Bypassing bms Idea

I’m not quite sure how this would work but it would be very helpful for people that bypass there bms. So normally if you bypass the bms you have no control over how much the batteries get discharged but by adding a simple led we should be able to fix this. So basically all you need to do is connect an led or light or any other thing to the output of the small discharge only bms. Now what will happen is that led will stay turned on as long as your cells are charged but when they drop down to the low cut off on the bms it will turn off the led and viola you know that the batteries are flat. In my mind this should work but I haven’t actually tried it. If anyone has a spare bms that can try this for me that would be great as this could help lots of people

Good day

Just realised the led will actually blow up from the voltage we run at but a small ubec could be added first to drop the voltage down

And the idea for some people is to not have the BMS be able to shut off the vesc

Yes and this will solve this for them. It would even be possible to add a more complex circuit that activates a buzzer or something to let you know

The idea is to bypass that shut off ability You don’t want anything being able to turn off the ESC other than a fuse or the ESC itself.

Ahh sorry typo that was meant to be led

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3 letters and so much confusion lol

Haha yeah I was wondering what you meant in the first post

He meant turn off the led.

This is possible, you would need a voltage divider to get only between 2v and 5v to the led.


Yeah or a Bec circuit that drops the voltage down to 5v

Simple resistor in line would work

Yes or even a small voltage regulator they cost a dollar for like 5 on ebay

Anyone able to test this for me?

Yes it would absolutely work. You would need a resistor in series with the led that would limit the current and thus prevent the led from blowing up. So say for example you would need a 42 kilo ohm resistor to limit the led current to 1mA @42V

I have 2x 5S4P packs in series for 10S4P 30Q lions. I could easily put a lipo checker with buzzer on balance leads. So it will beep at preset voltage.

That way I could monitor 8 cells out of 10 for example.

I have that checker too but it is quite inaccurate and you have to disconnect it every time you finish so it doesn’t drain the batteries

I have a BT module hooked to my focbox so I can monitor parameters without looking under the board. That’s accurate enough for me anyway.

Hey guys wanted to update this thread, I feel as though this could be very useful to a lot of members now as more people use charge only bms modules. So the idea is that you wire up the bms normally for charge only but then add a led or similar connected to the bms output, this way the led stays lit when the board is powered but when reaching LVC it will turn off without cutting the power to the board.

In my case I’ve got it set up with my led display showing battery percentage, this way I don’t need a resistor inline with the led and I can see my voltage percent too.