Build a Solar Battery Charger for Ni-MH Batteries | Hacker News Reader

Build a Solar Battery Charger for Ni-MH Batteries

allaboutcircuits.com

38 pointswhereistimbo7 comments

Well, that ignores the charge termination rules for NiMh, so the effect on long term battery life won't be great ...

Yeah if you’re going to do this and forget such things you might as well use a diode and resistor and be done with it. It’s no worse than this circuit.

how about this: https://create.arduino.cc/projecthub/aleksand1975/intelligen... ?

That looks a lot better, it recognizes the dv/dt condition and has a number of safety features.

Trickle charge (less than 15mA) for NiMH was fine for long-term battery life I thought?

EDIT:

https://data.energizer.com/pdfs/nickelmetalhydride_appman.pd...

>> Finally a maintenance (or trickle) charge rate of less than 0.025 C (C/40) is recommended. The use of very small trickle charges is preferred to reduce the negative effects of overcharging.

C/40 constant trickle-charge is good for NiMH chemistry.

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The simplicity of trickle-charge is one of the defining reasons to use NiMH over other chemistries. 15mA * 40 == 600mA-hrs, which should be safe for even tiny AAA-NiMH cells.

EDIT: Ah, I assumed the article was going for the Trickle Charge technique. Hmmm... it uses a 555-timer for "current limitations" which seems... harder than just using an OpAmp + transistor.

Here's a great kit I've built in the past. It's popular with remote radio operators, campers and sailors.

http://www.cirkits.com/scc3/

The 555-timer as a current-limiter seems... complicated... to think about.

I feel like an OpAmp can set a voltage across a resistor, and then a BJT transistor can be set into "current mirror" mode, and easily set the current-control needed to safely work with NiMH batteries. If you wanted 90mA or 100mA (or whatever), that seems like the most straightforward way to set a current across a changing voltage source (which a solar-panel is).

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