S-2000 Roadster
#1244
Do you have a patent number? I tried going to pat2pdf.org the other day and the site was down :frown:There are a number of tesla patents w.r.t ESS balancing. One of them describes how the car is constantly monitoring the battery balance.
Thanks for clarifying the term. I knew about the 11 sheets (9 series within each) but had lost the 'brick' definition in my notes. So, I guess that means there are 11 sheets and 99 bricks in the ESS, with exactly 9 bricks per sheet.Not exactly. Each brick has it's own voltage. 69 cell make a brick. You cannot measure the voltage of an indivdual cell.
The only way to measure the voltage of an individual cell would be to have an electronic switch that could disconnect the parallel brick to isolate one or more cells, but I recall seeing that those connections are all soldered permanently. So, of course you're right that individual cell voltages cannot be determined.
That said, within a brick there will be passive balancing. A voltage is applied during a charge, but each cell reacts slightly differently such that when charging stops the voltage of each cell can be slightly different. As soon as the external voltage is removed, current will flow between the 69 cells in a brick until they all settle to the same voltage. I suppose some of this will occur during charging, too, so I'm not sure how much passive settling remains to be done after charging is complete, but there is surely some non-zero amount of hysteresis and the hysteresis will not be identical for every cell in the brick. But whatever degree exists, it's probably more pronounced with a range charge than a standard one.
Thanks for bringing this up. It is, of course, undocumented, but some folks have been referring to those as max and min rather than average and min. There is, supposedly, a pair of brick numbers, which implies that it is actually max and min, since there cannot be an average brick number. If this reverse-engineering is correct, then the brick number is a byte, not a full word, and the upper byte represents the brick number for the max. I have not graphed the brick numbers to confirm whether this interpretation makes any sense with the data I have.The vehicle logs record the Average brick voltage, the min voltage, and the brick number of the min voltage. AFAIK, they don't record the max.
None of the above is intended to imply that Tesla Motors are not balancing between bricks and/or sheets, I'm merely pointing out that some settling occurs passively within a brick.
EDIT: I seem to have gotten my wires crossed between two separate threads. This one is more about whether Tesla Motors ever pulled power from an individual sheet for 12 V purposes, and another thread has been discussing balancing and settling in terms of final ideal range after a charge has completed. My point here is merely that they could make it work if they wanted to, and the story I heard was that they tried it at first and then decided to take a different approach - if only we had a Service Manual with a high-level wiring diagram!
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