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Understanding the origin and nature of Vampire Drain.

MaryAnning3

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Nov 3, 2018
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In benign weather and very ordinary circumstances, a parked and unused Model 3 will loose about 30% of its charge in a month. This is often called vampire drain or phantom drain and has been talked about extensively over that last few years, mostly from the point of view of complaining about it. In my view it is manageable. You can park at an airport for a month without being plugged in, for example, park at 75% state of charge (SoC) and return a month later at 45% or 40% SoC.

I don’t think this is self discharge; the self discharge rate of modern LiMnNCo battery is a couple of orders of magnitude lower than this rate I believe. Also, when you leave a car for a few weeks or a month I think that transient effects such as cabin overheat protection become negligible. The point of this post is to try to understand the origin and nature of power usage in a long-term parked Tesla.

I would be really interested if any of the experts out there know what this power is used for. What I am wondering is how a model 3 is using about 800 Watt-hours per day? What systems are involved? How often do they run and for how long? How much power do they draw? Does the battery management system (BMS) play a major role? Does the complex nature of a Tesla battery, which involves over 400 individual cells, imply the need for a particularly active battery management system which requires a significant amount of power each day? Any insights and ideas would be much appreciated.
 
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fbitz777

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Apr 6, 2016
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Your are lucky if you loose that little! My X is 3kwh per day (10miles).!
And my Bolt is ZERO (or at least not measurable after 7 days in freezing weather)

So no it not the self discharge of the battery cells.
 

MaryAnning3

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Nov 3, 2018
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California
scroll down and you'll find 11 pages of discussion in another vampire thread.....
Those do not discuss the origin at all. It is a completely different thread and topic.
I see what you mean. There is some pretty broad ranging discussion of the origin of ordinary drain as well as variation and anomalies. Still I would love to see a more focused explanation of the origin of ordinary (1%, 800 W-hour per day) power usage.
 
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Saghost

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Oct 9, 2013
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Tesla keeps some of the computers awake at all times to varying degrees - to respond to the mothership and your smartphone app when requested, to monitor the 12V battery and recharge it when needed, etc. Those computers are the vampire drain, and the main battery contactors are often engaged even with the car "off."

By contrast, GM installs bigger 12V batteries (2x the capacity I believe) and when the car is off only the OnStar module is active, and it only communicates by SMS I've read, which may reduce its consumption. The only time their contactors are energised is when the car is on or actively charging (including the limited remote start capability as "on".)

Tesla has made progress in the car sleeping more thoroughly and more often through the years - with occasional exceptions where the car gets stuck awake and annoys people. Some of those come at a cost in terms of responsiveness.
 
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Magnets!

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Jan 9, 2019
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Our leaf loses about two percent in a 4 month period. What systems remain on in a Tesla that don’t on a leaf.

I also read something that a three year old Leaf had lost 50% of it's capacity. This won't happen with a Tesla. It has a very sophisticated BMS which individually tests and balances cells...I am guessing that this a big component of 'vampire drain', along with the four bluetooth radios, wifi radio, battery heating and cooling, etc.
 
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Dan123

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Jun 19, 2018
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Miami
The only thing that is different about M3 vs Bolt is that M3 is constantly looking for the key card signal or the phone bluetooth signal. The RF card requires power to the B-pillar. And the bluetooth requires constantly working bluetooth chip. However, I don't think they should consume more than 5-10 watts of power.
 
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CCIE

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Aug 31, 2017
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CT
...
By contrast, GM installs bigger 12V batteries (2x the capacity I believe) and when the car is off only the OnStar module is active, and it only communicates by SMS I've read, which may reduce its consumption. The only time their contactors are energised is when the car is on or actively charging (including the limited remote start capability as "on".)
...

Coming from a Volt and Spark EV, the vampire drain of the Model 3 has been quite a shock. I could leave either sitting for weeks with no noticeable drop in battery charge. GM provides the same remote functions as Tesla does, so clearly it's possible to design an efficient system without sacrificing features.

The 12V batteries in my Volt and Spark EV were about the same size as the one in the Model 3. Definitely not twice as big. As with ICE vehicles, the onboard computers in those cars didn't run down the 12V battery even after weeks of sitting. Tesla should strive for the same thing.
 

Webeevdrivers

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Jan 2, 2017
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Canada
I also read something that a three year old Leaf had lost 50% of it's capacity. This won't happen with a Tesla. It has a very sophisticated BMS which individually tests and balances cells...I am guessing that this a big component of 'vampire drain', along with the four bluetooth radios, wifi radio, battery heating and cooling, etc.

Could be. But our almost four year old leaf has no appreciable range loss so it probably depends on the conditions it is used in. There are 7 year old leaf cabs in Madrid with 300,000 km that still have greater than 60 percent capacity. Painting with a wide brush is always a bad idea. We are buying a Tesla, model 3 or maybe waiting for a model Y, but I wouldn’t hesitate to buy another Leaf. Absolutely flawless experience in all conditions. And since the model 3 is not Chademo compatible we’ll probably have to wait for a model Y as Tesla Supercharger only vehicles in this Privince are pretty limited in where you can go. Loved our Tesla Model three test drive but without Chademo compatibility it’s not going to work. We have a little time though. Things may change in the next 6 months.
 

Saghost

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Oct 9, 2013
8,224
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Delaware
Coming from a Volt and Spark EV, the vampire drain of the Model 3 has been quite a shock. I could leave either sitting for weeks with no noticeable drop in battery charge. GM provides the same remote functions as Tesla does, so clearly it's possible to design an efficient system without sacrificing features.

Beg to differ. GM does provide a surprising amount of remote functions, compared to cars in the past - remote start, lock/unlock, map location, send destination to car, current electric/gas range, odometer, tire pressures.

(It's been a while since I gave up my Volt, so I might be missing one or two? My experience a few years back was it was unreliable to use and always took several minutes to work, but that might have gotten better.)

It's not even in the same league as what Tesla gives - Tesla has all of that (except gas range, of course, and I don't think it can do tire pressure,) and so much more - real time location, speed and power use. Locked/unlocked status, status of every door on the car. Real time voltage, amperage and power while charging. Interior and exterior temperatures in real time, and fan speed when climate control is active. Set a temperature for climate control. Individual control of the seat heaters for every seat and the steering wheel. Set a charge level. Start/stop charging. Keyless start (not just climate control - drive the car without a key.) Trigger homelink/garage doors and gates. Open and close rear hatch and sunroof, open Frunk. Set valet mode and speed limits. Even Summoning the car.

And it's consistent, reliable, and typically takes a few seconds to go through.

The 12V batteries in my Volt and Spark EV were about the same size as the one in the Model 3. Definitely not twice as big. As with ICE vehicles, the onboard computers in those cars didn't run down the 12V battery even after weeks of sitting. Tesla should strive for the same thing.

Meant what I said. :)

Volt 12V battery, 60 Ah AGM. Tesla model S/X battery, 12V 33 Ah Deep Cycle. Technically not exactly twice the size, but pretty close. For reference, my gasoline powered car before the Volt was of similar size to the Volt, and also had a 60Ah battery, though not AGM. Not sure what's in the Spark EV, but I'd expect it to be similar to the Volt.
 
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bedoig

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Nov 29, 2016
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It's not even in the same league as what Tesla gives - Tesla has all of that (except gas range, of course, and I don't think it can do tire pressure,) and so much more - real time location, speed and power use. Locked/unlocked status, status of every door on the car. Real time voltage, amperage and power while charging. Interior and exterior temperatures in real time, and fan speed when climate control is active. Set a temperature for climate control. Individual control of the seat heaters for every seat and the steering wheel. Set a charge level. Start/stop charging. Keyless start (not just climate control - drive the car without a key.) Trigger homelink/garage doors and gates. Open and close rear hatch and sunroof, open Frunk. Set valet mode and speed limits. Even Summoning the car.

Let's use a cell phone as a well optimized benchmark for a connected device. You should be able to do all this for 1-2 Ah per day, and that's being pretty generous. That shouldn't even be a rounding error on a 70+ kWh battery. I'd like to believe Tesla's electronics are well optimized and all this power drain is going into somehow maintaining battery health (temperature conditioning, balancing, etc), but I kind of doubt that is the case.
 

MaryAnning3

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Nov 3, 2018
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163
California
It has a very sophisticated BMS which individually tests and balances cells...I am guessing that this a big component of 'vampire drain',
I kind of wondered if that might be a key thing in daily power usage. The Tesla battery is pretty unique in design and might require significant power for daily BMS operations, as you say. I just have a feeling that Tesla is not randomly wasting 800 Watt-hours per day.
 

Saghost

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Oct 9, 2013
8,224
7,088
Delaware
Let's use a cell phone as a well optimized benchmark for a connected device. You should be able to do all this for 1-2 Ah per day, and that's being pretty generous. That shouldn't even be a rounding error on a 70+ kWh battery. I'd like to believe Tesla's electronics are well optimized and all this power drain is going into somehow maintaining battery health (temperature conditioning, balancing, etc), but I kind of doubt that is the case.

I don't know nearly enough about the Tesla systems to make an intelligent estimate of what it "should" require. The data and commands involved clearly reside in multiple modules, maybe in many modules. So how many of them do you keep awake to be ready to respond? Do you keep the CANBus running?

I don't even know enough about the architecture to know if Tesla can turn on individual modules as needed, or has to boot the whole car when it needs something outside of the core computer (traditional car would have everything ignition keyed except a few always on items. There's no ignition switch here, and I'm not sure if it's replaced by one switch or a string of them.) Maybe it can keep power to the modules, and order them to sleep individually over the network, then wake them over the network when needed?
 
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MaryAnning3

Supporting Member
Supporting Member
Nov 3, 2018
349
163
California
Tesla keeps some of the computers awake at all times to varying degrees - to respond to the mothership and your smartphone app when requested, to monitor the 12V battery and recharge it when needed, etc. Those computers are the vampire drain,
Thanks. These are really interesting points. I get the sense that you have some considerable experience in this area.
 

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