Prius Battery rebalance thread

Thanks mate. In 80's I was doing stuff - no one else in my city was able to - fixing JBL and other hugely expensive stage speakers - i.e. recoiling those burnt by the music bands - every rocker in the city knew where to go... The job required precision, measurements and patience...Designed and created special tools then for the job to be done... New century - new challengies. I've created Analyser because I new I needed a tool to make measurements... and wanted them to be accurate...

 

All those companies who say they can regain capacity in a faulty cell is correct or wrong??
What is reconditioning or refurbishing??
I have change to my Prius the hybrid battery and I have the old battery.
I want to reconditioning this battery.
Which steps should I follow?


Thanks

 

Have a look at the threads Re-hydrating battery modules combined with Gen2 individual module replacement. Both in gen2 technical discussion section.

John

 

If I want to charge and discharge the battery pack,how many amps and volts is the correct way??

 

The hybrid battery is made up of 28 separate 7.2 volt batteries (better known as modules). This makes for a total voltage of 201.6 volts.
To charge the complete battery you would need a charger with an output of around 250 volts DC current limited to about 350 ma.
The alternative is to charge the individual modules most often done with a hobby NiMH battery charger at about 2 or 3 amps.
All the details are in those posts I listed. If you have little or no electrical knowledge it may not be for you. This battery can kill you.
It is also not a quick process requiring at least 3 charge then discharge cycles for each of the 28 modules.
A module with a faulty cell (6 cells in a module) cannot be recovered or reconditioned.

John

 

I have electrical knowledge but I don't have any experience with prismatic batteries....
You think 2A for 2 hours charging and 3A for discharge it is ok for the complete pack?

 

The modules have a nominal capacity of 6.5 ah (amp hour) so charging at 2 amps for 2 hours even if the modules were 100% efficient which they are not would only charge them to 4 ah capacity (2 amps X 2hrs). So they would need to be charged for about 4 hrs. The idea being to overcharge the cells that have a good state of charge and allow those with a poor level of charge to catch up.
Are you charging the battery as one unit or as 28 separate modules you have not made this clear.

John

 

Which method has better results??

 

The individual charging of the modules with the "hobby" type chargers gives the ability to show the capacity of each module, and thus the knowledge of which to replace. but this method is slower even with a charger that can handle 4 modules at a time.
Using a high voltage charger you charge at a lower rate "typically 350 ma to prevent overheating the battery" but charge for 24hrs. this is faster but does not tell you the condition of the modules.
Read the posts below to get the detail.

Gen II Prius Individual Battery Module Replacement

Re-hydrating the battery modules.

John

 

That current 0.35 will keep them busy for a while...
There is no need for that low current limiting. Charger for NiMH has jsut to be Constant Current charger.
Charge currents in Prius could be as high as 95 Amps.
What you must have is a temperature management during charge and capacity control - if thresholds exceeded - expect nasty things to happen.
To charge 1.2NiMH cell - voltage must be more than that but not exceed 1.8V/cell, that is 10.8V per 6-cell 7.2V module.
That said 250DC will do the job for a 28x7.2V pack as well as up to 302 V DC Constant Current Charger.
I use 1.2A; 1.4A; 1.8A. 2A and 6Amps Constant Current chargers which I have built myself (not a rocket science).

6A / 0.35A = 17 times faster than what you suggest.

 

Awesome questions. I wish more people out there ask those as there is so much fudge from people who do not even know the Ohm's Law...

Regaining capacity:
There are at least 3 patents from the battery manufacturer: re-filling modules with the original electrolyte (not for you); process of heating modules for few days (don't even think about it); process of discharging modules and idling them for a week to reduce memory effect and hence re-gaining capacity.
Last one (idling for a week) does not provide any clue of the level of discharge but it is the only affordable and practical for you.
I have not noticed any capacity gain in that.
Asymmetric charging (one of my proprietary chargers - microcontroller based) was showing promising results in capacity gain on 10 year old modules until tested modules successfully died . Have tried on 5 year old modules with 160K miles - no effect.
Currently I do not discharge below 6V/module of 1V/cell. I do load test a week after charge to get more accurate results - which will be always lower capacity vs measured straight after the charge. Some standards suggest idling for a month before load test (to factor-in self - discharge rate).

Those first two patents are not known to be commercially implemented and most likely serves to protect the manufacturer rights.
Any claims of regaining capacity which are not supported by method of procedure and test results should be taken with the grain of sault.

Reconditioning or refurbishing:

Considering above - I suggest that both terms should apply to the assembled pack and not to the individual modules as some claim.

The process of reconditioning / refurbishing I suggest should include steps to segregate re-usable modules from the waste, dumping bad modules and compiling the new pack from tested modules which are in conformance with each other - i.e. have similar capacity, internal resistance, those will impact their charge/load V/A characteristics and those should be equally charged when the pack is assembled.

Usable remaining capacity of the rebuild/reconditioned/refurbished (whatever you call it) pack has to be available for the end user. (That is not the capacity of the individual module discharged to 6V which will be higher.)

I introduced that term Usable Remaining Capacity (URC) of the pack as the capacity of the pack measured under load of about 6A, discharged to the level where average Delta V on pairs is not exceeding 0.5V

I am the first in the world and (unless advised otherwise) the only one at the time of this post who made test results of Prius packs and method of procedure disclosed to end-users.
I've made my tools (High Voltage Battery Analyser) available and affordable for small business owners.

 

Thanks kiwi...
A 7 years old battery pack,after reconditioning how much "life" acquires??
Also why to charge the pack with 6A and not with 6.5A and why to charge it asymmetric.?

Thanks!

 

I do not do "life predictions". What I can do - is to test the pack for Usable Remaining Capacity within the specified period after agreed mileage. Whoever wish to commit to run that test on their battery pack (new, second hand or re-built) and located in New Zealand - are welcome.

My site has a brief summary and a link to 3-rd party tests on degradation (loss of capacity) of hybrid batteries with age:
Third Party Battery Test Results - HYBRIDS

You can get from that data an idea of what the rate of capacity loss is in fresh batteries.

When you re-built from used modules - Usable Remaining Capacity will be lower than in the new pack, hence lifespan of the re-build pack will be shorter. Whoever claims otherwise - is a lier.

That is the reason why I recommend re-builders to consider capturing that metric and disclose to the end-user. I also suggest their pricing structure should reflect that rather than providing a warranty in a hope customer will never come back (Fact: hybrid shop in California told me they do excactly that - give 2 year warranty and keep their fingers crossed)

There are at least 2 hybrid shops in US who claim "restoration to the design specification" of the modules and that is a fudge.

Some utilise "never used old stock modules NP1" in their re-builds - put them in new Priuses and sell them at discounted price. Although it is a workable solution - those who does that should not be doing those claims either as battery loose capacity even if not in use - it degrades with age and those old stock modules have been stored for at least 2 years now. New modules are NP2: Products | Development, manufacture, and sale of a hybrid car and the battery for electric vehicles (battery) | Primearth EV Energy Co., Ltd.)

Re: charger - assymetric pulse charger is just one of many chargers I have built following some claims of what it can do. That is different story...
High Voltage Chargers - can do 6.5 but 6A is very convenient for easiness of calculations - simply because there are 60 minutes in an hour . If I need to charge the whole pack and use just a charger without connecting all the gear - Computer, HV Battery Analyser - I will know that in 10 minutes 1AH will be pumped in, in 30 minute - 3AH. Make sense? For the same reason have built High Voltage Chargers - 1A, 1,5A, 2A Constant Current.

 

Thanks kiwi..
You have knowledge about hybrid batteries...
You discharge the battery even the modules has 6Vper module??

 

Panasonic tech specs [cylinder type 6.5AH HiMH] stipulates that minimal allowed voltage per cell is 0.8V.
That implies 0.8 x 6 = 4.8V if there are 6 cells in the module.
There are no publically available specs for NP1 or NP2 prismatic modules.

Some people on this forum discharge them down to zero in attempts to reduce memory effect. I see no benefit in doing so.

Hundreds of discharge graphs I have observed during tests on Prius NHW-11 (NP1) and NHW-20 (NP2 modules) suggest that even on the very good modules - there is not much capacity within the range from 7 down to 6 volts in discharge mode.

Stall [discharge] tests [about 5A in Live tests on the car] aslo evedential that modules do not drop below about 7V.

Hope that helps.

 

Thanks for your quick respond....
I already starting to build a high voltage charger....
The difficult is to make the capacity meter for 28 modules....
Also I have a Lexus GS-450h and I know if I can recondition this type battery

 

I understand you are in Greece and your Russian is better than your English. Send me an email via my site Testing Complex - HYBRIDS I may help you

 

hahahahahhah you have right...my english it is not good.....

 

I tried to get back some loss capacity on my Gen2 battery when I noticed the battery SOC dropping quite fast from 7 green bars to 2 bars then the engine would kick in. I tried to "rebalance" my modules while they were in the car, simply by dropping the battery SOC to 18% by keeping the car in Neutral and then letting it charge back up by driving. I did this several times and noticed my battery capacity seem to have improved. The discharge of the battery takes much longer than when I first started. Not sure if this will hold up, but it seemed to have worked and required very little effort to do.

 

i try to measure the capacity and charge/discharge with imax charger and the module increase the voltage to 9V with 2A in charging and i think the module is bending.I charge it in battery pack.