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Resetting the BMS

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D

darktrancer_la

Member
Oct 6, 2017
10
10
Los Angeles
#1
Today I updated the software on my Model S and then went into service mode to see if any changes were made. I found a new button under the HV section of service mode that allows you to reset the BMS. I was already on the an email chain with Re\cell to get a battery replacement because of the BMS_029 error. Has anyone run this process on their Model S? Does running the reset allow for the BMS to retest and recalibrate the battery? How dangerous is it to run this?

Thanks in advance.
 
#2
And the visual below:

IMG_5151.jpeg

I wouldn’t run it outside warranty :)
 
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#3
I have tried it in my Model 3 but it failed because somehow it expected the contactors to be opened before test and I did not know how to do that. The reset doesnt open the contactors so it must be done manually?
 

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#5
I have the BMS_u018 error, which have cleared on numerous occasions. I stubbled across the BMS reset in service mode and decided to give a try. This video shows what happened. If you have some addition info, please let us know here.
 
#9
Nothing new...
Already been talked about in few other threads. Nobody was successful yet to run that due to Contactors closed...
My bet its for cases when u have a BMS error that actually disables contactors like i had, f123/w123
 
#10
couple of notes:
1) the functionality demo’ed in this video is only available on MCU2 upgraded vehicles. the MCU1 just doesn’t have the horsepower to support this level of UI complexity.

2) the reset on the BMS just restarts/reboots the BMS it doesn’t reset any codes/alerts

3) the reset in this case likely failed because the contactors weren't open/couldn’t be opened (the pack is after-all in use). however on one of the other high voltage screens in the MCU2 there is (or at least there was previously) a button to open the contactors manually. once the contactors have been opened, the BMS reset should work. but again, it’s simply a reboot/restart. potentially valuable, but it’s unlikely to restore any ‘latched’ alerts such as a BMS_u029

4) the u018 error outlined in the video is the result of a genuine pack imbalance. some lengthy sessions with trickle charging *may* restore some balance and clear the error, but this problem is likely to return/only get worse. the only durable solution* for this kind of imbalance is to either remove one or more modules containing the lowest capacity bricks and then reconfigure the pack - for example into a 350V 14 module pack - or replace the pack altogether.

* the other option is to identify the individual cell(s) causing the capacity imbalance (more on this in an upcoming post) and then isolate the faulty cells from the brick. then proceed to isolate a similar number of cells for each of the remaining 95 bricks in the pack (in order to keep the pack balanced). of course with 7,104 cells in the pack, happy hunting… ;)
 
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#11
Recell said:
* the other option is to identify the individual cell(s) causing the capacity imbalance (more on this in an upcoming post) and then isolate the faulty cells from the brick. then proceed to isolate a similar number of cells for each of the remaining 95 bricks in the pack (in order to keep the pack balanced). now, with 7,104 cells in the pack, happy hunting… ;)
Click to expand...
Glad to hear this from a reliable source ;)
I mentioned this in some other thread (can't remember) as a theory but would be nice to see this in reality.
Not an easy solution but saves a pack from landfill/recycle if it still got life in it.

For isolating failed cell, i had an idea that maybe a current clamp can be used on each wirebond but i can't find small enough clamps for sale anywhere...
Maybe a custom one can be made...
 
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#12
isolating a cell requires some pretty precise equipment, since a current clamp/loop won’t fit - at least not predictably and reliably. while definitely spendy, a positional current probe based on a miniaturized fluxgate magnetometer has the level of precision, to within 10 milliamperes, needed to detect cell-level defects.

in fact, positional current probes have enough precision that you actually have to isolate/account for the earth’s magnetic field when taking measurements 😲

sure Pete Gruber and crew can tell you more on how they do this. 😉
 
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#14
xxaarraa said:
Hello, I am about to replace my 12V battery and I believe you have to disconnect the fireman's loop to do that. Wouldn't that open the contactors and has anyone tried resetting the BMS after disconnecting the fireman's loop?
Click to expand...
Thats how you do it. Make the screen selection, pull firemans loop, start reset, wait for it to complete, plug back in and done. Total process >4 minutes
 
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