Purpose of the 2 Low Voltage 12v Batteries?

[MPawelek]

Read about these in the on line manual but do not know their purpose…..

 

[DeaneG]

Wow, those are tiny! Like the kind you'd use for burglar alarm backup power.

 

[hydbob]

Supposedly was as a backup, that's what they told us at the factory

 

[MPawelek]

Back up to do what?

 

[copper]

Back up to do what?

Total speculation: Maybe redundancy for low-level controllers, doors and locks in case of complete battery pack drain. If you zero out the main cells this may be necessary to control the basic systems so you can actually restart the car or get it to accept a charge.

 

[Not Sam]

Teslas have 12V batteries too (well, except for the first year or so of the original Roadster). Not sure exactly why, though I've read speculation that if the main DC battery system needs to be shut down, the hazard lights can still operate, and as @copper suggests, in case the main battery shuts itself down to protect itself you still have control power.

 

[hydbob]

I thought that those batteries ran all the software and the big battery was used to do all the drivetrain stuff?

 

[Not Sam]

I think the climate control, lights, computers, sound system, etc all normally run off the main battery (with a DC-DC voltage converter), rather than running it off the 12V: Since EVs don't have an alternator to keep the 12V system charged, you have to use the main battery anyway to charge the 12V, and it's more efficient to just use that energy directly rather than store it in the 12V and just pull it back out. But I don't really know.

 

[DeaneG]

Yeah those little things are not going to operate the HVAC system for very long.

 

[KySerenity]

In the Tesla, the 12V battery is used to sense the key fob and run through a check of all systems prior to initial start-up. Without the 12V , the system would not be OKed to allow access to the main battery. It is critical to the system. When it gets weak, warnings are displayed very early to allow replacement.

As hydbob suggested, I ran a line off of my 12V that allows use of accessories that would trip the breaker for the cigarette plug, such as a powerful portable air compressor. This line also allows me to connect a trickle charger to the 12V when I do not use the car for several days. My Optima charger keeps the 12V in top shape when I am traveling in my ICE vehicle.

 

[hydbob]

From C&D

We asked Hyundai's EV engineers why the 12-volt battery persists, and Ryan Miller, manager of electrified powertrain development, responded. "All the ECUs in the vehicle are powered from the low voltage, as well as the power relays that separate power from the high-voltage battery pack and the rest of the high-voltage network in the car," he said. "That separation allows us to safely disconnect the high voltage from the low voltage when the vehicle is not being driven or in the event of a crash." You don't want first responders to contend with door locks powered by Doc Brown's Mr. Fusion.

 

[Slam08]

Interesting EV efficiency fact. In most EVs the climate (fans,ac,heat) is done by the main battery but the seat heating is run from the 12v. So theoretically you could get better range by using seat heating and less climate.

 

[borski]

Interesting EV efficiency fact. In most EVs the climate (fans,ac,heat) is done by the main battery but the seat heating is run from the 12v. So theoretically you could get better range by using seat heating and less climate.

Yeah, they actually mention this in the manual!