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solar circuit

Hiya,

I would like to design a circuit that is powered by a battery but the battery is charged continously by a solar cell, the circuit is required to work 24hrs a day hence the solar cell,

i basically just need to send a few bits of information over a radio transmitter (I can do this bit, its easy..) every couple of minutes, this would in turn take its power from the battery.

how would I go about ensuring the battery keeps a charge and the solar cell chargers it?

Im not sure what type of batterys to use, maybe some C type nicads or something, but Ive got a small 1.8W solar panel, that I would like to use.

any ideas??

thanks

Dave

Reply to
spleen
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Rewire the panel to do maybe 3 volts, and set up 2 AA Nicad batteries.

Reply to
Gary J. Tait

If the solar cell's nominal output voltage is greater than the battery voltage, a very simple solution would be to connect a diode and a resistor in series with the solar cell across the battery. The resistor limits the maximum current. The battery manufacturer's datasheet will say what the safe trickle charge rate is.

If the simple scheme above can't deliver enough charge, or the solar panel voltage is significantly greater or less than the battery voltage, you need a low-power high-efficiency switched mode converter with a current-limited output. This will still deliver charge even when the solar panel output voltage drops.

Reply to
Andrew Holme

Depending on your latitude and season, the solar panel will receive a worst case D of Joules/m^2 incident solar radiation which it converts to electrical energy with some dismal efficiency p1 to be stored in the battery with efficieny p2. The circuit will draw a certain energy E over this same 24 hour period so that you will want to select a solar cell area and battery technology so that D*p1*p2> k*E at worst case temperature, where k is sized to reduce the chance of occurrence of successive clouded days causing the D*p1*p2 to fall below E to some acceptably small level. Only after this arduous study is completed can you say things like "but Ive got a small 1.8W solar panel, that I would like to use."

Reply to
Fred Bloggs

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