Gen II Prius Individual Battery Module Replacement

Cell polarity reversing while on discharging is just a theory. This happens when a weak module sits self-discharging for weeks.
The battery I just cycled had been discharged for about 30 hours. I forgot about it because i didn't really care. That battery came from a recycling management, pulled from prius with over 200k miles.
The voltage was 0.3 volts for all 28 modules, after discharging the whole pack for ~30 hours.
On the same battery, I left it discharged to 1.5 volts for 4 hours with no load. Now it's charged to 239.5 volts. I'll test the battery in a few days when i have time.

 

When you are discharging a series string of cells (6 cells in series for a module in my case) and their initial SOCs differ, the lowest SOC will run out of charge before the others. As the same discharge current goes through all of the cells, if you continue to discharge the module you WILL reverse that "weakest" cell. That is what happened to my 2004 Prius battery at 195k miles which started me on studying the process of "balancing" modules.

JeffD

 

Hi all, I am just calling back past here after about oh 7 and a bit years lol

So the pack I rebuilt for my daughter's 2008 back at Easter time 2017 just let go after lasting almost as long again as it did from new! 7+ years and about 130/140k km.. not bad! sorry Kiwi.

After all these years the failed pack still has capacity but the car sat for 9 months while waiting for an engine swap then soon after getting back on the road .. P0AA6 526-612 = UR STRANDED! hey it's been 7 years, I'm not complaining.

So.. I put another "tested good" spare 2008 pack aside around a month after this one got built back in 2017, I have grid charged the spare pack (along with a few others I've picked up) every 12 months since

Last couple days I have been testing the spare pack ready to put it back in service, open circuit voltage suggested every module is still in great shape with the acception of positions #1&28 which are always bad around here even on the best packs! but I found this one module in position #7 with lower capacity and higher ir than all the others, then I noticed it suffered a broken vent neck while in storage, which leads me to question! ...

How or why would mechanical failure of the vent neck cause the said module to deteriorate faster than the others, I mean the vent it's self should still work fine right? just the neck for the "stinky tubes" has snapped off, what am I missing here?

My first thought when noticing the broken neck was to simply plastic weld it back down but obviously the broken vent has compromised this module somehow, I just can't quite get my head around how unless it's let oxygen through or something?


Matt

Posted via the PriusChat mobile app.

 

Why have you never restored the capacity in this battery in 7 years and just let it reach the point of no return?

 

Hi Carall,

Not sure how you got that idea sorry, I done quite a few grid cycles on it over the past 7 years that it was in service, it ended up failing with a leaking module not low capacity!

Leaking modules are becoming very common around here! particularly on J prefix modules!

Granted I should have done a cycle or two after the engine swap but didn't have time the daughter needed her car back, seeing the pack failed with a leaking module I doubt it would have helped anyway ..

The "spare pack" that I am currently working on was also deep cycled/ reconditioned before storage and topped up annually BUT it has a broken vent neck on one module which has somehow compromised capacity of that module, I'm wondering if anyone has ideas on why the broken neck would have such effect

Posted via the PriusChat mobile app.

 

You wrote that you rebuilt the pack in 2017, 7 years ago. I didn't know the whole story.
Where has this battery been used: city traffics, country roads, highways?

 

No worries Carall

Its mostly used in the city, not a lot of highway.. I only mentioned the failed pack for interests sake, and to lead on to my question about ....

Another pack which sat in storage (with annual top ups) for near the same amount of time (2017) one module in this pack has a broken vent tit and that module now has lower capacity compared to all the others In that pack, it's doing my head in trying to figure out how a broken vent tit could compromise capacity

Cheers

Matt



Posted via the PriusChat mobile app.

 

Perhaps evaporation of the liquid electrolyte..

JeffD

 

Hi JeffD

Good thought, maybe the broken tit let's it gas out more than all the others when I do annual top ups

Posted via the PriusChat mobile app.