Battery control design help needed, If you know how to deal with smart batteries, please help me on my project.

[cirthix]

I need to charge and discharge a 6 cell ltihium ion battery (3 seets of 2 cells in parallel). I have access to the smbus and a 5.5v or so input voltage.

I have to do three things: charge the battery safely, discharge the battery safely, and be able to use a battery monitoring program in windows. I have a 5.5v input voltage and access to both the smbus and i2c bus.

Can I use a dumb charger like the
http://datasheets.maxim-ic.com/en/ds/MAX745.pdf
and have the battery report it's own remaining capacity and other status to the system through the smbus?

The load will be using up to 80w, but typically around 15-20w. I have already chosen the dc/dc converter to supply the load with the proper voltage (5v).

I have two ideas on the general power distribution:
http://www.cryo-laboratory.com/upload/u...cirthix/power%20schematic%20wrelay.JPG
http://www.cryo-laboratory.com/upload/userfiles/cirthix/power%20schematic.JPG


I could do it slightly different by having arelay to select the power to the dc/dc module between battery and dc input and do away with the diode allowing for higher input voltages, but relays are significantly larger than a diode or two.

I need help making/finding the battery controller and charger

 

[cirthix]

I guess what i'm really asking is this:

If the battery is smart, it should keep track of it's charge status, time remaining, etc. What additional functionality does a smart charger add to the system?

 

[Rubycon]

Originally posted by: cirthix
I guess what i'm really asking is this:

If the battery is smart, it should keep track of it's charge status, time remaining, etc. What additional functionality does a smart charger add to the system?

Protection against over discharge (cycle ends around 3.0 volts for Li Poly) and (of course) excessive cell wall temperature. This cannot be ignored with this technology as it's been observed many times what happens when these cells are faulted.

 

[cirthix]

Originally posted by: MS Dawn

Originally posted by: cirthix
I guess what i'm really asking is this:

If the battery is smart, it should keep track of it's charge status, time remaining, etc. What additional functionality does a smart charger add to the system?

Protection against over discharge (cycle ends around 3.0 volts for Li Poly) and (of course) excessive cell wall temperature. This cannot be ignored with this technology as it's been observed many times what happens when these cells are faulted.

But isn't under voltage protection, over voltage protection, over current protection, and over temperature protection part of the battery side of things?

 

[Rubycon]

Originally posted by: cirthix

But isn't under voltage protection, over voltage protection, over current protection, and over temperature protection part of the battery side of things?

Bare cells have nothing to protect them - this must be incorporated in the pack itself. Some packs have this completely integrated and others have the logic in the powered device.