[Elecraft] New KX3 reverse voltage smoke

[Alan - G4GNX]

In which case I maintain my original point that the PSU is faulty, but 
it would seem to be by bad design rather than a developed fault.

Whilst the mains ground is there for safety, if there was a ground 
fault, it's quite possible that high voltage/current could be applied to 
the PSU  low voltage side and cause untold damage, a fire or even death.
If I had bought a PSU connected like that, I would return it if 
possible, otherwise it would be in the trash!

Apart from the perceived PSU fault, have Elecraft really connected the 
-ve input terminal to chassis? That would kinda negate the use of the 
reverse polarity diode. The KX3 circuit diagram is not entirely clear.

73,

Alan. G4GNX


------ Original Message ------
From: "Andy Durbin" <a.durbin at msn.com>
To: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>
Sent: 05/09/2020 19:59:14
Subject: [Elecraft] New KX3 reverse voltage smoke

>"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
>