# Tesla's Battery Module Covers - Mica Shields



## kennybobby (Aug 10, 2012)

i think they do that to save money during manufacturing and assembly--these are alignment features with one precision position (i.e. expen$ive) and 5 open tolerance positions (cheaper and quicker to build). 

It appears that they use some sort of red silicone RTV compound (e.g. Permatex gasket maker) to hold the white plastic buttons to the mica sheet. Generally the red has a higher temperature rating than clear or other colored products.

The white buttons appear to have a centering nipple.

The cover sheet in fig 2 with the circular and oblong shapes provides a recess for the centering nipples such that the mica sheet lays flat. The lower right circular shape in fig 1 has a smaller diameter recess into which a nipple fits tightly--this is the precision position that sets the alignment. Then the other shapes are larger diameter or oblong to allow tolerance in positioning of the nipples to lodge and let the mica sheet lay flat. 

So only one has to be exact, and the other five just have to be close, for the cover to fit. Imagine how difficult and expensive, and how many covers would be rejected, if all 6 positions must match up so the nipples fit tightly and exactly in the recess?

Do you know how to make some LED goggles?


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## Jbrewer106 (May 7, 2015)

You would be better off to resuse the whole battery pack, however it's rather large to fit under most project cars and would require raising the car frame suspension for mounting or better yet order a power wall and use the complete pack


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## Kildare (May 17, 2021)

Is Mica still used in this way?


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## electro wrks (Mar 5, 2012)

Enjinia said:


> I was researching Tesla's batteries and found that they use Mica Shields to cover the top and the bottom of the battery modules. However one strange thing I have noticed was, the thermoformed transparant cases had this circular shapes and same shapes were used on Mica shields to fit on the transparant cases(Shown in Fig 1).


The dimples(you call them circular shapes) on the transparent covers(you call them cases) are there to protect the delicate whisker wire fusible links that connect the cells to the main conductor plates of the module. The spacers glued onto the mica sheets are there to hold the sheets in place. The sheets are not glued to the battery housing (the outside metal part) and are only held loosley in place by a few small pieces of double sided tape. The spacers also generate a gap between the module and the mica sheet, as per Tesla's design patent, to allow hot gases to escape in the event of a thermal runaway.
The mica BTW has one of the highest temperature and electrical insulation ratings of any material. Tesla uses it to cover the sides, ends, and faces of the modules as well as exposed HV wiring. If you are buying Tesla modules, you should try to also get these mica sheets along with them. They would make a well designed battery box that much safer.


Kildare said:


> Is Mica still used in this way?


I believe the models S/Xs still use the mica sheets. as well as the 3/Ys.


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## Kildare (May 17, 2021)

electro wrks said:


> The dimples(you call them circular shapes) on the transparent covers(you call them cases) are there to protect the delicate whisker wire fusible links that connect the cells to the main conductor plates of the module. The spacers glued onto the mica sheets are there to hold the sheets in place. The sheets are not glued to the battery housing (the outside metal part) and are only held loosley in place by a few small pieces of double sided tape. The spacers also generate a gap between the module and the mica sheet, as per Tesla's design patent, to allow hot gases to escape in the event of a thermal runaway.
> The mica BTW has one of the highest temperature and electrical insulation ratings of any material. Tesla uses it to cover the sides, ends, and faces of the modules as well as exposed HV wiring. If you are buying Tesla modules, you should try to also get these mica sheets along with them. They would make a well designed battery box that much safer.
> 
> I believe the models S/Xs still use the mica sheets. as well as the 3/Ys.


Many thanks.


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