation transformers.
- Remember to use a resistor in series to absolutely limit the amount of current that is allowed to enter the circuit.
Thoughts, or suggestions?