MOSFET Driving - help needed

Thread Starter

mishra87

Joined Jan 17, 2016
859
Hi guys,

I am looking for cell balancing for 2 li ion series battery.
Could anybody suggest the best possible solution or approach , app notes ?

Thanks in Advance !
 

Thread Starter

mishra87

Joined Jan 17, 2016
859
For two cell Li Ion cell balancing which is the best method ?

1. Passive
2. Active
3. dedicated chip

Please suggest some low cost solutions here ?

Regards
 

KeithWalker

Joined Jul 10, 2017
1,308
The lowest cost solution is by using a bench supply that has current control, and a DC voltmeter. Charge each cell separately with the current limit set to 1 x C and the voltage set to 4.2V.
What exactly do you want to do? Are you planning on building your own charger?
The solution will depend entirely on the capacity of the cells. Are they 100 mAh or 10,000 mAh?

Keith
 

Thread Starter

mishra87

Joined Jan 17, 2016
859
The lowest cost solution is by using a bench supply that has current control, and a DC voltmeter. Charge each cell separately with the current limit set to 1 x C and the voltage set to 4.2V.
What exactly do you want to do? Are you planning on building your own charger?
The solution will depend entirely on the capacity of the cells. Are they 100 mAh or 10,000 mAh?

Keith
Thanks !

Cell capacity is 2000mAH.
No i do not want to build any charger.
In my application, i will use two series Li Ion series cell and i want to measure the voltage of each cell using microcontroller.
So i want to develop the circuit for cell balancing for 2 series cell.

Regards,
 

Audioguru again

Joined Oct 21, 2019
2,094
A lithium battery with more than one cell is charged with a balanced charger circuit to avoid the weakest cell from over-voltage and a big explosion.
Since you do not want to build a charger for your lithium battery then I guess you will buy it.

A lithium battery does not need a balancing circuit when in storage or during a discharge, then why do you need to develop a balancing circuit? Semiconductor companies have already developed balanced charger ICs.
 

Thread Starter

mishra87

Joined Jan 17, 2016
859
Hi All,

I am reopening this thread with some issue if someone suggest their opinion.
I want to measure the battery voltage for both cell (Li Ion - 2.5V to 4.2V) with cell balancing as well.
My first objective is measure the battery voltage then think about cell balancing.

Now i want to explain the power supply section.
TL431 is 4V supply on which microcontroller is connected so all measurement will be done with reference to MCU gnd. As it can been seen in drawing,
if VBAT = 8.4V, Voltage across TL431 = 4V and Vdrop_resistanece = 8.4-4 = 4.4V so microcontroller GND will be 4.4V above the actual bat ground and measurement will be done using microcontroller ADC.
if VBAT = 5V, Voltage across TL431 = 4V and Vdrop_resistanece = 5-4 = 1V so microcontroller GND will be 1V above the actual bat ground and measurement will be done using microcontroller ADC.

Hope now the concept is clear. My objective here is here to measure both cell battery voltage.
As i see we can not measure the 2nd cell battery voltage so my idea was to measure pack voltage and 1st cell voltage and then get 2nd cell voltage with these two values.

Any idea is highly appreciable !


1597770654643.png
 

Thread Starter

mishra87

Joined Jan 17, 2016
859
Hi All,

Please help me guys. I am stuck here !
I hope to see more participant in the thread.

Will microcontroller(MCU) be able to drive MOSFET Q1 and Q4.
Note : MCU 4.4V above battery ground as shown here.

1597859810661.png
 

KeithWalker

Joined Jul 10, 2017
1,308
If you plan on using something like an Arduino to make the measurements, that's a terribly complicated way of going about it.
Connect the GND of the MCU to the negative terminal of your two cell battery. Connect the junction of the two cells in the pack to an analog input on the MCU (A1) through a 10K resistor. Connect two 10K resistors in series across the + and - of the battery pack and connect the junction of the two resistors to a second analog pin (A0) on the MCU. The resolution of the voltage measurements on A0 will be 0.2% and on A1, 0.1%which will be far better than you need.
Regards,
Keith

Vbat.jpg
 
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