>> 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.
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.
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).
