Safe to Solar Trickle Charge Lithium Battery (18650)?

Thread Starter

ConnectedWeAre

Joined Oct 22, 2019
6
Greetings,

I present a question purely about safety. Is it safe to charge an 18650 with a low-current/constant-voltage setup as below? I have posed various questions to Google and everything seems to point to the "right" way to charge batteries. In short, is it safe to use an LDO or other constant voltage device to charge an 18650 to 4.2v?

Solar = 1W 6V
LDO = LM2596 set at 4.2v output
18650 = 9800mah lithium ion

All signs seem to point to yes. The maximum 0.02C charge rate is low enough to satisfy all stages of "safe" lithium ion charging. And, assuming the battery voltage is never discharged below 3.2v, could a device be powered directly from the battery at the same time?

Thanks for any help. The attached picture show the setup with every piece except the melted solder. Is the diode even needed?

ConnectIMG_5442.jpg
 

oz93666

Joined Sep 7, 2010
672
First off a small point about your cell ... you think you have a "18650 = 9800mah lithium ion " ... you haven't ... the largest capacity on the market is 3500mAhr ... none have been made with over that capacity , Chinese manufacturer just write anything on the wrapper ,it's probably about 2500 , if you are lucky ... You can trust panasonic , sony etc ... that's why they cost more...

As for charging you say "maximum 0.02C charge rate" for this cell ... that's wrong all 18650s can handle 0.5C charge (around 1A)

I don't know why you want to trickle charge?? You should have a BMS on this cell ($1 ebay many different types ) this will prevent any imaginable problems , you just leave it connected to charger and the BMS circuit will switch charging on and off when required ... ebay.co.uk/itm/1S-3-7V-3A-PCB-BMS-Protection-Board-for-1-Pack-18650-Li-ion-lithium-Battery-Cell/252580125401?epid=15024613399&hash=item3acef2dad9:g:krsAAOSwzaJX60Fj

 
Last edited:

Thread Starter

ConnectedWeAre

Joined Oct 22, 2019
6
I can't afford a bigger solar panel, so very low 0.1C-rating is my only power source (thank you for fact check; it's a pack of six so I bet 9800/6 = 1633mah).
I don't want the charge current to cut out at 4.2v.
Is it safe to "overcharge" at 4.2v? I was assuming nothing happens if the 4.2v battery meets 4.2v charge current.
 

oz93666

Joined Sep 7, 2010
672
I can't afford a bigger solar panel, so very low 0.1C-rating is my only power source (thank you for fact check; it's a pack of six so I bet 9800/6 = 1633mah).
I don't want the charge current to cut out at 4.2v.
Is it safe to "overcharge" at 4.2v? I was assuming nothing happens if the 4.2v battery meets 4.2v charge current.
They really are selling those as 9800 each cell .Beware of any cheap brand , I bought some ultrafire , when I removed the top +ve terminal button the cell +ve terminal had spot welding marks indicating it had been used ... taken from scrap laptop batteries ... it's a big industry , when a laptop battery appears dead , some cells still have some life left , these are taken out and given a new plastic sleeve and sold as new



You must stop charging at 4.2 or the cell will not last long or even malfunction completely ... if you get the BMS I linked to you can connect your panel through that to the cell and everything will be taken care of
 

BobTPH

Joined Jun 5, 2013
2,055
You do realize that, at 0.02 C charging, you will need 50 hours of charging for each hour of use, right?

That does not sound very practical to me. What is your usage scenario?

Bob
 

dendad

Joined Feb 20, 2016
3,084
Maybe one of these regulators...
https://www.ebay.ca/itm/1-2-5PCS-DC-DC-4V-12-24V-to-5V-3A-Step-Down-Power-Module-Buck-Converter-/263654215312Regulator.jpg
Feed the solar panel into it, set it for 5V out. Then feed one of these charge controllers.....
https://www.ebay.com/itm/2-5-10PCS-TP4056-5V-1A-Mini-Micro-USB-18650-Lithium-Battery-Charger-Board-Module/263736171391?hash=item3d67e69b7f:m:m1cNk-7Ox0OaN74HgcuxfTQLiPo charger.jpg
Make sure you get the version shown that has discharge protection. It will have separate terminals for the battery and the load.
 
Top