Here is the response I got from ISE about the 1510 Variac. Apparently they were reading some of your minds.
“1510 Variable Transformer, $770.00 each, 120VAC Single Phase 50/60 Hz Input;
0-120VAC or 0-140VAC Output (depending on wiring);15 Amps Maximum;
With this model, you will need to add a step-up transformer to its output to reach 0-24V.”
The question then is, will I find a step-up transformer (seems backwards; aren’t we talking about a voltage “step-down” from 120v to 24v max, or 1:5 ?) that has extremely low internal resistance that won’t contribute any significant added V drop at the power supply posts? I get that I’m recreating the Right of Way design in some measure. An advantage is that the 1510 only has 0.2v internal drop at 120v output. If the step transformer were about 1:6, that would place 19v at the sweet spot for the Variac feeding it. Or, a 1:1 isolation transformer with 15A capacity would put the Variac at its low end with low V drop as well. Looks like such are available, though haven’t found just the thing with limited online shopping this morning. None give voltage drop information in their online data. Recommendations welcome!
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