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Charger switching on-off every hour after charge in complete

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jjrandorin

Moderator, Model 3, Tesla Energy Forums
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Nov 28, 2018
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Where are 800W wasted exactly? Which component consumes such high energy, and why exactly, and how is such waste of energy justified? "Car being awake" is not an answer, it's incompetency.
Perhaps it would help you to think of "car being awake" the same thing as "car in accessory mode" in an ICE. Car being awake = car ON.

So, the "car" is wasting that energy. Its 'ON" the same way an ICE would be on if you had the old style regular key turned one click toward on, in accessory mode.

Not liking the answer is not the same thing as "the question has not been answered".
 
So I got three answers, and none of you seem to understand technical part of it. I know what "awake" is, and I know how much power it can use. It's not 800W.
800W can be used only if A/C was running, or if battery was being heated in this "awake" state. Since none of those are needed for computer to run, and if we assume A/C is not running' them I am asking you again, why is battery being heated? It's not needed for any of electronics to work. Lithium batteries can work well down to -20C.
 

Tam

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Nov 25, 2012
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So I got three answers, and none of you seem to understand technical part of it. I know what "awake" is, and I know how much power it can use. It's not 800W.
800W can be used only if A/C was running, or if battery was being heated in this "awake" state. Since none of those are needed for computer to run, and if we assume A/C is not running' them I am asking you again, why is battery being heated? It's not needed for any of electronics to work. Lithium batteries can work well down to -20C.

It sounds like you do know the answer to why there's a repeated trickle charge in your car.

I think your point is why Tesla wastes so much energy by just sitting idly.

We do know that Sentry Mode consumes a lot of energy. We know that by letting the car idle over night and comparing the loss between a night with the Sentry Mode on and off.

I don't know why Sentry Mode is an energy hog but I think it is not just a simple dash cam. I think it uses pure vision to detect objects. Pure vision calculation is an energy hog. Calculating all those pixels from 8 cameras would require a lot of computing energy.

Thus, it might be cheaper in energy consumption if it just uses a traditional car alarm system. However, Tesla seems to bet that Pure Vision is a panacea, so we won't see any decrease in the energy hog from the Sentry Mode anytime soon.
 

dmurphy

Active Member
Supporting Member
So I got three answers, and none of you seem to understand technical part of it. I know what "awake" is, and I know how much power it can use. It's not 800W.
800W can be used only if A/C was running, or if battery was being heated in this "awake" state. Since none of those are needed for computer to run, and if we assume A/C is not running' them I am asking you again, why is battery being heated? It's not needed for any of electronics to work. Lithium batteries can work well down to -20C.

It‘a fine that YOU think the batteries should be cooled down to -20C. Tesla disagrees. They actively warm those batteries - even 20 degrees is on the cold side for the battery pack.

Now whether you agree or disagree with warming the batteries doesn’t matter. The car will do so, when and how the system desires to whatever setpoint their smarter-than-us engineers feel is optimal.

Sentry mode on is typically 300-400W. That’s the base load for all of the car electronics to be powered and processing data. The other 400W I suspect is the battery heater cycling.

-22C is way below what the car will allow the battery to get to.

It’s going to take energy to keep the battery warm, especially when there’s at least a big delta between ambient and battery minimum temperature (which is north of freezing, FWIW.)
 

ucmndd

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Mar 10, 2016
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So I got three answers, and none of you seem to understand technical part of it. I know what "awake" is, and I know how much power it can use. It's not 800W.
800W can be used only if A/C was running, or if battery was being heated in this "awake" state. Since none of those are needed for computer to run, and if we assume A/C is not running' them I am asking you again, why is battery being heated? It's not needed for any of electronics to work. Lithium batteries can work well down to -20C.

The battery is not being heated. Listen to what you’re being told.

Continuous ~300+ watt draw for sentry plus massive inefficiency associated with extremely short duration 10kw charging cycles is the answer. Like it or not.
 
By the way Sentry was enabled, so maybe that's that. But it's still ridiculous to take 800W instead of 15-20W that video recording actually needs..."Car being awake" is not an answer, it's incompetency.

You shouldn't be so quick to criticize that which you do not understand.
  • All cars use power when asleep to listen for keyless entry and run security alarm sensors/processors. Tesla also communicates periodically thru cellular and WiFi networks to provide status updates, check for safety recalls or other software updates, and listen for remote wake commands on the cellular network.
  • Sentry is not a simple video recording system. There are 8 automotive grade cameras designed for extreme temperatures and vibration, not power minimization. They feed a powerful liquid cooled processor designed for autonomous driving and high reliability in harsh automotive environments, not a dedicated power-optimized MPEG compressor.
  • The small 12V battery in this car is heavily taxed by the above loads and yours is getting close to the ~3 year typical lifespan. And when lead-acid batteries are degraded they charge less efficiently, wasting more power. And charge more often - see next bullet point.
  • The 400V power source is converted to 12V by a very large DC-DC converter with large high-current FETs which of course require considerable activation power. There is a very substantial loss of energy inherent to this process which is why it relies on the lead acid battery to run the above systems and only turns on/off as needed to recharge the lead acid.
  • A wide array of sensors and processors is monitoring and reacting to countless conditions anytime the car is awake, as it is with Sentry, and especially anytime the 400V system is active, as it is anytime the lead-acid is being replenished. It's not just Coulumb counting, and monitoring dozens of temperatures and voltages, but it's heating/cooling various subsystems and possibly even dehumidifying the cabin if needed.
  • If Tesla's engineers think the battery might need to be heated for some reason, either accept it, or prove to yourself and the internet that you somehow have this vast expertise in battery management so amazing and so fantastically incredible that you are actually smarter than every expert in the entire industry - combined.
  • As others have noted, the typical power consumption is closer to 500W but varies with many factors. Yours being on the high end suggests possible 12V battery degradation and/or some minimal heating. You are correct that lithium cells can be stored safely at -5C, but they do not accept charge well at that temperature. Even if the cells aren't being explicitly heated, they may be passively self-heating as a result of their increased internal resistance at such low temperatures.
 

LoudMusic

Active Member
Jul 21, 2020
1,720
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He wants the power consumption itemized.

10w x 6 cameras is 60w
Sentry mode processing 100w
Cellular communication 50w
Etc...

Unless there is a Tesla electronics engineer in the discussion no one is going to be able to answer that question. And even if they were watching this thread I don't think they'd tell you because it's a secret. If you want that kind of information I doubt you'll get it from any existing manufacturer and exceptionally few consumers are equipped to figure it out.

You also say that it isn't necessary to warm the battery above -20c but that's your opinion and I suspect Tesla disagrees. I prefer to spend a little extra on electricity and not find out what happens when the battery gets very cold.
 
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Rocky_H

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Feb 19, 2015
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You're comparing it to a Celeron processor system that was DESIGNED to be able to actively run at very low power modes. The high power computer systems in the car definitely weren't. They are built for high processing of self driving analysis, so they are energy hogs. Trying to make it into something it wasn't designed for after the fact just isn't going to be power efficient. It's like bolting wings onto a car and then complaining that it doesn't function efficiently as an airplane.

But there's another factor no one has mentioned yet. For human safety with eventual full self driving systems, they cannot have the risk that a failure of the one single processor causes the car's driving to go crazy or stop suddenly and cause an accident. So this is an iron-clad requirement (by law in some places) that all autonomous car systems have to have full redundancy with DOUBLE computer systems with instant failover capability, so they both have to be on all the time that they are running!! So yes, the Tesla processor board does have double the computing power turned on and consuming power whenever this is operating.
 
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Tesla processor board does have double the computing power turned on and consuming power whenever this is operating.

Would you mind to post a picture of that processor board and make a guess the TDP (how much power it may use)? I think it will be 10W. There is nothing "powerful" in this car, especially when not driving in FSD mode. There is no reason to consume this much energy, and it is actually not possible to consume 800 watts without bursting in flames, unless something really big is being heated.

Can we end this "processing takes a lot of power" BS? And maybe discuss why it is heating the battery when there is no need.

And so someone is now deleting my inconvenient posts?
 
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Rocky_H

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Would you mind to post a picture of that processor board
Sure. This is pretty detailed itemizing of the architecture of what's on it.
 

dmurphy

Active Member
Supporting Member
Sure. This is pretty detailed itemizing of the architecture of what's on it.

To be noted - a small update to this article since publication.

The initial intent was for a fault-tolerant architecture between the SoC's on the HW3 board; that's *not* how it's currently operating. Each chip is actively running individual neural net workloads; simply, there isn't enough horsepower to operate in a fully FT mode.
 

Rocky_H

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Feb 19, 2015
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And as to that ridiculous assertion that's not possible to consume 800 W without it bursting into flames, I checked something on that.

I went to Newegg to check desktop computer power supply products. They have checkboxes on the side to filter search results. One of the filter categories is to only show power supplies that provide 1500 W or more.
 
Power supply does not consume what's written on it.
For computer to waste 800W, it should be a huge loud system. For comparison, typical home A/C is around 800W. Also, typical multi-fan video card is around 100W.

And that "neural board" from tesla has a TDP of 72W at full FSD load, or 36W per chip.
So 728W is still unacounted for, even if we think those chips run on full load while parked, which they don't.
 
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Rocky_H

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Feb 19, 2015
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Let's address these latest assertions:
Power supply does not consume what's written on it.
Not all the time of course. That's peak available output. It was just making the point that we're talking about something that is half the power of commonly available computer power supplies, so that's in the ballpark.

Also, typical multi-fan video card is around 100W.
That's quite outdated.

"NVIDIA’s GeForce RTX 4090 will be the GPU-maker’s first SKU to feature a power consumption of over 500W. Most sources place the TBP of the top-end 40 series graphics card between 450W and 600W. German journo Igor Wallossek has estimated the overall TGP/TBP at 600W, with the GPU itself drawing more than the entire RTX 3090 under load (450W). The remaining 150W are slurped by the memory, VRMs, fans, etc."

 
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ucmndd

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Mar 10, 2016
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For computer to waste 800W, it should be a huge loud system.
The computer is not "wasting" 800 watts. All of the systems combined in a Model 3 use about ~300 watts continuous when the car is on/idle (as it is when Sentry is running). This is well established and has been mentioned in this thread multiple times.

The rest of the consumption you're seeing is from charging losses inherent in repeated short-duration high-power charging sessions in cold weather.

This is easy enough for you to verify for yourself. Turn off sentry mode and watch the hourly charging spikes go away. I realize that probably isn't as much fun as being obstinate on the internet, but you have everything you need at your disposal to answer your own questions.

For comparison, typical home A/C is around 800W.
Lol, do you live above the arctic circle in Norway? My 16 SEER home A/C uses more like ~3.2kw.
 

Rocky_H

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Feb 19, 2015
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Lol, do you live above the arctic circle in Norway? My 16 SEER home A/C uses more like ~3.2kw.
Yeah, I noticed that claim of 800W for a whole home A/C was insane too. A standard 120V 15A outlet provides more than that, and you can't run a whole house A/C unit on that, but I didn't want to get into arguing about air conditioning when it was about computer system power.
 
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Ok, let's then put it this way.
Let's say sentry is somehow actually using 300W. Then 500W is missing.
Actual charging if the battery is not wasteful. I work with batteries, I know.
What's wasteful, is pre-heating before every charging session.

So what I suspect in this case is: sentry is consuming 300W, this is discharging the battery. Then it decides to re-charge and preheats for that, which increases the consumption to 800W and requires even more charging. This way it it trapped in a spiral of death on it's own.
And that is bad engineering, you like it or not.

As for A/C power, my house has 25cm foam insulation and 800W heatpump produces 3.5kW cooling/heat and is enough to heat and cool my 200m2 house in summer and down to -20C winter. It's your problem if you live in a non-insulated 18th century castle.
 
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ucmndd

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Mar 10, 2016
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Oh dang guys, he works with batteries.

EEB20CC4-AEE3-440D-95F5-E705A94AC16E.jpeg
 
Please apply at Tesla. We would all love for you to reduce the waste of energy. Those cold nights running Sentry and using 7-8% of the battery is a killer. While you’re at it. Maybe optimize the range, so we can all drive longer. Oh and also improve the charing curve, so we can get off those busy superchargers fast. Hope it’s not too much, but can you get rid of the battery degradation while you’re at it? Thanks
 
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