This is an idea build on top of repurposing an old laptop battery pack from my previous instructables.
It is time to put the battery pack into good use. First, we should have some way to charge up the battery pack. An easy and fun way to do this is to charge it up with solar power. This is an simple project of connecting a simple solar charge controller to the battery pack.
Step 1: Getting a Solar Charge Controller
Fortunately, today, it is easy to get a pre-made solar charge controller board for the battery pack. I manage to pick up one from amazon. This charge controller is designed for a standard solar panel with maximum power point voltage of 16V. The output voltage is set for battery pack with 3S battery configuration. The maximum charging voltage is 12.6V.
Link to the solar charge controller:
Step 2: Add a Barrel Connector for the Output
Add a barrel connector to the output of the charge controller so it can be connected to the battery pack.
The connector I used is:
Step 3: Add a Connector to the Input End
Add a female barrel connector on the input end so the solar panel can be connected. I put some RTV silicon on the wire connection points for strain relief.
Step 4: Putting the System Together
Putting the whole system together.
Connect the solar panel on the input, and the battery on the output. System is now complete and ready to receive free power.
The output voltage of the charge controller can be adjusted if you wish to use different battery type. R6/R7 control the output voltage.
Use the simple equation:
Vbatt = 2.416 * (1 + R7/R6)
A small modification I suggest is to add a 5.6M ohm resistor parallel to R7 to reduce the peak charge voltage to the battery down to 12.3V instead of 12.6V. This increases the cycle life of the battery significantly by using only 90% of the battery capacity.