The simplest solar charger?

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Wond3rboy

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i have already postd about my solar cell of 5.5v and 60mA.since that post got dead because of me not respnding in time so i have started a new one. i want to charge ni-cd/ni-mh batteries . i want o biult a solar charger a simple one which works like this.

i connect 3 batteries to my solar and cell and want some type of switch that would trip when the voltage across it is 3.6 volt. that way it would close the ckt and an led would be connected in series with the 'switch' to indicate that charging ahs been completed. i want to use passive components otherwise there would be no use of chaging the cells wehn you are using them in the proposed charger. i tried a zener and a schotky but to no vail since when i connect them in parallel they trip due to the full o/p of the cell.any way to circumvent this problem!!!please
 

Yes, use active components.
 
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60 mA isn't really enough to worry about over charging, so a plain simple diode is needed to block the batteries from discharging through the solar panel. A resistor in series with the LED will determine at what point you want it to light up. Suppose your batteries charge up to 4.2 volts (will drop to 3.6 quickly when under load), a red LED needs about 1.8 volts to light dimly, 4.2-1.8=2.4 volts, which your resistor needs to drop.
 
wouldn't it be better to use some sort of constant current approach rather than a dropping resistor? Then you would have a wider range of voltages that would work.
 
philba said:
wouldn't it be better to use some sort of constant current approach rather than a dropping resistor? Then you would have a wider range of voltages that would work.
Click to expand...

Was going for the cheapest/simplest. I've got a hunch there will be more requirements as we go a along with this, sort of secret project type of thing.
 
??

ericgibbs said:
Yes, use active components.
Click to expand...

this is the model for using active components.i want to include a resistor(a small one) on the - battery i/p so as to not drain the battery out completely.will it work.hope to use a 2n3904 transistor.and preferably an Lm10 or an Lm393 comparator.i dont want to use a resistor for the ref voltage(+ve i/p) because that would cause a voltage drop and the battery is 1.2v.

PS: Harvery if 60ma wont do any damage to a ni-cd battery since they are the most esily available ones then i will be more then happy to keep it simple.
I have heard ni-cd batteries have a tendency of becoming a time bomb when over charged.What do you say?
 

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Your zener diode and all the battery cells are drawn backwards.
A 1.2V Ni-Cad or ni-MH cell is 1.4V to 1.6V when fully charged.

Your '60mA" solar panel produces 60mA at noon on the equator of earth with it facing the sun. Any other location or time produces much less output.

Your opamp is powered from only 1.2V so its output high voltage might be 1.0V which is too low to turn on the emitter-follower transistor with a 1.8V LED at its emitter.

Your circuit has nothing to turn on the LED only at night.
 
You never stated the capacity of the batteries, nor what your actual goal is for this project. If all you want is a solar night light, there are plenty of simple circuits available. As AudioGuru pointed out, you aren't going to get the max rating of your panel for much of the day, if at all. I use 6 volt 50 mA panels to charge 3 and 4 cell battery packs with no damage here in central Florida.
 
 
I wonder why I thought your diode looked like a zener?
 

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lolz!told you drew it wrong.so what do you say about charging it the old fashion way with no fancy stuff for the ni-cd battery?
 
If your battery cells are not connected backwards then they can be charged from your solar panel in series with a diode. The solar panel limits its own current.
It might taks a week for your little 5.5V/60ma solar panel to charge three AA 900mAh Ni-Cad battery cells in series.
 
thanks!by the way we are supposed to connect the batteries -ve w -ve and +ve w +ve cause thats what i have done.
 
You have the battery cells connected in series to make 3.6V but they are ubside down and backwards.
 

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