Solar AA charger

[suppgp]

I am an electronics novice (1 month or so), working on a small solar cell project. I plan on building a AA/AAA solar charger using a resistor and LM317 chip, and will switch between the two different battery holders using a SPDT switch.

I would like the charger to light an LED when the batteries are sufficiently charged. How might I do this? I'm thinking a zener diode might be used. Thanks for any help you might give!

 

[audioguru]

It is winter in the northern part of Earth. Solar panels don't work well in winter because the sun is low in the sky and it shines for only a few hours.

An LED needs more voltage (1.8V to 3.5V) than a single Ni-Cad or Ni-MH cell provides (1.2V). My solar garden lights use an electronic circuit to stepup the voltage of the single 1.2V rechargeable cell.

Some of my solar garden lights use an LDR to turn the LED on and off with darkness and others use the solar panel.

I don't know why you have an LM317 and I don't know what a zener diode will do in the circuit.

The solar panel is small and cheap so it probably does not fully charge the battery cell so it doesn't need anything to stop the charging.

I don't know why you want to light the LED in the daytime. Maybe the solar panel can light the LED then a rechargeable battery is not needed.

 

[suppgp]

It may be that I am confused. I plan on charging either 2 AA or 2 AAA batteries at one time. The purpose of the LED would be to indicate that charging is complete. I thought the zener would allow sufficuent back voltage, once the batteries are charged, to light the LED. The sole purpose of the circuit would be to charge batteries, not to operate a load. I'm not concerned about the season; I will use this when the sun returns to Ohio in the spring.

I found the suggestion to use the LM317 (actually an LM317T) on a U.K. solar projects website:
http://www.reuk.co.uk/Solar-Battery-Charger-With-LM317T.htm[/URL]

 

[audioguru]

2 AA Ni-Cad or Ni-mH battery cells are 2.4V. Their voltage is about 2.8V when near full charge. A red LED is about 1.8V. The lowest voltage zener diode is 2.1V and it performs very poorly.