12V LVB MME start, MME Accessory Mode

[louibluey]

I took a first look at 12V LVB starting current today. There are certainly a lot of possible variables including seat heat, wheel heat and climate settings, not sure yet how important those are. Also, the headlights coming on might be a dominant load.

Anyway, what I am seeing on the negative black 12V battery cable is only about 2 seconds of substantial 12V battery (LVB) load, at which point MME comes on and the DC-DC converter takes over. The 2 seconds is a rough ramp to about 25A with a possible spike up to or over 50A for less than a tenth of a second. This run started from about 8A, maybe some lights were on from the last run, not sure.

On my original idea to run wires to the bumper for external starts, I am thinking now it is not worth the effort.

It is probably just as easy to always use the jump points, especially with the new idea to cut holes over the jump points.

Of course in the flat battery case, more energy is needed, because first, you have to pump enough current/energy into the dead battery to get near the 12V starting voltage.

Sample run, Each horizontal point is 100 mS, vertical axis is in current, but only valid from about -10A to +50A:

 

[Crilly]

What happens when you press start with out pushing the brake pedal?

 

[louibluey]

What happens when you press start with out pushing the brake pedal?

Excellent, the Dunkin Donuts parking lot question! (snacking while in accessory mode, Does MME run on the 12V battery?). The answer (anecdotal, only one test run this am) is sort of, yes some of the time.

Need to run this test again, maybe for a continous log of about 100 minutes. There was significant LVB battery drain at about 25A for about 20 minutes (35 Ah battery).

At first, MME ran on DC-DC converter, then, it went back on only battery (converter off), later, MME just turned off on its own (car left in garage, key fob in car, unattended), there may be a bit of converter activity at the end of the third screen print [this part has been edited/corrected]. There is some missing data (minutes) between the recordings.

Raw data screens are 4 - 20 mA loop, 4 mA is zero A (battery ground terminal cable), 20 mA is 50A, and it goes minus to about 12A (when converter is on, this is minimum limit for the DCCT sensor in this direction, the charging current is higher than shown). Any fine detail waveform patterns are suspect by "aliasing", a waveform that represents something much faster that does not show at a slow sampling rate. Data was 100mS samples, every 0.5 seconds, for 5 min, 20 min, then last two for 30 min.

I was thinking, okay, pretty standard start curve, then DC-DC converter (saturated battery being charged, more than 12A charging current, beyond my negative scale minimum for this direction of the DCCT sensor). Then, I saw the charging current easing up (less than 12A), and wondered if anything intersting would follow. (600 readings, .5s, 5 min)

In this next graph (1b), the converter turns off, and MME goes full on battery (battery discharge current about 25A, for the stuff I had running, I think seat heat 2, wheel heat, climate auto). (2400 readings, .5s, 15 min)

Next, after running on 12V LVB alone (about 25A), MME turned off on its own at about half way through this graph. --So, from last graph to this one, MME drained the LVB at 25A for about 20 minutes, that is a lot of energy/power for a relatively small 35A battery.-- Remember, anything above about 4 mA is battery only powering MME. After a while, the converter comes back on (I think) for a short period at the end. (3600 readings, .5s, 30 min)

Finally, the unattended MME, fob in the car, still off (~4 mA (need to double check exact number) is zero LVB current). Not sure what happened here after turn off, possibly just shedded another small load, probably not LVB charging.(3600 readings, .5s, 30 min)

The times on the screen prints are wrong, but still give a feel for duration, the actual start times were about 10:00 am, 10:07 am, 10:35 am, and 11:06 am.

 

[louibluey]

Accessory Run, MME does use 12V battery during accessory mode, after a time on DC-DC converter

In this run, MME started LVB battery only operation at about 4:09, and ran on LVB battery (about 25A) to about 4:40, so about 31 minutes of 25A load on the 35 Ah battery, then MME started to shut down by itself at about 4:40.

It looks like the initial DC-DC converter runs until it considers the 12V battery to be charged, then MME runs on the little 12V battery. Unclear if it turns off by some kind of time out, or because of 12V battery discharge? There is no follow on DC-DC converter charging in this example.

 

[MTNestr]

Good work & Thanks for sharing.

I also have a MME FE. Following your study, what are your recommendations and precautions for the MME and it’s Low Voltage Battery? When I park and lock my MME is there any remaining load on the LVB?

 

[Maquis]

Very good info. I was wondering specifically about this because I just leave the fob in the car while it's parked in my (locked) garage. Thanks for doing this and sharing!

 

[louibluey]

Just LVB operation, sitting in a parking lot in accessory mode from this last measurement. I would keep MME "On" (start with brake), even resting in a parking lot for now, as opposed to tens of minutes or more in accessory mode.

There could be so many combinations to explore, plugged in, not plugged in, key in the MME, etc., not sure how much more I will do short term.

Generally with past EVs, key fobs were not left in the car, just to be sure that the electrical systems shutdown into a normal sleep mode. No hard data on that one, mostly advice in the various forums.

 

[Finkerton]

In this run, MME started LVB battery only operation at about 4:09, and ran on LVB battery (about 25A) to about 4:40, so about 31 minutes of 25A load on the 35 Ah battery, then MME started to shut down by itself at about 4:40.

Note that with the MME on you can turn off the 30-minute shutdown. It will turn back on the next time the MME is turned on (for safety likely). I don't know if this is also true in accessory mode. But I'd be interested in knowing if you can keep ~25A load (half on one accessory socket, half on the other) for a few hours so long as you keep the MME on...

 

[louibluey]

Note that with the MME on you can turn off the 30-minute shutdown. It will turn back on the next time the MME is turned on (for safety likely). I don't know if this is also true in accessory mode. But I'd be interested in knowing if you can keep ~25A load (half on one accessory socket, half on the other) for a few hours so long as you keep the MME on...

I noticed the 30 minute button the other day (since the measurements). Also, can MME use the steering wheel camera (or other sensors) to know if it is occupied? I was out of the car during those tests, so maybe it did the 30 minute shut down thing once not occupied.

I may need to use a little caution. Even with non-contact measurements (the DCCT over the negative battery terminal), I sure do not want to cause a problem. For example, before these three or four runs of 25A battery drain, my radio presets were fine. Then, since my last test, I have now joined the club of lost presets. Maybe some systems are more sensitive to battery voltage below a certain minimum voltage?

I ordered (and received) a fused 12V lighter cord too, so I can also log voltage, but have not done more measurements yet.

Also, just called a local dealer to see if they can tell from OASIS if I have the battery software fix.

 

[Finkerton]

Not sure about accessory mode but if it's on and parked and you disable the 30 minute auto shutoff, you can leave the car and it will stay on. That's how I charged the LVB once I jump started it...powered the MME on while it was connected to the other car, disconnected it, disabled the 30 minute shut-off, walked out, and left it alone for a couple of hours. It was still on when I came back (LVB happy too).

 

[Crilly]

What do you think caused dead 12 volt battery? Was the door cracked?

 

[Finkerton]

What do you think caused dead 12 volt battery? Was the door cracked?

There is an issue where if the car is plugged into a charger, it doesn't properly turn on the mechanism that keeps the LVB charged from the HVB. So the various accessory bits -- wifi and bluetooth to connect to FordPass, any cabin preconditioning, etc. -- all drain the LVB but it doesn't get replaced.

There is a software update that fixes it. Technical Service Bulletin 21B02. But it seems Ford did not properly identify the list of affected vehicle VINs so even though the TSB says it's identified in Oasis/FSA VIN lists, a bunch of us are finding that's not the case, and it causes knock-on effects. See https://www.macheforum.com/site/thr...d-update-mach-e-jump-started.3457/post-135888 for more gory details.

 

[louibluey]

Just a quick update, we got another piece of the puzzle in this other post, the latch actuator is motor driven, which kind of makes more sense for a 2021 auto mechanical actuator (over a simple solenoid, very last century). Also, note the interlock functions. See post #8 of the link below. So, the next question (hmm, warmer sunny days coming soon here!) is how much current, power, time does it take to open the frunk latch using the red/black ring lug wires in the bumper access port in a simulated LVB fail (Fuse F72 pulled).

The front trunk release module (GFM) provides power to the electronic latch release actuator for the front trunk luggage compartment. ... The actuator consists of a single motor unit performing two consecutive release operations. The first operation releases the primary latch, and the second operation releases the secondary latch. When vehicle speed is less than 2 mph (3 km/h), both release pulses will be delivered by the module to release primary and secondary latch positions. When vehicle speed is greater than or equal to 2 mph (3 km/h), the module will only deliver the power signal to release the primary latch. Latch positions will be manually reset when the user applies downward force to the hood of the front trunk to place it back into closed position.

https://www.macheforum.com/site/threads/ssm-49672-–-front-luggage-compartment-closing-effort.4577/#post-136122

 

[MTNestr]

When the MME is Turned On by pressing the brake does the LVB begin to charge using the HVB? If so, does it continue to charge the LVB until completely charged?

When the MME is Turned On using the app does the HVB charge the LVB? If so, does it continue to charge the LVB until completely charged? Is the answer the same if the charger is plugged into the MME?

When driving the MME, is there a constant LVB charge? Could I put too big of a load on the LVB while driving with the addition of Dash Cams and Radar Detectors , etc?

 

[MTNestr]

Using a Volt Meter that is plugged into the cigarette lighter socket can I tell if the LVB is being charged or not?

Sponsored