Tesla Motors says you cannot brick a Model S

Following
the controversy over whether a Tesla Roadster battery pack can be
destroyed, Tesla Motors speaks saying the fears are “irrational”, based
on limited information, and oh by the way it’s nigh-on impossible to
brick a Model S.

Two days ago news broke from a single blogger, Michael DeGusta, claiming the Tesla Roadster has a design flaw
that can damage the battery pack beyond repair (bricking the Roadster).
Yesterday we learned that some details about the blogger and his
business partner, Max Drucker, didn’t quite add up, with the story
starting to smell a little fishy, and Tesla’s public image starting to take a hit,
but with the underlying risk remaining unaddressed. Today Tesla Motors
released a blog post that goes a long way to addressing the concerns.

To review the story, DeGusta claimed to have evidence, provided by an
unnamed Tesla Service Manager, that five or more Tesla Roadster’s had
destroyed battery packs because the state of charge fell too low,
requiring a complete pack replacement. The only verified case is
Roadster #340 owned by DeGusta’s business partner, Max Drucker. It
appears so far that the Roadster does not have an ability to proactively
reduce power draw when the car is idle and the battery state of charge
falls too low, leading to pack damage. It appears that some public
sentiment is stirring against Tesla Motors at a critical time when the
company is spending a lot of money heading towards launching production
of the Model S. If the public gets spooked by this, it could derail
Tesla’s business plan. For details see the two earlier articles linked
above.

Tesla Motors describes the controversy as a “single blogger spreading
a rumor” that is based on “an irrational fear based on limited
information and a misunderstanding of Tesla’s battery system”. That
single blogger, Michael DeGusta, received a huge boost when Jalopnik
republished his blog post, and a followup article the next day. As we
noted yesterday, he and Max Drucker have been business partners for over
10 years, and when DeGusta says he is an innocent bystander that’s not
quite correct. The battery pack in Drucker’s Roadster was damaged,
requiring replacement to the tune of $40,000, when he left it in a
storage unit not plugged in for two months. This much is fact, not
rumor, but DeGusta’s blog post made many other claims that may or may
not be true.

For example, who are the other four (or more) Roadster owners with
destroyed battery packs? And who was the unnamed service manager in
DeGusta’s blog post?

Another question that has come up is whether the battery pack is
actually destroyed, or whether it’s just the 12 volt system getting
discharged. If this were a simple case of the 12 volt system, then it
would be a simple process to wake the Roadster back up just by
connecting a 12 volt power source to the car. But this is a case that
requires battery pack replacement, indicating that Tesla believes the
pack is damaged beyond usability. Tesla’s own statement on this did not
explicitly deny such damage can occur, instead it said “All batteries
are subject to damage if the charge is kept at zero for long periods of
time” and “Tesla avoids this problem in virtually all instances with
numerous counter-measures” suggesting that there are scenarios which can
occur that leads to the pack being at zero charge for a long period,
damaging the pack.

Turning back to Tesla’s blog post, they say “Of the many pleasures
that Tesla owners have, one of the most appreciated is nearly worry-free
maintenance of their vehicles” and that in return for not having to
worry about oil changes, spark plugs, etc, that Tesla merely asks the
car owner to “remember to charge it”. This is because “A plugged-in Tesla is not only charging its battery, it is also keeping key systems within the car functioning properly“.
There is an analogy here with cell phones, all of us who own cell
phones know that it’s easy (and a good idea) to keep the phone plugged
in whenever possible. It’s not unknown for cell phone or laptop battery
packs to be damaged if these gizmos are left sitting and not plugged
in.

The counter-measures Tesla takes are that for Roadster’s with low state of charge, “the car is designed to let you know with repeated visual and audible warnings,”
and that if the owner continues “to ignore the warnings, they will
persist and increase.” That sounds useful and practical, except what if
the owner is nowhere near their car to hear the warnings. This is like
the old conundrum, if a tree falls in the forest and nobody is around
to hear it, did the tree fall? If a Roadster beeps its guts out warning
the battery pack is low, but nobody hears the warning, then what
happens? Tesla’s blog post says the Roadster “also protects the battery
itself by communicating with other systems in the car to conserve
energy when the state of charge gets too low” and “Starting with
Roadster 2.0, owners can also elect for their car to contact Tesla
headquarters once the state of charge falls below a specified level, and
we can then contact the owner.”

In other words, the core issue is that some Roadster
subsystems continue to draw power from the pack even when the car is
“off”. The concern we had was whether the Roadster itself had any
innate protection against draining the state of charge to zero. Tesla
claims here that the Roadster is set up to shut off some of the
subsystems in this case, which would reduce the rate charge is drained,
but does not reduce the drain to zero. Newer Roadsters can then notify
headquarters, with headquarters notifying the Roadster owner to plug in
their car. This combination of counter-measures should cover the
majority of cases.

But there are cases this will not cover. Tesla claims that even “in
cases of neglect” the Roadster does pretty good, saying “The earliest
Roadsters will take over two months to discharge if parked at a 50
percent charge without being plugged in.” This means a Roadster parked
at 50% state of charge would take two months to discharge to a dangerous
state of charge. However, taking Max Drucker’s letter at face value,
the state of charge on his car was probably higher than 50% and it took
two months of sitting idle in storage for the pack to be destroyed.
This doesn’t quite add up.

But, wait, it gets better with the Model S. For starters, “a Model S battery parked with 50 percent charge would approach full discharge only after about 12 months.”
This would be in part because the Model S has a larger battery pack
than the Roadster, assuming the 300 mile Model S, and also suggesting,
in part, that the the power drawn while sitting idle is less than it is
on the Roadster. Additionally, “Model S batteries also have the ability
to protect themselves as they approach very low charge levels by going
into a deep sleep mode that lowers the loss even further,” and that the
car “will not allow its battery to fall below about 5 percent charge” at
which point the car can sit idle for many more months with no damage.
Of course, says Tesla, you can ‘drive a Model S to 0 percent charge” but
even in this case all will be fine so long as you recharge the car
within 30 days.

These measures relieve the concerns we have over future Model S and
Model X owners. The behavior Tesla describes is the sort of automatic
battery pack protection one expects in an electric car, and indeed is
the sort of protection built into most cell phones and laptops for the
same reason. Namely, just as a modern cell phone or laptop emits
warning notifications and then shuts the gizmo off if the warnings are
ignored (or not heard), so too will the Model S shut itself off if the
pack state of charge falls too low. Then, just as with the cell phone
or laptop, recovery is a simple matter of plugging in to initiate a
recharge.

But does this mean that Model S batteries cannot be bricked? From
Tesla’s description it appears that a Model S owner who drives the car
to zero state of charge, then leaves it sitting for over 30 days, is at
risk. Just what the level of that risk would be, is unclear. In any
case it’s hard to imagine this combination of events would actually
occur in actual real life.

Roadster owners are in a slightly different situation, but Roadster
2.0 owners can opt to have Tesla Motors staff assist them in monitoring
and safeguarding their car.

This is a very nice response on Tesla’s part, demonstrating that
Tesla engineers have come up with a good solution for this scenario.
Our concern that as 10’s or 100’s of thousands of Model S and Model X
cars are sold, those future owners might not be as tech-savvy as the
Roadster owners, and could act like normal car owners today and ignore
service recommendations. Tesla has designed in the automatic
precautions necessary to preclude these future car owners from
accidentally damaging expensive battery packs.

Originally published at TorqueNews: http://www.torquenews.com/1075/tesla-motors-says-you-cannot-brick-model-s

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About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.