How to terminate charging of NiMh from solar panel

So, how would one terminate charging of NiMh batteries when charging with solar panels?

Solar panels produce varying current based on the amount of available light and charging NiMh is usually done with constant sources of current…

To maximize the efficiency of the solar panels, you would want to dump all the varying current into batteries… so how would you know when to stop and switch to trickle charge? The normal methods (negative voltage drop, etc) rely on the constant current.

One could use some temperature based method, but is there anything better? Anyone allready develop an IC for solar power charging? Would a Max712 work well with solar?

Would a super capacitor be useful?

Just some thoughts…

Thanks!!

You could just look at raw cell voltage and switch to trickle charge when it was “high enough” (AFAIR, 1.5V/cell or so). You wouldn’t get the fully-charged effect of negative dV/dt, but it would be safer than overcharging I would think.

I think temperature is very effective and wouldn’t rule it out.

I’m not sure it’s specifically designed for it but the Linear LTC4011 has been very good to me for NiMH charging in a wide variety of conditions. I think it’s a generation ahead of the MAX712.

I’m not sure how/why you plan to use a supercap. True, it can’t be overcharged (unless you overvoltage it…is that a verb?) but the energy storage density of supercaps is still nowhere near that of batteries: 5V 1F supercap–>12.5J, 1.25V 1800mAh battery–>8100J.