Arduino Assisted Battery Characterization and Logging

[jram112]

I need some help deciding if my battery characterization setup will work properly.

Background: I have a few different single cell LiPo batteries (3.7V). I want to characterize them using similar loads that my circuit will use.

Setup: I will use three LiPo's with each having a separate programmable load. I want to use arduino to log the battery voltages and to halt the discharge of each battery when they go below 2.7V. Attached is a schematic. Are there any concerns about having the three loads connected to the same ground? Should I use DPDT relays instead?

[Bloch]

Look´s ok

[mswhin63]

I haven't used LiPo batteries before but you will need to latch the relay as soon as you disconnect the load the Battery voltage may rise back above 2.7V otherwise it should work fine.

[waoj]

Would this same setup work just as well for 12v 7a SLA UPS batteries?  I have a bunch to test to decide if I want to replace them or not, and I wanted to base that decision on actual performance.

[ledtester]

To avoid overstressing your Arduino's GPIO pins I'd use base resistors on the transistors, like 1K.

A even more robust circuit would use pull-down resistors on the base, like this:



(taken from: https://stackoverflow.com/questions/20936347/spark-in-arduino-relay-and-bluetooth-module )

The main reasons I've found for using a base-emitter resistor are:

- prevents collector-base leakage current from turning the transistor on
- increases EM noise immunity if the base is disconnected

If you use a MOSFET instead of a BJT a gate-drain resistor is needed to turn the MOSFET off when no signal is applied to the gate.