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Trickle charge 12V battery to stop vampire drain?

For about the past year, I've noticed significant vampire drain in my 2013 P85. My car sits in the garage more days that it's driven, and I've noticed that I'm consistently losing about 0.4 to 0.5 mi/hr of range when parked, and this was after disconnecting all 3rd party connections. Long story short, I haven't been able to identify a cause except that I vaguely recall this level of parked power consumption starting after a software update in late 2020. At his point, I've given up trying to figure out what's causing my 12V battery to drain, so now I'm just trying to find a way to minimize the resulting vampire drain.

Has anyone tried keeping the car hooked up to a 12V trickle charger while parked so that the 12V battery charges from that and not the main pack? If so, how has it worked out for you, and do you have any tips you can share? I'd like a setup that I can quickly unplug when I need to leave and easily plug in when I return home (i.e. something that doesn't involve removing the plastic nose cone each time). Is the best hookup option the battery terminals behind the plastic nose cone, or could you possibly attach the trickle charger to an always-on circuit?


Thanks in advance,
Paul
 

Snowstorm

Active Member
Dec 8, 2016
1,575
1,508
Ontario Canada
I would say it would be easiest to hook up the trickle charger to an always on circuit. The amp on a trickle charger would be low, something like 1A so anywhere would do. You might be able to get a trickle charger that connects through the cigarette lighter, though you will have to replace a relay with a jumper to make that always on.

However, you should check that a trickle charger can supply enough current to keep the 12v from draining. You say 0.5mi/hr, so that is like average of 120w (assuming around 250wh/mi). It can be non steady and be even higher power burst. That is a rate that no trickle charger can keep up with.

Before trying the trickle charger (which is unlikely going to have enough power) try to reduce your drain.

Check:
Summon standby is off
Sentry mode is off
Always connected is off
 
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aerodyne

Nose cone car - to LR - 1-23 / 2-05?
Nov 19, 2018
3,737
6,084
Los Angeles
I would say it would be easiest to hook up the trickle charger to an always on circuit. The amp on a trickle charger would be low, something like 1A so anywhere would do. You might be able to get a trickle charger that connects through the cigarette lighter, though you will have to replace a relay with a jumper to make that always on.

However, you should check that a trickle charger can supply enough current to keep the 12v from draining. You say 0.5mi/hr, so that is like average of 120w (assuming around 250wh/mi). It can be non steady and be even higher power burst. That is a rate that no trickle charger can keep up with.

Before trying the trickle charger (which is unlikely going to have enough power) try to reduce your drain.

Check:
Summon standby is off
Sentry mode is off
Always connected is off


If you have Teslafi or other 3rd part app, make sure sleep settings are enabled.

I created a fused harness under the nose cone, that can be stowed and accessed through the frunk latch opening. I can pull out the connecter and hook up to a 4A battery tender brand trickle charger.

It does reduce battery drain, but not electricity cost to a significant degree.

My drain averages 30-70w
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,308
9,002
Boise, ID
@Manta Here is the thread where your question is asked and answered in great detail. It's 14 pages.

 

ucmndd

Well-Known Member
Mar 10, 2016
7,693
14,974
California
I believe this is likely due to the coolant pumps running continuously at higher rates of charge - a change introduced to early cars around the time you started experiencing this behavior.

Do you notice a humming noise coming from the front of your car when parked at a state of charge above ~80% or so? If you do, that's almost certainly what's going on. Adding a 12v tender isn't going to do much of anything to fix it.
 
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ucmndd

Well-Known Member
Mar 10, 2016
7,693
14,974
California
You may find this thread helpful.

 
I would say it would be easiest to hook up the trickle charger to an always on circuit. The amp on a trickle charger would be low, something like 1A so anywhere would do. You might be able to get a trickle charger that connects through the cigarette lighter, though you will have to replace a relay with a jumper to make that always on.

However, you should check that a trickle charger can supply enough current to keep the 12v from draining. You say 0.5mi/hr, so that is like average of 120w (assuming around 250wh/mi). It can be non steady and be even higher power burst. That is a rate that no trickle charger can keep up with.

Before trying the trickle charger (which is unlikely going to have enough power) try to reduce your drain.

Check:
Summon standby is off
Sentry mode is off
Always connected is off
Thanks, Snowstorm.

Yes, I came up with the same estimate of about 120W average draw, but that's what's going into the HV battery pack. I'm assuming there's significant loss when the battery pack charges the 12V battery and that something (running on 12V) is drawing more power than a year ago, hence the need to charge the 12V battery more frequently.

My car is pre-Autopilot, so Summon and Sentry aren't applicable. I did try unchecking Always connected, but that didn't make much of a difference.
 
If you have Teslafi or other 3rd part app, make sure sleep settings are enabled.

I created a fused harness under the nose cone, that can be stowed and accessed through the frunk latch opening. I can pull out the connecter and hook up to a 4A battery tender brand trickle charger.

It does reduce battery drain, but not electricity cost to a significant degree.

My drain averages 30-70w
Thanks, aerodyne.

I disconnected all 3rd party apps when I started logging my vampire drain. I've since reconnected one—Recurrent (they only ping the car 3x/day), and that didn't affect vampire drain.

Do you know how much electricity your car was consuming before you started using your trickle charger?
 
@Manta Here is the thread where your question is asked and answered in great detail. It's 14 pages.

Thanks, Rocky_H!
 
I believe this is likely due to the coolant pumps running continuously at higher rates of charge - a change introduced to early cars around the time you started experiencing this behavior.

Do you notice a humming noise coming from the front of your car when parked at a state of charge above ~80% or so? If you do, that's almost certainly what's going on. Adding a 12v tender isn't going to do much of anything to fix it.
Hmmm...that would make sense. I do notice a humming noise coming from the car (probably the front—I never listened closely enough) often when I'd go into the garage. Since I don't drive my car much (or far) on a daily basis, I keep the SOC around 50%.

Do you happen to know why the pumps run so often? It's not that hot in my garage, especially these days (here in Southeastern PA). Also, do the pumps run off the 12V battery? (I'm guessing yes.)

And thanks for the link to the post. I'll check it out.
 

ucmndd

Well-Known Member
Mar 10, 2016
7,693
14,974
California
Hmm. Last I heard the pumps stopped once the SoC dropped under 80% or so... so if you're storing the car at 50% and still experiencing issues with drain that might not be it.

Lots of speculation in that thread and others as to why the change in behavior, but as far as I know it's just that, speculation.
 
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aerodyne

Nose cone car - to LR - 1-23 / 2-05?
Nov 19, 2018
3,737
6,084
Los Angeles
Thanks, aerodyne.

I disconnected all 3rd party apps when I started logging my vampire drain. I've since reconnected one—Recurrent (they only ping the car 3x/day), and that didn't affect vampire drain.

Do you know how much electricity your car was consuming before you started using your trickle charger?
I don't use the trickle charger any more. It dropped the vampire drain to under 20 watts as I recall, but the charger used energy too, so not worth it.

If you have an 85 pack, the pumps should only run occasionally under 78% SoC.

If the are running all the time below this it might be time for a service call.
 
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I don't use the trickle charger any more. It dropped the vampire drain to under 20 watts as I recall, but the charger used energy too, so not worth it.

If you have an 85 pack, the pumps should only run occasionally under 78% SoC.

If the are running all the time below this it might be time for a service call.
Thanks. Good to know. I did ask the service center about the cause of my vampire drain back in the spring, and they said it was due to my "unauthorized accessories" (radar detector and laser shifter, both on a circuit that shuts off when I exit the car; I've also had them since 2013, and this issue was going on for only a few months at the time). They couldn't find anything on their end causing it. If you ask me, they came across as dismissive about it.

I'll have to ask about the pumps when I take my car in for the seasonal tire swap next month.
 

aerodyne

Nose cone car - to LR - 1-23 / 2-05?
Nov 19, 2018
3,737
6,084
Los Angeles
Thanks. Good to know. I did ask the service center about the cause of my vampire drain back in the spring, and they said it was due to my "unauthorized accessories" (radar detector and laser shifter, both on a circuit that shuts off when I exit the car; I've also had them since 2013, and this issue was going on for only a few months at the time). They couldn't find anything on their end causing it. If you ask me, they came across as dismissive about it.

I'll have to ask about the pumps when I take my car in for the seasonal tire swap next month.



Be lucky they were only dismissive, and did not try to blame a pack failure on a CANbus reader, like they tried to do to me...

Said reader and software, like SMT, scan my Tesla, will show all consumption and you can make a recording of same.

Be sure you remove the reader before you take it to Service!
 
I would say it would be easiest to hook up the trickle charger to an always on circuit. The amp on a trickle charger would be low, something like 1A so anywhere would do. You might be able to get a trickle charger that connects through the cigarette lighter, though you will have to replace a relay with a jumper to make that always on.

However, you should check that a trickle charger can supply enough current to keep the 12v from draining. You say 0.5mi/hr, so that is like average of 120w (assuming around 250wh/mi). It can be non steady and be even higher power burst. That is a rate that no trickle charger can keep up with.

Before trying the trickle charger (which is unlikely going to have enough power) try to reduce your drain.

Check:
Summon standby is off
Sentry mode is off
Always connected is off
These devices may draw additional power from the 12v battery:
- 3rd party dash cam
- USB cigarette adapter with LED light or device its powering
 

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