Author Topic: Will this Ni-MH Charger circuit work?  (Read 1161 times)

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Offline Reider

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Will this Ni-MH Charger circuit work?
« on: December 20, 2016, 08:59:06 pm »
Hello

I'm designing an Arduino powered device with an Ni-MH battery and charger.
Also I have an adjustable constant voltage, constant current board I want to use with a C/4 output current.
The micro would pulse charge the battery switching on and off the change voltage once a few seconds and when off measuring the cell voltage and temperature to detect dT/dt and -dV/dt.
I also don't really want to use a heat sink on the 7580 so I would just use it for logical stuff and using the internal regulator for the Arduino.

The battery is a 12 cell 14.4V Ni-MH battery pack so I would set the charge voltage for about 1.4V/cell 17V + the diode forward voltage so 18V
My main concern is the logic level FET. I have a fixed supplier in mind and not a lot of logic level types are available.

Thanks for any feedback, here are the datasheets:
http://www.alldatasheet.com/datasheet-pdf/pdf/84033/IRF/IRLZ24N.html
http://diotec.com/tl_files/diotec/files/pdf/datasheets/1n5400.pdf
« Last Edit: December 20, 2016, 10:18:30 pm by Reider »
 

Online amspire

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Re: Will this Ni-MH Charger circuit work?
« Reply #1 on: December 20, 2016, 10:00:15 pm »
NiMH batteries are not the easiest to charge and a battery with 12 cells becomes harder. The dV/dt method will probably be useless because each cell will have a slightly different state of charge and the dT/dt method may need sensors on every cell.

Not sure what the best method is for 12 cells - maybe to charge at c/4 till about 1.36V a cell (might get you to about 50%) and then drop down to 0.05C for 15 hours?

The NiCd batteries were much easier in battery packs as the individual cells could withstand a lot of overcharge, and in my experience, many of the NiCd batteries were still working fine after 20 years. Otherwise, everyone is now looking for lithium battery solutions in new designs.

Basically, it will be pretty hard to charge 12 NiMH cells to near 100% in 5 to 6 hours. If you can get to 95% in 24 hours without stressing individual cells, you have done very well.
 

Offline Reider

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Re: Will this Ni-MH Charger circuit work?
« Reply #2 on: December 20, 2016, 10:18:00 pm »
Hello yes I was not really clear on the battery. So they are in a 12 cell battery pack so they are always charged and discharged together. This should make them a little bit easier to handle. The pack also has a built in thermistor I will use to detect temperature. My main concern is the FET and did I do something stupid :) Also you are right I may have to implement a slow charge too.
« Last Edit: December 20, 2016, 10:40:43 pm by Reider »
 


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