Just bought this power supply and it turns out to be 24V as opposed to
12 as I'd hoped. It's a heafty beast and should be good for running my
HF mobile if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. I know I can buy a commercial
dropper, but that'd be cheating, so can anyone suggest how I might
acheive such a device through HB-ing? Which active devices would be
best for this purpose? I'd like over-voltage protection built-into any
design put forward if possible. Any pointers, please.
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Perhaps the transformer secondary winding has some lower voltage taps
which would enable you to use for 13.8 V operation ,having to waste less
energy and coping with the heat sinks and pass transistors fitted.

Another possibility is to connect the PSU transformer's primary 230/240
winding to a step down transformer's 115 V or similar lower voltage
winding ,provided the step down transformer has the same or higher power
rating than the one of the PSU
In principle the stepdown transformer could be an auto-transformer
(including a variac set in fixed position) ,obviously of adequate power
rating.
Some variacs (like the 8 Amperes unit I have) also have a fixed centre
tap , meaning that with 230V input they give a variable output as well
as a fixed 115 V output.

A stepdown transformer could also be a high voltage transformer say 230
to 500 V or similar but reverse connected (again : of adequate power
rating).

In all cases you would have to change the voltage control circuit ,such
that the voltage can be set to 13.8 V . The latter 'might' only involve
changing some resistors and/or a zener diode .


Frank GM0CSZ/KN6WH