this post was submitted on 24 Jun 2024
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It's worse than that: it requires the old school lead acid 12v battery to be charged, so even if the car's battery is full, it doesn't matter if that old car battery has failed
That's not unique to Tesla EVs, but it being required to open the doors may be (the 12v lead acid runs the general vehicle electronics rather than down converting the 400v or 800v main battery... I don't understand that decision, but I'm no electronics expert so there may be really good reasons for it...)
Let me start by stating that requiring the battery to open/close doors is a bad design choice overall. There should always be a way to open the door using a physical key.
Ok, having said that, the 12V is a better choice. It's easier to replace a 12V battery in case it fails and forcing the main battery to power everything runs the risk of draining that. Li-Ion batteries don't react well to being completely drained.
Besides, all EVs have a way to attach an external battery to the 12V system in case of total power failure, which will then allow you to do whatever you need. In case of Tesla Model Y there are two cables hidden in the tow eye cover that power the hood release. With the hood open you can charge the 12V battery directly.
Thank you for providing the good reasons for it, it makes much more sense now
James May made a video about how easy is to recharge Tesla's battery
I really don't understand why they still use those heavy lead acid ones. Couldn't you at least get a lighter lithium battery if it has to be a separate circuit?
To be fair I think it is there as a backup for low temperature climates, the Lithium batteries wont charge at temps that low, but they still could have setup the lithium batteries as an emergency backup for all the 12v stuff.
When the car isn't driving I believe the main battery isn't connected for safety reasons. It's a high voltage battery, and having it connected all the time even when the car is being serviced is an unnecessary safety risk.
Yeah they could and probably should use a different battery technology than lead acid. Preferably something with a wide temperature range. Lithium Titanate Oxide anyone?
I can understand why. I'm guessing it's for a couple reasons, maybe fluctuations in the voltage depending on driving conditions ( if you're stomping on the throttle allowing everything to flow through the motors it may provide inconsistent voltage to the sensitive computers and electronics, I would imagine there is a step-down converter somewhere that charges that 12v battery, essentially that battery is used as a buffer. But the link between the big batt. and little batt. isn't active unless the vehicle is on. And "On" requires the 12v system to turn on computers and close a relay.
Doors relying on ANY electronics is a bad idea. Even most cars with keyless entry have a hidden key somewhere to physically get in the vehicle if the battery dies. If the main battery in a tesla is toast you have bigger problems than a locked door. But anyone who has been driving for more than a few years has likely dealt with an OG battery decides to stop taking a charge. And you probably won't get much of a warning in an EV that doesn't have an engine that starts turning over slower and slower.
I know that hybrids like the Prius (at least the older ones) use the inverter to charge the 12v battery with the EV battery to make the ICE beltless (no AC compressor, alternator, etc driven by the ICE) which is supposed to increase fuel efficiency.