How to change cutoff voltage of the controller

Controller is chinese YK31C 24V 500W.
6S battery - cutoff voltage at 3.45 is to high. Panasonic NCR18650BD have lot of energy stored between 3.45 and 3.2.
How to change cutoff voltage from 20.5V to 19.2V ?

Controller have IC with this marks

339
ST MZH9830

LM339 if im not wrong.
I guess (with my small electronics knowlege) there is some voltage divider to control this.
How to identify resistor responsible for this?



I managed to find schematics - not sure if this is correct

I would buy a controller designed for adjustability and the range I wanted

Can you reccomend some?

Probably not me, but many here could if you start a new thread listing your motor and all other relevant parameters.

Assuming the schematic is at least generally correct, it's the two resistors on the far left edge of the diagram.

Which ones those correspond to on the PCB you'd have to trace out on your actual controller.

Alternately, you can measure pins on the LM339 chip as DC volts to ground, as your battery drains, and see which one keeps dropping proportionally with the battery voltage.

Then measure the resistors from that pin to ground and battery voltage. You can use math (which I'm terrible at figuring out formulas) and determine the ratio of the resistors as they are, vs the LVC as it is, and then use the LVC as you want it to be to calculate the ratio of resistors you need them to be to get that. Or you can experiment with different values for one or the other of the resistors, until you get hte LVC you want.

Yeah i figured that also - those 2 resistors are responsible for voltage cutoff. Will try to test with my variable PS and after that i will use math to change resistor value. Only strange thing - it seems to me those 2 resistors are in series in my case - not parallel. Will check later with multimeter.

Yes, they are series in the schematic as well--they're just using two paralleled resistors in each case to get the specific resistance they wanted.

amberwolf said:

Yes, they are series in the schematic as well--they're just using two paralleled resistors in each case to get the specific resistance they wanted.

Click to expand...

Yeah they are in series in my case also. 1.5kΩ+10kΩ - 11.5kΩ total.
My controller stopped at 20.25V. I will now try use different value of smaller resistor - will try with 2kΩ and check cutoff voltage.
After that it should be easy to calculate right value.

Yeah - i managed to set cutoff voltage to 18.06V with 1.68kΩ resistor. This should be good enough - will test tomorrow.