Gen II Prius Individual Battery Module Replacement

With a subject such as this I suppose there are always going to be to be differences of opinion, and I respect that. However 0.9 volts is considered to be a complete discharge of useful capacity with NmHi cells. I agree that reverse charging a cell will damage it at high currents, but at low current bearing in mind the lower the module voltage the lower the current will be. At 0.65 volts per cell the current will be well down.
Jeff652 recommends if I read him correctly going down to 0.1 volts per cell, but not on the first discharge. This is something I have not tried "as yet", but I have found definite improvement by taking the modules to lower voltages.
Again I must repeat taking NmHi cells down to 0 volts is not harmful, but I agree as stated earlier reverse charging at to high a current is. What that limit is at present is unknown.

John (Britprius)

 

Britprius,
I agree with the ability to take nimh below 1v per cell.

Any high current charging at high SOC is not a good idea. No discharging at high current at low SOC.

 

This charger i have(link) and can set discharge rate up to 2.0A, it's like four chargers packed in one box

Thanks everyone for answers, again difficult to decide because different opinions here, i think i will go to 1v per cell since everyone in this thread that way used and many got good results

 

If you look at Danny's figures in post #655 for module 28 where he took the discharge down to 4 volts. In one cycle he gained over 400mah in capacity on an already fairly healthy 5464mah module with one previous cycle with no comparison figures for any gains on that first cycle.

John (Britprius)

 

John,

You can get away with a deeper discharge on a well balanced module, but when I balanced my 27 modules at 195k miles (9 years old), they all recovered to >6500 mAh (at 0.1C discharge rate) without going below 6v per module. The 28th module had an in-car cell reversal and was not recoverable.

JeffD

 

Yes Jeff I do appreciate what you are saying, but cell reversal in the car occurs at discharge levels of 50 amps or more. At very low currents this damage can be avoided.
In ongoing test "limited at the moment by the availability of modules to test I can even work with modules with a damaged cell". I am consistently seeing better results capacity wise by taking the cell voltages down to lower levels. I am doing this in 0.1 volt steps to try to see if there is an optimal discharge voltage. I strongly suspect that this figure will be at or near zero, but will not let that get in the way of actual results.
I am also testing with higher discharge currents for capacity measurement "30 amps" continuous" to give more credibility to the results.
I also find consistently that charging input of 7000mah is not enough to fully charge the modules with a capacity believed to be at 6500mah. This would be an extremely high acceptance rate for a NiMh cell of 93%.
Again I am in no way trying to discredit your valuable input, and feel a healthy discussion more valuable than an insult throwing argument so please do comment good or bad on any of my posts. I am giving information on real test results with as much accuracy as I can in a home environment.

John (Britprius)

 

John,

I fully agree that this discussion is healthy and informative. I was reporting that I had good results in my case (moderate climate and mostly flat geography) without risking cell reversal by going below 1v per cell. Perhaps the capacities could have been increased further, but the 6 individuals who reused my balanced modules to repair their Prii HV batteries all reported successful rebuilds.

JeffD

 

Thanks for the update. I to live in a moderate to cool climate, but in a hilly location. Most of the roads in my area are also very winding meaning straight stretches of road more than 300 yds are rare. So lots of braking and accelerating. This seems to keep the battery in the green zone most of the time. My car has done 113000 miles and is a 2008, and due to the way Toyota extend there guarantee on the battery here in the UK hopefully it will be still covered until 2018 irrespective of millage.
I have however rebuilt batteries for other people where for some reason the extended guarantee could not be applied. I also enjoy researching such things now I am retired and have the time.

John (Britprius)

 

In multiple paid business-coaching sessions I have conducted over the years to the very "self-confident" individuals who, being new to the high-tech business [I am in] were in the state of "unconscious incompetence" I kept reminding them that the assumption is the last resort where there is absolutely no way to find out the right information....especially when it is one click away and can be given to you in your own native language.... You did not ask and assumed the price ...
Good luck, just read the name of this thread "Individual ...module replacement" and bear in mind that if you can not measure and match capacity of individual modules - there is no point ...

 

With due respect, whereabouts have you read that recommendation? Could you point at the sourse please?
That statememt can confuse many people...
"Completely discharged" in my (and many other people) terminology is ZERO volts - that what I recommend to do when dumping dead modules - for the safety reasons.

Please define "complete discharge" for the Prius 7.2 Volt module: is it 6 volts, 4.8 volts or zero volts in your terminology?

FYI - if modules are down to 6 volts - Toyota Techstream [so loved by yourself] will show SOC (state of charge) = ZERO. That is "complete dischage" in Techstream terminology.
Self-discharge will kill batteries eventuallly.
Toyota technical guidelines suggests charging batteries which are kept with no usage once every month.
Another governmental [leave you to guess which country} Official Standard prescribes keeping NiMH bateries charged and checking self- discharge level monthly.
Have you tried yourself to keep battery "completely discharged" for months and see whether they be able to take charge again at all?

 

Well, if that happened - the battery is condemned (for business-type repairs) - it is an indication that overall capacity is very low (can speculate that it is < 2AH) and - working on that battery is waste of time. Put it simple - if car [which suppose to use battery in the "shallow range" ] is able to make module reverse - when that excact capacity is drained during kick of the MG - then the battery is of no use.
Real life test in 2014:
50 amp discharge in Prius 2009 (as observed on my HV Analyser connected to the real car during stationary stall test) showed battery voltage dropped to the 7volts per module. At that level ACE kicked in and charging have started.
Delta V for a moment was down to 0.5V (above allowed threshold) but because lasted only for a moment - it did not throw error codes.
In that particual test there was an indication of the early module unbalance .
Measured capacity also revealed that capacity loss was significunt to suggest that 5-year old imported 2009 Prius (test was conducted in 2014) had little "juice" to spend over remaining 5 years of the esimated battery life.
We conducted that test for the dealership before car was sold... and warned them not to give warranty on that battery...
I guess new owner may come to this forum in the next few months....

 

Within the range from 7v down to 6 volts per module - the capacity stored in the battery is minimal.
Although one may wish to discharge below 1V, say down to 0.8V in rare ocasions (4.8 per module) - there is no immediate benefit in doing that for any particular purpose.
Eric, my battery hero, I do not beleive you've been hooked-up by a preaching of "complete discharge with extra low current and then slowly charge with low current charger". If you really, really busy, as the business implies you to be - then you woudln't have time for that kind of nonsense....
Are there ...ashers, collecting for a "greed" charger and low voltage "dis-charger" still around? I would have thought - they are "preaching" at the Honda "isightcentral" forum where that nonsense has started....

 

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With most of these units you can read out the discharge and charge mAh at the end of the selected cycle (as long as there is no interruption of power).

JeffD

 

Completed today 1st cycle, the modules looks very bad... maybe will be imposible to restore it at all, at end of cycle charger show only the mAh of charge so the numbers of discharge below are not acurate

now instead of dsch>charg function i will use manually discharge and then charge to see acurate numbers

#1 D3200 C8000 D4498
#3 D2400 C6870 D3595
#5 D2400 C6700 D3459
#7 D2000 C7100 D3110

now discharging second time and noticed that the #7 voltage drop much faster than #3 and #5, when the #3 and #5 has 7volt the #7 has already 6.6v at same time of discharge, i think those modules which are in middle they will be completely weak

and looks like the the delta peak trigered even at 0.7A charge rate and highest d.peak setting on charger

after discharge i measured the voltage of #7 module with multimeter and it about 6.3v, when the discharge stoping the voltage slowly rises, but that's still 1.05 per cell i think that's normall right? no need to set lower discharge?

Thanks, i will update when all modules will done

 

Try setting the delta peak to zero as this may turn it off.
For the modules that are showing very poor discharge capacity if they do not improve on the next cycle. Disconnect them from the charger, and connect a 6 watt side lamp bulb to discharge them slowly to zero or near zero volts. While doing this you could use the charger to cycle another module. After discharging charge again to 8000mah and check the results.
Bear in mind you have nothing to loose in doing this as the module would be useless anyway if it does not recover.

John (Britprius)

 

My charger does not have d.peak zero, i can select only between 3mV-15mV per cell...

 

It is the discharge reading that tells you the module capacity, not the charging reading.

JeffD

 

Yes I understand that, just trying to charge much as I can to be sure that cells are equalized... Looks like my average capacity per module will not be more than 4Ah... If the #7 module is that bad can't imagine how bad will be the #19-#20 modules...

 

Poor module health is a symptom of overheating the HV battery:

• Warm climate
• Hills/mountains
• Not using AC to help cool battery
• Blocked HV batter vent

JeffD