Power Supply Switching Off a Capacitve Load

[piguy101]

I am borrowing a Keysight  N8928A power supply (rated 10 kW, 500 Vdc) to do some testing on an inverter and a permanent magnet motor. The inverter has about 400 µF of DC link capacitance. The power supply has an output on/off button. Can I use the on/off button to switch the output? I set a low current limit to reduce the capacitor charge current when turning on. But I worry that when I switch the output off, the DC link capacitance in the inverter could backfeed the power supply. Is this an issue? For now, I have been slowly stepping the output voltage on the power supply down to 0V in order to turn off because of my concern.

[Eka]

It can be a issue. It all depends on how well protected the power supply is. See if you can find the manual for the power supply online and see what it says. You can put a diode inline with the positive rail to block discharging back through the power supply. That will create a voltage drop, and the diode does need to be able to handle the expected current, and be heatsinked if needed.

[Paul Price]

When in doubt, always download and read the manual for this instrument.

In general, if the switch is directly connecting the power supply output to the output terminals, or even if it does the same thing with a relay, the surge current flowing into or out of the P/S would easily damage the relay or the switch upon turn on or cause the power supply to be severely damaged.

The use of a series diode would certainly prevent a load dump back into the power supply, but would not protect the contacts of a switch or relay within the P/S from damaging surge currents into the power supply load.