need a very nice lithium ion charger circuit for homemade

[kugua]

hi friends. i need to build a nice lithium ion charger for my 4.2v lithium ion.i made this one **broken link removed**
this circuit working well.but it has a problem.it can not chargering the battery to full.it can chargering it to 4.14v not 4.2v.so i think i can change the circuit ?no .i have not enough knowledge to change it .so could anyone do this or recommend some good lithuim ion battery charger circuits to me?thanks

 

[Sebi]

VR1 for proper voltage setting. When not enough at max. value, change R5 to 3k3.

 

[Oznog]

The circuit you reference is dead wrong for charging lithiums. It can damage the cells quickly and may cause a fire.

Lithiums are charged by providing a well regulated constant voltage, and limiting the current early on if it is excessive. It is 4.1V on some battery chemistries and 4.2V on others.

It is extremely important not to overcharge a lithium, cell damage/fire results. Full charge is signaled when the charge current is below a certain threshold while the specified voltage is being applied. The charger should latch into an idle state and cut off all charging current.

This charger uses a constant voltage and expects the cell to stop drawing current when it's fully charged. In fact the cell's current will reduce, but not stop (which is basically wrong). This is the same as just taking an adjustable voltage reg and adding a resistor for current limiting.

 

[kugua]

oznog

The circuit you reference is dead wrong for charging lithiums?your mean this circuit is a wrong circuit?i made one and charging lithium. it can charging it to 4.14v,and i test it ,i turned the vR1, it can make the output voltage to 4.2v,and connect the battary to charging it,it has not wrong,but only to 4.14v voltage .maybe you can show me some good circuits? not use d the ic .like the max ic ,because i have not chance to get it,thank you for your reply

 

[Oznog]

Re: oznog

The circuit you reference is dead wrong for charging lithiums?your mean this circuit is a wrong circuit?i made one and charging lithium. it can charging it to 4.14v,and i test it ,i turned the vR1, it can make the output voltage to 4.2v,and connect the battary to charging it,it has not wrong,but only to 4.14v voltage .maybe you can show me some good circuits? not use d the ic .like the max ic ,because i have not chance to get it,thank you for your reply

It'll charge it just like putting it on a power supply with a resistor will charge it. It doesn't do what a lithium charger is supposed to do- latch into a shutoff mode when it's fully charged. Failure to do so will still charge the battery, but the resulting overcharge as they are left on will damage them every minute it's on there and it's possible to cause them to catch fire.

The latching behavior makes the circuit a bit complicated. Tricky because when you first put the battery on, the current begins at zero and it's not supposed to latch that. I would use a PIC myself, but I use them for everything.

The charging ICs are a good idea. You can even order them as samples for free.