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Dead 12 V battery in my Model S Plaid

brkaus

Well-Known Member
Jul 8, 2014
8,058
6,557
Austin, TX
But, the HV battery is not charging when the door is open. I get 3 or 4 amps of juice from the wall connector. You think that dribble is going to the HV battery and not the 12 volt? Why?
There is no path from the wall plug to the 12v system w/o going through the DC2DC converter (unless changed on the plaid). They can control how much goes into the HV battery by controlling the voltage on the main DC bus. But it still goes to HV DC first.
 
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ucmndd

Well-Known Member
Mar 10, 2016
6,936
13,082
California
But, the HV battery is not charging when the door is open. I get 3 or 4 amps of juice from the wall connector. You think that dribble is going to the HV battery and not the 12 volt? Why?
It's splitting hairs where the "dribble" is going when it's actually dribbling. My point was to to suggest that the conditions under which the car will draw shore power are well defined and discrete:

* When actively charging the HV battery
* When the car is "on" (i.e. door open, butt in driver's seat, etc)
* When the climate control is on

To my knowledge, that's it. The car doesn't arbitrarily close the contactors here and there to power the chargers and DC-DC converter to draw small amounts of shore power under other circumstances.
 
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PCMc

Member
Jul 1, 2016
256
223
Columbus, IN
But, the HV battery is not charging when the door is open. I get 3 or 4 amps of juice from the wall connector. You think that dribble is going to the HV battery and not the 12 volt? Why?
3-4 amps on initial start-up can likely be the HVAC system drawing that much power. You're only talking about 1 kW, so about what you full size microwave over could be drawing from a power consumption standpoint.
 
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Tam

Well-Known Member
Nov 25, 2012
9,242
7,935
Visalia, CA
...shore power...

In think in 2012, the HVAC would use the power from the battery and not shore power. Sometimes after that, it would use shore power whenever it's plugged in.

Could it be that is happening with the new 12V lithium battery too? And that it would now use shore power whenever it's plugged in but there's a HPWC software bug that's now just fixed?
 

CBGPE

Supporting Member
Supporting Member
Jan 15, 2020
20
28
SPRING VALLEY
When I am plugged into the wall connector, and open a door, the wall connector starts supplying the car with small amounts of power to power the accessories. It stops shortly after I close the door. I assume if you have Sentry on, or the car needs some power while plugged in, it does not use the HV battery for everything. I think if this process is not working, the 12V battery could die causing the problem described in this thread
My sentry was and is off when plugged into the wall charger. I did note this morning when I went into the car to take a photo of my signal light fix/tactile reminder the wall charge system woke up and provided a minimal level of current. I suspect this is to prevent main battery draw.
 

DerbyDave

Active Member
Jul 2, 2020
1,116
659
Kentucky
My sentry was and is off when plugged into the wall charger. I did note this morning when I went into the car to take a photo of my signal light fix/tactile reminder the wall charge system woke up and provided a minimal level of current. I suspect this is to prevent main battery draw.
Everyone says this is not correct, but this is also my experience.
 

Wol747

Active Member
Aug 26, 2017
1,063
530
Tea Gardens
My understanding is (Raven, not Plaid) the 12v battery is charged from the drive battery. Period. And the drive battery is charged from an external source. Period.
Perhaps the Li 12v battery is sensitive to relatively small drawdown, triggering a brief charge from the HV battery which in turn triggers a short charge from the wall? The same sort of thing happens with the Raven, with frequent clattering of connectors, fans starting up etc. There appears too little tolerance of hysteresis margins in the software.
 

DerbyDave

Active Member
Jul 2, 2020
1,116
659
Kentucky
Apparently, this short charge of the drive battery from the wall connector limits itself to only the amount of current needed to sustain the 12 volt battery charge and the drive battery at its current level of charge. It never draws more than 7 or 8 amps during a door opening event, even though I have the charging rate set to 48A. It does this sustain charge no matter the setting to delay charging for off-peak low rates for energy. It was a matter of concern to me that it came on at any hour, until I realized it was a "trickle" charge.
 

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