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The gas savings Tesla quotes (on the design studio) are for 5 years. So for widodh, in the Netherlands, Tesla says he'll spare 8600€ in gasoline savings (over 5 years), but that fails to take into account the 912€ (for 5 years) of vampire drain the MS has and that no other car has.
So in widodh's case, the vampire drain removes 10% of the estimated gasoline savings.
[Edit :] @Cottonwood: Haha !
mknox
Well-Known Member
That's exactly right, but I don't get why the cycling of the 12v leads to an expected life of only 1 year (mine has been replaced at least once, possibly twice by Tesla already). A 12v lead acid battery in an ICE is arguably cycling as much or more than a Model S. An ICE has 12v accessories, including a number of always-on loads, just like the Tesla and certainly cranking over the ICE, then replenishing the battery from the alternator cycles the battery quite a bit.
Cottonwood
Roadster#433, Model S#S37
No other car works the 12V, lead-acid battery as hard as the Model S.
Cranking currents in an ICE are high, but very short duration, so are a very small percent of total charge. For example, 200 Amps for 10 seconds is only 0.33 Amp-hr. The background load of the Tesla is so large (40 Watts and up), that the 12V battery has to be recharged many times a day by the main, traction battery. No other car has to do this. The only one that I know of, that is even close, is a Toyota Prius. It has a fraction of a Watt background load, and a small battery.
Experienced Prius owners know that if you are leaving the Prius for more than a few weeks without running (charging the 12V battery), you must put it on a trickle charger, have someone start it every couple of weeks, or come back to a dead battery. That's a charge lasting for a few weeks rather than a fraction of a day with a similar sized 12V battery. The background load on a Prius does about a 100% cycle per month, while the Model S does about one 100% cycle 2.5 times a day. That is a 75x greater background load.
The Model S Vampire is a very thirsty beast!!!
mknox
Well-Known Member
But... but... WHAT exactly is making it such a thirsty beast? My previous Cadillac CTS had an always connected OnStar telematics system, had computers and such that stayed on. Used a fob-based keyless entry system pretty much identical to the Model S (except for the extending handles). I'm not getting what exactly that the Model S has running all the time that is so significantly different than comparable modern ICE vehicles.
glhs272
Unnamed plug faced villian
Anecdotal data point: my original "old style" (grey I think) 12 volt battery lasted almost 2 years. It did not fail or ever give error messages. It's just that during my second annual, knowing it hadn't been replaced yet and all the horror stories on the forum I asked them to replace it. And they did, and were shocked to find it was the old failure prone version as well.
Cottonwood
Roadster#433, Model S#S37
That's the rub, it does not need to be thirsty, but is is...
My guess is that the design process went something like this:
Elon: Get the design finished and into production ASAP. The company's success depends on customer deliveries happening ASAP. However, the car must have a great feature set, beautiful touch-screen center console, etc...
Engineers: We can finish the design of the control electronics sooner if we don't worry too much about a power efficient design, and the production cost will be less. The energy we will use per day is tiny compared to the capacity of the main battery, only 1-2 kWh per day. Our battery is huge compared to a little ICE starting battery; why bother with a power efficient design for those pesky control issues.
Safety Design: We need to keep the DC HV contactors open whenever possible; when the car off, just run on the 12V battery until it needs charging.
Product Support: The car is eating 12V batteries!
Engineers: Oh yeah; we did not think about eating 12V batteries. That is a big redesign to go to a low power design of the control electronics. We are still working on Elon's long list. Keep feeding the Vampire with lead-acid batteries; they are cheap, and lead-acid is so boring!
Traditionally deep cycle batteries were used in golf carts so had ~365 deep cycles per year since they typically do one round of golf per day which is what they were designed to do. These are the big ~65 lb 6volt batteries, Crown & Trojan brands, designed to be brought down to 15 to 20% charge on a regular basis without harm. They have a useful lifetime of 10 or even 12 years.
Now you've got wheelchair batteries that are designed to do the same thing but on a smaller power level. These are the ones that the MS and Roadster use for their unique requirements, the MS being quite a bit more demanding.
So the question is: when has a Tesla put a full cycle to its 12 volt deep cycle battery? Not so easy to figure as an 18 hole round of golf. Maybe a few (3) per day. Several (4-7)? Many (8 or more)? Soon enough there will be more Teslas than electric wheelchairs so the battery industry will re-profile their product (if they haven't done so already).
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Now you've got wheelchair batteries that are designed to do the same thing but on a smaller power level. These are the ones that the MS and Roadster use for their unique requirements, the MS being quite a bit more demanding.
So the question is: when has a Tesla put a full cycle to its 12 volt deep cycle battery? Not so easy to figure as an 18 hole round of golf. Maybe a few (3) per day. Several (4-7)? Many (8 or more)? Soon enough there will be more Teslas than electric wheelchairs so the battery industry will re-profile their product (if they haven't done so already).
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mknox
Well-Known Member
One of the things that the car does, and may be contributing to all this 12v cycling, is that it seems to power everything up every time you open a door. Most ICE's will just turn the interior lights on, but the Model S seems to do the equivalent of turning a key to "ON" or "ACCESSORY". I can hear the contactors work, and even the HVAC comes on. I kinda wish it wouldn't do that. In fact, I dislike the going on and off with door opening so much that if I have to open another door, for example to get something out of the back, I'll leave my driver's door ajar so that the car doesn't do a shutdown and a re-start 10 seconds later. I figure the fewer contactor cycles and systems cycles (i.e. the screens) the better.
In my view, it would be better if the car "came to life" only after you tap the brake... maybe one tap to put it in "ON" mode and a second tap to put it in "RUN" mode. I don't need the car coming to life if all I'm doing is opening a door to get something.
EDIT: Or maybe just come to life with the driver's door. If any other door is opened, just turn on the interior lights. You're not going to be driving the car from the back seat, after all.
In my view, it would be better if the car "came to life" only after you tap the brake... maybe one tap to put it in "ON" mode and a second tap to put it in "RUN" mode. I don't need the car coming to life if all I'm doing is opening a door to get something.
EDIT: Or maybe just come to life with the driver's door. If any other door is opened, just turn on the interior lights. You're not going to be driving the car from the back seat, after all.
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That's actually not true. Every car has the exact same amount of 'vampire drain'. It's the computer system and battery management that uses power. But it needs that amount of power weather you are driving or not. When you don't drive, you can see and measure the losses. When you drive, it;s mixed into the other usage and thus hidden, but the energy is use no matter what.
mknox
Well-Known Member
Fair enough and exactly right. I was coming from the point of view that when you're driving the car, the power these systems consume is "legitimate" and just part of the energy cost of running the car. I think it becomes questionable when the car is off and parked that the consumption continues.
I believe the car will automatically shut some things down to save power after being left a few days alone.
It shuts off the key fob antenna. My measurements in this mode still indicate 3-4 miles lost/24 hrs. So about 1 kWh.
From what I've been able to tell, the biggest offender is the center display. It contains the cellular modem and is always on to varying degrees.
I'm not sure why Tesla doesn't give us the option to completely shut down the car, which would be useful if we were going on a trip, etc. Of course we can disconnect the 12v battery and then there is no vampire drain, but Tesla didn't make this easy.
There is a "shut car down" button on the screen, but it doesn't really seem to do what it's labelled.
I suppose another option would be to enable constant shore power, such that when plugged in and this feature is enabled, it would keep the DC-DC powered from the wall and thus not cycle the 12v battery at all. In theory, This could even be done with the main contactors still open, to keep the main pack isolated.
I'm not sure why Tesla doesn't give us the option to completely shut down the car, which would be useful if we were going on a trip, etc. Of course we can disconnect the 12v battery and then there is no vampire drain, but Tesla didn't make this easy.
There is a "shut car down" button on the screen, but it doesn't really seem to do what it's labelled.
I suppose another option would be to enable constant shore power, such that when plugged in and this feature is enabled, it would keep the DC-DC powered from the wall and thus not cycle the 12v battery at all. In theory, This could even be done with the main contactors still open, to keep the main pack isolated.
Hmm... I left the P85 and P85D sitting for 10 days last month and both hadn't even lost 1 mile per day with energy saving turned on (I think the P85 lost 9 miles and the P85D 7 miles). Plugged in, but no AC power usage either (monitoring both HPWC via TED) since I slid the charge sliders down to 50% before leaving because I didn't want it randomly activating all of my inverters while I was gone.
That could work, but you'd still get high voltage all over the car (even with the pack isolated.) And it would be quite inefficient. No idea what the no load consumption of the chargers (or the DC-DC converter) is, but I doubt they tried to minimise it.
The whole point of this thread is to understand why and to try to reduce the power consumption at the socket.
It seems quite low. If you are plugged into shore with a charged pack, you can enable the climate control and it will enable the pilot and begin drawing from the EVSE to provide power. It definitely can get below 1A. (according to Tesla's screen)
I've measured the Gen 1 DC-DC (made by TDI power) on the bench, and it's quite efficient. The Gen 2 is made by Delta, I haven't measured it yet, but I doubt it's going to be too much worse than the TDI.
Yes, ideally Tesla fixes the root cause instead of a band-aid.
Pretty solid. I've never seen those numbers before. May have made some improvements along the way.
The MCU has a lot more attached to it than just the ipad screen. It controls a lot of key functions and is responsible for logging so I'm not surprised Tesla doesn't let us disable it easily.
The logging functions are all handled by the Gateway controller, which is a 32 bit microcontroller located in the center display housing, but can run independent of the center display's Tegra 3 processor. All security related stuff is part of the body controller which is located in the passenger footwell.
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