Vibration is killing your cells!

Batteries, Chargers, and Battery Management Systems.
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jonescg
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Vibration is killing your cells!

Post by jonescg » Jan 10, 2018 9:15 pm

Well its obvious that physical trauma is a bad thing, but this paper describes how the authors took 18650 cells and shook the shit out of them for 100 hours and measured capacity and IR. Holy crap! Double, even quadruple the internal resistance! Capacity was down, but not a long way. Z, Y and Z axis were all used, however I suspect the Z axis might have had the most impact.

http://www.mdpi.com/1996-1073/9/4/255/htm

I wonder if this is due to the fact that the active material (aka jellyroll) is wound around the mandrel, and is not supported by anything other than it's own tension.

Make sure your cells are snug inside their packs!

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Re: Vibration is killing your cells!

Post by whereswally606 » Jan 12, 2018 5:26 am

thats interesting, i wonder whether the cells in the packs on my bike are in the best orientation now. They lie length wise across the downtube (macallister B&Q 36v packs on my norco team race). This might sugest the worst way is to have the 18650/26650 cans pointing toward the floor like they would if you had an old golden motors battery on top of a pannier rack. This was how my first bike was but not for long as all that weight on the back on a hard tail caused me no end of punctures 7 or so years back.

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Re: Vibration is killing your cells!

Post by fechter » Jan 12, 2018 3:05 pm

I guess it would be good to know which axis is the most sensitive. Most of the vibration on a bike is in one axis.
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Re: Vibration is killing your cells!

Post by Voltron » Jan 12, 2018 3:51 pm

It's a lot to plow thru, but the vertical z axis shaking of a cell seemed the worst. The central mandrel starts banging up and down causing micro damage to the ends.

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Re: Vibration is killing your cells!

Post by jonescg » Jan 12, 2018 8:34 pm

Well for cylindrical cells, X and Y are identical - and it's fairly snug in that dimension.

But the Z has the mass of the jelly-roll moving about a central mandrel. There is nothing holding the roll together other than tension, so I can see how the active layers could start to wear down.

I think most e-bikes have them laying X-Y. Only Alta (Redshift) has their in the Z :shock: We'll see how their batteries hold out.

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Re: Vibration is killing your cells!

Post by fechter » Jan 13, 2018 1:57 am

jonescg wrote:
Jan 12, 2018 8:34 pm
Well for cylindrical cells, X and Y are identical - and it's fairly snug in that dimension.

But the Z has the mass of the jelly-roll moving about a central mandrel. There is nothing holding the roll together other than tension, so I can see how the active layers could start to wear down.

I think most e-bikes have them laying X-Y. Only Alta (Redshift) has their in the Z :shock: We'll see how their batteries hold out.
That makes sense. So we should avoid building packs where the cells sit vertically.
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Re: Vibration is killing your cells!

Post by macribs » Jan 14, 2018 8:32 pm

How are the cells oriented on Tesla battery pack? Tesla probably got the most miles on 18650's so far.

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Re: Vibration is killing your cells!

Post by amberwolf » Jan 14, 2018 8:38 pm

They are vertical.
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Re: Vibration is killing your cells!

Post by jonescg » Jan 14, 2018 9:43 pm

I'd say the vibration in a car battery is far lower than say, an e-bike on a trail, but it's interesting to see that Jaguar are pursuing a battery where the cylindrical cells lay on their sides. Perhaps their findings in this paper (one of the authors is from JLR) drove that decision?

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