Is it possible to charge a 44.4 V LiPo battery with a lower voltage LiFePO using a boost converter and some form of overcharge protection? I have a battery powered plane using a 12s lithium polymer battery, and I am wondering if it is possible to extend the flight time (even if marginally) using solar cells. The solar cells would be connected via an MPPT controller to a lithium iron phosphate battery and this would be connected via a boost converter to the lithium polymer battery. A problem I can see occurring is balancing.
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1\$\begingroup\$ I'm just guessing, that if you use the same kind of rigid, crystalline cells that are used for most stationary solar panels, the added weight will rob your plane of more power than the cells produce. I'm guessing that you'll need some kind of fancy, light-weight thin-film cells to get any benefit at all. Maybe find thin-film cells printed onto some flexible substrate that also can be used as the skin of the airplane. \$\endgroup\$– Solomon SlowFeb 3, 2022 at 23:19
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\$\begingroup\$ mass is indeed an issue but there's plenty to trade if all you want is time in air. have you considered a blimp instead? Usual solution with solar cells is to connect enough small ones in series to get the voltage you need. its less massive than the same cells plus another battery. \$\endgroup\$– AbelFeb 4, 2022 at 0:14
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\$\begingroup\$ Eliminate the second battery. Just boost the solar panel voltage to the LiPo pack voltage (or ensure the panel already exceeds it). \$\endgroup\$– user16324Feb 4, 2022 at 0:44
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I am wondering if it is possible to extend the flight time (even if marginally) using solar cells. The solar cells would be connected via an MPPT controller to a lithium iron phosphate battery and this would be connected via a boost converter to the lithium polymer battery.
The main problem with charging an auxiliary battery and using it to charge the main one is the extra weight. The solar panels won't be powerful enough to charge the battery quickly, so unlike eg. an electric vehicle with dynamic braking there is little advantage in storing energy in another device for later use when you can just make the main battery larger. This will also be more efficient than charging a battery and then discharging it to charge another one.
If you must have solar panels then use the MPPT controller to charge the Lipo battery directly while the sun is shining. As soon the battery has run down a little (ie. shortly after takeoff) it will have the 'room' to store more energy. If the plane can handle more weight then better to have that weight in the main battery where it can achieve higher capacity.
A problem I can see occurring is balancing.
Balancing shouldn't be a problem if your lipo battery is in good health. The cells should maintain 'top' balance without any help, so in the unlikely event that the solar panels manage to fully recharge it balancing shouldn't be necessary.
answered Feb 4, 2022 at 0:30