Hall effect circuit to switch ANT BMS ON and OFF.

[zeroToe]

I'm building a battery pack for an efoil using an ANT bms. I want to be able to turn the battery on an off without a mechanical switch so am designing a small PCB using an Arduino. The circuit has:

• 5 leds for voltage display,
• Voltage divider to measure pack voltage
• A hall effect sensor as the input to turn the battery on and off using an external magnet.
• Optoisolator to switch the BMS on and off.
• A piezo speaker
• A water ingress sensor.

I know just enough about this stuff to get me into trouble, and i have hit a snag that i can't figure out. Usually by writing a post like this I figure out the issue, but i haven't yet!

The problem - With the ANT bms you only need a momentary switch to turn the BMS on and off. Therefore i need a method of sensing which state the BMS is in so the circuit does not try turn it ON when its OFF, and OFF when its ON. If the BMS switched positive, i could measure the output voltage as the signal, but since the BMS switches ground it has me stumped.

I could get around all of this by using UART, but i haven't seen a decent example this online, so think it might be above me skill level.

any advice would be much appreciated!

thanks

 

[amberwolf]

Does the BMS have a status LED? If you need isolation you can use a photosensor to detect it's state. If you don't, you can read the state of the LED's switch (it's probably active low, grounding the LED, that's common).

Or you can add a wire to the BMS's MCU lines that go to the gate drives of the FETs, which directly lets you see if the BMS is enabling or disabling the output / input. It's not a direct indicator of the state of the BMS, but if the BMS is off then both charge and discharge ports should be in disabled state; if either or both are enabled the BMS has to be on..

The BMS MCU may have other lines on it that have states exclusive to being on, or off, that you could tap.

 

[zeroToe]

Does the BMS have a status LED? If you need isolation you can use a photosensor to detect it's state. If you don't, you can read the state of the LED's switch (it's probably active low, grounding the LED, that's common).

Or you can add a wire to the BMS's MCU lines that go to the gate drives of the FETs, which directly lets you see if the BMS is enabling or disabling the output / input. It's not a direct indicator of the state of the BMS, but if the BMS is off then both charge and discharge ports should be in disabled state; if either or both are enabled the BMS has to be on..

The BMS MCU may have other lines on it that have states exclusive to being on, or off, that you could tap.

Great ideas - i'll do some probing and see what i can find