I want to hold a group of cells at constant voltage (anywhere from 3.0V to 3.6V). I plan to hold them in parallel so I can use a single power supply. Once the cells reach stabilization at their designated voltage the current should reduce to under 1mA. The problem is if a cell shorts out it will slowly short out the other cells too! I need a reliable solution to drop one cell from the circuit if it shorts out (soft or hard short).

So, I want something to detect an anomaly in the current being requested by each cell that will break it off. I'd like to hear your ideas; any help is greatly appreciated! More details if needed.

 

I was thinking of something like this bad boy ( http://sensing.honeywell.com/index.cfm?ci_id=140301&la_id=1&pr_id=146379 )... but can't figure out how to incorporate it into the system... I need it to trigger a contactor/relay that will work off the 0.4V output but have low resistance (under 1mOhm at least).

 

Use a PolyFuse in series with each battery, then parallel the fuse/battery strings. If a battery is shorted, the PolyFuse will open, allowing the remaining batteries to charge normally.

 

Where can I find this Polyfuse? What sort of resistance will they be adding?

 

PolyFuse on Wiki

 

1 Why should a cell short out?
2 A diode in series with each cell will stop reverse current with a cost of .1's of a volt on the cell. For a si diode about .7 v which is a lot for a single solar cell.
3 The current to "blow" a poly fuse may not be available.
4 A skematic of you setup and data for the cell would be useful.

 

I want to hold a group of cells at constant voltage (anywhere from 3.0V to 3.6V). I plan to hold them in parallel so I can use a single power supply. Once the cells reach stabilization at their designated voltage the current should reduce to under 1mA. The problem is if a cell shorts out it will slowly short out the other cells too! I need a reliable solution to drop one cell from the circuit if it shorts out (soft or hard short).

So, I want something to detect an anomaly in the current being requested by each cell that will break it off. I'd like to hear your ideas; any help is greatly appreciated! More details if needed.

All the Sony battery packs contain a small PCB with a sense/cotrol IC's that control mosfets to open the current path to their LI-ION batteries. You can use a similar approach. In the national Semi chip we designed for this purpose, we sensed the curent through the lead frame of the IC (voltage drop) to trigger a detector to open the FETs.