I want to build a circuit that will monitor the voltage of all 12 cells in my pack and tell me to stop when any one of them drops below the cutoff. Here's what I had in mind.
Each cell will be connected to an independent comparator's inverting input using the balance plugs. A 12V regulator will power each device, and a voltage divider will provide the reference cutoff voltage for all comparators (somewhere between 2.0-2.5v). Using the values here 2.5v should be around 2.6kohm on the pot. A little hysteresis will be added by putting a 100k or so resistor from the outputs to the + inputs. The outputs will be connected directly through small indicator LEDs, lighting up independently whenever the cell voltage drops below the reference. In addition, if any LED lights, a buzzer will sound to annoy me enough to disconnect the batteries.
Being a very inexperienced circuit designer, I've got some concerns. Firstly, each LM339 chip has four comparators built in. If I use 3 LM339's pulling from the same reference voltage, will I have to worry about it dropping? Should I use a more stable reference voltage like an LM317 regulator or something? Also, if all of the outputs are routed through the LEDs before being wired to the buzzer, can I count on the LEDs to prevent current flowing from one output to the next, or should I design this differently? My intent is to have 12 separate LEDs but just one buzzer. Might have to wire the outputs to a small transistor to drive the buzzer. But anyway, that's the general idea. I plan to mount the comparators on/near the pack and run some wires from the comparator board to the LED board on my handlebars. Please let me know what you think!
Each cell will be connected to an independent comparator's inverting input using the balance plugs. A 12V regulator will power each device, and a voltage divider will provide the reference cutoff voltage for all comparators (somewhere between 2.0-2.5v). Using the values here 2.5v should be around 2.6kohm on the pot. A little hysteresis will be added by putting a 100k or so resistor from the outputs to the + inputs. The outputs will be connected directly through small indicator LEDs, lighting up independently whenever the cell voltage drops below the reference. In addition, if any LED lights, a buzzer will sound to annoy me enough to disconnect the batteries.
Being a very inexperienced circuit designer, I've got some concerns. Firstly, each LM339 chip has four comparators built in. If I use 3 LM339's pulling from the same reference voltage, will I have to worry about it dropping? Should I use a more stable reference voltage like an LM317 regulator or something? Also, if all of the outputs are routed through the LEDs before being wired to the buzzer, can I count on the LEDs to prevent current flowing from one output to the next, or should I design this differently? My intent is to have 12 separate LEDs but just one buzzer. Might have to wire the outputs to a small transistor to drive the buzzer. But anyway, that's the general idea. I plan to mount the comparators on/near the pack and run some wires from the comparator board to the LED board on my handlebars. Please let me know what you think!