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0 pointsChuckMcM14y ago0 comments

This was my take away as well but the mastery part is where it sounds like they are refuting something. Basically, having read that post three times, I conclude that if you ignore the warnings and let your battery pack completely discharge your car will be unusable, aka a 'brick'. Which completely validates the 'rogue bloggers' point that it is a 'known issue' and one to be aware of.

I found the 'no oil' comparison to be weak. Sure if you run your gasoline engine vehicle with no oil it will likely seize up and require an engine block replacement. However, you can leave a gasoline powered car in a barn for 20 years and then re-discover it, fill up all the proper fluids and run it. (assuming it was in running condition when it was stored). You won't have to replace the engine.

The part that is missing from the Tesla response is, if your car is in this state (fully discharged), what can be done. Is there a way to 'reboot' the car? And if so what is the procedure? Can anyone do it or only the factory? And why? If the batteries become disconnected does that also brick your car? Or can you just re-attach them ? Why doesn't the Tesla vehicle have a 'full power down' state for storage?

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5 comments · 1 top-level

nuclear_eclipse14y ago· 4 in thread

"Why doesn't the Tesla vehicle have a 'full power down' state for storage?"

I assume this is because of the nature of Li-ion batteries. Even if you aren't pulling any current from the battery, they will still discharge over time, and eventually go through a chemical process rendering them unusable and/or dangerous. Having a "long-term storage" mode for the vehicle would only serve to make it more likely to happen by lulling owners into a false sense of security. Better to simply reinforce the need to constantly keep the vehicle in a charged-or-charging state.

ChuckMcMOP14y ago

I would like to understand where you get that information.

I've had a lot of experience with rechargeable batteries over the years in doing robotics, and a variety of chemical makeups. My experience is that the "self discharge" function is the result of the anions managing to convert by one means or another not related to electron injection at the anode. The mechanisms that enable this are things like electron tunneling which are probablistic, such that the discharge curve is asymptotic toward zero charge while never achieving it. That sort of discharge does not lead to the development of dendrites in the battery which would create shorts or other hazards to recharging.

My understanding is that because the Tesla has a constant drain on the battery it can drive the battery to zero.

It would be interesting to know the answer to the question can you just disconnect the battery for storage. Not willing to invest $100,000 to find out :-)

ChuckMcMOP14y ago

Thanks guys for the links, one of the references in the Wikipedia section was this one: http://www.gpbatteries.com/html/pdf/Li-ion_handbook.pdf which has a bit more information.

According to the GPBatteries guys LiON have no self discharge if they aren't being drawn down by a monitoring circuit. But they also mention that embedded safety circuits can run the batteries down a bit until those circuits stop working because there is insufficient charge in the battery to run them, and then the battery can't be charged (aka its a brick).

Of course you could charge it if you could get around the safety chip in that case it would just require a bit of cleverness.

Again my experience with LiON cells is that once they get to about 3V if you don't put a load on them they don't discharge any further on their own. That would seem to be supported by the chemical energy needed to absorb the anions but I am not a chemist, just an aging EE. Thanks for the links.

URSpider9414y ago

Here's a nice graphical rendition of what can happen. The undervoltage situations are not driven by current travelling outside the cell, they can happen even if the cell voltage drops by self-discharge.

http://www.mpoweruk.com/lithium_failures.htm

nuclear_eclipse14y ago

http://en.wikipedia.org/wiki/Lithium-ion_battery#Safety_requ...

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5 comments · 1 top-level

nuclear_eclipse14y ago· 4 in thread

"Why doesn't the Tesla vehicle have a 'full power down' state for storage?"

ChuckMcMOP14y ago

I would like to understand where you get that information.

My understanding is that because the Tesla has a constant drain on the battery it can drive the battery to zero.

It would be interesting to know the answer to the question can you just disconnect the battery for storage. Not willing to invest $100,000 to find out :-)

ChuckMcMOP14y ago

Thanks guys for the links, one of the references in the Wikipedia section was this one: http://www.gpbatteries.com/html/pdf/Li-ion_handbook.pdf which has a bit more information.

Of course you could charge it if you could get around the safety chip in that case it would just require a bit of cleverness.

URSpider9414y ago

http://www.mpoweruk.com/lithium_failures.htm

nuclear_eclipse14y ago

http://en.wikipedia.org/wiki/Lithium-ion_battery#Safety_requ...

j / k navigate · click thread line to collapse