# using solar cell to charge battery

Discussion in 'The Projects Forum' started by mrel, May 21, 2011.

1. ### mrel Thread Starter Active Member

Jan 20, 2009
97
1
Hello
using solar cell to charge battery different size (AAA,AA,D ) which is more important more voltage OR more current to charge the batteriers.
Second question when hookup solar cell in paralel OR in series and one cell is bigger than the other would bigger cell damage the smaller solar cell.
Thank for infor mrel

Dec 26, 2010
2,147
300
Unless you plan to use a voltage converter, in order to work at all the solar cells will have to have an output voltage at least equal to that required to charge the battery. The current available will determine how quickly the battery can be charged.

Connecting panels of different voltages in parallel will result in current circulating between them. Depending on the current level, this may or may not result in damage, but is certainly wasteful. Cells or panels should only be connected in series if they have similar current outputs - otherwise the current available from the weaker cell dictates the maximum overall.

3. ### #12 Expert

Nov 30, 2010
16,350
6,840
Charging batteries is mostly about current. As long as you have ENOUGH voltage to drive current into the battery, then the amount of current is the determining factor. Small amounts of excess voltage will be dragged down to the battery voltage because the current flow loads the solar panel.

4. ### Georacer Moderator

Nov 25, 2009
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1,266
What I 'd like to add is that you should buy identical solar panels because it seems you 're not in position to decide whether you can connect different one together or not.

It would be ideal if each one covered your voltage requirement. If not you should tie some in series until you get the desired voltage. Then tie identical strings of panels in parallel until you get the desired current output.

5. ### wayneh Expert

Sep 9, 2010
12,156
3,063
Another thing to consider: A solar cell delivers power most efficiently if it is not loaded down to reduce its voltage below about 90% of the no-load voltage. So putting several in series to get high voltage, which is then loaded down to roughly the battery voltage, is not ideal. You want just enough unloaded voltage to exceed 1) the battery voltage plus 2) the blocking diode's voltage drop plus 3) ~10% more.

6. ### garybuska New Member

Aug 12, 2014
23
0
I created a circuit using four solar cells with the same voltage outputs in parallel and connected one AA battery holder and one AAA battery holder to their output using a blocking diode for each battery holder. This allowed me to charge two types of batteries at the same time fairly quickly.
Since a solar cell is basically a variable battery if you put them in parallel the voltage stays the same but the current is increased thus allowing for a quicker charge. It worked great
The solar cells came from old garden lights that I no longer wanted.
The unloaded output of each cell was 2 to 3 volts.
I used the blocking diode to prevent the battery from back feeding the solar cells.