12V Battery backup question

[TheVirtualTim]

figure if you need a "jump" you are going to actually need a tow to either the dealership or charging station so no need to keep anything extra in the car

Possibly not. I have not read through the manual, but on my Ford Escape Hybrid, the vehicle basically gives itself a jump-start.

The 12v system battery latches or unlatches the 330v traction battery (on the Escape Hybrid). When the car is off they are de-coupled. When you start the car, the 12v latches to the 330v and the car starts.

If the 12v battery dies, there is a button inside (in the driver's footwell) that connects the 12v and 330v batteries (transforming voltages of course) and uses the 330v battery to jump the 12v battery so that it can latch the normal power path and start the car.

If this is similar, then it's possible you could kill the 12v battery dead enough to not even be able to open the doors ... but still have loads of power in the traction battery array.

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[UW2]

Why would they design the car so it needed a 12v battery when there is a gigantic main battery right there?

 

[macchiaz-o]

Why would they design the car so it needed a 12v battery when there is a gigantic main battery right there?

I think for safety. This way the ~400V battery is physically disconnected while the car is off.

 

[UW2]

I think for safety. This way the ~400V battery is physically disconnected while the car is off.

They could use capacitors to power the start - that's the only use of the 12v anyway. But I don't know what I am talking about.

 

[macchiaz-o]

They could use capacitors to power the start - that's the only use of the 12v anyway. But I don't know what I am talking about.

Admittedly, I don't either.

 

[hybrid2bev]

Why would they design the car so it needed a 12v battery when there is a gigantic main battery right there?

See if this helps. It’s towards the end but basically everything except propulsion is run on the 12 volt system.

 

[macchiaz-o]

See if this helps. It’s towards the end but basically everything except propulsion is run on the 12 volt system.

I may have missed it, but I don't think Professor Kelly explains why they can't just leave the high voltage battery connected into the DC-DC converter at all times, and thereby remove the 12V battery altogether.

My guess is that they want physical separation for various safety scenarios (e.g. the vehicle is involved in a crash or the vehicle is being serviced).

If that is true, then a capacitor may not be a suitable replacement for a large 12V battery because while propulsion capability might be "off," you still need to provide power to lights, radios (modem, bluetooth, wifi, key fob), antitheft, and other stuff. These services will require much more power than an inexpensive capacitor could maintain.

 

[sockmeister]

To me this also means don't leave anything valuable in the frunk if the car will be unattended. Anybody with a screwdriver and a power source can open it fairly easily.

I believe this only works if the battery is actually dead, otherwise it's bypassed.

I think we don't know this for sure, yet. Someone will need to test the theory. The owner's manual isn't detailed enough on this topic.

Ok, take this with a grain of salt, since maybe he doesn't know, but I actually asked the Ford Rep about this during the Mach-E tour when I saw the car in November.

He said the jumpers to open the frunk require the keyfob to also be nearby. So not anybody can just come by and do it unless you're standing there with the keyfob in your pocket.

I am not sure if the Phone-As-Key also satisfies that; I'm guessing not.

 

[macchiaz-o]

Ok, take this with a grain of salt, since maybe he doesn't know, but I actually asked the Ford Rep about this during the Mach-E tour when I saw the car in November.

He said the jumpers to open the frunk require the keyfob to also be nearby. So not anybody can just come by and do it unless you're standing there with the keyfob in your pocket.

I am not sure if the Phone-As-Key also satisfies that; I'm guessing not.

That would make an already bad situation worse. My battery dies while I'm far from home and I can't even jump start the car because the key fob is at home. This seems unlikely and more complicated than necessary.

 

[RunningHorse]

My understanding is the doors have capacitors that hold charge to allow door open in the event of 12V power loss. You should also receive a notification via ford pass if this error state occurs so that you can access vehicle before capacitor charge depletes.

 

[MailGuy]

I've been driving Hybrids as my primary vehicle since 2007 and an EV owner since 2017. All of these cars have a similar configuration where there is a DC-DC inverter to charge the 12V system with a 12V interconnect that disables the high voltage battery until the ignition is powered on. These cars all use an AGM 12V battery similar to what is in the MachE. I experienced the first failure of the factory installed 12V battery two months ago after 13 years of use.

In my experience, the "dead battery" scenario just doesn't exist with these types of cars the same as it does with an ICE. I say that having owned my fair share of ICE's as well. My daughter's 2012 Fiesta couldn't sit idle in the garage much more than a month without requiring a boost to start the car. I also grew up in the midwest and had many a 12V battery fail at the onset of winter.

EV's and hybrids are different animals. They only need enough power to operate the computers and close the high voltage relays to power the car, vs. an ICE which needs a high current draw to turn the starter and rotate the ICE crankshaft to start the car. I've never felt the need to have an auxiliary 12V power source for any of my hybrids or EV's. I don't expect the MachE to behave any differently despite the new type of door lock. Ford has done their homework on this one, I think.

 

[CHeil402]

I've been driving Hybrids as my primary vehicle since 2007 and an EV owner since 2017. All of these cars have a similar configuration where there is a DC-DC inverter to charge the 12V system with a 12V interconnect that disables the high voltage battery until the ignition is powered on. These cars all use an AGM 12V battery similar to what is in the MachE. I experienced the first failure of the factory installed 12V battery two months ago after 13 years of use.

In my experience, the "dead battery" scenario just doesn't exist with these types of cars the same as it does with an ICE. I say that having owned my fair share of ICE's as well. My daughter's 2012 Fiesta couldn't sit idle in the garage much more than a month without requiring a boost to start the car. I also grew up in the midwest and had many a 12V battery fail at the onset of winter.

EV's and hybrids are different animals. They only need enough power to operate the computers and close the high voltage relays to power the car, vs. an ICE which needs a high current draw to turn the starter and rotate the ICE crankshaft to start the car. I've never felt the need to have an auxiliary 12V power source for any of my hybrids or EV's. I don't expect the MachE to behave any differently despite the new type of door lock. Ford has done their homework on this one, I think.

While I have full faith that Ford thought it through and the MME will likely fall closer to the 12 year life time, Tesla has had plenty of issues with their 12 V battery...

https://electrek.co/2020/09/15/tesla-fix-dying-12v-batteries-software-update-musk/

 

[sockmeister]

That would make an already bad situation worse. My battery dies while I'm far from home and I can't even jump start the car because the key fob is at home. This seems unlikely and more complicated than necessary.

I agree with you, and I think we'll have to have someone test this out willingly (at home) once we all get our cars to see how it really works.

But the alternative seems bad, too. Anyone with a 12v source can come on by and pop open frunks. Limiting it to when the battery is dead is slightly safer.

 

[generaltso]

He said the jumpers to open the frunk require the keyfob to also be nearby. So not anybody can just come by and do it unless you're standing there with the keyfob in your pocket.

Yeah, I'm pretty confident he's wrong about that. The procedure is detailed in the owner's manual, and that would be a pretty important step to leave out.

 

[ajmartineau]

We had this same discussion before. I will not be happy if you can pop the drunk with a 12v source when the auxiliary battery is not dead.
If it is that way they might be able to fix it with an OTA. That would make the drunk useless.
Opening the drunk with a dead battery is also in the manual.

I'm not an expert, please explain. How can the car know if I have the key fob if it's dead? Thanks.

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