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I have a battery pack of 8 Ni-MH 2400 mAh cells connected to a load that draws ~700 mAh (a Raspberry Pi Zero, display, WiFi dongle, USB hub, and a wireless keyboard dongle). I want to add a led that changes from green ( around full battery) to orange (around halfway) to red (nearly empty) depending on the battery voltage. What voltage are Ni-MH batteries at when full, halfway and nearly dead?

  • Pack's datasheet says? – Ignacio Vazquez-Abrams Jul 21 '16 at 14:13
  • Thier regular duracell batteries that normal (not electronic) people use so they didnt come with a data sheet. I cant find the amazon page i bought them from either. –  Jul 21 '16 at 14:22
  • [So what?](http://www.farnell.com/datasheets/1960165.pdf) – Ignacio Vazquez-Abrams Jul 21 '16 at 14:33
  • Please try and use google before posting I found a few good examples of circuits here https://www.google.com/search?q=battery+voltage+monitor+led or https://www.google.com/search?q=battery+voltage+monitor+led+ni+mh+circuit see http://electronics.stackexchange.com/help/how-to-ask Also, you can make a voltage discrimination circuit with comparators, the output can be used to light an led. Additionally look at the charging curve for one 1.2V nimh cell, then multiply that for the number of cells – Voltage Spike Jul 21 '16 at 16:55
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    Im not looking to make a voltage detector circuit, im going to do all that with the pi and an ADC. I just need to know what voltages to use for each colour. –  Jul 21 '16 at 17:03

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Individually, it's 1.4V max charge, 1.3V ~ 1.2V nominal for most of its drain cycle, 1.1V to 0.9V dead, 0.8v you broke it.

Since this is a pack, of I'm assuming series cells, multiply these values by the number of cells.

And since you want to use an external, make sure to use an appropriate resistor voltage divider to bring the voltage range down to acceptable levels for it, as most will not accept a direct 10+ Volt input.

Passerby
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  • Thanks i think ill do 1.3v an above for green, 1.3-1.1v orange, 1.1-1.0v red –  Jul 21 '16 at 15:05
  • The pi doesnt have an onboard ADC so it depends on the external ADC whether i need a voltage divider or not. Thanks for your help –  Jul 21 '16 at 18:24
  • @blaablaaguy edited. Most ADCs won't accept 10+ volts directly, so it probably will. – Passerby Jul 21 '16 at 19:22