How to best charge 3 x NiMH batteries from a 12V solar panel?


Newly Enlightened
Jul 27, 2016
How to best charge set(s) of 3 x AA NiMH batteries from a 12V solar panel?

Since both the power from the solar panel and the surrounding temperature can change suddenly, I suppose it would be most reliable to charge with C/10 from morning to evening, without any fancy algorithms?

I'm consider trying to use the solar charger witch is based on LT3652. That charger is supposed to charge a lithium cell, but the charging current can easily be modified to match C/10 of the NiMH batteries. However, its charging voltage is 4.0V (not 4.2V) and that would be more difficult to change. 4.0 / 3 means charging with only 1.3V per NiMH battery. Lets say the solar panel provides power for 8 hours a day.

How would NiMH batteries react if charged with 1.3V and C/10 for about 8 hours:

- I assume they would not be charged up to 100%, but about how much of their capacity can be expected?

- Would there be any long term issues if the NiMH batteries are seldom charged to 100% of their capacity? (e.g. memory issues, sulfation like issues, etc)

- Would it be acceptable to mix batteries with different charging levels if charging only with 1.3V and C/10?

Are there anything else I should think about? (I'm more concerned about safety and number of battery life cycles, than using their full capacity.)


Newly Enlightened
Mar 7, 2021
Not sure if it's the "best" way, but I've been charging my NiMH with an Opus BT-C3400 hooked up to a battery box and Powerfilm solar panel. A bit more complicated than that, but I got most of my configuration from OH8STN on youtube.
He's mainly talking about how you can use solar as a way to run ham radio stuff, but could still be informative.

Also, if your solar panel is a regulated 12v, you could probably make a cable with the correct connectors on it to an Opus or equivalent charger.