Hansjörg von Gemmingen Roadster pack out of juice?

[hcsharp]

This architecture would require you to monitor and balance each individual cell because the 99 cells in series in each brick all have a risk of being over-discharged (in top balance case) or over-charged (in bottom balance case). And given the strings are all independent (the only commonality is the overall pack voltage), that essentially means you have to monitor and balance all 6831 cells.

The assumed architecture where 69 cells are in parallel per brick means these 69 cells self balance and can be monitored as a single group. The BMS then only has to monitor 99 bricks, rather than each individual cell.

I agree with all that except that it doesn't require you to monitor each individual cell. Consider that it's possible to keep the cells in a brick connected in parallel most of the time to prevent the problems that you mentioned (over/under charge/discharge). It's also possible to remove a string from the ESS output if necessary so all bricks are affected equally if one of them has a few bad cells. But 90% of the time that will be unnecessary because you won't be discharging the battery very far. If the 69 strings are always permanently connected in series and used transistors/mosfets to connect them in parallel with the other cells in their respective bricks, it helps prolong and prevent the runaway failure.

I'm not saying this is correct. I don't believe any of us knows for sure unless you helped design the system. We always just assumed the cells in a brick were permanently wired in parallel. But there are a lot of benefits to having them permanently wired in 69 series strings.

That's why I want to know the pack behavior when Hansjörg's ESS began to lose capacity. It will help us figure out what's really going on inside it.

 

[JRP3]

We know the S pack has groups of cells physically connected in parallel, there is no possible switching mechanism to disconnect them, nor does there need to be. I'm quite sure the Roadster is the same. Cells in parallel do not need individual monitoring or balancing. (Larger capacity pouch and prismatic cells are just a bunch of smaller layers connected in parallel). If some cells in parallel fail then the amp hour capacity of that group is lowered but the pack can still function. Yes that group of cells would see relatively greater stress but only significantly so under high loads, so they may be aging faster but possibly not fast enough to impact continued range loss significantly.

The Roadster in question seems to have had good capacity up until a certain point where capacity quickly dropped then stabilized. That does not sound like degradation across the entire pack to me.

Isn't there someone here rebuilding a Roadster pack?

 

[stopcrazypp]

If the 69 strings are always permanently connected in series and used transistors/mosfets to connect them in parallel with the other cells in their respective bricks, it helps prolong and prevent the runaway failure.

I'm not really following how this would be designed in a way that can avoid parallel cells taking up the slack. If you remove a whole series string, that means instead of only the weakest brick having extra stress, all bricks (besides from the removed string) will have extra stress. However, the extra stress on the weakest brick isn't lessened in any way (it's still missing cells, except the failed cells are now disconnected instead of connected).

I get that your idea is that it spreads out the stress, but you are neglecting that it adds additional stress to the other bricks. In absolute terms the stress on the weakest brick remains the same (even though in relative terms all the bricks are stressed equally).

The only way I can tell to truly avoid this issue (and not be limited by the weakest brick) is with active balancing (so you can shuttle charge between bricks while discharging) or have all the interconnects be completely configurable (such that each individual cell can essentially connect anywhere relative to other cells).

 

[Mark77a]

With the recent Patent sharing announcement maybe more info about ESS construction and monitoring will come out into the public domain.

Maybe the 'big announcement" (that apparently 'will effect several aspects of the roadster' ) IS a release of the Roadster 'factory technician manual', so technicians other than tesla, and even end users, can maintain and repair Roadsters. That would be good for extending their usable life. It may also help Tesla as many technicians with valuable 1st hand experience of roadsters and their repairs have moved on.

Here in UK we are lucky to have one such guy (who is also on TMC as 'Supercharged20v' ) and has offered help / support etc to Roadster owners.

 

[JRP3]

The latest update: http://www.manager-magazin.de/lifes...lfahrer-hansjoerg-von-gemmingen-a-996916.html

The first battery had to be replaced after 40,000 km, but that was a guarantee damage. The next has clearly lost after 200,000 km of capacity and had to be replaced.

mm: Quenched It has not all that you have a Model S risen. Could you imagine, yet again to buy next car a car with combustion engine?Gemmingen: No, definitely not.