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Sloar battery charger...

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I'm planing to build a solarpowered battery charger... I'm planing to use a couple of 5.5V 33mA slolarpanels to charge 2-4 Ni-Cd (or Ni-MH) recargable batteries. Can i just connect the solarpanels directly to the batteries via a diode or do i have to have some more advanced systems? Thx for any help!

And if you know can you please explain te difference between Ni-Cd and Ni-MH to me?

Greets: Hanto the newb!


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Yes, you can simply connect your solar cells to the batteries in along with a diode in series. You said that you are going to use 2 solar cells of 5.5V each. So you should connect them in parallel to double the output current to 33mA+2=66mA @ 5.5V. Any general purpose diode will do the job here like 1N4001 to 1N4007 or 1N4148.
This charger will just keep on charging no matter what is the condition of the battery (over charged or full charged). So if kept connected for long time it will damage the battries due to over charging.
So its better to use an automatic circuit which will disconnect the power to the batteries as soon as they are fully charged. To maintain the charge on the batteries, you should use trickle charging in which around 1/10 to 1/15 times of the rated charging current is supplied to the batteries. This charger assures long battery life. A very good automatic Ni-Cd battery charger IC is available from MAXIM. The number is MAX712/MAX713. You can download the datasheet from www.maximic.com. The charger schematic is also given in the datasheet.
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