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carlmart 8th September 2012 06:28 PM

Schematic for 12v NimH battery charger
I have a 12v 4500mA nimH battery that I need a charger for.

I am not sure if it's easy or not to design a charger that might allow me charging them for now.

There two things I am not sure of: charger voltage and if I should use a series resistor, to allow 10% or 20% current only.

Any suggestions?

DUG 8th September 2012 08:46 PM

Take a look at this. or search Digi-Key for others.

carlmart 8th September 2012 08:53 PM

I was thinking of something much simpler. Something like the Microchip project does need

a specifiic pcb board, which I don't know where to get, and several parts.

Not too easy, and probably not too cheap.

Something like this is probably closer to my idea:

stratus46 9th September 2012 01:47 AM


Originally Posted by carlmart (
Something like this is probably closer to my idea:

Charging NiMH Cells

That will work but you have to monitor the charge status or you'll ruin the cells. I used to do that with Ni-Cads running 500 mA AA cells from dead to full in 20 minutes. The time I forgot to turn them off wasn't pretty.


counter culture 9th September 2012 03:35 AM

Take a look at the LM317 datasheet, it shows a current limited voltage regulator suitable for constant current/constant voltage charging with a Max. 1.5A output.

DUG 9th September 2012 05:26 AM

As counter culture says: "a current limited voltage regulator"

Or a voltage limited current source is what is needed for these types of batteries.

The simple resistor limited battery chargers were OK for lead-acid types.

My dad used to say: "A job worth doing is worth doing right."

Your choice.

Take care.

AndrewT 10th September 2012 09:40 AM

Ni-mH need more than just CCS limited and Vreg charger.
This works for lead acid and Nicad.

The new battery technologies need much more sophisticated charging.
Just read the extract from the post2 link

The MCP1630 Low-Cost NiMH Battery Charger has the following features:
• Programmed parameters - modified in firmware
• Factory Settings:
- Preconditioning Charge Current =170 mA
- Preconditioning Threshold = 3V
- Constant Current Fast Charge = 1.35A
- Charge Termination based on delta - VBATT / delta time
- Charge Termination based on delta + TBATT / delta time, with external
thermistor installed
• Top Off Charge Current = 130 mA for 1 Hour
• Overvoltage protection (battery removed)
• Overcharge protection to prevent damaging the battery
• Overcurrent protection in the event of a shorted battery
• Battery reversal protection
• Input short circuit protection
• Overtemperature protection to prevent the battery from reaching too high a temperature
during charge
• Soft-start capability by holding the reference voltage low during power-up
• The MCP1630 Low-Cost NiMH Battery Charger has the flexibility to optimize the
charging algorithm for new battery technology, different battery chemistries or
different battery pack configurations
• Proprietary features can be added by modifying the firmware contained in the
• The factory-programmed source code is available
• Ability to adapt to environmental effects, such as ambient temperature

DF96 10th September 2012 11:52 AM

To charge NiMH safely you need manual intervention or overvoltage foldback or temperature rise foldback. They need more care than NiCd cells.

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