Trickle charge 12V battery to stop vampire drain?

[Manta]

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]

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

 

[aerodyne]

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]

@Manta Here is the thread where your question is asked and answered in great detail. It's 14 pages.

Any reason not to hook up a battery tender to the 12 volt battery ?

My neighbor who does not work on cars just had his 12 volt battery replaced. He does not look forward to doing this every 12-18 months. He asked me if I could hook up a Battery Tender to his 12 volt battery. It looks pretty simple to me to do this. He would like to top off his 12 volt battery...

teslamotorsclub.com

 

[ucmndd]

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.

 

[ucmndd]

You may find this thread helpful.

Continuous Faint Humming Noise When Parked

Parked the car in the garage after a 20 miles easy drive today. Plugged in. The temperature outside ~78F, and ~68F inside the garage. About 6 hours later I'm still hearing a faint humming noise, the kind I usually notice when the car is being charged at home off the HPWC (the car is not charging...

teslamotorsclub.com

 

[Manta]

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.

 

[Manta]

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]

@Manta Here is the thread where your question is asked and answered in great detail. It's 14 pages.

Any reason not to hook up a battery tender to the 12 volt battery ?

My neighbor who does not work on cars just had his 12 volt battery replaced. He does not look forward to doing this every 12-18 months. He asked me if I could hook up a Battery Tender to his 12 volt battery. It looks pretty simple to me to do this. He would like to top off his 12 volt battery...

teslamotorsclub.com

Thanks, Rocky_H!

 

[Manta]

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]

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.

 

[aerodyne]

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.

 

[Manta]

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]

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!

 

[The Enterprise]

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

 

[Manta]

So my car is continuing to drain power while idle (see below for stats while parked), and I asked Tesla about it at my most recent service visit. They said everything checked out as normal and they couldn't find anything wrong with the car. They did give me a P85D as a loaner, and I noticed that that car is always quiet (i.e. no coolant pump running) when I go into the garage. I suppose I can hope for a software update that addresses this, but at this point, it looks like I'm just going to have to live with this.

 

[aerodyne]

So my car is continuing to drain power while idle (see below for stats while parked), and I asked Tesla about it at my most recent service visit. They said everything checked out as normal and they couldn't find anything wrong with the car. They did give me a P85D as a loaner, and I noticed that that car is always quiet (i.e. no coolant pump running) when I go into the garage. I suppose I can hope for a software update that addresses this, but at this point, it looks like I'm just going to have to live with this.

View attachment 798166

Since the SvC seems to be unhelpful, I'd get a CAN bus reader, it will tell you where the energy is going. As noted before, 1-2% per day is normal

 

[Manta]

Thanks, aerodyne. As much as knowing what's going on "under the hood" of my car appeals to the geek in me, I'm afraid I won't be able to do anything with the information. When I offered the Service Center the data I posted above to show how much energy my car is losing while idle, I was told that they don't use anything that comes from 3rd party sources. In addition, the rep practically read me the riot act for using any 3rd party software. "We're not responsible for any damage done to your car," "It's like giving them the keys to your house," and of course "They can constantly ping your car and keep it from sleeping." For the record, I only use two 3rd party apps now. One monitors battery health and pings the car 3x/day (didn't affect drain in earlier observations) and the one I use to collect the data above with the option to "not wake the car on app launch" selected.

While looking over my 3rd party app data, I did notice that my car only lost about 3.3% per day while parked in the Service Center lot vs. the 4.8% my car loses per day in my garage. It's just a hunch, but I'm going to disconnect my car from my home wifi network to see what happens.

 

[aerodyne]

Thanks, aerodyne. As much as knowing what's going on "under the hood" of my car appeals to the geek in me, I'm afraid I won't be able to do anything with the information. When I offered the Service Center the data I posted above to show how much energy my car is losing while idle, I was told that they don't use anything that comes from 3rd party sources. In addition, the rep practically read me the riot act for using any 3rd party software. "We're not responsible for any damage done to your car," "It's like giving them the keys to your house," and of course "They can constantly ping your car and keep it from sleeping." For the record, I only use two 3rd party apps now. One monitors battery health and pings the car 3x/day (didn't affect drain in earlier observations) and the one I use to collect the data above with the option to "not wake the car on app launch" selected.

While looking over my 3rd party app data, I did notice that my car only lost about 3.3% per day while parked in the Service Center lot vs. the 4.8% my car loses per day in my garage. It's just a hunch, but I'm going to disconnect my car from my home wifi network to see what happens.

I can't sugar coat this, the SvC is full of "Sugar"

SMT just reads the CANBus. It does not keep your car awake.

The CAN bus data shows many things including how much volts and amps are being used by the HV and 12v systems.

 

[brkaus]

Are you sure your 3rd party app is allowing sleep?

You did mention trying without 3rd party apps (changed password? So that’s probably not it.