Cheap easy charging of Li batteries

[OperaHouse]

I have lots of Li batteries scavenged for computer power packs.  Since they were always
free I never cared if they got a proper charge.  I would just connect a resistor to them
and let them charge for a while and hope I got back to them before they overcharged. Last
year I finally bought a pack of ten TP4056 boards for about 35 cents each.  As shipped
these operate from 5V, charge at 1A and have 2 LED indicating charge and finished.

The charge current can be changed by removing a tiny SMD resistor on the bottom of the
board.  I wish you the best of luck with that, the foil is tiny and fragile.  Instead
I just add a resistor in series with the power. The data sheet does recommend up to a
half ohm resistor to prevent chip heating.  I have found a 4.7 ohm resistor works to
limit current to 220ma.  I like this value because it allows me to charge questionable
batteries with less worry.  I use cell phone wall warts, many of them are rated at only
700ma.  I use these on my 50V raw solar power and their maximum current output is then
only about a quarter amp at these reduced voltages.

This chip provides a maximum charge voltage of 4.2V and when the charge current reaches
100ma the charger shuts off.  This factory shipped value is defined by the small on board
SMD charge resistor and the shutoff current is 10% of the maximum charge current.  Even if
you desire higher currents I suggest you use at least a one ohm external resistor to prevent
damage to the chip.  The maximum input voltage is 8V. The chip is analog and any voltage drop
produces heat in the chip if an appropriate series resistor is not used.

For thrty five cents this this is an easy way to have unattended battery charging.  Cheap
enough to permanently include in each project. You can't see it, but the blue charge finished
LED is on in the picture.  See data sheet for more details.

[Bruce S]

OperaHouse;
That chip looks very familiar! I was given a broken "PowerBar" purchased from a local store here.
Nifty little thing is was, came with the bar and a dual use USB cable that had the standard USB on one end and Micro USB on the other.
Plug it into a regular USB port and it charges once you plug the USB micro into the powerbar, has two of the smallest LEDs I've ever seen , RED is on for charging Blue comes on when it is finished.
Being that I too get "Spent" Laptop batteries, I decided to make use of the chip on the inside once its battery began loosing power pretty quick. I also happen to  have one of those fold-able Panels 6Vdc out types.
I was able to rescue 4 of the batteries, using some soldering skills, I now have this setup (including solar panel) that gives me 3.7Vdc at about 10,000mAh.
Sure it takes it a week of full sun to recharge them , but so what

Thanks for the post!

[Norm]

 Brice,
Wondering how many of those AA yellow batteries (nicad) I can charge
with a VW solar panel in a day with just ambient  cloudy day sunlight ?
yeah I still got about a dozen of those since about 10 or so years ago
(has it really been that long ago )?
Norm

[Bruce S]

Hi Norm!!
Since those nice VW panels are 12Vdc but only 2.5watts?
I'd say no more than 6.
Of course the batteries will pull it down , but that's the whole idea.
With winter here and depending on whether it's snowing or not  , 6 hours should do it. That's about right for them at 600 - 700ma batteries.

Cheers!