Need advices, how can i charge batteries 3.6v with small solar panels

Thread Starter

OrSimhon

Joined Dec 13, 2019
3
hello

as a mechanical engineering student, i need to charge batteries for drone at far point with solar panel.
now my first mission is only to can be charge batteries with those little solar panels.
i need to add to the circuit components (1 or 2) that will stabilize the voltage from the solar cell (mppt i think) and also Something to make sure the current is flowing in one direction only, from the panel to the battery and not the other way around.
i added a photo of the exactly solar panels i have.

MOD: Deleted your whatapp number, to prevent you being spammed.E
 

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ericgibbs

Joined Jan 29, 2010
9,117
hi Or,
Welcome to AAC.
Those solar panels are very low power, what is the rating of the drone battery pack you need to charge, ie: V/A
E
 

ericgibbs

Joined Jan 29, 2010
9,117
hi Or,
This PDF is for a typical 3.7V battery, the mAh capacity is higher than your battery, but the charge requirements are similar.
Using that Solar Panel it could take a very long time to charge, as the voltage output is only 3.6V, at 50mA, for full Sun.

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AAA 083 10.29.gif
 

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Bernard

Joined Aug 7, 2008
5,335
Operating V of S C is about 3.6 V, or with blocking diode , 3.1 V, so I would but 2 in series = 6V. 10 parallel pair should give 500 mA - 1 hour charge time. Shunt S Cs with 5W, 4 V zener diode before blocking diode or diodes or equivalent.
 

MrSoftware

Joined Oct 29, 2013
1,615
If this is a one shot deal, get something off-the-shelf that is optimized for charging batteries from a solar panel. One challenge with a solar cell is the voltage and current will be up and down depending on the sun exposure. A properly designed circuit can take what power is available and boost or buck the voltage to a level that makes the most efficient use of the available power. Here is one example:

https://www.kr4.us/sparkfun-sunny-buddy-mppt-solar-charger.html
 

Audioguru again

Joined Oct 21, 2019
553
You need a battery charger circuit made for charging your one cell Li-PO battery. All toy drones come with one. Mine have a USB input from my computer. The maximum charge for a single Li-PO battery is 4.20V so your battery might explode or catch on fire when the solar panel overcharges it to 4.8V.

The Sparkfun charger has a 6V minimum input so your solar panel voltage is too low and a output current that is too high for your battery.
 

Bernard

Joined Aug 7, 2008
5,335
I would not use anything but a commercial charge controller for Li batteries with the exception of Li-Fe-PO4 batteries. Solar panel V can be shifted down or up with buck or boost- buck converter to match charge controller.
 

Audioguru again

Joined Oct 21, 2019
553
The solar panel is too weak for its voltage to be boosted. It produces 4.8V with no load and it produces 50mA when its voltage is only 3.6V. If its 3.6V is boosted to 4.2V then the current to charge the 400mAh battery will be so low that the battery will not charge in one full sunny day.

The 280mAh Li-PO batteries for my RC airplanes use a Li-PO charger that has an output of 300mA and the batteries charge in a couple of hours or less, depending on if they were discharged all the way down to the 3.6V storage voltage or down to 3.8V when the flying was still good.
 

oz93666

Joined Sep 7, 2010
702
Panels output max 0.18W each (output on an average day about 0.5Whrs) .... Battery capacity is 1.5Whrs

Accounting for losses ten panels will charge battery in around 3 or 4 hrs
 

Thread Starter

OrSimhon

Joined Dec 13, 2019
3
Hello
Trying to chart Lipo battery (3.7V ,800mah) with 8 solar panels (2 units in parallel each of 4 panels in series ).
I connected the panels to the mppt and also the battery, the panels provides 16V, i have set the output voltage (from the mppt) to 4.5V.
the problem is that instead of charging the barttery, the battery is dicharging.
Maybe someone know what could be the problem ?
Photos attached below.
 

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If you add a diode in series with the battery then it will never become any where near fully charged. The charger circuit might even reject charging the "defective battery" that never becomes fully charged.

Maybe the Sunny Bunny circuit is defective or is not made correctly. My Li-PO battery chargers fully charge a battery then detect it and shut off the charging, and light a "finished" LED. I can leave a battery for weeks and it does not discharge like yours does.
 
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