Voltage Divider Battery Monitor

Hi all.

44v battery pack that I want to monitor on an analog pin.

Thinking of doing this (with a 5.1 Z Diode) connected to stop any nasty things....

Thinking r1=18k and r2=2k

That will be 5v and 50v....

Are there better options?



That'll work OK but at what voltage is your 44volt battery charged. If it's a rechargeable battery rated at 44 volts then the charge voltage could be as high as 60. As to the zener diode for protection, you could eliminate it by placing a resistor of say 10k connecting the junction of R1/R2 and your analogue input. This resistor will limit the input current and so prevent damage.

I would select higher values for the resistors.
The zener is not needed with the higher values and with the higher values I would omit extra protection resistor as jacrae wrote.

The impedance of the voltage divider for the analog input should be 10k or less for a good ADC value.

So I would choose 10k for R2 and 120k for R1.
The impedance would be 10k parallel 150k which is near 10k.

The measures voltage is 0 .. 65V. The accuracy would be 100mV or 200mV (63mV in theory).

In case R2 doesn't make contact, the current into the analog port would be 44-5 / 120k => 0.3mA
I think the analog input is not destroyed by that (I hope).