Old robot not working on rechargeable batteries due to low voltage

Other Hardware General Electronics
9

6hearts:
Perhaps I can stick a volt-meter it to monitor the voltage.

The board I referenced, includes a voltmeter. So, if you find a way to mount the board on the outside of the bot, the "two birds" would be cool, exposed, robot-ish electronics -- and a voltmeter for monitoring the batteries.

6hearts:
Maybe also a Zener diode that would disconnect once the voltage is too low, but then the question is what voltage is the limit?

If the rechargeable batteries are NiMH, then 1.1V per cell. NiCads can go a bit lower -- I've seen 0.9V, but it's been a long time since I worked with NiCads. Lithium's a different story and I will defer to others, since my experience is limited. One of those 5V USB Battery Packs would shut it self off, so there's that :wink:

Shutting the battery off would be an excellent job for an Arduino (perhaps a Pro Mini, or Trinket). Monitor the battery(s) with a voltage divider and Analog port, and shut off the battery(s) with one or more Digital Outputs and a transistor or two.

High Side switch:

OldBotBatterymanagerHighSide.png

Low Side Switch:

OldBotBatterymanagerLowSide.png
OldBotBatterymanagerLowSide.png708×412 64.4 KB

R1 = [100k(VBMAX - VA0MAX)] / VA0MAX
Where:

  • VBMAX is the Highest expected Battery Voltage
  • VA0MAX is the highest voltage to allow on the A0 pin (4.5V recommended)
    The 100nF capacitor is to reduce the impedance to below 10k to satisfy the ADC sample time requirement. Since the voltage divider will be across the battery, we want it to have as little impact on discharge time, as possible. In fact, that 100k resistor could, probably be increased in value [remember to increase it in the formula, as well].