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Topic: 2W solar panel to charge 18650 battery - e-waste upcycle project  (Read 275 times) previous topic - next topic

swavone

Hi All,

I've been going trough my old electronics drawer, to see if I can re-use some.

I hooked 4 small solar panels in series , and am measuring about 300 mA - 400 mA current at 5,95 - 6.3 V (in full sun at 13:00).

I'm looking to use these panels to charge one 18650 2.5Ah cell.


A)

I want to kindly ask you if I am thinking in the correct way, and if the charge controller has enough juice to charge a 18650 OK:

1. Assuming that the buck conversion from solar 5.9V to ~3V (during CC charging) will loose about 20% of power, then :

solar panel power = ~1.8W

1.8W - 20% =   1,44W - power available to charge the battery?
1,44W/ 3V =   480mA - max charge current during CC mode?
1,44W / 4.2V =     340mA - max charge current during CV mode?

- This math can't be that simple , can it? Please could you tell me if my general / ball-park-figure thinking is wrong?
- Will the 6V solar panel voltage be enough for the buck/PMIC in charge controller to operate well switching down to 3.0V ~ 4.2 V?


2. When I read datasheets of 18650 batteries I struggle to find the minimum charge current. I read somewhere "charge cut off  = 65mA", but I imagine this will only keep the charge level, not increase it.

- In your experience, what is the minimum charge current on 18650s at which they start to gain some reasonable charge?


The project idea I'm playing with is to power 6x 48BYJ-28 motors with a single 18650 (2.5Ah or 3.0Ah ) , this is for window blinds, so max 30 sec operation at a time, couple of times per day; low torque as there is a reduction worm gear in the fixture, so also can disconnect the servo in Arduino sketch not to consume power when idle. FYI.


B)

These solar panels are from an old power bank, but the battery bulged up and so it was safer to dispose of the battery safely before it blows up.

The power bank was using a YLN-135V board - I am not sure if it works well, I cannot remember if it was charging well on USB power in before I took the battery out, and I forgot what type of battery it was using and how it was connected - I thought board is well annotated but I cannot get it to charge no matter what I connect to B+ B- or even if I connect USB power in. Now, the charging LED are switching OK and  showing charging / full charge, the LED torch lights turn on OK with button press.


3. Each of the panels has connection for Vout and Vin to connect in series on the side of panel market with minus "-" and another Vout on the side of the panel marked with plus "+".

- Why are there two separate Vout on one panel and how to use them?

- The separate Vout on the "+" side is the final load connection?


4. The power bank board, when connected to 4 panels in series via S+ S-, gives voltage on battery pins (B+, B-)  fluctuating between 5.0V - 5.4V @ 300mA - 450mA
I tried to charge power bank by connecting it's micro USB charging port directly to B+ B- :) but off course no charge.


- I imagine minimum current to start charging via micro USB is 500 mA ?

- What battery uses 5.0V - 5.4V to charge, would it be 2S Lipo battery ?




I'm quite rusty with my EE , I would appreciate greatly your lesson.

I'm trying to see what junk I can use that I already have lingering about, instead of buying new stuff all the time, but it's good opportunity learn why it wont work, and what I need instead and why.



All the best to you all.

kaseftamjid

18650 batteries require special care, theres a LOT of factors to consider when charging them.. its not as simple as just giving them a fixed voltage.
I suggest you get a new "regular" powerbank ic/ 18650 charger and check whats the input voltage, If its within your solar panels output, then use it with it. I highly suggest ditching the current controller as it may have failed already..

swavone

18650 batteries require special care, theres a LOT of factors to consider when charging them.. its not as simple as just giving them a fixed voltage.
I suggest you get a new "regular" powerbank ic/ 18650 charger and check whats the input voltage, If its within your solar panels output, then use it with it. I highly suggest ditching the current controller as it may have failed already..
Thank you for your reply, yes I found a few controllers that could work with 6V solar input - but it will be always at the limit - so needs to be tested. Apart of the low voltage, I am also concerned about the min charge current. I wanted to throw this at you all to see if this is a definite no-go , before I start buying stuff and testing to no avail:


Based on CN3722:
https://www.aliexpress.com/i/32874974495.html
https://www.aliexpress.com/item/32874974495.html


Adafruit ADA-390
https://www.kiwi-electronics.nl/usb-dc-solar-lithium-ion-polymeer-lader?lang=en

I was only looking specifically at "1s 6V sollar charge controller" - as you can imagine not many options ...

If you say it's OK to use a simple Li-Ion charger, then there are some options, but since they are all designed to work with USB bus, I think 5V Vin would have to deliver min 500mA to start the charge ? (again I'm struggling to find good information / datasheet)

Based on DD23CRTA:
https://www.aliexpress.com/item/32992417346.html?spm=a2g0o.cart.0.0.69383c009G5GhY&mp=1

If this is a no go, then I'm wondering what battery could work with the YLN-135V board I have (ref. attached photo) ... I should have made a note what it was before I disposed it. Now I cannot figure out which battery can be charged by 5V - 5.4V @300mA - which is what this board is outputting to B+/- pin


kaseftamjid

You should go with the dedicated solar charge controllers.

As far as i know, Theres no minimum limit on the charge controllers input, may it be usb or solar. As soon as the battery starts to draw current that your panel cant deliver, the voltage across it will drop. so basically the input current dictates how fast the battery can charge, as long as you have an optimal voltage.

Once again, I would suggest to ditch the previous board. We will never know if it was the batteries that were faulty or the YLN board that was faulty. And the way of finding that out might not end up so pretty, cut your losses. get a new board.

Tamjidk

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