Li-ion battery charger schematic

[bpelec]

Hi everyone.

I found attached schematic for a Li-ion battery charger. (My battery has 4 cells of 3.2V, 3500mAh).
But, after do a search of info, it looks that Li-ion charge must be a controlled process wich has different stages.

I built the ciruit below for doing measures, and the current sourced by the 317 is under current specified in the battery datasheet.
The battery seems to be charging, but very very slow.

The charging time semms to be much longer that specified in the datasheet with this circuit but...
may the circuit damage the battery or affect it in anyway?

Thank you.
Regards

 

[Lauris]

seems that you trying to charge litium with constant voltage. if your voltage won't go higher than max charging battery voltage it will work. but as u said it is taking ages. it will be that way. for max voltage alowed for lithium it depends on chemistry, so to find out look for battery characteristics from manufacturer, or google it.

For normal litium cherge u need to keep constant current (usualy up to 1C) untill max battery voltage is reached on bettery terminals. then swich to constant voltage till current will drop till 0.01C or something like that.

also there r other more exotic ways to increase charging current but maybe not this time.

 

[D.A.(Tony)Stewart]

Simple Li-ion chargers use thermistor to sense when to shutdown charger.
Smart charger chips are now cheap, <$1 from D-K.

https://ww1.microchip.com/downloads/en/DeviceDoc/22036b.pdf


https://www.digikey.ca/product-detail/en/MCP73811T-420I/OT/MCP73811T-420I/OTTR-ND/1626617

Report your charge voltage pls. 3.6V?

 

[bpelec]

Here is some battery specs:

Nominal voltage: 3.2V
Voltage at end of discharge: 2V
Charging voltage: 3.65V
Internal impedance: =< 50 mOhms

STANDARD CHARGE
Constant current: 0.2C (700 mA I suppose)
Constant voltage: 3.65V
Cut-off: 0.01C

FAST CHARGE
Constant current: 0.5C
Constant voltage: 3.65V
Cut-off: 0.01C

Sunny, are that chips valid for 4 cell packs?

 

[Lauris]

from what I see in that datasheet these chargers r not good for you. since they charge up to 4,2V and in your case u would need 3,65V (correct me if I'm wrong) and for 4 cell pack you need to dissasemble that pack in a way to charge cells individualy with this type of charger. for pack you would need 4x3.65V (14.6V) charger and cut off @ same 0.01C. thought u havn't mentioned what capacity r your cells.

 

[bpelec]

Hi again.

The cells are 3000 mAh.
After doing a search, I've seen that some Li-ion charge systems use switching methods to get a controlled charge process.
Maybe I could buy one of this charging boards, but it should be of reduced dimensions because battery and electroniics will be inside of a small space.

I would like also power the charging board from a 5 watt solar panel.

What do you think?
Any reference?

Thanks a lot