2025 MME Rally left me stranded... HVBJB failed...

[JohnFoxeSheets]

I know I'm the one that brought up the 12V battery as a likely cause, but there was another person here recently (don't recall the thread title) who had a similar issue and it turned out it wasn't the 12V battery.

Something I'm still not clear about. Is the 12v supposed to charge from the HVB or only when the car is on a charge?
I also wonder about the necessity of a 12v at all, why not replace the 12v with a voltage converter from the HVB. The idea of have to "jump start" an EV seems kinda silly. I have a Zero motorcycle that uses a 80v to 12v converter eliminating the need for any additional accessory only type battery.

This has been discussed at length on this forum. Yes, the HVB is supposed to keep the 12V battery charged. In the past there were a lot of problems with the choices Ford made to make that happen. Since then they've improved it but there can still be holes. Keeping the DC-to-DC converter on all the time is problematic - it draws current so it would run down the batteries faster. And there're also the risks associated with having ~400V energized in the car all the time. So instead the engineers need to figure out exactly when to charge the 12V battery and do it in a way that doesn't prematurely age that battery. It's a delicate balancing act.

I do think that Ford should require that the 12V battery be fully charged before customer delivery. No more of this drive the car off the truck, remove the plastic and the suspension blocks and call it good.

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[Paul H. Martinez]

Makes more sense now. That kind of clears it up.
Thanks

 

[MellowJohnny]

If 12V, it's ridiculous. At this point, tech should keep it charged.

Is there any feasible way to eliminate the 12v altogether? I appreciate stepping 400v down to 12v is "a lot" but could it be done? Let's ignore cost for now

**EDIT**

Seems this was answered earlier in the thread...

 

[moog]

^^ Yea, you don't want 400V flying through all of the vehicles electronics.
Very much NOT a good idea.

 

[highland58]

There was previous discussion of moving to a 48V LVB system, I think the dumpsterTruck was doing this? Would this help with this particular issue, or would it just complicate the issue?

 

[jsus]

There was previous discussion of moving to a 48V LVB system, I think the dumpsterTruck was doing this?

Yup.

Cybertruck uses a 48V lithium-ion low voltage battery. The 48V battery powers the windows, doors, touchscreen, and other low voltage vehicle systems when the high voltage Battery is unavailable. The 48V battery also provides a redundant source of power for critical systems (such as power steering).

https://www.tesla.com/ownersmanual/cybertruck/en_us/GUID-2233D4D1-D4E5-4897-9A41-DE8593381CAA.html

 

[E90alex]

There was previous discussion of moving to a 48V LVB system, I think the dumpsterTruck was doing this? Would this help with this particular issue, or would it just complicate the issue?

12V vs 48V in and of itself wouldn’t make a difference. But a 48V battery would most likely be a proprietary Li-ion.

The issue is relying on a lead acid battery. A Lithium-ion LV battery would be designed to last the life of the car like the HV battery would and would basically eliminate all 12V issues, but there’s no standardized/commoditized off the shelf 12V Li-ion battery and it would be much more expensive than lead acid.

Tesla has switched to proprietary Li-ion LV batteries since like 2022 and is the only EV company that has done so I believe. Some high end German cars use a Li-ion 12V for weight savings but they’re like $1500+.

 

[Snakebitten]

The Powerboost F150 has similar vulnerabilities to 12V shortcomings. Or put another way, it goes from Jeckyl to Hyde big time if the 12V buss is anemic.

But one advantage it has over the Mach-E is that Ford equipped it with a small auxiliary battery under the rear passenger seat. So the 40+ modules onboard can still talk and successfully handshake as long as one of the two batteries can provide the necessary voltage.

Also, if you push the start button without pressing the brake, therefore putting the truck in accessory mode, it turns on the DC/DC converter, thus providing the necessary robust voltage necessary to support a weak AGM battery(s).

Still, the Powerboost is just as notorious as the Mach-E for having issues related to 12V battery management shortcomings.

I wonder if on a Mach-E that puked, like the OP's did, might have been temporarily rescued by choosing accessory mode first, for a few seconds while the low voltage modules all booted up, and then pressed the brake and start button a second time to go to Ready Mode?

 

[Atmj]

Wow! Sorry for your problems. I agree, this whole 12 Volt battery issue should have been resolved by Ford years ago.
I just bought a jump start unit, and a new battery charger in anticipation of any problems.

 

[XPLOR]

Yes, it's Velocity Blue with the gray wheels...

 

[XPLOR]

Regarding...

I wonder if on a Mach-E that puked, like the OP's did, might have been temporarily rescued by choosing accessory mode first, for a few seconds while the low voltage modules all booted up, and then pressed the brake and start button a second time to go to Ready Mode?

I did try this, but didn't work....​

Regarding...

The 48V battery also provides a redundant source of power for critical systems (such as power steering).
You should have seen the tow truck driver trying to steer this 5,000lb brick! Nearly impossible!

 

[Kamuelaflyer]

^^ Yea, you don't want 400V flying through all of the vehicles electronics.
Very much NOT a good idea.

I grounded a B-747 in Chicago O’hare one morning when I went to move a fuel control valve switch as part of a test and got shocked with full 120v ac instead of nothing (the switches were all supposed to be 12v dc operated). Imagine such a glitch with 400v.

In our case it was a blessing, cause who wants to go to Columbus, Ohio when they could stay in downtown Chicago by the lake?

 

[JohnFoxeSheets]

I wonder if on a Mach-E that puked, like the OP's did, might have been temporarily rescued by choosing accessory mode first, for a few seconds while the low voltage modules all booted up, and then pressed the brake and start button a second time to go to Ready Mode?

It is my understanding that accessory mode on the Mach E is a very bad idea, as it specifically does not turn on the DC/DC converter and instead just runs all 12V modules from the 12V battery. So attempting to do that with a low 12V battery could simply result in the 12V battery dying instead of it powering up enough to get the DC/DC converter running... ?

 

[Snakebitten]

It is my understanding that accessory mode on the Mach E is a very bad idea, as it specifically does not turn on the DC/DC converter and instead just runs all 12V modules from the 12V battery. So attempting to do that with a low 12V battery could simply result in the 12V battery dying instead of it powering up enough to get the DC/DC converter running... ?

Interesting.

I'm sure that there are those at Ford on the Mach-E team that could give a very good reason for accessory mode NOT enabling the DC/DC converter. But I wish, naively perhaps, that it did.

For lots of reasons and scenarios.

 

[JohnFoxeSheets]

Interesting.

I'm sure that there are those at Ford on the Mach-E team that could give a very good reason for accessory mode NOT enabling the DC/DC converter. But I wish, naively perhaps, that it did.

For lots of reasons and scenarios.

I'm less confident the folks at Ford could give us a good reason, but like you, I think it should enable the DC/DC converter in accessory mode (or do away with that mode entirely).

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