[Elecraft] Report on cheap power supply for K2

[Geert Jan de Groot]

On 29/12/2021 04:06, elecraft-request at mailman.qth.net wrote:
> A concern might be if the battery is fully charged using the 14 volt supply, and then a conventional 13.8 volt supply is accidentally connected with the battery turned on in the radio, then the voltage regulator of the conventional power supply might get confused.

That should not be the case unless your K2 circuit is modified. D10 on 
the RF board prevents voltage from the battery to reach the DC power 
connector on the back. So there is no voltage from the battery to the 
power connector and the power supply does not get confused.

It is the same D10 that makes power supply selection for charging 
difficult, BTW. In order to get 13.8V on the battery for charging, one 
must pass D10 *and* the resistor in the KBT2 kit. Note that D10 got 
changed to a schottky diode as part of the K2 A-to-B kit. Still, I have 
my K2 power supply set to 14.2V for this reason.

Note that "hey, I found a power supply that doesn't generate noise" for 
me is just one selection criteria for power supplies. Other 
considerations are safety and protection: correct fusing and the like. I 
had a cheap charger explode within 8ft distance in a shack a few years 
ago. The explosion ripped the casing out of the wall socket, ripped the 
casing apart and left the electronics smoldering on the hotel carpet. 
The thing sounded like a pistol shot but didn't even trigger the mains fuse.

My question, then: would you mind if something like this were to happen, 
in your shack, at night, and the resulting situation starting a fire? 
There is a reason that "brandname" power supplies have more protection 
circuitry: if there would be a fire in your shack, then with a brandname 
power supply this is a liability case.
With an Amazon Special, whom would you make responsible?

That is why I either use brandname power supplies or only charge when I 
can attend the charge process. I don't want to badmouth your purchasing 
decision, but perhaps this gives something to ponder.

Geert Jan