I'm tweaking an old coffee roaster using a variac. Originally, I used
it simply to compensate for variations in the line voltage at a
particular power outlet, but I have since started to deliberately
adjust the voltage up or down to control the temperature, usually in a
range between 110-135 VAC. Essentially, the roaster is nothing more
than a hot air popcorn popper with a motor driven fan and a heating
coil. I was wondering - if I increase the voltage by, say, 10%, how
does that affect the power consumption? Since the coil gets hotter,
it's clear that it's consuming more watts. Would total watts also
increase by 10%, or does the efficiency of the heater coil change?
The motor speed changes with the voltage, as well. If watts increase
at a faster rate than voltage, then, at some point, I will probably
trip the breaker (although the heater coil probably would have already
failed). In general, how tolerant are heater coils and electric
motors to higher voltages?