Electronics > Power/Renewable Energy/EV's

Charging a Li Ion battery: 3.7V, 4400mAh

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fourfathom:
I'm using a 18650 3.7v 4400mAh 1S2P Li ion Rechargeable Battery Pack, and was planning to use a STC4054 charge controller chip between my small 2W @ 5.5V solar panel and the battery.  But when I look at the battery specs, it appears to have a controller already built in, and isn't just a couple of bare Li cells.  The specs show that the pack can handle an overcharge at 14.4V, 3C without leakage or explosion. 

I haven't yet peeled off the shrink-wrap cover to see what's inside, but do I actually need a Li charge-controller or can I just feed the battery from the solar panel?  I would actually put a pre-regulator between the panel and the battery to keep any voltage > 5V  from hitting my board's 3.3V regulators.

tunk:
I think some cheap solar power banks have this setup:
solar cell -> (schottky) diode -> BMS -> cell/battery
A bit puzzled by the 14.4V, there's no way two cells
in series or parallel can use 14.4V directly.

fourfathom:

--- Quote from: tunk on September 20, 2022, 05:39:39 pm ---I think some cheap solar power banks have this setup:
solar cell -> (schottky) diode -> BMS -> cell/battery
A bit puzzled by the 14.4V, there's no way two cells
in series or parallel can use 14.4V directly.

--- End quote ---

I was puzzled too.  I'm going to peel off the cover and see what's up.  The spec doesn't mention it, but I did see Polyswitch mentioned in some of the documentation (similar batteries), so perhaps that's all it is (and that would explain how a two-wire connection would work like this).  If so, I still need to properly limit the charge voltage.

TimNJ:
Packs like this often have a protector chip which controls two back-to-back MOSFETs which can be turned off in the case of a fault condition. Sometimes an all-in-one chip is used which integrates the controller and MOSFETs in a single package. Almost all packs will have over-voltage protection (and usually under-voltage protection). Some packs will have over-current protection.

An onboard charger is not a given. Probably easiest to just peel back the shrink wrap and check if you see some sort of buck-looking circuit on there. If not, you can discharge the battery to ~50% or so, and then check if it draws a constant current when you a apply a voltage to it (I guess do that through some sort of current limiting resistor). Li-ion charges charge by CC for the bulk of the charge cycle.

Faringdon:
A purist would say put a switch mode battery charger between the solar panel and the battery.

But you solar panel is 2w, 5.5v and is pretty weak.

So therefore, i bet knowing the impedance of a solar panel...you can probably connect it directly to the battery, and just put in a comparator based overvoltage charge shut-off.
Add some hysteresis with the comparator.

Otherwise you need a buckboost SMPS  with output current control...or in fact, input current control would be fine.....to charge the battery.

I dont think you can abuse that battery with a 2w, 5v5 solar panel though....but best keep battery voltage  below 4.2v.....mind you as you say, it may already have an OV shutdown fet cct in itself.

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