# Lithium Ion battery charging

Its just a simple Question

Lets Say, I have 4 x Lithium Batteries each 6800mah capacity and Lithium Battery Charger IC BQ24618 from texas instruments.

Will I be able to charge these batteries keeping them in series with this IC?

If not what should I do to charge them? I do not want to buy ready made Battery Charger. Any suggestion would be appreciated.

In section 3 of the datasheet, it states that the device supports charge currents of up to 10A.

The controller needs external support circuitry to do this, see the typical system diagram (from page27 of the datasheet):

The current is set by external components for the constant current phase, as is the cut-off current level when in constant voltage mode. On page 27 of the datasheet, it states:

Refer to the EVMuser's guide (SLUU396) for EVM information.

Although you may not use the evaluation module, it will feature a more complete description of the various circuits and will give greater insight into successfully implementing the charger.

Normally, we do constant current at the C rate, so for your 6.8Ahour battery, I would normally set that current at 6.8A, but check the battery datasheet as not all batteries are made equally. The battery manufacturer datasheet is your final guide here.

I suggest you thoroughly read section 9 in the datasheet, where a very detailed description of device operation and implementation is given.

HTH

When charging series stacks of Lithium batteries, the individual voltage of each should be indepently monitored for safety reasons. Linear Technology, Maxim, TI and others have solutions for this.

For batteries in series, use the charge current for each - in this case, the charge current for a single battery.

• Capacity should be like four times 6.8 AH, shouldn't it be? I need 25Ah capacity for my thing and voltage around 5v. How am i going to achieve this? – Arjun Aug 7 '15 at 13:37
• You can charge the batteries at a lower rate to stay within the limits of the controller at the expense of longer charge time. The controller has provision for multiple batteries. – Peter Smith Aug 7 '15 at 16:38

Here is the answer as in the datasheet page no:3

• Thanks Sanjeev , but I am curious , it does not specify the battery capacity. So it means I can charge these batteries with this IC? – Arjun Aug 7 '15 at 11:45
• yes only thing is that charging time will vary based on the capacity and also its a Synchronous Buck Converter so will have to supply voltage greater than the charging voltage – Sanjeev Kumar Aug 7 '15 at 11:57
• You can set the charging current to C/10 where C is the capacity of battery – Sanjeev Kumar Aug 7 '15 at 12:03
• That means supply voltage should be greater than 3.7*4= 14.8V? – Arjun Aug 7 '15 at 13:31
• Generally the 3.7v battery gets charged up to 4.2v. So here charging voltage should be 4.2*4=16.8v so supply voltage to the ic should be more than 17v and charging current you can set as 6.8*4/10ams=2.7amps – Sanjeev Kumar Aug 7 '15 at 16:02