Traction battery refreshing???

You could get a ScanGauge to monitor the HV battery cell voltage to see if that is a problem. But if the car is showing no difference in MPG and no warning lights I would think there is nothing to be concerned about.

 

I am seriously considering doing this to my own battery at 100,000 miles.
I have the ability and equipment to do this as a complete unit rather than individual modules without removal from the car.
I will still be able to check the AH capacity of the complete battery both before and after the "balance charge". The charge would be done at a low rate to help overcome the problems of heat and pressure bulging.
I can see no logical reason why "given the safeguards" on a working battery "no dead modules" that such a procedure would not improve the working capacity and possibly extend the life of said battery. This would reducing the risk of reverse charging cells with a lower charge level within the modules.

John (Britprius)

 

Hi Alex. You've nicely described exactly what myself and one or two others here have also noticed regarding an apparent anomaly in the way that SOC (state of charge) is displayed.

It is my belief that this is related to the loss of capacity of the traction battery and that this causes errors in the estimated SOC. I have documented my theory of what's happening here: Traction Battery SOC "Meta-States" | PriusChat

 

In the same manner as you do a single module.
The difference being in the voltage required to charge the complete battery. A module has 6 cells in series, the battery has 168 cells, but still in series. This means you need a charging voltage of around 250 volts DC instead of 9 volts.
The principle of controlled over charging the cells with a higher charge level to let those with a lower charge level catch up is exactly the same.
Those cells with a full charge give off the over charge as heat "why things must be taken steadily" the cells not at full charge will continue to charge until they too become fully charged and start giving off heat.

The complete battery can then be discharged at a known rate "in the UK a 1kw heater rated at 230 volts will be very close to 4 amps" down to 168 volts measuring the time taken to calculate the AH capacity. This may not be perfectly accurate, but will give reasonably good comparison figures to show any improvements.

John (Britprius)

 

Yes, I also feel that module imbalance is the the most likely cause of this. Whatever the underlying cause of the loss of capacity, the following is what I believe is happening. After you've fully max'ed out the battery (8 green soc) then the battery controller is Coulomb counting down, thinking it has more capacity than it really has, until it suddenly notices a lower than expected voltage on one or more modules - which is when you suddenly start to get unexpected loss of SOC bars despite the engine running and the arrows on the display showing the battery charging.

BTW. Mine has been like this for over a year now, fortunately without any significant worsening of the condition. I've also been trying to figure out if it's worth the effort of pulling it down and re-balancing.

 

I am a retired electronics engineer so there are a number of ways to do this. The simplest "and the most dangerous" is just to rectify and smooth our mains supply since our rated voltage is 230 volts AC. This gives a DC output nearer 300 volts.
Another way is to use a 12 volt DC to 230 volt AC inverter readily available here built into jump packs, and go through the same process as above. This was actually used on the first version of the Prius in Japan fitted in the trunk as standard equipment.
There are many other ways to do this but everyone should be aware of the dangers of high voltage DC supplies. This is not for the untrained or unskilled.

John (Britprius)

 

I only gave a brief summary of the basis of the method. The control of the system is comparatively easy. My last line does state "this is not for the untrained or unskilled".

John (Britprius)

 

If you cannot control over discharge on 168 cells you cannot control over discharge on 6 cells where the difference will be exactly the same.

John (Britprius)

 

Over discharging Nimh batteries is not a problem, it is reverse charging that does the damage.

John (Britprius)

 

We are not talking about batteries with faulty modules we are talking about refreshing good working batteries. Read post 4.
In use in the Prius a module with a cell with only 680 mAh would have given out a fault code for a faulty module pair. The Prius uses a battery capacity range of around 40%, 680 mAh represents only 10% of capacity and any cell with that capacity would be reverse charged in use. You can discharge a Nimh battery to zero volts without damage, it is reverse charging it that does the damage.

John (Britprius)