Instructables

Can I connect a trickle charge solar panel directly to a battery recharger?

I have a 1.8 W 125 mA solar panel, and a GP battery recharger. There is a connector that came with the solar panel that fits the recharger. I connected them and did a quick test with a bright light and it lit all four lights without batteries in the charger. Is it possible to connect a solar panel directly to the charger without some other device/inverter between the two and be able to charge NiMH batteries? I have attached a pic of the items including the information on the back of the electrical plug that came with the charger. It says input AC 120V-60Hz, output DC 12V 1.5A. The picture shows the rest.

I look forward to the answer and will not attempt to connect these until I know it is safe and effective to do so.  Thank you.


Picture of Can I connect a trickle charge solar panel directly to a battery recharger?
iceng9 months ago
If you don't put a little schottky diode in series your battery Will Discharge at night.

When dark ... a solar panel becomes a Resistor that sucks the battery dry.
NotaryBlue iceng8 months ago
Did not know that thanks, would 125mA charge tho? I have noticed most of my cells are 1500mA to 2000mA the wall charger is only rated at 200mA would that contribute to the time it takes to charge? Cells confuse me just cant grasp the concept.
blodefood (author)  iceng9 months ago
So you are saying that it could work as long as I unplug it as soon as the light is not enough? My biggest concern was whether the batteries would explode or overheat.
iceng blodefood9 months ago
Correct !
If you remember to un-plug it as soon as the light is not enough it will work well.
You can buy ten 40v 3A schottky diodes for $1.60 at Jameco that is 16¢ each.
And prevent discharge when a cloud hides the sun too.

I don't think that little solar panel can overpower the batteries.

Set the batteries in the shade and touch them at noon to convince yourself..
blodefood (author)  iceng9 months ago
Thank you! Now I would need to figure out where to put the diodes and what other materials I need to use them. I tried looking for an instructable on how to do this, but I'm new to electrical stuff and I am not exactly sure what to look for. Would you be kind enough to point me in that direction?
iceng blodefood8 months ago
Here is a very simple circuit using a 9¢ diode from Jameco.

If your solar panel can deliver more current then 3 amps
or more then the battery can receive you can use the
current limiting optional circuit by turning the switch down.

There are ibles on using the LM317 regulator if you need to set a current limit.

A
Solar-lm317.jpg
Does the charger allow you to charge only one battery at a time?

If you must charge 4 batteries at a time you may need a small 12 volt battery buffer between the charger and the solar cell.

The solar cell charges the deep cell battery and the battery supplies the current necessary to power the battery charger.

You may be better off getting an 12 volt AA 8 battery pack and charging them directly from the solar cell.

And do as iceing said add a diode to the + to the batteries I would use a 1N5817 schottky diode. The 1N5817 is a 1 Amp but the solar cell is only pushing 125ma so it should be more than enough and the voltage drop across the diode is 0.45 volts.

Joe
mpilchfamily9 months ago
Sure but the panel isn't going to be able to offer enough amperage to do much good. You may find that once you connect batteries it doesn't work.