marce002
100 W
Hello is there a resistor you can mod to lower this to 12v ( from 40v ) it has an op amp LM324N and the picture of the board is this but do not have schematic.
Mod this charger 40v down to 12v
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marce002
100 W
in case i want to learn i mean
Most likely you can do that. It would be necessary to trace out at least part of the circuit. Can you post a picture of the back side?
Somewhere there should be a voltage reference and a divided output voltage going to one of the sections of the 324 that regulates the voltage.
Somewhere there should be a voltage reference and a divided output voltage going to one of the sections of the 324 that regulates the voltage.
marce002
100 W
pins 1 2 and 3 of lm324n are not connected. the chip pins in the pic below... 
It's a little hard to see everything in the pictures, but the two resistors pointed out appear to be in series. These look like the voltage sensing part. Also the "431?" in the picture, take a look at the number on the part and see what it is. I suspect that is the 2.5v voltage reference. Try measuring the resistance of those two resistors as I can't make out the color bands.
If you can power it up and measure the voltages on either side of those resistors with respect to the negative output, it will give you a clue. If those are the right ones, lowering the resistance will lower the output voltage.
If you can power it up and measure the voltages on either side of those resistors with respect to the negative output, it will give you a clue. If those are the right ones, lowering the resistance will lower the output voltage.
marce002
100 W
thks fechter , yes its 431 and resistors are in series , lower one arround 8kohm and other is 5.15kohm , volts in common point is 9.15V.. lower one is 42v at left and other 2.48v at right. (output gnd for the measurement.)
i can put a variable resistor 10k pot instead of one of the resistor and test? wich one would you pick?
i can put a variable resistor 10k pot instead of one of the resistor and test? wich one would you pick?
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marce002
100 W
none of those resistor did change output vol... placed a trimpot 10k instead one of a time .. in one case 101v!! appears and other one fixed 41v...so there might be other resistors....
The next best guess would be these resistors:
They look like they're in parallel. Try removing one and see what that does. You might be able to remove both of them and use a pot. There may be a limit to how low the supply can go and still function properly. I'm being lazy and avoiding tracing out the entire schematic, but 431 based regulators are pretty common. The resistors are part of a voltage divider and the circuit will try to keep the node at 2.5v. We tried the upper divider resistors last time, but there seems to be some extra circuitry tied into them. The lower resistors will probably work out better.
They look like they're in parallel. Try removing one and see what that does. You might be able to remove both of them and use a pot. There may be a limit to how low the supply can go and still function properly. I'm being lazy and avoiding tracing out the entire schematic, but 431 based regulators are pretty common. The resistors are part of a voltage divider and the circuit will try to keep the node at 2.5v. We tried the upper divider resistors last time, but there seems to be some extra circuitry tied into them. The lower resistors will probably work out better.
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marce002
100 W
thanks to all and it seems that the lower Vol it can reach is 25Vol, it cant be lower than that ,due maybe to the HF transformer and its turns.... or im with the wrong resistors. in my case to lower up to 25v only im touching the "high" part of the divider they are two res in series and the lower RES i can place is 20k to get 25V...that is all....
The GND part of the divider and its resistor can be tweaked instead? maybe can find my 12v in there? or I should only tweak the high voltage positive part of the divider as i did?
The GND part of the divider and its resistor can be tweaked instead? maybe can find my 12v in there? or I should only tweak the high voltage positive part of the divider as i did?
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You could try it, but my guess is you'll run into the same limitation. On Meanwell power supplies, they usually adjust the low side of the divider. This way if the pot wiper goes open, the voltage drops instead of going too high. With fixed resistors, that's not an issue.
