Charging the Li-Po batteries with Solar Panel

Hello everybody. We built an autonomous boat. We would like to charge the our lipo batteries with solar panels. We have pixhaek 2.4.8 and raspberry pi. The raspberry pi system is completely different and it is for sensors only. What we have:

-8000mAh,25C,3S1P Li-Po battery for pixhawk and motors
-3500mAh,25C,3S1P Li-Po batter for raspberry pi and its sensors
-12V,7A rechargable lead acid battery
-4 pieces solar panel 50W-12V solar panels.

We would like to charge the lipo batteries to increase the flying time. It means we would like to charge them while batteries are in use. How we can do that?

you will need a 12v MPPT solar charge controller to regulate the power from the solar panel to the battery. other than that it will work fine.

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Sir how will be the connection? Can I can the batteries during batteries are in use?

yes you can connect it to the battery while its in use.

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Sir how will be the connection please can you explain me? 4 pieces of solar panel output will go where? Should I use lead acid battery? Because lead acid battery is normally not in use in the system. We bought it to charge the lipo batteries.

Do your batteries have a BMS? you will need a BMS for your LIPO batteries if you plan on charging then with the solar panels as its very easy to overcharge them, the Battery management board will cut off charging to the batteries if the cells get too high.

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No sir we don’t have bms, but if it necessary we can purchase. We don’t know what we need. As far as I understand bms is just a board.

yes its a protection board for the battery, it will stop it getting over discharged or overcharged, this is essential when using solar to charge.

be careful not to discharge the batteries too low as the bms will cut off power to protect them. you can bypass the bms for discharge by connecting the negative discharge wire directly to the battery negative terminal, that way you have the protection for charging and the boat wont cut out if it gets too low.

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you can get bluetooth BMS boards that will let you monitor each battery they are also fully programmable. I plan on adding some kind of support for monitoring them via lua script at some point.

Thank you so much sir but if you don’t mind can you draw me a wirinf diagram. Because no of us doesn’t know how to do it. We just would like to charge the 2 lipo batteries with 4 solar panel. Lipos are 3500mah-3s-25c and 8000mah-3s-25c. We bought also lead acid battery 12v-7A if necessary. The solar panels are same and 50w-12V.

are you mounting the panels on the boat or are you planning on charging on shore.?

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We will mount sir. Otherwise we can’t use them while lipo batteries are in use.

the problem is you have 2 separate batteries, means you would need 2 separate charging systems, is there any reason you cannot join them together and run everything from both batteries? it would mean you would only need a single charging system.

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Yes sir because 3500 mah lipo battery will supply power to our raspberry pi with dc-dc converter(lm2596). Some sensors will be connected to the raspberry pi. 8000 mah battery will supply power to the pixhawk for motors etc. That is why we will use 2 seperate battery.

do you just want to charge the motor batteries or both of them?

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If possible both Sir.

your going to need to find out your power consumption and how long each battery lasts so you know how to distribute the solar power.

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Sir can we use the 3 solar panel for 8000mah battery and 1 solar panel to 3500 mah battery. We did not test the consumption but when we were using 3500 mah battery for pixhawk, duration was only 4-5 minutes not more. I think wirh 8000 mah battery, it will be around 10 minutes. Raspberry pi is not using so much power. So it will be around 10 hours as we calculate.

you should just connect all your panels to your motor batteries since your auxiliary battery is going to run almost the whole day anyway

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Again and again thank you sir. Can you please draw me a wiring diagram with pieces that we have to buy, if ypu don’t mind?