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Help: DIY Solar Li-Ion Battery Charger Answered

Heylo, I’m a mechanical engineer by trade but lately I have taken up a fascination in building some fun DIY electronics. I wanted to make a device that could charge 18650’s via solar and then could use those batteries to charge my phone. So I found an instructables tutorial that seemed legit so I bought the following things and tried to wire it all up: Dual 18650 Battery Holder TP4056 Protection Circuit MT3608 5V 2A Boost Circuit Voltmeter Screen So I wanted to kind of figure things out on my own so I wired things up without referencing anything and I’ve done it multiple times but I cannot get anything to work. I have attached photos for reference. Basically, I bought 2 18650 holders and pulled the switch from one and wired it to the other. My thinking was that if I had switches on both the positive and negative terminals, I could switch it between solar charging mode and battery powered mode. It doesn’t work at all and I’m not sure what I did wrong. None of the lights even turn on, on the TP4056 yet alone the LED on 5V 2A circuit. I feel like everything I did was sound. But it’s probably not. Please don’t judge my soldering ability, I know it’s awful. I’m learning and I have awful hand tremors which makes soldering especially difficult. Anyways, thanks for your help in advance. If you need any more photos please let me know.



18 days ago

Oh: I forgot to mention this: Normally, the charging-Boards with the TP4056 charge at a moderate current. If you want to increase / decrease the current of the LiIon-charging, change the resistor R3 according to the attached image. Have fun!


19 days ago

I see some problems...
First, it looks like your 18650-holder sets them in SERIES and not in PARALLEL. This makes around 7.4V instead of 3.7V as intended by the charging board.. See, those very handy and nice 18650-charging-board are designed for a single cell.

Now, I dont see you wrining up the input of this board. Only the battery and the
output. You cannot charge the 18650 like this... You have to go thru the
input of the charging-board. :)
Thats why no LED come up on it: You dont power it.

See, you propably are a bit puzzled by the 3 connections of those charging-boards:
- The IN is where the external power from your supply goes IN to charge the batteries.
- The BAT is where your batteries are connected. They, as it, have no direct connection to OUT.
- The OUT is where your Output of the power flows towards. See, in betwheen the BAT and the OUT, there is the complete savety-circuitry: If the battery.voltage is too low or a shortcircuit on the OUT is detected, the battery gets disconnected from the OUT. Thats the job of this board. So it can be that the batteries still have 2.5V but the output shows 0V because 2.5V is too low for a LiIon to work and needs to be charged first bevore the OUT gets connected back to the battery at above lets say 2.7V voltage of the battery.

Also, i think those boards require 5V and not the 0-??V of the solar panel.

Also, it looks like you have 2 DC/DC-Converter in the line from the batteries
to the USB-plug: One dedicated (The board in the middle with the trim
pot) and one on the board with the USB-receptacle. The exact model of
the USB-receptacle is unknown to me, but similar designs like https://www.aliexpress.com/item/32829660987.html are boost.
Only one boost converter is needed there. I suggest going with the one in
the back of the USB-receptacle as it is there already and often designed for LiIon-to-5V...

My suggestion:
1.: solar to a buck-boost converter to 5V with a low start-voltage (Something like 2-12V to 5V)
2.: Buck-boost-converter output to the input of the charging-board
3.: The 2 18650 in parallel (!!) onto the "Bat"-Terminal of the charging board
4.: From the "Out" of the charging-board to the 5V boost converter of the USB-receptacle.
If you want, you can add a switch betwheen the charging-board and the batteries (to disconnect everything and save the charge in the 18650) but apart from that, no switches aree really needed...

For the Buck-Boost, i would suggest something like https://www.aliexpress.com/item/32834043072.html
Of course, if your Solar panel really fast goes to above 5V, you can go with a buck only instead and go with more efficient stuff like https://www.aliexpress.com/item/32742116421.html

See the 2 attached images for blockdiagram and wiring

2019-10-01 10.34.00.jpg2019-10-01 10.57.51.jpg

19 days ago

Well, at a first look I can say your switch is wired incorrectly.
The middle terminal is common and the either side is contact when you push the switch.
Right now you have it conneted to two open terminals and it can't do anything ;)