Battery Connections

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Battery Connections

Electric Vehicle Discussion List mailing list
With all the discussion about Tesla batteries, how do they attach all the thousands of  batteries together?  Soldering, welding?

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Re: Battery Connections

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Welded. By a robot.

Solder is a terrible idea if any heat at all is anticipated because it
loses all structural integrity when melted. In fact solder is used as
slow blow thermal protection in relays.   High heat brazing would do
better, but you can't heat the cells that much.

Here is a close up.
http://files.wizkid057.com/teslapack/2014-08-19%2019.12.44-1280.jpg

Here is a bunch of images of the pack.
https://www.google.com/search?q=Tesla+pack+teardown&rlz=1C1AOHY_enUS710US714&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi__-qJsqXTAhWHdSYKHVw1DRwQ_AUIBigB&biw=1325&bih=898&dpr=1


On Fri, Apr 14, 2017 at 8:53 PM, ROBERT via EV <[hidden email]> wrote:

> With all the discussion about Tesla batteries, how do they attach all the thousands of  batteries together?  Soldering, welding?
>
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Re: Battery Connections

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In reply to this post by Electric Vehicle Discussion List mailing list
Robert,
Welding. Their 24V modules consist of 6 series banks of several dozen
cells in parallel,
It really is enlightening to look at some high-res pictures of a module,
you can even find them
On Ebay. You will see that each module consists of a "U" where
alternatingly (starting from one
Contact) the metal plate with the welded wires carries the current back
and forth in 3 sections
In each leg of the "U" and the contacts on the top of the "U".
It is clearly visible in this ad for example:
www.ebay.com/itm/10x-Tesla-18650/162462368115
Cor.

-----Original Message-----
From: EV [mailto:[hidden email]] On Behalf Of ROBERT via EV
Sent: Friday, April 14, 2017 5:53 PM
To: [hidden email]
Subject: [EVDL] Battery Connections

With all the discussion about Tesla batteries, how do they attach all
the thousands of  batteries together?  Soldering, welding?

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Re: Battery Connections

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On Sat, Apr 15, 2017 at 3:06 AM, Cor van de Water via EV <[hidden email]>
wrote:

> Robert,
> Welding. Their 24V modules consist of 6 series banks of several dozen
> cells in parallel,
> It really is enlightening to look at some high-res pictures of a module,
> you can even find them
> On Ebay. You will see that each module consists of a "U" where
> alternatingly (starting from one
> Contact) the metal plate with the welded wires carries the current back
> and forth in 3 sections
> In each leg of the "U" and the contacts on the top of the "U".
> It is clearly visible in this ad for example:
> www.ebay.com/itm/10x-Tesla-18650/162462368115
> Cor.


​It seems to me the reason for each cell in a parallel group being attached
to that common sheet with a small gauge wire is that if any cell fails
short it will pop that wire as a fuse and prevent all the other cells from
shorting through that cell and setting it on fire.  Am I correct in that
assumption?  It this something that's missing from all the other
aftermarket BMS systems?

Chris​
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Re: Battery Connections

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You are correct. I doubt it is absent from other automotive systems. Too
much liability. Other packs like eBikes are another story.

On Apr 15, 2017 6:09 AM, "Chris Tromley via EV" <[hidden email]> wrote:

> On Sat, Apr 15, 2017 at 3:06 AM, Cor van de Water via EV <
> [hidden email]>
> wrote:
>
> > Robert,
> > Welding. Their 24V modules consist of 6 series banks of several dozen
> > cells in parallel,
> > It really is enlightening to look at some high-res pictures of a module,
> > you can even find them
> > On Ebay. You will see that each module consists of a "U" where
> > alternatingly (starting from one
> > Contact) the metal plate with the welded wires carries the current back
> > and forth in 3 sections
> > In each leg of the "U" and the contacts on the top of the "U".
> > It is clearly visible in this ad for example:
> > www.ebay.com/itm/10x-Tesla-18650/162462368115
> > Cor.
>
>
> ​It seems to me the reason for each cell in a parallel group being attached
> to that common sheet with a small gauge wire is that if any cell fails
> short it will pop that wire as a fuse and prevent all the other cells from
> shorting through that cell and setting it on fire.  Am I correct in that
> assumption?  It this something that's missing from all the other
> aftermarket BMS systems?
>
> Chris​
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>
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Re: Battery Connections

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In reply to this post by Electric Vehicle Discussion List mailing list
That is exactly the reason for the thin welded wires, doubling as fuses in error (shorting) situations. The usual failure modes of cells are open or short. Open means less capacity and is not a problem the BMS can't handle. But a short is not something a BMS can solve, the paralleled cells will simply dump all available energy in the shorted cell, so you need a fail-safe, which is typically a fuse. The model S has 74 parallel cells so losing one cell from either open or a short and blowing the fuse wire will affect capacity but very minimal. The BMS will be able to measure a slight imbalance in capacity between the series groups comparing voltage at high and low SoC and thus warn when such an imbalance starts affecting range.
Traditionally packs are made from large capacity cell, though Prismatics are often using multiple pouch cells in parallel. Even Lead acid packs have been built with buddy paired batteries and i know of at least one car burned down from a fire in such a pack and another car burned down where a manufacturing defect is suspected in the pouch cells, because the plastic cases burned away and a part of the pouches appeared folded double during insertion into the plastic case.
Both cars were not charging when they burned.
I currently have a double Leaf pack in my truck. Technically each Leaf module is a parallel of 2 cells and this would need a fuse between them, but i do not want to open each module, i hope Nissan did a good enough job.
However, to avoid a problem in one pack to progress to the other (they are in separate box halves), i added a pack fuse in each string (mid pack, at the double pole disconnect switch) so that each pack is only connected at the full voltage and not in between. As consequence, i am running two independent (Leaf) BMSes on the two packs.
Hope this gives some ideas.
Cor

> On Apr 15, 2017, at 3:09 AM, Chris Tromley via EV <[hidden email]> wrote:
>
> On Sat, Apr 15, 2017 at 3:06 AM, Cor van de Water via EV <[hidden email]>
> wrote:
>
>> Robert,
>> Welding. Their 24V modules consist of 6 series banks of several dozen
>> cells in parallel,
>> It really is enlightening to look at some high-res pictures of a module,
>> you can even find them
>> On Ebay. You will see that each module consists of a "U" where
>> alternatingly (starting from one
>> Contact) the metal plate with the welded wires carries the current back
>> and forth in 3 sections
>> In each leg of the "U" and the contacts on the top of the "U".
>> It is clearly visible in this ad for example:
>> www.ebay.com/itm/10x-Tesla-18650/162462368115
>> Cor.
>
>
> ​It seems to me the reason for each cell in a parallel group being attached
> to that common sheet with a small gauge wire is that if any cell fails
> short it will pop that wire as a fuse and prevent all the other cells from
> shorting through that cell and setting it on fire.  Am I correct in that
> assumption?  It this something that's missing from all the other
> aftermarket BMS systems?
>
> Chris​
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