MME Plugged-in overnight cold power usage and 12V LVB

[louibluey]

I got my first look at power usage in detail (Sense high resolution power graph) and LIN BMS LVB 12V data (BMS is the micro computer on the 12V negative battery terminal). Unheated garage, but still a bit warmer than outside it seems (original owner built it onto the side of the home, shingles and all still there on the home side.)

First DC/DC converter operation in the blue LIN data is where I ran a 15 minute precondition cycle. The DC/DC converter came on once more on its own at about 10:48 pm and stayed on for just under 15 minutes. The total energy draw the second time was about 1.7 kWhr. That is more than just charging LVB, so MME was probably doing some heating too. On this first look, I do not see any excessive L2 energy use plugged in over a cold night, as others have reported. Also, I did not observe any low level continuous draw (other than 1 or 2 watts for the chargepoint itself). The usage curve looks like what others with good resolution power graphs have previously shown. The spike on the right in the blue LIN graph, is where I unlocked and woke MME to open the frunk and retrieve the SD card from LIN monitor. That small negative .4V or so dip at 6:34 am is very likely the lights and pony coming on, not sure what woke it. It is possible that spurious wake events are part of the reason some LVB are discharging. As best as I remember, I was sound asleep, iPhone off, fob not moving.

There are a few more cold days, so I will try to add more graphs, still anecdotal to my FE, but hopefully I can add a few more, so more than just one observation.

zoomed in a bit

temperature on the outside wall of the unheated garage

 

[kltye]

I was under the impression that AGMs love to be kept at a very high SoC; I'm a bit disappointed that they let it drift so low, even when plugged in to L2.

 

[Murse-In-Airy]

I think you’re exaggerating. It isn’t that cold in Northern New York.

 

[louibluey]

I think you’re exaggerating. It isn’t that cold in Northern New York.

I think you are running 10-15F colder than us lately (-20F and colder?). We are usually 10-15F colder than downstate (NYC-Long Island).

 

[generaltso]

The MME uses more power than I would have thought to maintain the HVB temp over night. I usually keep my car unplugged in the garage since I have free charging at work. But with it getting down to -12F, I decided to leave it plugged in overnight to see what would happen. The garage is unheated, but stayed at around 26F. From 10pm to 8am, the car consumed 5.5kWh of power, which costs over $1.00 at my current rates. I don't see the need to spend an extra $30/mo without adding charge to the battery, so I'll continue leaving it unplugged.

 

[louibluey]

I was under the impression that AGMs love to be kept at a very high SoC; I'm a bit disappointed that they let it drift so low, even when plugged in to L2.

yea, it's definitely odd that they cycle the soc almost like the HVB. I too would have thought it might be better to keep the LVB mostly charged, maybe 80%?

That said, everything I know about AGM batteries, I learned recently from @Mach-Lee 's threads.

 

[louibluey]

The MME uses more power than I would have thought to maintain the HVB temp over night. I usually keep my car unplugged in the garage since I have free charging at work. But with it getting down to -12F, I decided to leave it plugged in overnight to see what would happen. The garage is unheated, but stayed at around 26F. From 10pm to 8am, the car consumed 5.5kWh of power, which costs over $1.00 at my current rates. I don't see the need to spend an extra $30/mo without adding charge to the battery, so I'll continue leaving it unplugged.

I wonder how much of that is heating the HVB or other parts of MME? Does it still do that if unplugged using HVB, do you see any reduction in range the next morning?

I don't think my MME does this overnight draw except for bitter cold (not sure yet), but even if it did, it would be about $10/mo for me. I did blow my solar net metering budget this year, so now, I am actually paying too.

The way they ask us to plug in when cold, there must be some intended power use strategy.

 

[generaltso]

I wonder how much of that is heating the HVB or other parts of MME? Does it still do that if unplugged using HVB, do you see any reduction in range the next morning?

The way they ask us to plug in when cold, there must be some intended power use strategy.

I don't see any reduction in battery percentage overnight when it's not plugged in, so I assume it's not doing any heating. My guess is that the battery heating when on plug is more about long term health of the battery than anything else. But since I doubt I'll have the car for more than a few years, I'm not too concerned about it.

 

[MachEZRt1]

I did a similar, yet less scientific test this morning. Got very cold here in VA last night (7F was the low). MME sat outside garage not plugged in all night. I plugged it in this morning and the FordPass app indicated “Preparing for Drive” and Juicebox reported charging for almost 21 minutes with 1.4 kwh delivered. FordPass indicated 0 miles added with 0 kwh consumed.

No way for me to tell if the energy was used to top off the 12V or precondition the HVB. MME is set to charge to 90% SOC at home.

 

[Nklem]

The MME uses more power than I would have thought to maintain the HVB temp over night. I usually keep my car unplugged in the garage since I have free charging at work. But with it getting down to -12F, I decided to leave it plugged in overnight to see what would happen. The garage is unheated, but stayed at around 26F. From 10pm to 8am, the car consumed 5.5kWh of power, which costs over $1.00 at my current rates. I don't see the need to spend an extra $30/mo without adding charge to the battery, so I'll continue leaving it unplugged.

Agreed. Mine sucked down 7.74 kWh last night (-5F) in the driveway, $1.85! this does not include a departure setting that occurred later for a toasty interior for another 1.25 kWh, or $0.30. So well over $2.00 per day.

 

[Astraea]

I think you’re exaggerating. It isn’t that cold in Northern New York.

I couldn't help but stay up last night just to see the temperature keep dropping and praying my car didn't just put up a little white flag and flop over and die. Coldest I saw before giving up was -23F. Thankfully she stayed plugged in all night but geez I'm over the cold! ?

 

[generaltso]

Agreed. Mine sucked down 7.74 kWh last night (-5F) in the driveway, $1.85! this does not include a departure setting that occurred later for a toasty interior for another 1.25 kWh, or $0.30. So well over $2.00 per day.

Yeah, it uses more power for this than I ever would have predicted. As a comparison, my wife's RAV4 Prime has a resistive heater built into the battery tray that runs at 13V and only kicks on when the car is plugged in and it's very cold (via the DC/DC converter). That used less than 1 kWh over the same night in the same garage. Of course, that battery is only 18 kWh, so it has a lot less thermal mass. But I still won't be leaving either car plugged in overnight.

 

[MachEZRt1]

did another test last night. This time left it plugged in for about 24 hours and noticed a clear pattern (high of 23F and low of 16F overnight with car outside in the driveway). My MME was pulling 1.7-1.8 kwh on average about every 8 hours.

 

[RickMachE]

For those that leave it sitting on the driveway unplugged, are you noticing any change in the battery % charged? In other words, is the car doing the same thing and depleting the battery? If so, what's the difference between having the battery go down X% and then having to put that back on the charger, and having the battery maintain it's level by hitting the charger every now and then?

Mine charged last night from 7PM to 7:43PM. Then, at 4:18AM it charged until 4:33AM, i.e. 15 minutes. It seems that 15 minutes is what the hit often is. It used 1.683kWh, which is about 21 cents.

 

[murphy62]

The SOC of my HVB has never dropped even after sitting unused and unplugged for a week.
During the same period the LVB went down to 11.8 volts, which is basically discharged but still enough to activate the car.

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