Starting an Arduino Advanced Charger and Analyzer for NIMH batteries

Projects General Guidance
1

Hey Guys

I am planning on building a charger for nimh batteries. I was thinking of building a buck converter controlled by the arduino depending on current, voltage, temperature and of course everything else to charge the battery. Now the problem is that I would like to have 8 separate channels and I don't feel like building 8 buck with their own current sense etc etc. Are there any simple charger IC's that I could use that I can control the current with the arduino and from which I can get a current reading? Do you know of a buck converter IC that can be controlled via pwm or serial has an integrated current sense that can be read by the arduino? Or do you have any other sugestions? Basically it should be as simple and as solderable as possible.

Thanks!
Adrian

2

Hi Adrian,

Are you planning to have 'fast charge' capability? If so I think you need both terminal voltage and current per cell?

So a MEGA with the 16 analog inputs for < $30 might be good...

But why would you want to do this, for AA's etc.?? Good cheap chargers out there.

UnLess you will also do Amp Hour testing and logging. THAT's the charger I want. I built one a few years ago for testing / charging 12V NiCad packs, but it's 1 circuit and runs on a DOS PC. Ancient History.

What are your ideas??

3

My Idea Is to build an absolutely awesome charger =) I know there are a lot of chargers out there, but none of them do exactly what I want. The charger will include everything from reviving to logging to testing through discharge capacity metering or charge capacity estimation. All the data will be displayed on a nice 320x240 display for all the batteries charged. Of course it will have fast charge capability too. It will not only charge aa batteries when it's finished but for now that is the plan.

I am mainly trying to keep costs and labor down, meaning I don't want to build 8 buck converters... More specifically, do you guys know if there's a way to control a LM2596 other than with a variable resistor, for example with an arduino?

Cheers,
Adrian

4

Go browse maxim-ic.com, they have a lot battery charger/control chips, you can incorporate that with your arduino control/display.

5

Well I actually don't want to use a charger IC, except if I could control it through bus communication. The problem with the arduino is that the max pwm of 31Khz results in a large inductor etc etc. So I decided not to use the arduino as a buck converter but use it to control one.

Abusing something like the TLC5940 (16 channel PWM unit with 12 bit duty cycle control, 6 bit current limit control) and a higher current output would have been absolutely amazing...

Anyhow, starting small, the charger will have 4 charging channels.

The components used will be:

  • 4 x Buck Converters: MP2307 circuits cheaply bought of ebay for 1$ each (in a 10 pack) with an average efficiency rating of up to 95% and a beautiful 340Khz.
  • 4 x digital 100k digital potentiometers: MCP4151
  • 4 x current sensors: ACS712 (A digital ic2 one would have been nice, but don't know of a cheap one)
  • 1 x 12bit, 8 channel Analog to Digital Converter: MCP3208 for voltage and current measurements
  • 1 x 19v 3.75A power supply

A multi channel buck converter would have been nice but I couldn't find anything suitable. This charger will be able to charge each battery with up to 2 amps. The components where of course selected so the charger could easily be used to charge lipo or lead acid batteries etc.

Adrian