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Why Tesla Cars Aren't Bricked By Failing Batteries
itwbennett writes "Don't believe recent claims made by a blogger that non-functioning batteries in the Tesla Roadster cause the electric cars to be bricked, says IDC analyst Sam Jaffe. 'Here's the primary fact that the blogger in question doesn't understand: the Tesla battery pack is not a battery,' says Jaffe. 'It's a collection of more than 8,000 individual batteries. Each of those cells is independently managed. So there's only two ways for the entire battery pack to fail. The first is if all 8,000 cells individually fail (highly unlikely except in the case of something catastrophic like a fire). The second failure mechanism is if the battery management system tells the pack to shut down because it has detected a dangerous situation, such as an extremely low depth of discharge. If that's the case, all that needs to be done is to tow the vehicle to a charger, recharge the batteries and then reboot the battery management system. This is the most likely explanation for the five 'bricks' that the blogger claims to have heard about.'"
There seems to be a fundamental misunderstanding of the terms 'battery' and 'cell'. A battery is the collection of cells. So a Tesla could be bricked by a failed battery but it is tolerant to a failure of individual cells. This is not surprising.
Good thing slashdot is here to help us debunk everything I'd never have heard about from random dipshit bloggers.
It's a shortcoming of LiIon technology that if the cell becomes over-discharged, the cell may fail short circuit, and a subsequent recharge may cause an "exciting" failure (think flames). That's why all LiIon packs have a protection circuit that permanently disables the pack if it's discharged to the danger zone. Given the massive size of an automotive battery pack, it's easy to believe they have some very conservative safety devices in them. And it's also easy to believe that the cost of individually testing/replacing cells and "rebooting" the protection circuitry in a pack that has tripped its safety limits is prohibitive.
AHA!!!! SEE? They admit it!!!
I'm a leaf on the wind. Watch how I soar.
Regenerative braking requires some pretty sophisticated power electronics, controls, and software. The Tesla's motor is an AC induction motor. (The AC induction motor was invented by Nikola Tesla.) An AC induction motor has copper coils for both the rotor and the stator. This is different from a DC motor (brushed or brushless) where (usually) the rotor has permanent magnets on it.
Backdriving an induction motor will result in no power generation unless the stator is energized. Even then, the associated power electronics have to commutate which phase of the stator is energized in sync with the spinning rotor. In other words, you need at least some external (i.e., battery) power in order to regenerate - this is true of all induction generators. Without the stator being energized, you're just spinning one set of copper coils past another set (this is different from a DC motor, where the rotor has permanent magnets, which will induce current in the copper coils).
So the Tesla cannot be "jumpstarted" by towing it or rolling down a hill if the battery has discharged so deeply that it has disabled itself.
If you can afford a Tesla, you can afford to RTFM and get a trickle charger.
Probably (although I am sure that many people who have enough money to buy one won't read/understand all the technical stuff and will want the car to "just work") - but that still leaves us with the point that the battery pack can go kaputt within a couple days if the car is not charged (if the car was already at low charge) - which is something which needs to be communicated to customers far more clearly than just a sentence here and there that it is not good to let the battery go completely flat. Because I am sure that for almost every person who is not very familiar with battery technology, the EXPECTED consequence of a flat battery would be "recharge it again and you're good to go". If there is the possibility of making a $40k mistake, I'd expect the car to go full "star trek red alert" on me when I park it somewhere at less than 10% charge, and to start sending "help! I am dying!" SMS when the battery goes below 5%.
Having RTFA'd, it is a negative opinion piece full of half truths and misinformation. That article is a horribly blatant attempt to discredit the vehicles from somebody who does not understand the underlying technologies. It needs to be taken as an opinion piece - there are zero references on his five examples (it's simply a chat with a service manager), and he is stating things as fact which simply aren't.
:P
First: yes, there are cases with batteries where they can be discharged to the point where the cells themselves are damaged and cannot be recharged. This is the case with *most* battery chemistries and is not going away any time soon. The blogger calls this a "Devastating design problem" when it is simply a part of the technology, like not storing your fuel cans near the furnace or leaving fuel to sit in a carburetor. There is a pretty clear warning in the car's manual not to let the battery voltage flatline for long, our intrepid blogger even provided a a PDF file with that page out of the manual. It states that the battery must be charged immediately if the charge level falls to 0% and has a great deal of information on the care and feeding of the battery.
Even if we take the five failed battery packs as truth, that is 0.2% of vehicles with an issue - an issue that in each example was due to the owner not charging the vehicle with one possible exception. His extension cord example could present a possible issue with the Tesla chargers. A typical cheap "heavy duty" extension cord will have 16 gauge wires, which over that distance is going to have some noticeable resistance. I don't know the current draw of the battery, but if it is expecting to pull 10 or 20 amps, the charger will see a significant voltage drop and likely cut off the charging (unless it has a "trickle charge" mode, dunno...). If the vehicle didn't report that it wasn't charging (or inaccurately reported it was), then I could see this being a design issue. I'll also note that this particular example did not state whether the customer had to pay for the repair.
What it comes down to is all electrical systems have ways they could be improved. That doesn't make this a devastating problem, it is simply an aspect of this class of vehicle that the owner needs to pay attention to. This blogger has a bone to pick or wants to stir the pot with a sensationalist report. Apparently it's working, after all, we both read his article
+1 Disagree