Electrically secure connection of battery tabs

[Andy Haard]

Hi
I'm working on a way of connecting prismatic LiFePo4 pouch cells into a battery pack.

I'll probably use G10/FR4 for the isolators, as suggested by MQuack in the Mechanical section of this forum, see this animation (the green parts are the FR4 isolators):http://www.youtube.com/watch?v=mh9fptEnvcM The animation only shows a portion of the complete pack that will be made up of 152 pouch cells, 2p76s
My concern though is if pressing the isolators together using 3 M8 threaded rods will create enough pressure to secure the connections between the battery tabs in the long run in an automotive environment...?
Any taughts on that?

 

[the_emi_guy]

I would think you would want to separate the contacts from any source of moisture such as and ambient air. The DIY way of doing this is to gob Vaseline on the contacts.
If you are trying to make an electric car battery, there are other considerations as well (which you may be aware of): thermal monitoring, fusing and service disconnect.

 

[Topher925]

Battery tabs of pouch cells are normally welded together to bus bars or zipper fuses. Any other method such as clamping or some type of crimp has more resistance than what's allowable for most applications. And BTW, the battery tabs are the hottest part of the battery pack due to higher current densities and ohmic losses.

If welding isn't an option (as its very difficult to get right) you may want to try bar clamps onto a bus instead.

And don't ever ever ever put anything in between the battery tabs such a vaseline or what ever else. Thats just a recipe for disaster. The only thing that would be OK is something like electrical tape or a material that's designed for electrical applications.

 

[Andy Haard]

Thanks Topher, I certainly won't put anything between the tabs, other than alcohol to make sure there absolutely clean before pressing them together.
Welding isn't an option, as you say; it's very difficult to get it right and I like the possibility to be able to replace a bad cell without to much difficulty.
fyi, the load will never be more then 150 amps.
I'm also considering using isolators like this:

The pointy sharp screws will press through the battery tabs.

 

[the_emi_guy]

With this many amps going through non-welded contacts you probably should consider doing something to mitigate moisture. Alcohol often contains water. You may be better off cleaning with something like MicroCare Pro-clean. There are products out there that provide a more professional moisture seal than Vaseline such as 3M Scotch 1600 anti-corrosion spray.