Additional Battery Project - Possible Extra 40 kwh

[jimbo69ny]

Here is the Rav4 Battery pack.

Pack power holes

 

[jimbo69ny]

Fiberglass battery box.

 

[jimbo69ny]

I needed a way to run wires through the floor to the R.E.T. I found this online but it wasnt large enough for 2 awg wires. So I made one. https://www.amazon.com/dp/B0111RNZD...colid=KP6FZYXMMC1N&psc=1&ref_=lv_ov_lig_dp_it



This is going under the rear of the car to pass wires to the trailer.

Matt tracked down the BMS/data plug for me.

Tesla pack dimensions for my eventual Tesla RET

 

[miimura]

I saw this video and thought of you, Jim.

https://www.youtube.com/watch?v=d2FCvW6S6Wk

 

[jimbo69ny]

No cell fuses like the Tesla modules though. Fine for a small bike that you can jump off of but in a car with high amperage demands you need cell level fusing in your modules. It would be nice if I could put it together like his though. It would be soooo much easier!

 

[miimura]

No cell fuses like the Tesla modules though. Fine for a small bike that you can jump off of but in a car with high amperage demands you need cell level fusing in your modules. It would be nice if I could put it together like his though. It would be soooo much easier!

So how are YOU planning on implementing fusing?

I still maintain that designing the pack connection for constant moderate amperage discharge is a better approach than tying it directly to the main pack and letting the current flow however it needs to.

 

[jimbo69ny]

No cell fuses like the Tesla modules though. Fine for a small bike that you can jump off of but in a car with high amperage demands you need cell level fusing in your modules. It would be nice if I could put it together like his though. It would be soooo much easier!

So how are YOU planning on implementing fusing?

I still maintain that designing the pack connection for constant moderate amperage discharge is a better approach than tying it directly to the main pack and letting the current flow however it needs to.

Watch the video in the very first post. I am going to be using 6 awg ground wire instead of bus bars but the same idea applies. His fuse wires are also quite short which increases the amperage needed before they blow. I am going to make sure I dont make them too short. In testing, it could take 20+ amps to blow fuse wires like he has them.

Building a pack so each cell sees the least amount of amps possible is a fine solution. However that makes the pack larger. In order to lower the amperage that each cell sees you would have to add more cells in parallel. As you can see in my previous post, my onboard battery pack is already quite large, larger than I wanted it to be in fact. Ignoring differences in resistance, I would be at 3.97 amps per cell. (350 amps / 88 parallel cells)

The biggest reason to have cell level fuses is to protect against a runaway "thermal" cell. Cells fail. If one goes thermal it will set of the cells around it. Its horrible. I have done quite a bit of research and cell fuses are a good first line of defense against an explosion. Cells go thermal when power continues to be dumped into it after it fails. With bus bars or the modules that you shared, nothing would stop a bad cell from receiving current. It would explode and catch all the cells around it on fire, then they explode too. With cell fuses, the fuse wire would blow before the cell is overloaded. No fire, no dead family.

 

[miimura]

I would be wary of soldering directly on the battery cells. This guy built a 18650 based pack for his scooter. He set up spot welding. If you soldered the wires to a tab and spot welded the tab to the cell, I think that would be a better solution. Even better, figure out how to spot weld or wire bond the wires to the cell like Tesla does.

https://blog.widodh.nl/2018/01/building-a-lithium-battery-for-my-electric-scooter/

 

[jimbo69ny]

I would be wary of soldering directly on the battery cells. This guy built a 18650 based pack for his scooter. He set up spot welding. If you soldered the wires to a tab and spot welded the tab to the cell, I think that would be a better solution. Even better, figure out how to spot weld or wire bond the wires to the cell like Tesla does.

https://blog.widodh.nl/2018/01/building-a-lithium-battery-for-my-electric-scooter/

I wont be soldering. I am going to be spot welding. Soldering hasnt proven to be harmful but I didnt like the idea either. Not to mention soldering will take much longer than spot welding. And when your doing both sides of 3700 cells, time matters.

 

[miimura]

Here is a screen shot taken from the video on the Kickstarter page for the modular pack building system, showing a possible fusing method. Of course, you would only have to do this on one side, the other side could use their screw-on busbar tabs.

https://www.kickstarter.com/projects/1354698863/diy-li-ion-battery-building-kit-make-your-own-1865/faqs

 

[jimbo69ny]

Here is a screen shot taken from the video on the Kickstarter page for the modular pack building system, showing a possible fusing method. Of course, you would only have to do this on one side, the other side could use their screw-on busbar tabs.

https://www.kickstarter.com/projects/1354698863/diy-li-ion-battery-building-kit-make-your-own-1865/faqs

Interesting. I didn't know they could do this. I still dont like it though. Id have to try to thread on a tiny fuse wire to each cell. That doesn't seem easier. Id rather tap it quickly with my spot welder and move on to the next.

Also, I do plan on doing both sides. If I only put a fuse on one side and it didn't blow for some reason. Or it did but somehow mated to a cell next to it, it could potentially continue to see current. A fuse on both sides is twice the work but I want it to be safe. I am going to be transporting my family and dog in this car. I am doing everything I can to make it as safe as possible. Of course there is still risk but my goal is to mitigate it as much as possible.

 

[jimbo69ny]

Did a little more work tonight. For the record I am so sick of working in 15 degree weather, crawling around under my car with a winter jacket and knit hat that constantly falls over my eyes.... I am really hoping spring arrives before summer this year but at this point I would accept fall.