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12 volt battery issues and charging protocol. Relationship to very low vampire drain?

MaryAnning3

Supporting Member
Nov 3, 2018
349
142
California
I just read Syonyk's blog post on the Model S 12 volt battery issues and charging patterns from 2016, which is really interesting. I guess at that time there were some issues with how the 12 volt battery was charged and used and there were a lot of failures at that time. I was wondering if anyone has looked at data logs pertaining to the voltage (etc) vs time for a model 3 12 volt battery (basic data logging). This would presumably show how often it charges, how deeply it discharges before charging, whether it uses a float charge state much and maybe some other cool stuff. This should be intimately connected to "vampire drain" and I think would be different pre July 2019 (when drain was about 1% = 750 watt-hours per day, vs post July 2019 when drain is a lot less (maybe 200 watt-hours per day? It is so low now it is a bit difficult to measure accurately unless you leave your car for a couple of weeks or more.)

On those 2016 data logs, Syonyk found that the battery was charging about 50% of the time, but that the charging stopped before it got to a fully charged state, with is not a good protocol for a AGM acid battery at all. (It was almost as if they were following a Li-ion protocol?) Probably now it is a much better and different charging pattern now in the 3. I would be interest what people think or if anyone has had issues with their 12 volt battery. I have measured the 12 V battery voltage under the frunk and each time I found about 14.9 volts, which I am am pretty sure means the battery is charging. (I think that is a pretty high charging voltage btw.) I have never been able to catch the battering in a not charging state, which i think would be indicated by a voltage between about 12.4 and 12.8 volts, or in a float (trickle) charge state (13 to 13.9 volts or so). Does any one know of any data logging or info on the 12 volt? Does it discharge as low as 12.4 V (50%) before charging kicks on or does it start charging at a higher voltage like 12.55 volts (70%). Does it tend to float charge while driving??
 

rrolsbe

Member
Feb 18, 2017
232
129
Albuquerque
Vampire Drain/Loss Tracking

Check out my post #226

Several months ago my M3 would go to sleep with the frunk lid open allowing me to take the voltage/current readings in post #226; however, a firmware update a few months back changed that, it now appears the car will NOT ever go into sleep state if the frunk lid is not closed. Has anyone recently seen their car go into sleep state with the frunk lid open? The best way to confirm the M3 is in sleep state is to listen closely at the charge port door, if you hear a clicking sound it is NOT sleeping. Some people are replacing their 12V batteries with a Li-on, I like you, wonder if the Model 3 AGM charging protocol might be detrimental to a 12V LI-on battery? I am pretty sure cold Li-on batteries need to warmed before they can accept a high charge rate and the current charging system has no method of warming the battery (other than charging at a very low rate).
 
Last edited:

MaryAnning3

Supporting Member
Nov 3, 2018
349
142
California
Vampire Drain/Loss Tracking

Check out my post #226

Several months ago my M3 would go to sleep with the frunk lid open allowing me to take the voltage/current readings in post #226; however, a firmware update a few months back changed that, it now appears the car will NOT ever go into sleep state if the frunk lid is not closed. Has anyone recently seen their car go into sleep state with the frunk lid open? The best way to confirm the M3 is in sleep state is to listen closely at the charge port door, if you hear a clicking sound it is NOT sleeping. Some people are replacing their 12V batteries with a Li-on, I like you, wonder if the Model 3 AGM charging protocol might be detrimental to a 12V LI-on battery? I am pretty sure cold Li-on batteries need to warmed before they can accept a high charge rate and the current charging system has no method of warming the battery (other than charging at a very low rate).

Thanks. That is a very cool post!

If you have a blue tooth data logging voltmeter, you could hook it up to the 12v battery, close the frunk, and log voltage for a while and just read it on your phone with the frunk closed. (Maybe turn off the Tesla app so that the car does not wake up due to your proximity.) I don't think the system can detect the high impedance volt meter and you could learn about all the sleeping and waking cycles. I think a graph of voltage vs time would tell us all there is to know about:
how deeply the 12 v battery discharges,
how long it charges,
what the car does when asleep,
charging protocol while driving,
etc.
 

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
3,732
Buford, GA
The Model 3 batteries haven't been exhibiting the same issues as the other cars. I believe that the engineers saw the issue and resolved the problem.

The battery doesn't stay in float charging, should be easy to tell, are the main batteries even connected?
 

MaryAnning3

Supporting Member
Nov 3, 2018
349
142
California
The Model 3 batteries haven't been exhibiting the same issues as the other cars. I believe that the engineers saw the issue and resolved the problem.

The battery doesn't stay in float charging, should be easy to tell, are the main batteries even connected?
Agree. I am not thinking there is any problem. Just curious.

Not sure what you mean about the main batteries.
 

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