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12v battery is now charging 24 hours / day

sorka

Well-Known Member
Feb 28, 2015
8,151
5,933
Merced, CA
Ah, found the post:




Now, doesn't this mean that on pre-2015 contactors stay closed and 12V battery is charged with the "regular" DCDC? On post-2015 contactors are open and MCU is powered from the standby DCDC..

Anyway, I'll measure how my 12V behaves on 2013 car.. :)

Yup. Good catch. I mis interpreted what @wk057 said initially and it explains an unsolved mystery.

When I first got the MCU2 upgrade, my vampire drain was higher than before. I also noticed that my 12v battery was constantly being charged and realized my contactors were never opening. When coming to the car after sitting for hours, opening the door did not result in the normal clackity click noises from the contactors closing. Hence the reason I started this thread. I assumed that it was because the contactors were staying closed all the time and it turned out it WAS the reason hence my increased vampire drain.

I then got those BMS errors and took it into Tesla. They said my HVL nodes were misconfigured and they corrected them. Later I reported that my vampire drain was higher after the MCU2 upgrade but then I turned Teslafi polling off and the drain dropped to pre-mcu2 upgrade levels. Well it turned out not to have anything to do with that at all. What made the vampire drain lower was them fixing the HVL node configuration to properly use the standby converter. So after I got the car back, my vampire drain was lower but I thought it was because I'd turned off Teslafi polling.

So this morning I verified that when I open my door that the contactors are indeed clicking closed as they used to do before the MCU2 upgrade.
 

wk057

Senior Tinkerer
Feb 23, 2014
5,692
11,810
Hickory, NC, USA
Yup. Good catch. I mis interpreted what @wk057 said initially and it explains an unsolved mystery.

When I first got the MCU2 upgrade, my vampire drain was higher than before. I also noticed that my 12v battery was constantly being charged and realized my contactors were never opening. When coming to the car after sitting for hours, opening the door did not result in the normal clackity click noises from the contactors closing. Hence the reason I started this thread. I assumed that it was because the contactors were staying closed all the time and it turned out it WAS the reason hence my increased vampire drain.

I then got those BMS errors and took it into Tesla. They said my HVL nodes were misconfigured and they corrected them. Later I reported that my vampire drain was higher after the MCU2 upgrade but then I turned Teslafi polling off and the drain dropped to pre-mcu2 upgrade levels. Well it turned out not to have anything to do with that at all. What made the vampire drain lower was them fixing the HVL node configuration to properly use the standby converter. So after I got the car back, my vampire drain was lower but I thought it was because I'd turned off Teslafi polling.

So this morning I verified that when I open my door that the contactors are indeed clicking closed as they used to do before the MCU2 upgrade.

Unless you got a battery upgrade to a last gen 2015 85 pack or newer (90/100) ... then your pack doesn't even have a standby supply. This started in the v2.0 packs and only once the X was close to shipping (its body control module was the first thing to utilize the standby supply). HVIL nodes has nothing to do with that. That's just a count of resistors on the HVIL safety loop... which wouldn't change or have anything to do with the MCU, except that the MCU houses the gateway which had the HVIL node count configuration parameter. If it's incorrect I could see this preventing BMS sleeping, but has nothing to do with the standby supply.
 
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Zuikkis

Member
Aug 19, 2020
248
288
Finland
Ok.. I measured the +12V voltage several times during the day. It seems to follow the pattern which shows in @murphyS90D 's graphs. +12V is charged periodically a few times per day. Voltage is about 14.3V while charging. Then when charging stops voltage starts to fall slowly. After about 12.5V it starts charging again, but it takes several hours until it drops that low.
 

ShawnA

Supporting Member
Nov 13, 2017
948
687
Edwardsburg, MI
Hi All,

I will add my data to the collection.
The car is a Model S 85 D manufactured 4/15 delivered 5/15.
Upgraded to MCU2 in August 2020.

Model S Voltage Graph.png


The graph is from a 12 volt bluetooth battery monitor on Amazon.
It has an odd scale in that in the left axis one division is 1 volt in the center
and 2 volts at the top and bottom.

The voltage decays to below 12.5 Volts and charges at above 14 volts.
Generally after the charge stops the voltage drops quickly to below 13 volts.

The time scale is in one hour increments starting and ending at midnight.

Measurements are taken at the battery terminals.

Shawn
 
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sorka

Well-Known Member
Feb 28, 2015
8,151
5,933
Merced, CA
So after I got my car back from the second time trying to get Tesla to diagnose sporadic u008 and w094 BMS errors, I went about a month with 5 long distance trips (more than usual during the last year) and no return of the errors. They insist they could not find the cause and to just keep an eye on it and they'd leave the ticket open for a few months so that I could text through the app if the problem came back. My service advisor said she'd see it instantly if it was during work hours and would have someone remote diagnose the issue. Two weeks later the ticket closed which is the normal amount of time after a service visit but the problem hasn't returned yet anyways.

I also started to realize that the low voltage behavior was different it was after the MCU2 upgrade but before this last visit to fix the errors. I started to realize I was hearing contactors open and close while I was in the garage and hearing the inverter firing up. So I put a voltage logger on the 12v battery with the frunk out yesterday and logged 12 hours.

chart (1).png


So it appears the low voltage system behavior is NOW like it was before the MCU2 upgrade but with the following difference. Before the upgrade, the contactors would close and fire up to charge for a few minutes like you see in the chart above between hours 3.5 and 9 except that instead of every 70 minutes like above, it was between 4 and 6 hours. If the 12v battery was near the end, it would be every 4 hours but went to 6 hours right after I replaced the 12v battery 18 months ago.

Right after the MCU2 upgrade to the right before the second visit to daignose the BMS errors, the 12v system stayed on 24 hours a day and kept the battery topped off all the time. @wk057 , I think you said this was needed because the the MCU2 draws more power and if you don't have the standby inverter, the contactors stay open 24/7 and the inverter runs 24/7 and the pumps run at a very low rate 24/7, right?

So I have the MCU2 upgrade and this chart represents the current behavior. Can you speculate on what's going on here? Did Tesla reconfigure the behavior to be like it was before even if it means more frequent contactor cycling? Could this have been done to try and fix the BMS errors I was getting ever since the MCU2 upgrade?

Also, one odd thing. During the spikes of charging that only last a few minutes between hours 3.5 and 9, you can hear the inverter buzzing away AND two pumps that sit right under the frunk tub (tub is currently out) pumping away. But during the long 70 minute periods of charging, no inverter sound and the pumps and moving any fluid at all. What does this mean?
 

sorka

Well-Known Member
Feb 28, 2015
8,151
5,933
Merced, CA
Hi All,

I will add my data to the collection.
The car is a Model S 85 D manufactured 4/15 delivered 5/15.
Upgraded to MCU2 in August 2020.

View attachment 659638

The graph is from a 12 volt bluetooth battery monitor on Amazon.
It has an odd scale in that in the left axis one division is 1 volt in the center
and 2 volts at the top and bottom.

The voltage decays to below 12.5 Volts and charges at above 14 volts.
Generally after the charge stops the voltage drops quickly to below 13 volts.

The time scale is in one hour increments starting and ending at midnight.

Measurements are taken at the battery terminals.

Shawn

I noticed that your cycling is slower than mine. i.e. comes on and charges for 3 hours and then off for 7 hours. I'm guessing that your 12v battery is newer than mine and has more capacity so it'll take longer to fill up and can draw more watt hours before needing to be topped off again.
 

wk057

Senior Tinkerer
Feb 23, 2014
5,692
11,810
Hickory, NC, USA
So after I got my car back from the second time trying to get Tesla to diagnose sporadic u008 and w094 BMS errors, I went about a month with 5 long distance trips (more than usual during the last year) and no return of the errors. They insist they could not find the cause and to just keep an eye on it and they'd leave the ticket open for a few months so that I could text through the app if the problem came back. My service advisor said she'd see it instantly if it was during work hours and would have someone remote diagnose the issue. Two weeks later the ticket closed which is the normal amount of time after a service visit but the problem hasn't returned yet anyways.

I also started to realize that the low voltage behavior was different it was after the MCU2 upgrade but before this last visit to fix the errors. I started to realize I was hearing contactors open and close while I was in the garage and hearing the inverter firing up. So I put a voltage logger on the 12v battery with the frunk out yesterday and logged 12 hours.

View attachment 669988

So it appears the low voltage system behavior is NOW like it was before the MCU2 upgrade but with the following difference. Before the upgrade, the contactors would close and fire up to charge for a few minutes like you see in the chart above between hours 3.5 and 9 except that instead of every 70 minutes like above, it was between 4 and 6 hours. If the 12v battery was near the end, it would be every 4 hours but went to 6 hours right after I replaced the 12v battery 18 months ago.

Right after the MCU2 upgrade to the right before the second visit to daignose the BMS errors, the 12v system stayed on 24 hours a day and kept the battery topped off all the time. @wk057 , I think you said this was needed because the the MCU2 draws more power and if you don't have the standby inverter, the contactors stay open 24/7 and the inverter runs 24/7 and the pumps run at a very low rate 24/7, right?

So I have the MCU2 upgrade and this chart represents the current behavior. Can you speculate on what's going on here? Did Tesla reconfigure the behavior to be like it was before even if it means more frequent contactor cycling? Could this have been done to try and fix the BMS errors I was getting ever since the MCU2 upgrade?

Also, one odd thing. During the spikes of charging that only last a few minutes between hours 3.5 and 9, you can hear the inverter buzzing away AND two pumps that sit right under the frunk tub (tub is currently out) pumping away. But during the long 70 minute periods of charging, no inverter sound and the pumps and moving any fluid at all. What does this mean?

I never said the HV battery stays on 24/7 after MCU2 with no standby DCDC in the battery, I just said it would increase the need to close the contactors to engage the DCDC, thus increasing vampire drain.

Tesla's definitely been trying to find ways to address this, but the lack of standby supply and the increased power usage of MCU2 when powered by the normal 12V system makes this a pretty impossible task. Either they short cycle the 12V system all the time (killing the 12V battery in the process), or they keep the main contactors closed (wasting as much as ~20 rated miles per day, depending on conditions). So they're trying to find a spot in between.
 
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