# li-ion battery charging

Discussion in 'Power Electronics' started by hrishib, Oct 22, 2013.

1. ### hrishib

34
0
Aug 30, 2013
I'm trying to build a battery backup system for a door lock. I'm using the LTC4353 voltage monitor and switch that switches between the battery and a regulated DC supply depending on the AC mains availability.

Now I also need to charge the Li-Po pack and I was hoping someone could suggest me a suitable IC for this? The battery backup is 4, 18650 batteries in series (with a total voltage of 14.8 volts and current of about 2200mAh). I did a bit of research and found so many that I'm totally confused. The main criteria for the charger are,

1. Should be able to stop charging after they are fully charged
2. Should be capable of a trickle charge
3. Low cost and low part count
4. High charge efficiency

2. ### EDSedov

3
0
Oct 21, 2013
Hello. I'm sorry. I'm bad speak english, because i'm from Russia.
To do charge the battery, you must use a special device, which controls the voltage and charge. If you can read Russian, i can give links to these schemes. Otherwise i can send pictures of these schemes without describe their work.

3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,500
2,840
Jan 21, 2010
As suggested above, you need a charger.

You'll probably find there are many available -- check out shops which deal with radio controlled models. The cost may be more than you expect. You would need one which can be left permanently attached.

Note that 2200mAh is not a current rating, it is a capacity.

It is almost exactly like "Miles" is not a speed, it is a distance.

2200mAh says the battery can supply 2200mA for 1 hour.

2200 miles says if you travel at 2200 mph you will get there in an hour.

In both cases you divide by hours.

2200mAh divided by hours = 2200mAh/h (the hours cancel) and you get 2200mA

2200 miles divided by hours = 2200m/h (the hours DONT cancel) and you get 2200mph

(lecture over )

A simple charger for those cells might be a current controlled voltage source which limits the total voltage to 4 times the charged cell voltage and which tapers a (limited) current as that voltage is approached.

More complex chargers will stop the charge at certain points and use lower or higher currents in certain charge phases.

In addition a good charger will have a method of balancing cells so that individual cells are not overcharged.

I can't point you to a good 4 cell solution on a single chip, but others may be able to.

4. ### hrishib

34
0
Aug 30, 2013
Thanks Ed and Steve. I think most charger chips (atleast the ones I found limit the charge voltage to 4.2V). But they charge 4 cells at a time. I'm guessing they charge them all connected in parallel and not in series.

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,500
2,840
Jan 21, 2010
Possibly, show me a link and I'll give you an opinion (and hopefully an answer!)

34
0
Aug 30, 2013
7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,500
2,840
Jan 21, 2010
No, they really mean in series. The fisrt stop should be the datasheet. It's going to give example circuits (normally).

And it does (but it doesn't do balancing).

8. ### EDSedov

3
0
Oct 21, 2013
It is scheme charger on Russian.

Quote (translation from Russian into English):

During the charge any battery, you have to control the process of charging, so you do not overcharge and not to spoil it. The control I chose chip LTC4054ES5-4.2. She has only 5 findings, easy to set up and is powered from 5 volts.

Vcc - plus source from 4.5 to 6.5В. I used the charger from the phone to 5.5V, 500mA.
GND - minus
The BAT to the battery plus
PROG - specifies the program entry.
CHRG - charging indicator.

In this scheme, the PROG is connected resistor sets the current from the battery.
Current is calculated by the formula:
Ichg=1000V/Rprog
That is, when you connect a resistor at 2000 Ohms current is 0,5A
Charging indicator is an ordinary led. Until the led lights - charging goes. As goes out, the charging is completed.

Last edited: Oct 23, 2013