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Powering the 12v port to run a fridge, can an app keep the Tesla awake?

bradtem

Member
Dec 18, 2018
24
5
Sunnyvale, CA
In any case as I said, whatever api calls you use would just keep the car awake, and that would consume the same thing as sentry afaik. Why not just use sentry?
There may be some misunderstanding. While the best goal would be to get access to 12v power without turning on the main system and drawing 300w, that may not be possible, or may cause too much load on the 12v battery, at least in the opinion of some. One would have to test it. I don't think this would count as "using the car as a stationary power source." This is powering a 12v accessory inside the car.

What I propose is not at all the same as turning on Sentry mode full time, which of course I would do if that were what I was proposing.

Failing a way to get 12v without going out of sleep, the next best thing is to make the car be awake about 1/3rd of the time during the night, and sleep the rest of the night. One could do that by tracking how much the car is sleeping (as Teslafi does) and waking it up every so often to keep it awake 1/3rd of the time. You can't force it to sleep but you can watch it and you can force it awake. The compressor will run and cool the fridge when the car wakes up. As long as it wakes up every hour for 20 minutes that's probably enough. That would mean 1/3rd the drain, so instead of losing 15 miles overnight losing 5, which is much more reasonable though not ideal.

I have suggested this to insiders at Tesla. They can do even better because they can watch the current on the accessory port. They could wake up the car, let the compressor run until it turns off, and then sleep immediately after that, then wake up again in 20 minutes and let it run as long as it needs to.

Better of course would be if they just had a way to keep the DC->DC converter on without turning on the computer. That would waste a little power but nothing like having the main system on.

Tesla debated having a 120vac plug powered off the main battery but decided not to do it. Now that other companies are putting that in, they will probably do it at least in some vehicles, certainly cybertruck. Perhaps an aftermarket add-on could appear for the Model 3.

Another option would be a $250 Jackery (costs as much as the fridge.) Or a $30 lead-acid could also do the job if you had a circuit that could charge it from the accessory port (never drawing more than 12a, and keeping the voltage on the battery at float level when it was full.) One could build such a charger fairly cheap, but I don't know if anybody does.
 

positiv

Member
Jul 20, 2021
45
25
Sydney
I think it is a bit of madness to start trying to defeat the power system to run a fridge since it would clearly void the warranty of the car as Tesla have said that the car cannot be used as a power supply.
My compressor fridge is rated at 0.77 Ah/hour at 12v. That about 10w, which is a fraction of the power draw of sentry mode.
It would be madness to suggest that a compressor fridge could damage the car but sentry mode wont.
 
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dc443

Member
May 11, 2021
46
26
Taxachusetts
As I understand it, (older?) model S (of which I have one) is ok to tap 12v (and draw from it at rates that are within sane reason). For 3 and Y this is not as feasible due to the car detecting the drain on the 12v battery and assuming at that point that the battery is degraded/defective.

But that’s just a summary of what I’ve read about this so far, which has not been comprehensive enough to even begin planning the project.

I have accomplished so far an interior lighting upgrade (so cheap! So much brighter!), plus the little logo puddle light projectors, and I’ve installed a dashcam (for which running the cable for the rear camera was a very involved process in which I’ve compromised the integrity of a few panel clips on the right side, but I made sure to have the cable run clear all airbags). All small upgrades so far.

My more ambitious projects will involve first enabling onboard fridge (which may involve a 12v battery tap) and then once that is successful I’ll look into doing a 120VAC inverter off that as well. I want at some point to be able to bring and run my SFF pc in the Tesla. It’s a bit ridiculous but I think it would be pure awesomeness.
 

bradtem

Member
Dec 18, 2018
24
5
Sunnyvale, CA
As I understand it, (older?) model S (of which I have one) is ok to tap 12v (and draw from it at rates that are within sane reason). For 3 and Y this is not as feasible due to the car detecting the drain on the 12v battery and assuming at that point that the battery is degraded/defective.

But that’s just a summary of what I’ve read about this so far, which has not been comprehensive enough to even begin planning the project.

I have accomplished so far an interior lighting upgrade (so cheap! So much brighter!), plus the little logo puddle light projectors, and I’ve installed a dashcam (for which running the cable for the rear camera was a very involved process in which I’ve compromised the integrity of a few panel clips on the right side, but I made sure to have the cable run clear all airbags). All small upgrades so far.

My more ambitious projects will involve first enabling onboard fridge (which may involve a 12v battery tap) and then once that is successful I’ll look into doing a 120VAC inverter off that as well. I want at some point to be able to bring and run my SFF pc in the Tesla. It’s a bit ridiculous but I think it would be pure awesomeness.
There are 12v PC power supplies, which should be more efficient than running an inverter. It would be nice to know if there is a solid answer on whether putting a long-term draw on the 12v battery (ie. the 35 watts, 1/3rd of the time of a fridge overnight, amounting to about 125 wh or so) is a problem. It would be nice to just be able to keep the dc->dc converter on, while that comes with a cost it should be a small fraction of the cost of running the full 300w computer!
 

dc443

Member
May 11, 2021
46
26
Taxachusetts
There are 12v PC power supplies, which should be more efficient than running an inverter. It would be nice to know if there is a solid answer on whether putting a long-term draw on the 12v battery (ie. the 35 watts, 1/3rd of the time of a fridge overnight, amounting to about 125 wh or so) is a problem. It would be nice to just be able to keep the dc->dc converter on, while that comes with a cost it should be a small fraction of the cost of running the full 300w computer!
Yes. At this point in time, there are not quite any widespread adoption in high end pc parts of 12v only motherboards but I think it will come around within the next 5 years for sure.

I forgot to mention I also had the diagnostic port under the MCU hooked up to an OBDLink MX+ and was using the Scan My Tesla android app just fine until the latest software update and now SMT is not working. Anyway, I was going to use that and maybe do some logging in order to determine the behavior of the 12v battery dc-dc activity during vehicle idle overnight. Hopefully SMT will continue to work since I've only recently set it up!
 

FalconFour

Supporting Member
Supporting Member
Mar 25, 2016
334
654
San Jose, CA
Just gonna slide in here, a bit late to the party, to add: Sentry seems to only be "in operation" when the car is locked. When it's unlocked w/ Sentry enabled, it still stays awake 😮 but only consumes in the ballpark of 150W. I've not done deep dives on that, though, but I have spent weeks, every day, using Sentry to allow me to siphon 1kW~ish continuously out of the 12v bus using the PCS terminals under the rear seat. When it's idle (when I'm not choking down a hundred 12v amps), I saw it sipping just 150~175W.

Only open question is whether or not the car would still go to sleep if Sentry is on, but not locked. Seems that it's processing/writing video (using the hardware encoders on the AP computer, then feeding the compressed data to MCU then to USB - all low power activities), but not processing it (analyzing it using the AP computer for faces/movement/etc).

So your USB drive might get worn out ;) But I use a spinning hard drive, which doesn't get worn out by writing. Lasted me about 2 years so far. No anxiety worrying about writes wearing it out while in Sentry for days on end.

BTW, useful PSA: there is literally nothing you can do in a Tesla vehicle to touch the 12v battery at all (with the car itself / its settings, ports... obviously you can screw things up by tapping the 12v battery directly). Any time the car is awake (that is: any time it's been interacted with), it's running the whole 12v system off the main battery. The car shuts everything off (including your ports, lights, etc) before it turns that off and starts relying on the 12v battery. So, the battery doesn't even come into play here, be it S, 3, X, or Y.
 
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stopcrazypp

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Dec 8, 2007
10,987
6,099
Yes. At this point in time, there are not quite any widespread adoption in high end pc parts of 12v only motherboards but I think it will come around within the next 5 years for sure.
I think he's talking about these, ATX power supplies that work with conventional motherboards, but run off 12VDC rather than 120VAC.
Power Supply - List of DC-ATX power supplies.
High reliability 12V Input PC ATX computer DC-DC Power Supplies, 12VDC Input, autonomous vehicle computer power. car computer power supply, 12 volt, 320W, 450W, 500W, 650W, 1000W, ATX DC-DC

After all, the highest voltage rail in your typical motherboard is 12V, all of it runs on DC, so there is no point to convert the car's 12VDC to 120VAC then back to those lower DC voltages again and possibly waste energy.

Of course it makes it so it's not plug and play (you can't just yank the power cord on your computer and then take it out of your car and then use it at home; you would have to replace the power supply with a conventional one).
 

dc443

Member
May 11, 2021
46
26
Taxachusetts
I think he's talking about these, ATX power supplies that work with conventional motherboards, but run off 12VDC rather than 120VAC.
Power Supply - List of DC-ATX power supplies.
High reliability 12V Input PC ATX computer DC-DC Power Supplies, 12VDC Input, autonomous vehicle computer power. car computer power supply, 12 volt, 320W, 450W, 500W, 650W, 1000W, ATX DC-DC

After all, the highest voltage rail in your typical motherboard is 12V, all of it runs on DC, so there is no point to convert the car's 12VDC to 120VAC then back to those lower DC voltages again and possibly waste energy.

Of course it makes it so it's not plug and play (you can't just yank the power cord on your computer and then take it out of your car and then use it at home; you would have to replace the power supply with a conventional one).
Nice, I haven't exactly seen those types of units, that is cool. Yeah I think a DC powered PC build would be neat. But for my personal use I would want a single high spec SFF PC that can take as input either 120VAC or 12VDC with reasonably practical hotplug interface and 400W or so of capacity and nothing portable that fits that bill exists on the market just yet. But I reckon once the 24 pin ATX interface on motherboards gives way to some kind of 12VO standard this will become a piece of cake.

Actually it's already pretty doable since you've got the little doohickeys like this picoPSU-160-XT, 160watt (200watt peak) , 12V input DC-DC ATX Power Supply but I need more than 200W peak to have an interesting setup (at 200W a gaming laptop would get you there)
 

dc443

Member
May 11, 2021
46
26
Taxachusetts
I have spent weeks, every day, using Sentry to allow me to siphon 1kW~ish continuously out of the 12v bus using the PCS terminals under the rear seat. When it's idle (when I'm not choking down a hundred 12v amps), I saw it sipping just 150~175W.
This is neat! Unfortunately I'm on AP1 and don't get sentry mode, so not sure how much I could benefit from this knowledge myself, but under 200W is decidedly not too bad. I'm very curious what your 1KW load is!

Any time the car is awake (that is: any time it's been interacted with), it's running the whole 12v system off the main battery. The car shuts everything off (including your ports, lights, etc) before it turns that off and starts relying on the 12v battery. So, the battery doesn't even come into play here, be it S, 3, X, or Y.
Based on my ScanMyTesla app observations I could agree with this but I don't know if what you wrote is how I would have phrased it. Basically it looks like the 12V system delivers well over 10A a lot of the time when systems are active on the car and often 30A or more. So the HV contactor is closed, and DC-DC converter which charges/tops off the 12V battery is pretty much constantly engaged and charging the 12V battery with about as much current as is being drained out of it, this in effect you could say is the HV battery powering your 12V systems. But I'd argue (perhaps pedantically) that your 12V battery is still powering those systems even though it's not being actively drained in order to do so. Hope that makes sense.

But I use a spinning hard drive, which doesn't get worn out by writing.
I would suggest not using a spinning hard drive for dashcam storage because one of the the purposes of the system is to reliably record events leading up to a crash if one is to occur. There is a liability scenario in which the crash jostles your HDD in such a way that it is unable to write to it in the critical moments following a physical impact.

Many dashcams employ a capacitor or supercapacitor internally which provides it with several seconds of extra recording time, I believe this is to address the power out survivability to ensure the footage leading up to an event is successfully written even when power gets cut off. Capacitors are preferred over batteries due to the possibility of periodic high temperature exposure (damaging to lithium chemistries) over the lifetime of the unit.

Sentry mode is maybe not exactly the same as a dash cam but it seems reasonable for me to conflate them together, we all use them for the same purposes. Probably we should maximize the survivability of it! I am not sure but even if I had Sentry mode, I would be tempted to install an independent dash cam. My understanding is that many users have gone this route but it's definitely gonna be seen as over-paranoid by many. So great for Tesla to include features like Sentry Mode.
 

FalconFour

Supporting Member
Supporting Member
Mar 25, 2016
334
654
San Jose, CA
Nice, I haven't exactly seen those types of units, that is cool. Yeah I think a DC powered PC build would be neat. But for my personal use I would want a single high spec SFF PC that can take as input either 120VAC or 12VDC with reasonably practical hotplug interface and 400W or so of capacity and nothing portable that fits that bill exists on the market just yet. But I reckon once the 24 pin ATX interface on motherboards gives way to some kind of 12VO standard this will become a piece of cake.

Actually it's already pretty doable since you've got the little doohickeys like this picoPSU-160-XT, 160watt (200watt peak) , 12V input DC-DC ATX Power Supply but I need more than 200W peak to have an interesting setup (at 200W a gaming laptop would get you there)
Just know that you're not gonna get very much out of the 12v port in the console. It's only good for... what, 15 amps at most? 15a * 13v = 195w (and that's optimistic).

There's no way in a frozen hell that you're going to power any "real" desktop GPU and CPU with that 12v port. You can suck nearly infinite power out of the PCS under the rear seat, but it's not plug-and-play - have to nerd out on it a bit (keep it stealth to the car / not detectable on shutdown; keep it smooth, no inrush/surges).

Honestly, a gaming laptop is probably the best bet - those almost always stay under 200W except for some outlandish ones. They're better suited to the task, and incredibly optimized for power consumption, while a desktop absolutely is not (a desktop CPU/GPU will be happy to barrel along at full power, even though it's only partially utilized, because power is freely available).

But I think we're a bit far away from the, uh... topic of the thread, no?
 

stopcrazypp

Well-Known Member
Dec 8, 2007
10,987
6,099
Nice, I haven't exactly seen those types of units, that is cool. Yeah I think a DC powered PC build would be neat. But for my personal use I would want a single high spec SFF PC that can take as input either 120VAC or 12VDC with reasonably practical hotplug interface and 400W or so of capacity and nothing portable that fits that bill exists on the market just yet. But I reckon once the 24 pin ATX interface on motherboards gives way to some kind of 12VO standard this will become a piece of cake.

Actually it's already pretty doable since you've got the little doohickeys like this picoPSU-160-XT, 160watt (200watt peak) , 12V input DC-DC ATX Power Supply but I need more than 200W peak to have an interesting setup (at 200W a gaming laptop would get you there)
Kind of off topic, but there are those that use an external power 12V power supply (usually a Meanwell) and that does allow something closer to plug and play.
Power Supply - Collection of builds using DC-DC PSUs (aka: picopsu, nano-psu, G-unique, ATX plug-in PSU)

But as pointed out, if you go above 200W the car's 12V port can't supply that much anyways. You may need a buffer battery (kind of like the people who have aftermarket subwoofers or amps).
Just gonna slide in here, a bit late to the party, to add: Sentry seems to only be "in operation" when the car is locked. When it's unlocked w/ Sentry enabled, it still stays awake 😮 but only consumes in the ballpark of 150W. I've not done deep dives on that, though, but I have spent weeks, every day, using Sentry to allow me to siphon 1kW~ish continuously out of the 12v bus using the PCS terminals under the rear seat. When it's idle (when I'm not choking down a hundred 12v amps), I saw it sipping just 150~175W.

Only open question is whether or not the car would still go to sleep if Sentry is on, but not locked. Seems that it's processing/writing video (using the hardware encoders on the AP computer, then feeding the compressed data to MCU then to USB - all low power activities), but not processing it (analyzing it using the AP computer for faces/movement/etc).
That's still only about half of what normal Sentry mode when locked draws (which is about 300W from memory, although things may have changed with updates). You may be on to something that may help the OP.
 

FalconFour

Supporting Member
Supporting Member
Mar 25, 2016
334
654
San Jose, CA
Based on my ScanMyTesla app observations I could agree with this but I don't know if what you wrote is how I would have phrased it. Basically it looks like the 12V system delivers well over 10A a lot of the time when systems are active on the car and often 30A or more. So the HV contactor is closed, and DC-DC converter which charges/tops off the 12V battery is pretty much constantly engaged and charging the 12V battery with about as much current as is being drained out of it, this in effect you could say is the HV battery powering your 12V systems.
The DC-DC is called the PCS (power conversion system), and it's part of the battery pack in the Model 3 - specifically, part of the onboard charger (the PCS as a whole). Here's the fun part: it's capable of just under 200 amps. Yes, 200! The way it works is, when the car wakes up, the PCS checks to see if it's safe to power up (it should have no shorts, and it should also have no voltage - it runs checks for both), then it powers up, and in effect "takes over" the 12v bus using one of the "soft fuses" that forms the "fuse-like" architecture of the 3 (have you noticed there are no fuses in the 3? :) except the main battery, of course). From there, the front body controller ("VCFront") attaches to this 12v bus, and it connects to the 12v battery. It basically bridges the two together, and monitors the current going to the battery. The trick to its charging operation is this: it'll modulate the voltage of the PCS (the whole 12v bus) to keep the battery trickling in 10.0 amps, until it reaches a fully charged 14.4v. Then it'll back off to float voltage, where the 12v battery is simply idle. It only lets the 12v battery get 10 amps, but the 12v bus as a whole can suck down a total of "just under 200". The only thing the VCFront and the PCS cares about is making sure the 12v battery is only getting 10 amps thrown into it.

This process happens any time it's awake. It'll also keep the car from sleeping until it's satisfied that the 12v battery is charged and stable enough to wake itself up again after it goes to sleep. Thus, it also seems to do some tests, requesting a lower PCS voltage and watching the current flow out of the 12v battery, raising it up again and watching it flow back in a bit... but only very lightly. In effect, the PCS is doing *all* the 12v work.

The PCS is capable of around/a bit over 2000 watts of 12v output, because that cooling fan is an absolute monster (it's the biggest consumer of 12 volts) - you ever hear it when you're done at a Supercharger? Watch Scan My Tesla at that moment and see how much 12v juice it's drawing ;) Add in the headlights, and decide to roll up all 4 windows at once... and voila, you now have your 2000 watts of 12v consumption.

I'm very curious what your 1KW load is!
Power export 🙃 Couple of DC-DC converters dumping power into a big battery I've got at home. A little, shall we say... Robin Hood grid arbitrage. lol.

I would suggest not using a spinning hard drive for dashcam storage because
Nyah. It's already come in handy at least a few times in the past 2 years/60k-odd miles. Accidents aren't often massively tumbling wreckages. Plus, now that Tesla stores video internally as well as externally, I worry zero about it. For the risk/benefit, this is highly tilted towards the benefit in my opinion. I can't stand wearing out Flash just writing constantly. Writing/erasing on Flash is destructive to the media. I'd rather have something I know is being refreshed by constant writing, than have something that's constantly wearing out and we'd never know when it's dead until it takes everything with it at once.

A little light entertainment on the PCS subject :)
 
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bradtem

Member
Dec 18, 2018
24
5
Sunnyvale, CA
Hmm. More reading suggests the wires under the back seat that connect to the DC->DC system are disconnected from the 12v battery during sleep, so that's not very useful for powering the fridge full time. One would need to connect to a bus including the 12v battery, but not in a way that drains the 12v battery too much and makes the Tesla decide there is a fault.

One option could be to continue with the accessory port put but in a 1U wheelchair battery. These only cost around $45 and provide about 400wh. The idea would be that while the car was awake and the battery full, you would draw 40w from the port while fridge was on. When the system was asleep, the fridge would draw from the battery, which could last most of a day. As soon as the car wakes up, you have 12 amps combined to recharge the battery and power the fridge until the battery is restored. You want to provide a 14v charging voltage to the battery and after it is full, a float voltage, and you don't want to feed any power back. I wonder if there's a simple off the shelf circuit to manage that (a 12v battery charger in effect, which does what a standard battery charger does but runs on 12v instead of 120v.) You need to limit current to the battery, and control the voltage. The fridge will be happy with any voltage from 11.5 to 14.4. The fridge will even turn off if the voltage goes below 12 if you ask it to, which can devote more current to charging the battery right after morning wake-up.
 

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