Li ion charging in parallel

[siddhant9850]

hi guys just wanted to know can anybody help me with circuit for li ion battery charging for 3.7V and actually i have to connect around 20 batteries in parallel. I need overcharge protection for li ion
 can anybody suggest a suitable circuits/ can anybody suggest such circuit using MC34063A or any other ic which can help in cutting of connection after battery full detection.
in short :
3.7v charging
current should be adjustable
battery full notification


please guys need it badly
 
thanks
 

[poorchava]

imo charging multiple li-ion cells in parallel is acceptable. They will balance each other, but under a condition that they cannot be discharged separately (while disconnected from each other). Electric-wise as long as they are connected together they behave as a single cell with large capacity.

[siddhant9850]

Thanks 
but what about battery full notification circuit have you got any idea

[void_error]

but what about battery full notification circuit have you got any idea

Comparator or schmitt trigger.

[tszaboo]

TI has 226 different battery charger to chose from...
And for your information, battery manufacturers (well, the good ones at least) bin their batteries very carefully before making a pack with them.

[siddhant9850]

Thanks every1 solved my many questions..
Just this last one. I have these unprotected battries, so actully I need to know whether I should charge with voltage control or charge control circuit, and if so how to detect if its full.


PS I know the dangers of unprotected batteries  so m being a bit paronid, that's why m asking so many questions of how to get exact battery full indication



Thanks in advance

[Mr.B]

I use CN3083 devices made by Consonance.
They can be a bit difficult to find.
A similar device, CN3065 is available from SeedStudio and probably others.
http://www.seeedstudio.com/depot/OPLopen-parts-library-catalog-c-136_138/?ref=side
http://www.seeedstudio.com/wiki/images/a/a5/1320040P1.pdf

Programmable charge current up to 1000mA.
Charging indicator pin.
Charged indicator pin.

I have used many of them in projects. They are very good.

Edit: And they are cheap... ~US$10 for a pack of 20.

[NiHaoMike]

In general, just charge them to 4.1V and then hold that voltage for 15 minutes or so before ending the charge. Unless faster charging is needed by the application, limit charge rate to 0.5C or less.

[Ton]

  advice here from NiHaoMike

treating your Li ion cells this way will give you excellent life on you cells while you are loosing almost no capacity.

But be aware over discharging Li ion cells will kill them.

ton

[IanB]

hi guys just wanted to know can anybody help me with circuit for li ion battery charging for 3.7V and actually i have to connect around 20 batteries in parallel. I need overcharge protection for li ion
 can anybody suggest a suitable circuits/ can anybody suggest such circuit using MC34063A or any other ic which can help in cutting of connection after battery full detection.
in short :
3.7v charging
current should be adjustable
battery full notification

In principle lithium ion cells can be connected in parallel as others have said. However, check the manufacturer data sheet for specific advice. Often the advice will be to connect no more than 2 or 3 cells in parallel this way. Connecting 20 cells in parallel seems like a no-go.

For charging you should use a proper charge control IC. A homebrew solution will lack reliability. You also should include a protection circuit to guard against shorts, over discharging, over charging, etc.

Treated badly these batteries will happily turn into incendiary bombs and burn your house down. Don't take chances.

[poorchava]

Typical 3-stage charging goes like this: if voltage is below certain threshold (deep discharge) then charge with low current,  when voltage rises above deep discharge threshold charge with constant current until the voltage reaches 4.1V, then keep the voltage constant until charge current drops below 0.1C.

[sacherjj]

I'm agreeing with Ian on this one.  The only possible way to charge in parallel is fairly low speed charging.  However, for longevity to have to quit charging at a still fairly high current to keep from plating electrodes. 

Our LiFePO4 are low current lifted if the voltage is very low, then cooked at 0.5-1C to their 3.6V max voltage, then held constant voltage as the current trickles off.  It IS NOT GOOD to trickle it to zero, as it will KILL your capacity.  Most charging chips will drop the charge at 1/10th the set fast charge current.  Then you will see a large dive in cell voltage, but the battery is full.

If you have multiple cells in parallel, the lower capacity cells will hit voltage faster.  So the current will go to the other cells.  But they will live in a trickle charge situation longer than they should and they will continue to plate. 

Stand alone charging chips and inductor and passives are just a couple bucks.  They do the job very well.  They also have thermistor safety controls.  It is the right way to do it.

[NiHaoMike]

Tesla parallels several dozen cells, but each one is connected by small gauge wires that act as fuses.

The 4.1V (for conventional lithium ion) point is fine to leave on indefinitely. With a more usual charge to 4.2V, after charging and letting it sit for many hours, the cell voltage would stick around 4.13V or so. There are a few specialty cells that can take as much as 4.35V for a short time but I still recommend lower charge voltages to increase service life. Another trick is to have the charger shut off immediately (in practice meaning at least a few milliseconds of delay to reject EMI) when the 4.2V point is reached.

[microbug]

I'm agreeing with Ian on this one.  The only possible way to charge in parallel is fairly low speed charging.  However, for longevity to have to quit charging at a still fairly high current to keep from plating electrodes. 

Our LiFePO4 are low current lifted if the voltage is very low, then cooked at 0.5-1C to their 3.6V max voltage, then held constant voltage as the current trickles off.  It IS NOT GOOD to trickle it to zero, as it will KILL your capacity.  Most charging chips will drop the charge at 1/10th the set fast charge current.  Then you will see a large dive in cell voltage, but the battery is full.

If you have multiple cells in parallel, the lower capacity cells will hit voltage faster.  So the current will go to the other cells.  But they will live in a trickle charge situation longer than they should and they will continue to plate. 

Stand alone charging chips and inductor and passives are just a couple bucks.  They do the job very well.  They also have thermistor safety controls.  It is the right way to do it.

Or, even better, you can buy pre-made single-cell lithium battery protection boards from eBay. They will do what you need. Example here. I got some protection PCBs from DX for less than a dollar each, but I couldn't be bothered to find them.

EDIT: this was it. It's sold out, but I'm sure similar items are available. Personally I like Aliexpress for this sort of thing.

EDIT 2: Yes, stand alone chips are better. If you don't use a stand alone chip, disconnect the batteries from each other when they aren't charging.

[siddhant9850]

I use CN3083 devices made by Consonance.
They can be a bit difficult to find.
A similar device, CN3065 is available from SeedStudio and probably others.
http://www.seeedstudio.com/depot/OPLopen-parts-library-catalog-c-136_138/?ref=side
http://www.seeedstudio.com/wiki/images/a/a5/1320040P1.pdf

Programmable charge current up to 1000mA.
Charging indicator pin.
Charged indicator pin.

I have used many of them in projects. They are very good.






 


Thanks great idea actully just 1 question are these ics availble in 1500mA programmable, i mean to say does it have models for 1500mA
 

[siddhant9850]

 


Thanks great idea actully just 1 question are these ics availble in 1500mA programmable, i mean to say does it have models for 1500mA
 

[Mr.B]

They have a whole range of LiPo charge management devices.
I chose the one that I use because it only requires one additional component - the charge rate setting resistor.

This is a datasheet for devices that can do up to 5A, however a lot more support components are required.
http://www.consonance-elec.com/pdf/Application/CN3701_02_03_04_E/CN3701_02_03_04%20application%20circuit.pdf

Go have a look at their website: http://www.consonance-elec.com/index-E.html

EDIT: They have plenty that appear to meet your requirements: http://www.consonance-elec.com/Single-cell%20lithium%20battery%20charge%20IC.html

[siddhant9850]

Mr.B    I think the B stands for BRILLIANT, thanks man you helped a lot, one can say you spoon fed me....thanks for pointing in right direction.....i hope i can repay by helping you in some way...



  kudos bro

[nowlan]

I have 10x kokam cells ear marked for a project.
I find you need to have a charger, a protection circuit, and possibly a fuel gauge if feeling fancy.
suddenly trying to get all 3 to play nice just complicates things.

Havent seen any chips, under the impression need a proper battery management system.

[siddhant9850]

facing a problem with Cn3722 its very good ic but cant get the mosfet they specified. i live in India, they have said the value of mosfet for RDS and VDS and Crss affects the circuit can any1 please tel me whether this should be really considered. i know this should be considered but please tell me how much compensation can be made in the ratings of the mosfet.

[siddhant9850]

http://www.consonance-elec.com/pdf/datasheet/DSE-CN3722.pdf

this is the datasheet for CN37322 they said a few things about using the mosfet in there but its hard to find the mosfet they have mentioned or the mosfet with their specification. please read the mosfet selection area and let me know which of the values we can ignore because i will have to ship them all the way from hong kong.

[Mr.B]

I am not a MOSFET expert by any stretch.
There are plenty of others on this forum who are.

Firstly, in order to help you out we need to know the following:
VBAT is the maximum battery voltage
VCC is the minimum input voltage
ICH is the charge current (maximum)

You can probably safely ignore:
dT is the temperature difference between actual ambient temperature and room temperature(25 C)

These are the two semi-flexable values you will be wanting to match to a MOSFET spec:
Pd is the power dissipation of the power MOSFET
Rds(on) is the power MOSFET’s on resistance at room temperature

Then, using a search on a site like Mouser:
P-Channel
Vgs(th) of less than 6V (Datasheet says "The peak-to-peak gate drive voltage is set internally, this voltage is typically 6.5V")
As low an Rds on as you can afford.
Something that will handle the charge current times say 1.25 for headroom.
(Always check the SOA in the datasheet before purchasing as you may need to increase this headroom factor)

A quich search for AO3407A at Mouser brings up a cross reference match as IRLML9301TRPBF
http://nz.mouser.com/ProductDetail/International-Rectifier/IRLML9301TRPBF/?qs=%2fha2pyFaduhk8M%252bingpDzSghYHzpUQ%252b47Aw2zvVseSU%3d