by sich » Thu Oct 26, 2017 11:25 am
It's not advisable to charge 7.4V 2-cell lipo battery with a 6V 3W solar panel. Solar panel ratings are stated based on the optimum condition. The output voltage is already less than 2-cell lipo battery, you have to boost it up and expect energy loss to the already very limited power converted from solar energy. Besides we should always balance-charge lipo cells too. So you will need to design or add a balancer to your circuit to protect/preserve the lipo battery. Charging 1-cell lipo is more straightforward in this case. Assuming your circuit is working perfectly, you also need to consider the time needed to fully charge your 900mAh lipo battery with a solar panel.