Possible modification to HV battery

Well... I've been chatting with a guy who often takes his gen3 2011 to the race track and we've definitely gone through what it would take to have easily swappable packs...

I've used loaner packs to help Gen2 people get by while I repair their pack and while swapping a pack can be done quickly, it always seems like a lot of work and the all the nuts and bolts involved were not designed for repeated use... However a redesign of how fast you can swap a pack is probably more effort than its worth just for wack-a-mole. But maybe for the racetrack?

From what I know of Gen2 cars, I'd work on vehicle chassis stiffening via welding a secondary frame around where the battery pack goes to take place of all the bolts and plates around the pack. Then I'd have a metal frame that would drop down on the pack that could be lock in place with a single metal pin or bar. Then redesigning the interior upholstery to speed things up to. But someone would have to show me a nice stack of money if they wanted to see that dream come true.

 

The pack is squeezed together with a lot of force by design. If you could somehow pull a weak module out, the clamping force would instantly reduce that space making it impossible to slide a new module back in. Also, the cheese grater exterior of each module locks them together so sliding in/out without a lot of clearance would be next to impossible.

Some folks have used an engine hoist to remove/install the pack.

KISS: ask a friend or just hire the neighborhood kid who mows grass for 30 minutes labor.

 

I played the wack-a-mole game and getting the pack in/out is easily the hardest part and yes I definitely considered trying to work on the pack inside the car after the second time. IMO, that would actually make the job harder especially for someone physically impaired.

There's also the safety issue of doing 100% of the procedure with a grounded pack.

 

The clamped assembly of modules is kept in place (laterally) by the 4 studs (1 on each corner). As designed, only 2 studs have nuts installed. Each module has one machine screw locking it to the bottom base plate of the case. Being fastened to the base plate of the case ensures the 28 modules remain in straight alignment even when swelling pressure is present, allowing the clamps to do their job. If a person were able to design a suitable replacement to keep the modules firmly pressed against the base plate, then I see no problem. If this means a bracket device at the bottom, then so be it. The main concern is that it MUST keep the modules clamped to the base plate.

The 28 modules can be thought of like a coke can. I can take an empty coke can, set it on a level table, and put 25 pounds on top of it and it won't crush. If any side of the can deforms even slightly, like if I poked the side of it, the can will instantly give way and crush. The module pack is the same way. As long as it's maintained in straight alignment with the swelling force, everything is fine. If it's allowed to start bowing upward or downward, even slightly, it will pretty much instantly go out of control and turn into a horseshoe, including blowing out the metal bars.

There is air gap between the metal bars and the modules, which would allow this slight "bowing" to occur if the modules were not fastened to the base. The metal bars are designed for tension stress not the bending stress that would be applied if the modules bowed upward. This is one of the reasons that crazy lady from the UK failed when she tried to add multiple Gen 2 battery packs to her car to make it more of an EV. She had no baseplates, just clamps holding the modules.

 

You might want to chat with my buddy Joe at 2nd Life Battery... He's wheelchair bound and rebuilds many battery packs every day without much help. He'll have some tips and tricks for you.

As for packs that are warped by heat... Had a pack where the plastic end caps melted outward on the bottom and still look normal from the top. The modules on the ends bowed out with the plastic with each inner modules warping less, but still slightly, about four modules deep on both sides. So I replaced the caps and the two most warped modules on the ends and a few thousand miles later remaining modules that were only slighty warped had flattened out and were no longer warped. As in there's a lot fluidity to the structure once it gets hot and any room/opportunity from them to move, bow out or turn into horseshoe they'll quickly do it if given the opportunity. So they need to be locked down as best as possible!

 

Even modules with blown tops give pretty good voltage readings... It's once things heat up that they act like jello so it doesn't matter how good the voltage readings are if they can't hold their shape or vaporize or leak electrolyte.

 

Not sure your point @ASRDogman ? When they swell they are indeed damaged, but there's degrees of damage. You have to look at my pics to see it... The swelling on the modules on the ends showed no damage from the top, but flip them upside down and you can see the plastic heating up caused the bottom of the two outside modules to push out into the near melted plastic. Those modules had relatively decent voltage readings and were not damaged enough to cause cells to fail, but I replaced those two. The neigboring four modules on both sides had decreasing amounts of bottom of cell bending, but much, much less than the ones on the end. The person who owned the pack couldn't afford to replace more that a few modules, so I made do with what I had. Then almost a year later when it was time to replace the next bad module I found the the slight warping of the bottom of the modules was gone now due to replacing the white plastic end caps so they were again a solid flat surface and not bowed out. This, over time, especially when he hybrid cooling fan started to fail do to corrosion in the wires flattened out the slightly bent remaining modules.

 

yes, for a year now...

 

Once a battery is damaged, it won't heal. How long will it last after the damage??? Only God knows.
I agree sometimes you have to make do with what you got, and hope for the best.
This person should start putting money aside for a new battery. If you are not charging them for the
work you are doing, then that helps them. But factor in your labor, and you've bought a few battery kits.

I had a a caliper with a sticky puck, on my van. When the pads got low, I swopped then to the other side.
So when it came time to replace them, all 4 front pads had even wear.
Eventually, I took the front calipers apart and cleaned them and now they wear evenly.
But it doesn't matter, I drive my Prius!

 

Then their ya go!
Are you buying new cells, or used ones?