Friday, August 14, 2009

#140 needs some new modules

#140 has two bad modules. Not sure what that means other than it involves taking apart the entire back part of the car that houses all the batteries. This is the first time the Flying Doctors have had to do a module replacement (at least in Oxnard, CA). Hope to have car back early next week. The problem was discovered during my first scheduled service visit. I had no indication anything was wrong and the car was driving great. Will update more when I know. Will be cruising in the S until the E's return.

Matt Walton via the MINI E group on Facebook provided this updated info:

Per spec sheet;

Battery Design - 53 cells connected in parallel constitute a unit, 2 units connected in series constitute a module, 48 modules connected in series constitute the battery; 5,088 individual cells in total.

Pictured at link below, scroll down to year 2005;

Based on this explanation, 212 out of 5088 have gone bad.


  1. Hi Todd,

    Hope you are back on the road very soon in #140.

    Just a clarification on the battery issue. Only the AC people will know this for sure, but you most likely have only 2 bad cells out of the 5088.

    Since the Modules are in series they are like a chain. So the strength of the whole chain is controlled by the weakest link. If one Module has a bad cell, it limits the strength of the whole string. They need to be matched and balanced together to insure the strength of the whole chain.

    The other issue is that you may remember stories about fires with lithium Ion laptop batteries. They have since figured out the voltage and current limits that can damage a cell causing it to overheat during subsequent charging cycles. The Modules contain chips that monitor voltage, current, and temperature on every single cell. For small variations, many can also “balance” during charge and discharge so that all cells stay in sync during charge and discharge.

    If one cell in a Module starts to exhibit values beyond the monitoring chips ability to balance them out, preventive maintenance dictates they should change the cell so it does not over heat during subsequent charge and become a safety issue.

    The Modules were assembled and tested in the AC manufacturing plant in China. I would expect Oxnard to replace a Module, rather than attempt repair in the “field”. This would reduce your down time, provide a tested balanced Module unit that has been through the quality control process, and let the factory and engineering have time to better evaluate the problem in the defective Module. If they follow ISO 9000 quality procedures, there will eventually be a failure analysis of the Module at a component level, most likely done at the production plant in China. This may take time as it must follow the product test quality control process to produce root cause for engineering evaluation.

    This would improve future product reliability.


  2. Thank you Matt for this information!