Tesla car cells

[bagmaker]

comments?

https://www.ebay.com/itm/Tesla-Model-S- ... ASPuAVxADg

[T1 Terry]

https://www.youtube.com/watch?v=WdDi1haA71Q

[Greynomad]

Frightening, T1!
On the narration, he admits not connecting the batteries to a management system.
How do you spell ‘fool’?

[T1 Terry]

That is the really scary bit, backyards with no idea about what they are doing building lithium batteries and selling them on evilbay etc.
Everyone seems to think the Tesla cell chemistry is safe, that shows it is not, the safety is in the thermal management and cell voltage management. A failure in either of those systems and the whole thing does not shut down and ....... can you imagine that going off on the wall inside your house? Same chemistry cells and I haven't seen a coolant system radiator or heat exchanger as part of the Tesla Powerwall .... is the aim of mounting them inside the house to keep them cool thinking no one has high temperatures inside their house .... That workshop didn't look like it was a really hot day in there, they had all the doors closed after all. I can see people buying these used battery packs and building their own lithium house battery in the garage with the aim of cutting down the power bills or going off grid ..... will they understand the complexity of the thermal and electrical management required to stop these cells doing the same thing when there is no one there watching them?
Imagine if that had not happened there while they were in the workshop, but after it was delivered back to Disney?

T1 Terry

[Busman]

I see even Jaycar is now into Liths, you don't get much for a grand though

https://www.techbrands.com/store/catego ... b2203.aspx

[T1 Terry]

I see even Jaycar is now into Liths, you don't get much for a grand though

https://www.techbrands.com/store/catego ... b2203.aspx

This bit is interesting, "26650" LiFePO4 cells, so they are built using cylindrical cells, I wonder if they have included fusing between each cell and the busbar so if one cell goes short circuit it doesn't kill the rest of the cells. At least if they are LiFeP04 cells they won't explode or catch fire like the Tesla cells did, but that limit of 50 amps continuous and 100 amps peak for 5 secs is a bit restrictive.
The trick that catches many unsuspecting punters is the 50 amp limit, this doesn't mean 4 x 100Ah batteries in parallel will give you a 200 amp limit, the limit is still 50 amps because there is no way of current sharing between the batteries.

T1 Terry

[native pepper]

So the short circuit protection they claim, is over the entire pack and not each cell protection. They are extremely expensive for what you get.

[T1 Terry]

So the short circuit protection they claim, is over the entire pack and not each cell protection. They are extremely expensive for what you get.

Unknown NP, they don't actually say one way of the other. I would think that if they had gone to that level of protection they would have been proud to show it, but lack of verification doesn't mean it isn't there, but it doesn't mean it is either.
The big risk using cylindrical cells is the heat/degradation problem. Unlike a prismatic cell that has a lot of plates all separated by a nylon porous sheet and the liquid electrolyte comes into contact with the outer case to transfer heat, the cylindrical cell is one pair of plates (with the separator material between them) wound into coil with the positive attached to the button top and the negative attached to the case and end cap. The only path for heat to move from the inner coils to the outer case is through the outer layers. Heat is the big killer, it causes the electrolyte to separate and this coats both plates and can cause the separator to actually seal its pores and not allow the electrolyte and therefore the lithium ions to move between the positive and negative plates.

T1 Terry

[native pepper]

So the short circuit protection they claim, is over the entire pack and not each cell protection. They are extremely expensive for what you get.

Unknown NP, they don't actually say one way of the other. I would think that if they had gone to that level of protection they would have been proud to show it, but lack of verification doesn't mean it isn't there, but it doesn't mean it is either.
The big risk using cylindrical cells is the heat/degradation problem. Unlike a prismatic cell that has a lot of plates all separated by a nylon porous sheet and the liquid electrolyte comes into contact with the outer case to transfer heat, the cylindrical cell is one pair of plates (with the separator material between them) wound into coil with the positive attached to the button top and the negative attached to the case and end cap. The only path for heat to move from the inner coils to the outer case is through the outer layers. Heat is the big killer, it causes the electrolyte to separate and this coats both plates and can cause the separator to actually seal its pores and not allow the electrolyte and therefore the lithium ions to move between the positive and negative plates.

T1 Terry

Agree, was told years ago not to use cylindrical cells and saw what you describe happens to them. At the time my questions as to why was met with a lot of technical jargon and the normal big smile, which always frustrated me. But was given a demo of high charge high discharge from both prismatic and cylindrical cells, quite a messy outcome when a cylindrical cell collapsed and melted. It required disconnecting all the cells quickly before the whole pack did something dramatic.

Still waiting for my 12 year old portable pack to lose some capacity or to fail in some way, but they just keep on going and getting the feeling, which may be totally wrong and an illusion they seem to be improving. Have been using it a lot lately for transferring 3000lt of veggie oil and welded up a bracket on my earthmover, but it still sits at 13,16v. Haven't charged it for months and even tried another couple of multimeters to check if the voltage was right. They still amaze me after all this time and in those 12 years, have never needed to take them below 13v.