Lithium Ion Charger (10 Cells/Batteries - each 2400mAh)

Hi guys, I have a simple question, is it possible to create one charger who could charge 10 Lithium-Ion batteries in parallel (each capacity 2400mAh - "DealExtreme: $9.57 TrustFire Protected 18650 3.7V True 2400mAh Rechargeable Lithium Batteries (2-Pack)") - source would be wall-socket (Europe - 230V) ofcourse with transformator, rectifier...

What current/voltage I need for these guys?

I searched over internet and I could find charger for max 3-4 lithium ion cells, do I need to split up these (10) in smaller "groups" and charge them seperately or..?

When they would be full, they would go on USB port (5V) for charging mobile phones, MP3 and so on....


Tnx. for any kind of information.

Ideally, you could stack all 10 batteries and place a 37VDC source on the stack. The voltage would divide equally among the cells and they would all charge to 3.7V. However, due to variations in manufacturing, there are deviations among the cells. For instance, some will have a higher internal resistance. These deviations will cause some of the cells to drain current more rapidly and charge more quickly than others. You will have to check the internal resistances and maximum charging current for this model so that it is not damaged. If damage is likely, you will need a cell balancing circuit.

There are two types of cell balancing circuits you can design: active and passive. Passive cell balancing circuits are simple and easy to design. One such circuit is made by placing a resistor in parallel with each cell in the stack. These resistors must each be the same value. An example of an active circuit would be to use comparators over each cell to equally divide the 37V. The passive option is slower to charge, and consumes more power. However, the active circuit is more costly and complex.

trav1s said:

Ideally, you could stack all 10 batteries and place a 37VDC source on the stack. The voltage would divide equally among the cells and they would all charge to 3.7V.

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if I stack them in series, wouldn't I have the same capacity - 2400mAh but larger voltage (37V)? ("When connecting your batteries in Series you are doubling the voltage while maintaining the same capacity rating (amp hours).")

trav1s said:

There are two types of cell balancing circuits you can design: active and passive. Passive cell balancing circuits are simple and easy to design. One such circuit is made by placing a resistor in parallel with each cell in the stack. These resistors must each be the same value. An example of an active circuit would be to use comparators over each cell to equally divide the 37V. The passive option is slower to charge, and consumes more power. However, the active circuit is more costly and complex.

Click to expand...

do you have examples of these two? So I could know the price of each :wink:

if I stack them in series, wouldn't I have the same capacity - 2400mAh but larger voltage (37V)? ("When connecting your batteries in Series you are doubling the voltage while maintaining the same capacity rating (amp hours).")

Click to expand...

The overall capacity will increase proportionally as well. So with 10 2,400mAh batteries to a stack you will have a 24,000mAh capacity.

do you have examples of these two? So I could know the price of each

Click to expand...

I know that frequently such chargers are sold as packages with what they are charging because there are a lot of various types of batteries. I will look around later and try to get back to you. At the very least I can provide you with schematics.

could I use then 10 x LTC1733 circuit? Datasheet (http://cds.linear.com/docs/Datasheet/1733fs.pdf) - last page "Full Featured Single Cell Li-Ion Charger"?

So for every battery I would use that circuit, connect them (those circuits) in series/parallel (?) with input voltage of...50V (10x5) from wall wart (from 230V to 50V with transformer and rectifier)?

svebee said:

Hi guys, I have a simple question, is it possible to create one charger who could charge 10 Lithium-Ion batteries in parallel (each capacity 2400mAh - "DealExtreme: $9.57 TrustFire Protected 18650 3.7V True 2400mAh Rechargeable Lithium Batteries (2-Pack)") - source would be wall-socket (Europe - 230V) ofcourse with transformator, rectifier...

What current/voltage I need for these guys?

I searched over internet and I could find charger for max 3-4 lithium ion cells, do I need to split up these (10) in smaller "groups" and charge them seperately or..?

When they would be full, they would go on USB port (5V) for charging mobile phones, MP3 and so on....


Tnx. for any kind of information.

Click to expand...

So your preference is to have all ten cells in parallel, yes? That certainly makes your life easier - you don't have to worry about balancing. There don't seem to be specifications for the cells on DX's website - but you can safely charge any li-ions (that I've worked with) at 0.1C.

So - let's do some math here - 10 cells in parallel => 10 * 2400mAh = 24000mAh. 0.1C = 0.1 * 24000mA = 2400mA = 2.4A.

So I would recommend charging at a constant current of 2.4A. When the pack voltage reaches 4.2V limit the voltage to 4.2V and wait while the current trickles off. Cut off at 0.01C (240mA).

Hope this helps.