Modification of a PC supply to an output of 13,8V at 20A
Last edited: 23.11.2019
I have modified a PC power supply, it is a “Leadman LM-530”,
which was kindly sponsored by OZ1DNR, Thanks Finn.
I choose this one because it was build more powerful than other 200-250W supplies.
I was not able to find a schematic on the net so I had to reverse engineer it myself to understand how it works.
I have drawn the schematic PSU_diagram in an old version of OrCad (9.2).
It got a whole rebuild, the main toroid was remade with only one winding to change the original 5V to 13,8V.
A big problem with these supplies is to get the overcurrent sense to work right.
Normally the PC supply shut down when overloaded.
This is not very convinient when starting a HAM radio station with high start current.
In this supply i succeeded in building a current limiter, so the supply does not shut down.
To test this I build a electronic variable load (20A) inspired by OZ2CPU.
Use this only as an inspiration, no detailed rebuild instructions are provided.
The final instrument, it needs a new instrument scale to show 0-20A.
Toroid with one winding. Shunt 0.01ohm for current meter. 5V regulator for the fan. 10V capacitors changed to 16V
Large heat sink, 30A rectifier, shunt with sense wire.
New current limitor at 20A, before the shutdown triggered at 26A
Over voltage protection at about 16V.
Resistors for adjusting voltage to 13,8V.
PCB with changes so the 12V vinding from trafo is used in the original 5V circuit
Separate board with large capacitor 470uF / 250V, this part is unchanged.
Large heatsinc and redone toroid.