BMS with Li-Battery

Kaho,

I am not familiar with how parallel batteries are monitored, balanced and protected.

Analog Devices has some devices for series connected LI batteries such as the AD7280A and AD8280.

ADI offers the main components required for a complete Li-ion battery monitoring and protection system: 

• Voltage measurement device - monitors and balances the cells (AD7280A) 
• Current measurement device - monitors the cell stack’s current (ADuC703x or AD821x) 
• Isolator - brings the measurement signals across the high-voltage barrier to the battery management unit (ADuM140x or ADuM540x) 
• Safety monitor - enables creation of a fail-safe circuit and safe environment to the user (AD8280) 
• Battery management unit – controls and manages battery functions to optimize operation (Blackfin ADSP-50x)

Good luck and thanks for looking at ADI for solutions.

LucaV

If there is no charging you could connect each pack through a suitable diode to a common battery rail.  This would prevent one pack charging another should they be charged to different levels or of a different age.  I would suggest that each pack makes use of monitoring such as the solutions Luca suggested, particularly with regard to monitoring the stack current, voltage and temperature.  Should any pack experience over discharge, increased temperature or exceed its discharge current specification it should be disconnected from the circuit.

Dear Luca and Tim,

So, does it mean I also need to develop a switching circuit?

Is it something called OR-ing circuit?

Thanks

KaHo

An ORing circuit should work for this application as you are trying to maximise standby rather than the peak current from the battery pack. There is a good example using the AD8619 opamp and a MOSFET to overcome the losses associated with using a diode at http://www.edn.com/design/analog/4368307/Use-op-amps-to-make-automatic-ORing-power-selector 

Thanks to all,

I am now going to develop some current sensing circuit and use a MOSEFT to control the power input,

If there are any errors detected, like over current flowing or low voltage, the MOSEFT is controlled to cut the power.

KaHo

Kaho,

in case you are interested we have some ICs that can handle some of the functions you are looking to implement:

ADM1171:  2.7 V to 16 V Hot Swap Controller with Current Sense Output

ADM4073:  Low Cost, Voltage Output, High-side Current Sense Amplifier

AD8420:  Wide Supply Range, Micropower, Rail-to-Rail Instrumentation Amplifier

AD8214:  Fast Response, High Voltage, Current Shunt Comparator

AD8207:  Zero Drift, High Voltage, Bidirectional Difference Amplifier

Best Regards,

LucaV