Cell Cycling and Matching

Two threads I think that will answer all your questions (I have all my charger settings in the end of both):

Gen II Prius Individual Battery Module Replacement | PriusChat
Prius Battery rebalance thread | PriusChat

Keep in mind RC racing and HV battery longevity don't always go hand in hand so I prefer a bit more conservative settings to ensure I don't overcharge them when cycling for capacity.

 

Single cells cannot be worked on in the Prius battery only a module of 6 cells, as there is no way to get to the interconnections. Safe charge and discharge rate is high as in use they see currents of 80 to 100 amps in both directions. If you are talking about balancing modules then the maximum and minimum rates are governed by the RC chargers normally used by most here. Typically .7 to 1 amp discharge, and up to 5 amps charging. Module capacity is around 6.5 AH.

John (Britprius)

 

For the discharge cycle (done first) 6 volts "one volt per cell" not going lower than this to help protect against reverse charging any possible low charged cells in the module.
I personally do not use an upper voltage limit preferring to use a charge capacity limit of 7.5 AH (7500 MA). Some may disagree with this, "but there are going to be 6 different knee thresholds as each cell reaches full charge".
This allows some cells in the module to be over charged, but allows any lower charged cells to catch up as they will continue to charge. As you have probably noticed the consensus of opinion is for a three full cycle operation measuring any capacity increase on each discharge cycle. More cycles may be added if it felt that more capacity will be regained.
Any knowledge you can share will be appreciated by myself, and other members here.

John (Britprius)

 

In operation the battery only uses 40% of it's capacity. It only discharges to 40% and charges to 80%. This increases the cycle life to many many tens of thousands.

John (Britprius)

 

X2

This is the difference between hyper cycling (to maximize life in HV's) and performance cycling (like that used in RC racing) hence my comment above.

 

The problem is with the Prius system you have "for the gen2/3" 168 cells in series with no cell management system.
If one cell losses 1 mah in conversion losses each time it is charged and discharged compared with the rest in 6500 cycles it will have no charge. However it will have been destroyed long before this by being reverse charged. It is remarkable how well the system stays in balance for so long.
Charging the battery to 101% of capacity every cycle would keep all the cells balanced, but of course cell life would be shortened dramatically. Over charging is normal practice with 12 volt lead acid batteries to keep the cells balanced, and this is for only 6 cells in series.

John (Britprius)

 

I think in the Prius application one or more cells get out of balance and are then destroyed by being reverse charged at high currents. Something that they will not recover from.

John (Britprius)

 

Most technicians dont have even a fraction of the battery knowledge of those on here, combined with Toyotas standard procedure for handling a weak battery block code and the incentive for dealers to maximize your bill, I suspect ALOT of HV packs with only one bad cell in one module get replaced.

 

I would suggest keeping the current lower (1-2A) and start with 7000 mAh on the first cycle and increase the capacity slowly if it shows improvement.

 

Dave try to keep the terminology correct "not easy I know". A Nimh cell will only have a voltage of around 1.2 volts depending on it's state of charge. The readings of 7 volts plus are for a module of six cells. The use of cell, module, and battery helps members giving advice " hopefully myself among them" to allow other members trying to follow the advice not to get confused.
The module you found at 7.1 volts sounds like it has one reverse charged cell, the reason it is down 1.2 volts on the other "good" modules. It may be recoverable "worth trying", but I doubt it will. The other modules look good voltage wise because they have held the voltages well, probably for some time.
It would be worthwhile doing a set of balance charges on those modules to see there AH capacity.

John (Britprius)

 

With the low module you have nothing to loose, it works or it does not.
I suppose technically a a module is a battery. A group of cells in series to provide a higher voltage, but using the term module, as a number are required to make up the complete battery, makes sense.

John (Britprius)

 

For what it's worth, you can save some money by ordering the regular x4(50W). I originally bought an x4-80 and two x4's, one of which was an x4 with the built in A/C power supply called x4 A/C plus. This way I had at least one that was sure to work. After using them to redo a gen 2 pack, I decided to sell the 2 d/c units so I didn't have to tend to a battery charger to keep them going.
Now I'm going tomorrow to buy a gen1 car to redo and I plan to buy another a/c plus unit to go along with the 3 chargers I didn't sell so I can do 16 mods at 1 time. The 50W chargers work great and are less money unless you get the a/c plus, which will run around $200. But I've found a battery shop where I can save about $200 on the 12V battery. He has one the same size only with the larger, normal sized posts for a mere $65. The dealer wanted $250 plus tax. I'll just change the battery cable ends or the whole cable if I have to. Hope this project goes as smoothly as the 1st one did.
Thanks again Britprius and Ryousideways and others for the valuable information and help.