Prius traction battery question

No the Prius HV battery has 28 modules with six cells in each module making a total of 168 cells. Each cell is 1.2volts each module is 7.2volts (6x1.2) and (28x7.2) no of module x voltage =201.6volts voltage of complete battery.

A good amp/hr capacity is 6.5 , voltage of all modules (you cannot get to individual cells) should be as close as possible to each other or within 0.1volt.

 

Although 201.6V is the "nominal" voltage rating for the 28 modules, typically you should expect to see battery voltage 10-20% greater than that value when the battery is operational.

 

The cells can be fully charged to 1.5 volt making each module 9v or discharged down to 1volt module voltage 6v this is used to balance the cells, but the Prius charging ECU never allows this and uses a maximum charge of 80% and a minimum charge of 40%.

 

My personal opinion is that after rebalancing and assembly of the complete HV battery I would discharge the battery with a 300watt load (a quarts halogen work lamp works fine) till the voltage has dropped to around 230v. Other people may have a different view.

 

I'd also like to ask some question about "re-balancing" modules, as I may have to do some work on my traction battery if it loses any more capacity.

Is re-balancing essentially just (almost) fully discharging, and then fully charging the modules independently (meaning not in series).

Would it be best to finish the balance in the "bottom end" state (with all the modules discharged) and then charge them in series before returning the pack to service. My thinking is that this state would give all the modules the same amount of charge and make it less likely that the weaker modules could get overly discharged (or even reversed biased) while in service.

Are the above correct?

 

The theory is that when you charge a module (6 cells in series) effectively you over charge by a small amount the "good" cells in the module, and when fully charge they give any excess charge off as heat any cells that were low on charge will catch up by continuing to charge. doing this three times should give the weaker cells a chance to become fully charged without damaging the "good" cells.

Doing this should make all the cells in a module equal. All the modules can be checked for capacity in amp/hrs by the dc6 charger final discharge time on each module the ideal being all modules being the same capacity.

In my opinion all the cells/modules being fully charged the partly discharged in series by a common load should keep them balanced. but if there is a slightly week cell you may reverse charge it by fully discharging that module that the cell is in. However that module should have bean discovered and discarded on the capacity check.

I have been contemplating doing a balance charge/discharge on the HV battery as a complete unit as I have equipment capable of this, but I think excess heat in the battery may be a problem.

No doubt Seilerts will enter the discussion with his particular expertise and knowledge of the subject.

John