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Failed Model 3 HV Battery - Out of Warranty - DIY

I'm a complete laymen, and know that you're already past this point, but just wondering - could you have dumped the bad module out of the original pack and just kept the functioning 75% (or whatever) capacity of the original pack?

possibly. but you cant replace modules (despite what musk says). If one module fails the entire battery will fail and for the BMS to work all modules have t be degradating similarily otherwise the BMS gets confused.
 

miimura

Well-Known Member
Aug 21, 2013
7,319
7,304
Los Altos, CA
I'm a complete laymen, and know that you're already past this point, but just wondering - could you have dumped the bad module out of the original pack and just kept the functioning 75% (or whatever) capacity of the original pack?
The modules in Tesla vehicles are all arranged in series. If you take one out, you no longer have the correct working voltage. In a S or X, there are 14 or 16 modules, so taking one out has a smaller effect. However, there are only 4 modules in the 3 & Y 2170 packs, so running without one is completely out of the question.
 
One thought would be to use your original parts and consider the ones from the replacement pack to be spares. In general it just seems less risky to me. Of course the experts might have much better insight into this.

Did your $35k net included parting out the old pack?
No, but I honestly don't expect to get much from that. Maybe $2-3k. Car was $23k, battery was $9k, shipping and taxes added up to $3k. Best-case is probably $32k and many, many hours of learning. :)

I found a video on YouTube related to this.
This is not a solution, unfortunately, as explained above by @wk057 - anything short of entire pack replacements will eventually lead to a voltage imbalance that will result in the BMS refusing to close the HV contactors. Model 3 BMS appears to be extremely sensitive.

This is the first documented instance I am seeing of a Model 3 battery imbalance issue. I was under the impression the "new battery chemistry" (if that's even a real thing) in model 3 would alleviate these types of problems.. Perhaps a naive/ill-informed assumption.

Should we expect similar life in our batteries as much as earlier Model S/Model X? Maybe 250-300k on our batteries if we're lucky?
I still haven't found why this brick is discharging, but I think signs point to a tiny internal short in a cell. There are 4,416 cells in this pack, so it is entirely possible for a ~150k mile car to have an issue with one of them. The draw isn't enough to melt the fusible link, but it's plenty to overcome any balancing. I think (and hope) that this is a rare event, but it's still a little early to tell since most Model 3s are still under 50k miles, much less 150k.

I'm a complete laymen, and know that you're already past this point, but just wondering - could you have dumped the bad module out of the original pack and just kept the functioning 75% (or whatever) capacity of the original pack?
Definitely not on the 3. Even if you could magically make the software ignore the missing BMS board, you're well below minimum voltage requirements for the inverter. With some configuration changes, it COULD be possible to remove 2 out of 16 modules on an S depending on the pack, I guess. I don't think it's been worth it for anyone to even attempt, though.

As for an update on the car, stay tuned. Going to make another post for that.
 
No, but I honestly don't expect to get much from that. Maybe $2-3k. Car was $23k, battery was $9k, shipping and taxes added up to $3k. Best-case is probably $32k and many, many hours of learning. :)


This is not a solution, unfortunately, as explained above by @wk057 - anything short of entire pack replacements will eventually lead to a voltage imbalance that will result in the BMS refusing to close the HV contactors. Model 3 BMS appears to be extremely sensitive.


I still haven't found why this brick is discharging, but I think signs point to a tiny internal short in a cell. There are 4,416 cells in this pack, so it is entirely possible for a ~150k mile car to have an issue with one of them. The draw isn't enough to melt the fusible link, but it's plenty to overcome any balancing. I think (and hope) that this is a rare event, but it's still a little early to tell since most Model 3s are still under 50k miles, much less 150k.


Definitely not on the 3. Even if you could magically make the software ignore the missing BMS board, you're well below minimum voltage requirements for the inverter. With some configuration changes, it COULD be possible to remove 2 out of 16 modules on an S depending on the pack, I guess. I don't think it's been worth it for anyone to even attempt, though.

As for an update on the car, stay tuned. Going to make another post for that.

ithought the modules are wired in parallel not in series? so removing a module should just reduce capacity, not voltage?
 
Spitballing…. In theory if you replaced a “bad” module from a 143K Model 3 with a “good” module from a 100K Model 3 it should work because the good module is similarly degraded (similar IR, similar max voltage), right?

143K miles on a 300 mile Model 3LR is about 500 full charge cycles. I’ve seen NCA li-ion lifetimes listed between 500-1000 fully charged cycles. Is it worth salvaging any part of the battery at his point?

I also assumed your FLIR could find a bad individual cell… say if you put a load on the module that would force all cells to discharge and the cell with a high IR would immediately heat up more than others. Still, replacing an individual cell sounds extremely difficult.
 
Wanted to provide an update since it's been over a month and some progress has been made.

The pack I bought had damage to a coolant port at the front that would require lid removal to repair, and some heavy scratches and dents to the bottom of the pack casing. Not sure how much of it was from the accident (rollover) vs. from the salvage yard forklifting things everywhere, but oh well. Decided to use the old, good casing with the newer lid + penthouse.

Removing the lid is fairly easy (as explained in the original posts), so there weren't any issues there. We were surprised to see a small amount of coolant in the back left corner of the case. It had been there for a while. The damaged coolant port was at the front of the case, so we're not sure if coolant came from there after the accident or if some coolant had leaked from the nearby module connection. Coolant leaks are a concern, especially since it is hard to check for them once the lid is on and the pack installed into the car.

We used some straps and heavy duty suction cups to lift the modules out, which worked well. Setting the modules down a soft surface was important since the fusible links on the bottom of the module are very delicate. If one of the links got broken, we're back to doing this all over again eventually. It's possible we wouldn't know about it for weeks until multiple charge/discharge cycles.

Interestingly, one of the locater tabs that sticks out of the inner modules had been broken off before removal (there were absolutely no plastic pieces in the battery case, which would be very obvious). To me, this means that Tesla had installed the module despite some minor exterior damage to the plastic casing of it. Not anything safety-critical, but interesting to note nonetheless.

After the new modules were transferred to the case and connected, we pressure tested the lines by capping open ends with balloons and inflating them with ~5psi (as far as I know, the coolant system only sees a few psi anyway). The balloons didn't deflate at all after 10 minutes, so we figured the pack coolant connections were good and proceeded to putting the lid on after plenty of triple-checks.

For resealing the lid, I decided to use a combination sealant/adhesive known as Teroson MS 5510. It wasn't anything fancy, and at $17 a tube I wouldn't expect it to be, but I think it will last. A tube and a half was plenty. Scraping off the old sealant from the lid and case and then cleaning any dirt/grease took an hour or two, sealing and installing the lid took 10 minutes.

Continuing in another post to be able to attach more photos.
 

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Once the lid was sealed and installed, I was able to start putting the penthouse components back in. Honestly, the penthouse is a beautiful work of engineering. The only thing that scares me about it are the PCS coolant lines, because a leak from those would probably be a bad time, but they are a necessary evil.

Since I was using the new lid anyway, I decided to leave as many of the new components in whenever I could. The only "old" component I used was the pyro fuse, since the new one was blown (as expected) when the airbags deployed. Everything else, including the HVP and PCS, were from the "new" pack.

Installing the pack into the car took an hour or two, mainly because everything needed to be lined up perfectly and torqued in a specific order. After connecting everything, the car turned on and gave some expected errors about version mismatches and HVIL (high-voltage interlock). A redeploy/update takes care of the mismatches, and putting the penthouse cover on fixes the HVIL errors (I was wanting to watch for coolant leaks in the penthouse, just in case). As far as I can tell, there are no errors related to the accident, and no major errors shown currently.

The SOC was at 41%, which is 1% less than what I had guessed based off of the module voltages earlier. The estimated range at full charge fluctuates around the 310-312mi area. I am hoping the fluctuation evens out after a discharge to 5% and charge up to 95% or so. I have already ordered a diagnostic cable and OBD-II reader to use to monitor brick voltages and other parameters.

To be safe, I removed 5 nuts that secure the breather and fire vents on the left and right sides of the rear of the pack and used a borescope to check for coolant. Luckily, there didn't seem to be any coolant anywhere, and the sealant looked great on the inside.

Sidenote: it is somewhat concerning to see so many potential openings in the penthouse/platter area as well as the rear of the case. Many of them are only sealed with simple rubber compression seals. Contrary to popular statements, driving your car through bodies of water will always be a gamble, so please keep this in mind. Internal coolant connections are another risk, but they use two o-rings and appear to seal well when in good condition. Due to their importance, I used o-ring lubricant and inspected each one closely before reusing them.

The car still needs various plastic pieces on the outside and inside installed, but it appears to charge and HV components such as the AC compressor and PTC heater are working properly. The drive unit works, too. My main concern now will be discharging and charging a few times and seeing if everything remains well with the brick voltages/BMS.

I anticipate another recap/update in about a month or two, and I appreciate everyone's interest in this topic. I'll try to answer any questions you all might have.

So far this has been a very long, educational project. If things all continue to go well, I believe I may be one of the first Model 3 owners to successfully swap their own modules like this.

I would also like to add that it is going to be difficult to find good replacement packs to use if anyone decides to try to perform a similar repair. Collisions, especially frontal (which I intentionally avoided when buying a pack), are not friendly to these packs, and transferring modules and removing/replacing penthouse components is much harder than just changing out an entire battery pack.

I can see many points that even Tesla service centers could mess up a "simple" pack swap, and there's a reason they don't refurbish these packs at your local service center. I genuinely feel bad for any service tech that has to change out these packs in the future, especially as more and more start to fail in the next few years. At least they're not doing module swaps.

Hopefully Tesla makes service center expansion a priority soon. In 5 years, there will be tens of thousands of these vehicles with similar mileages or potential for battery issues, and service centers/techs are already plenty busy with existing vehicles.

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Still on V10, so I get to have an actually good charging screen. Seriously, why is V11 so bad?​
 

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I thought the Model 3 battery and motor had an 8 year unlimited mileage warranty. Don't they? My 3 is an April '18 build, and I'm hoping for the original battery to make it 7 years and 10 months then crash out then get a FREE warranty replacement pack!

Are there flaws in my plan?

Tesla changed the warranty for vehicles 5 years ago. See Vehicle Warranty

Older vehicles have the 8 year warranty you mention.

1648327977318.png
 

timk225

Active Member
Mar 24, 2016
2,083
2,396
Pittsburgh
I'm going to have to go through my papers for my car. I remembered it being 8 years unlimited miles, not 8 years OR 120,000 miles.

And now there's more confusion. At the time I got my 3 in May '18, there was no AWD model. My 3 was the Long Range version, despite the fact that there was no shorter range battery for over a year after I got my 3. Now my 3 is being called the RWD version, which it is. So do I follow the Long Range or the RWD guideline?

Essentially, I'm looking for a way to get something for nothing, which in this case might be a free new battery at almost 8 years. My 3 already has 82,000 miles on it after a little less than 4 years, so I'd be up around 160K by the time I get to 8 years.
 

Knightshade

Well-Known Member
Jul 31, 2017
15,709
29,859
NC

SteelClouds

Member
Supporting Member
Nov 12, 2021
295
445
CA
I would expect to see specialty shops for this kind of work to start appearing. A dealer would sub this out to the special shop vs trying to do it in house. Much like dealer dont rebuild engines or transmissions much any more in house.. they just treat the old as core and order up a rebuilt unit. I have two shops near me here that specializes in Hybrid cars so it's starting to happen. They will install a rebuilt pack or let you do a DIY job.
 

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