"Jim Wilkins" wrote in message
...
...
....variable power supply I built from a 50A, 20% duty cycle arc
welder transformer and a variac ...

Arc welding transformers have a fairly high internal impedance to
cheaply provide high no-load voltage to start the arc and current
limiting when welding, especially when the electrode sticks. The
tradeoff is low efficiency. This means that the voltage drops
significantly as load current increases, and conversely the voltage
rises if the load's current demand decreases, as when a battery nears
full charge.

This voltage and current regulator is a good match to the 50A
transformer:
https://lygte-info.dk/review/Power%2...-USB%20UK.html

The rectified transformer output is almost useless and high enough to
be considered dangerous without either the variac or DPS5020 to
control the voltage.
https://www.osha.gov/laws-regs/stand...ons/2015-09-04
"OSHA considers all voltages of 50 volts or above to be hazardous."