Hello guys!
Literally one of the worst circuits I have seen in my life, and there were so few components in it...
Lithium ion batteries have become so popular that tiny single-cell charging ASICs are now widespread. Have a look at this one-dollar eBay item:
eBay auction: #www.ebay.com.au/itm/Durable-1PCS-5V-Mini-USB-1A-Lithium-Battery-Charging-Board-Charger-Module-B98B-/370821427180You can see the tiny 8 pin SMD that does most of the work. When provided a useful voltage (eg 5v) that's all that is needed. Beautiful, isn't it?
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
Charging lithium ions isn't as complex as you would think (
wiki). They require a constant current charge for most of the process and then a slower constant voltage toward the end. The biggest risk is over-charging them, in both terms of over-current or over-voltage.
Hence I
really recommend you use protected 18650s. Protection circuits, amongst other things, prevent over-charging. If yours are not already protected, buy some cheap protection circuits off dx.com or ebay and attach them with some electrical tape:
![](http://members.optusnet.com.au/amerricka1/forums/EEVblog/18650s_protected.jpeg)
Arguably this looks extremely dodgy
![Cool 8)](https://www.eevblog.com/forum/Smileys/default/cool.gif)
. The flat wire coming up the side to the positive terminal only carries power for the protection circuit itself, and to allow cell voltage measurement. In a properly manufactured protected cell they spot weld all of the connections (FYI you can't solder onto 18650s -- too much thermal mass), but I (unfortunately) don't have such equipment.
Update:
I finally got around to do some testing on this charger and the result is that it works. As per mazurov's suggestion, I used a 10K resistor to simulate a thermistor and the charger started charging right away. The status light turns yellow indicating that it's charging. Without the resistor, the charger won't charge the battery. Below were the stats.
Awesome! I never would have guessed that the thermal circuitry was so simple.
Next step is to put together a proper adapter/battery holder for it. Thanks everyone for taking an interest in this.
'18650 holders' can be purchased for <=$1 on dx.com or ebay.com . Don't do what I have tried before: aluminium foil and lots of electrical tape. It doesn't work well
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)