[Elecraft] New KX3 reverse voltage smoke

[Andy Durbin]

"If that really is the case, there would seem to be a fault with your power supply. The secondary (low voltage) side of a PSU should never be connected to ground. Both poles should always 'float'."

Many of the currently marketed small switching supplies have the same internals and only differ in branding, rear connectors, and metering.  I own two Jetstream switching supplies and there quite a few "badge engineered" power supplies that use the same internals.

These power supplies most certainly do have the negative output terminal connected to chassis and mains supply ground.   No, you can't isolate the output terminal.

I was remined that the negative terminal is not isolated when I used one of these power supplies to drive the reversible DC motor that tunes my magnetic loop.  One direction works ok, the other direction lets smoke out of the wires.  If you want to feed reversible polarity DC up the coax using a pair of bias T then the PSU better be isolated!

Opinions on whether PSU output terminals should float seem to be quite stong so I expect a protracted debate.

73,
Andy, k3wyc