PLCProf posted:Actually, to continue down your path, measuring the primary current/power is a good way to see if a transformer is at or near overload, but the math involved in calculating output headroom in amps or watts is likely to be unpleasant to many.
The way to deal with this is to come up with an Excel spreadsheet that does the heavy lifting, then anyone could use it. 
Do I hear any volunteers? 
