JR-T450 Battery 67.8V/5A Charger - Modify to 57V?

[Papa]

Help modifying the JR-T450 (67.8V/5A) Battery Charger output to 57V?

There is 3 blue trim pots, all side-by-side (note RED arrow). Searching I discovered one of them adjust output voltage - turning it CC, I managed 64V... but no less. Any suggestions appreciated.

 

[amberwolf]

What other resistors are in series with that particular pot? It is very likely that one of them is the main voltage-set resistor, and the pot is just a fine-tune for it. If changing the pot to lower resistance adjusts voltage down, then changing a series resistor with it to a lower value would give a lower voltage base range. How much lower should be calculable: The fixed resistor value multiplied by the ratio between the max voltage it already has vs the max voltage you want should give the new resistor value. (if upping the resistance decreases the voltage then you'd reverse the last two terms, I think). It might be more complicated than that, but probably not.


But...there is a limit to most of these adjustments based on the output of the big transformer and the switching circuitry, and it's possible you've already reached it. (most likely the lower value can be a lot lower than it already is, and it's just the higher value that's limited by this. depends on the design).

 

[Papa]

What other resistors are in series with that particular pot?

Too much in the way to see - I'll need to pull the board to verify the related resisters to the trim pot.

Also, my web searching revealed nearly identical charger models, but differing output voltages. Some as low as 58V and as high as 84V. I also noticed C4060 Power Transistors (14 Amps?)

Thank you AW