Fastest way to charge 3 AAA NiMh, 3.6V@100mAh or 1.2V@300mAh (series vs paralel)

[nuambenzina]

Assuming that the solar panel is very small, and gives about 4.2-5V with 10-30 mAh,
and the NiMh cells are 1.2V @ 100 mAh,
which is the faster way to charge them?

The lower charging time will be archived by connecting them in:
Series (3.6V @100 mAh) Versus Paralel (1.2V @300 mAh).

[inetdog]

Assuming that the solar panel is very small, and gives about 4.2-5V with 10-30 mAh,
and the NiMh cells are 1.2V @ 100 mAh,
which is the faster way to charge them?

The lower charging time will be archived by connecting them in:
Series (3.6V @100 mAh) Versus Paralel (1.2V @300 mAh).

If you are not using a DC to DC convertor, and I think you would not to keep the device simple and low cost, then as long as the panel voltage is higher than the series voltage of the three batteries you will make the most efficient use of the power by charging in series.
But if you cannon guarantee that the batteries will always start out with equal charge, and you will be charging at higher than the allowable constant charge current of the NiMH cells, then you will still have to incorporate some way of monitoring individual cell voltages and either diverting current around those cells or shutting the charger down.

To allow charging single batteries or two batteries instead of always requiring groups of three will take a little more attention in the design. (And, no, I do not know how to do it, sorry.)

[nuambenzina]

If you are not using a DC to DC convertor, and I think you would not to keep the device simple and low cost, then as long as the panel voltage is higher than the series voltage of the three batteries you will make the most efficient use of the power by charging in series.
But if you cannon guarantee that the batteries will always start out with equal charge, and you will be charging at higher than the allowable constant charge current of the NiMH cells, then you will still have to incorporate some way of monitoring individual cell voltages and either diverting current around those cells or shutting the charger down.

To allow charging single batteries or two batteries instead of always requiring groups of three will take a little more attention in the design. (And, no, I do not know how to do it, sorry.)

Then I will go with them in series, for this little toy.

I already have at hand some mini DC to DC converter with the input of 1.2-4.2 V and selectable output of 4.5V, 5.5V but I guesed that If I will charge the acumulators in paralel and then convert from 1.2 to 4.5 then I will loose some power on the way, and I was thinking to charge them in series as I need around 2.8-4.8 Volts for powering up 3 white 5 mm led. This way, I can make use of the dc to dc on another aplication.

Eventually I will upgrade the 100mAh AAA cells with more potent ones of AA or C size and more mAh, anyway the charging rate I assume is very very slow, like a tickle charging as the solar panel is small, is located in shadow (north) and has full sun only in summer at the dawn, What I am worried about is controling the charge and discharge on NiMh, but for this I will open a new thread.

Thanks! Marcel

[Mike90250]

NiMh cells are generally sealed, with a safety vent. Once the vent pops open, the cells will die soon (weeks).

For charging batteries, you need to have a controlled charge. Some circuit that will regulate and not overcharge the cells. If your panel is in shade, it won't put out much amps, so that may save your batteries. 30mA charge into a 100mA cell, unregulated, could be a problem in warmer weather.

[Sunking]

The fastest way to charge any battery is with maximum allowable charge current.

So if you have a 10 ma panel and 100 mah batteries you are looking a 12 plus hours. In the solar world would be several days. In winter a week or more.

[nuambenzina]

A controlled charge. Some circuit that will regulate and not overcharge the cells.

I have opened two new threads as this one was about how is the most optimal way to connect for charging on a solar panel 3 nimh batteries.

This is a thread about Using a LiIo or LiPo on NiMh to keep one cell at a maximum voltage of 1.4V

http://www.solarpaneltalk.com/showthread.php?13657-Prevening-the-NiMh-overcharge-or-discharge-with-a-LiIon-or-LiPo-Protection-Circuit

This is a thread if - delta V method can be used on a combo of solar panel - nimh, with a dedicated circuit or connecting directly a smart charger to a solar panel

http://www.solarpaneltalk.com/showthread.php?13658-NiMh-and-Minus-Delta-V-Circuit-or-a-Smart-Charger-directly-to-a-solar-panel

Maybe someone that will know will answer as these questions where hunting me from 6-8 months keeping my mind busy in background when time free was available.