Gen II Prius Individual Battery Module Replacement

Tech,

You have one module with a bad cell. When a module is charged, it will get to 8+ volts. The surface charge will then dissipate leaving a good module at about 7.8-7.9 volts where they will stay (with a slow self discharge rate of about 0.1v / 3 months). The 1.2 volt difference is one cell with no voltage.

A better test than self discharge rate is a load test (pull several amps for 30 seconds and read the voltage drop. the voltage should recover to almost its initial value when the load is removed. Any modules that drop significantly more than the others are not worth using.

JeffD

 

The video below is about the difference between the Prius transaxles in the (first and) 2nd and 3rd Prius generation transaxles. I gave me some insight into how the Prius works in general, so I hope everyone will consider it at least somewhat helpful even though it is "off topic". It was originally posted in 2012 but it appears the author had updated it with at least one correction correction.

I did not realize that MG1 and MG1 (the two electric motors) are inside the transaxle case. They are also much smaller than I realized. Since he does not cover the complete assembly of the tranxaxle, I am not sure if he is also showing the "continuously variable" transmission.

 

The video shows most of the eCVT of the Gen 3 Prius. The Gen 4 eCVT is even more compact.

And yes, the video shows how the continuously variable transaxle functions except that the stators are not shown, just the rotors.

 

Hello everyone, this is my first post here and i found some very helpful information around the community is great of helping so... i figure why not ask

I'm rebuilding the battery pack of my 2007 Prius Gen II
Currently on my last step - equalization of all the modules before i put them in the car.
I have my harness ready to go.
All my modules are between 5000mAh and 5500mAh (except 8 who are 5900-6400mAh)
I know that i have to discharge them down to 7.6V or around 4500mAh (before i put the equalization harness on)

1st question:
I read somewhere here that even if you discharge the modules to 7.6v the ones who had the better/higher capacity will start to creep up very fast anyway - should i just do a extra cycle DCHG/CHG cycle 6.3v to 4500mAh to avoid the creep up - or the equalization will take care of that?

2nd question:
I read here that even if i discharge all to 7.6V i should pair them by the final DCHG mAh they had when i did all cycles and as close as possible to each other like (5047 mAh pair with 5055mAh and no more then 200mAh diference) so... since i have 4 pair's that are with way more capacity and in very good condition (5900-6400mAh) where do you advice me to put them in the pack? Is it better to put all of them in the middle of the pack. Since GEN 2 have 28 modules that would be from position 10 to 18 - OR - split them on... 2 pairs in the beginning and 2 pairs at the end - OR - spread them evenly across the whole pack?
Basically where is the best place to position them?

3rd question:
I have a single charger and a quattro charger so the max that i could work with is 5 modules at a time. Could i just use a 55W Headlight bulb paired with a volt meter so i see the voltage drop and discharge to 7.6v drop ( i was using the same method when i check the OCV and CCV to determent which module have a bad capacity from the get go)

Thanks in advance i would appreciate any advice.

 

Hmm, read through this thread. After getting the triangle of doom, let the car sit for a few days and pulled the battery Friday morning. I was going to buy a rebuilt but after pulling the cover and putting a meter on the cells I am considering just rebuilding myself.

The two outer cells read 7.97v after sitting for 5 days. 1 cell reads 6.7v (obviously bad) The rest are at 8.05 to 8.068v. What would you guys do? I hate to get a rebuilt battery with unknown cell quality when it appears most of mine are pretty good and have a really low voltage bleed off.

 

Well the 6.7 is one that is likely bad right now. Eventually over time you will have others fail.
The one you replace will not match what you have, but hopefully it will be close enough to work for a while.
Periodic rebalancing may help mask the discrepancies... well... at least until it doesn't

 

I'm reconditioning our Prius battery now and just wondering about the charge rate. I've read mixed suggestions on different forums. Some say 5A, others 3A, 2A, etc. Another site about reconditioning NiMH batteries suggested to start out the process with a .6A current for a long time to slightly overcharge the module and let cells with less capacity get to a higher SOC. I would love to get some advice from the more seasoned reconditioners out here. Also, has anyone else had issues with the (chinese knock-off) Imax B6 chargers not properly detecting the delta voltage? Thanks for the help!

 

Hi Tedd, I found hobby chargers don't seem to detect delta peak very well under 1c so I always charge at 1c/ 6.5a clamped in the pack with a pile of fans running.

If charging under 1c I tend to watch the charger screen and as soon as I notice the voltage delta peak the module has usually started to swell just a tiny bit I then manually terminate charge!..

b6 knockoffs do not properly detect delta they are useless for this application, you could maybe use them at 5a charge rate if you carefully monitor them once above 80% soc so you can manually terminate charge if they don't. Not sure what chargers to suggest these days the ones I use are no longer available by about 10 years!

 

I used a pair of Hitec x4 chargers at 2A charge rate and it worked fine for me but having said that I would probably do it differently now knowing what I do. I would have instead bought a Hybrid Automotive charge/discharge setup, installed it and then grid charged the entire battery. I would then pull out the battery pack and load test every module individually looking for large (bad) voltage drops. Source good modules and then replace the ones that tested bad. I would also make sure you have a mini VCI cable and techstream installed on a PC laptop because it is invaluable to be able to view the battery bank voltages in realtime under both accel/decel. If you have a bad module you will see the worst offender drop to the min bank voltage under accel and then it will jump over to the max voltage under decel (charging mode). Once you have your battery working again I would use the HA setup to run the 3 step discharge/charge process in a effort to minimize any capacity mismatches which might exist afterwards.

 

The other reason you will want to use a HybridAutomotive charger after you do a replacement is because the replacement module will never perfectly match your original modules.

There will always be some drift between the original modules and the replacement. The more drift, the more often you will need to use the charger to compensate for it.

Until the next module fails.

And then you get to start all over again.

But the charger will definitely help mask the differences between the mismatched modules.

 

Not like this thread isn't long enough but I thought I would post these Techstream screenshots since it may help others see what a bad vs good battery looks like and what to looks for. The first 4 shots are of the bad battery (had a bad module in block 1, you can read all about it back on pages 11-13 of this thread) and the last 2 photos are of a new low mileage battery I just got for cheap (around 40K miles on it) for comparison. I was having another issue with the vehicle (no EV mode) when I picked up the new battery but turned out my old battery (after replacing the bad module) was just fine so now I have a spare. You can really see why the block 1 is bad under hard acceleration as seen on the 1st photo below but the others also give hints too. Biggest thing you usually see is that the weakest module drops to low voltage on discharge and then swings to highest voltage during charging. If you consistently see the same block appearing and the voltage difference under acceleration is large, then it's almost assuredly at least 1 bad module in that block. All I can say is mini VCI is an absolute lifesaver, anyone doing DIY on these hybrids should have one IMHO.

 

Good data MTL, there's a pattern forming for first and last modules, i see this all the time in high cycled prius packs, 1&28 (and others) often have low cap and high SD

 

Welcome to the Wicked side of Techstream.....lol
That is what is required on all Car's this day's...
Thank you for posting...i was trying to Start new Thread on OBD but this will be good enough

Posted via the PriusChat mobile app.

 

I took your advice and picked up an HA reconditioning package. Thanks for the suggestion! Is it safe to complete the grid charging and equalization while the battery is disconnected from the car, like say, in my living room or garage at a good temperature? I have seen much documentation stating to perform the charge while the battery is hooked up to the car, but I've already got the battery out with the cover off and everything exposed. Maybe like @ozmatt, I will surround it with fans during the process. Any suggestions would be greatly appreciated. My plan at the moment is:

1. Record voltage drops on individual terminal load tests
2. Grid charge the battery to full capacity
3. Record voltage drops on individual terminal load tests AGAIN
4. Decide which modules are bad, and replace.
5. Battery reconditioning and equalization (3 full charges and discharges)
6. Reinstall battery in car. Leave HybridAutomotive charging harness in place for easy future reconditioning maintenance

 

Hi Ganta.
normally when grid charging a pack in car you would have the prius blower fan powered up with an external 12v power source forcing fresh air past the modules evenly, modules wont charge as efficiently without good cooling. If your restricted to charging the pack external to the vehicle you could run a few powerful fans directly over the top of the pack blowing air past each module but its not ideal, atmosphere cooling is nowhere near as efficient as cooling a sealed pack with the factory blower running. Your method/ plan seems reasonable to me.. Good luck with it

 

See my suggestion above. Make sure to keep the modules as cool as possible during any charging process (no sun, lots of moving air, etc). The other critical part of this process above is to ensure you source good modules with decent capacity left. You aren't testing capacity in the above scenario (which the Hitec X4 did do) so it is important to source them from someone who did test them for having good capacity remaining.

 

Here's an update on my experience for the non recondition crowd. I replaced a pair of module 6 months to the day ago (1 was bad I was told better change a pair) and now battery trouble and troubleshooting shows 1 bad module. (different than the replaced 2). I had 1 module sitting in the garage for 6 months that was from the original battery modules and it tested at 7.6 volts so has lost no voltage in 6 months of storage. I replaced the bad with this module and all is well again. Car is 2005 with 242k miles. I will order 1 extra module to keep in garage for when it happens again.

This time when the module went bad and the dash lit up my car continued to run near perfect. I felt comfortable with driving it for 3 days after xmas lights.

 

****update**** The Nov25 triangle of death replacement lasted about 3 m 1 w --- I should learn to keep my hand off the EV button i installed - in heavy traffic after a long day at a long light, you tend to forget to push it again back when u want the engine -- likely that is why i had the failure again just before Feb25 -- i recall what happened, i was sick and under heavy accelration i think soc was at 30% and that through the triangle .. i was getting code for bank 9, which i think it counts from the computer (bank one) to the end (bank 14)... all were about high 7v except one which was 6.6 .. which was replaced and so far so good and its better to not use ev if u think u might for get to turn it off again -- better to drop a few mpg then to risk having another cell drop out when the car has nearly 150k miles .. i was able to jack up one end of pack and slide about 10 cells down and replace the bad one without dismantlying and removing the whole pack, i did it in one day , actually about 3 hours on a sat am, back torsions, i saved buttoning up most of the rest of the upholstery and seating until the next day ...

 

On the Gen II to module count starts at the end opposite the HV battery ECU.

Except if you are using the EV button to cut the ICE while stopped at a light with a long cycle, you are misusing the EV button, it will be costing you MPG, not saving it. You also may be missing the opportunity to move from stage 3a/3b to stage 4 in the hybrid warm up if this ICE running while stationary is happening in the first 10-15 min of the trip. If you find yourself in heavy slow moving traffic for an extended period, you are just best to let the car "smarts" manage the battery charge. It will do just the bare minimum to keep the battery at 3 bars, and when you finally break free it will charge back up to its happy place. Unfortunately, you will take a (MPG) hit in that type of traffic. In any case, if you forget, the system will kick you out of EV (but not limited to) whenever you request power, go above 42 mph or the battery gets low.

 

this am ()mar 14 2017)( the 12v battery died ? i was using a 20ah sla battery that goes in a rechargeable lawnmower for i dont know how long .. car started fin this morning.. got half way to work and in a 55mph area the whole thing just died, as if the wind got sucked from it, no engine no power no lights, just coasted and hard breaked (no power assist) to the curbside and luckily was able to further push to a half decent safe area .. then paid road side service 3.5$ / gal because i asw the stupid fuel guage blinking 1 bar when i knew it was half full.. and after driving about a mile , the fuel gueage went back to 3/4 full .. damn thing ... really pissing me off with that stupid stuff ... the battery does not nee td to be a glass matt or exotic agm chemistry , 12v lead acid works .. its very wierd that the thing died cold like that in the middle of highway speed though .. btw , 7/11 was wanting $15 for a 2 gal fuel container.. i wasnt going for that !!!