MASTER THREAD: Powering house or other things with Model 3

[cali8484]

I'm still confused as to why you'd need to hook in under the rear seats. Every "power from EV" article or video I've ever seen has a 2k or 2500w inverter wired up to the 12v battery terminals. Prevent the car from going to sleep and you have 2000+w continues available, since the HV battery is constantly recharging the 12v battery.

I see people easily running HVAC system for days with these setups, and multiple articles claim the 3 can handle almost 3000w continuous if tapped in at the 12v terminals. The CLA port is limited to about 150w max as it is in almost every other car.

Where does the rear seat plug come into play, I just don't get it.

In short it's because of the VCFront module in Model 3. The DC-DC converter on Model 3 does not connect directly to the 12V battery. Instead VCFront takes power from the DC-DC converter then modulates it to the 12V battery at a much lower current than what the DC-DC converter can provide. Based on what I have seen, the 12V battery even with the car on can't even provide 1000W safely.

 

[cali8484]

Thanks for the great writeup. You mentioned you were able to run 1300W microwave. Can you elaborate on the DC-DC converter voltage with the microwave load? What was the voltage? How much lower was it than the no load voltage?

Answering my own question, the DC-DC converter can easily provide more than 1500W with only ~0.1V drop (14.9V to 14.8V) from no load voltage at the DC-DC converter terminals. The voltage at the inverter shows ~0.6V drop mainly due to 1/0 battery cables. It looks like a fully charged Model 3 will be able to provide emergency power to run 1000W+ of essential loads (e.g. lights, fridge, laptops) for a couple days or longer.

 

[n2mb_racing]

Answering my own question, the DC-DC converter can easily provide more than 1500W with only ~0.1V drop (14.9V to 14.8V) from no load voltage at the DC-DC converter terminals. The voltage at the inverter shows ~0.6V drop mainly due to 1/0 battery cables. It looks like a fully charged Model 3 will be able to provide emergency power to run 1000W+ of essential loads (e.g. lights, fridge, laptops) for a couple days or longer.

Nice! Did you have to use the soft start relay circuit mentioned earlier? Or can you use the turn-on switch in your inverter to cut down the inrush current so that the DC/DC will start up ok?

Also, I like how the inverter has a smiley face on the LCD. They don't take themselves too seriously...

 

[cali8484]

Nice! Did you have to use the soft start relay circuit mentioned earlier? Or can you use the turn-on switch in your inverter to cut down the inrush current so that the DC/DC will start up ok?

Also, I like how the inverter has a smiley face on the LCD. They don't take themselves too seriously...

No, I don't use a relay circuit but as general practice with larger inveters I do use a precharge resistor that is easy to manually connect for 10+ seconds then disconnect before turning on the inverter. I prefer not to have the voltage drop of a relay.

 

[n2mb_racing]

No, I don't use a relay circuit but as general practice with larger inveters I do use a precharge resistor that is easy to manually connect for 10+ seconds then disconnect before turning on the inverter. I prefer not to have the voltage drop of a relay.

What about the switch on the inverter? Does that work? I.e. leave it connected all the time and then turn on the switch after?

 

[neurocutie]

There is a fairly large red cable running directly from the DC-to-DC penthouse port located under the passenger side rear seat to the 12V Power Distribution Center PDC module mounted near the middle of the firewall in the frunk area. There appears to be a somewhat smaller red cable running from the PDC module to the positive 12V battery terminal. From what I have read in other forum posts, it appears the maximum current delivered to the posts of the 12V battery might be limited to around 6 amps.

What's the actual voltage of the high powered "12V" output of the DC/DC converter? If it really is 12V then clearly it needed to be up-converted again to charge the 12V battery (which probably needs at least 17V or so to charge).

 

[n2mb_racing]

What's the actual voltage of the high powered "12V" output of the DC/DC converter? If it really is 12V then clearly it needed to be up-converted again to charge the 12V battery (which probably needs at least 17V or so to charge).

From the photos above, it looks like 14.9 volts.

Looks like the max charging voltage for an AGM battery is 14.8 volts, so sounds about right.
https://www.centurybatteries.com.au...alk/issue-2-battery-talk-battery-charging.pdf

The VCFront mentioned above probably regulates that voltage down to control the charging rate of the 12V AGM battery.

 

[neurocutie]

From the photos above, it looks like 14.9 volts.

Looks like the max charging voltage for an AGM battery is 14.8 volts, so sounds about right.
https://www.centurybatteries.com.au...alk/issue-2-battery-talk-battery-charging.pdf

The VCFront mentioned above probably regulates that voltage down to control the charging rate of the 12V AGM battery.

depending on the design of the charging circuit, one generally wants at least 2-3V headroom to give the charging circuit a differential (voltage drop) to work with, which is why I suggested at least 17V.

 

[PhysicsGuy]

You can connect a big inverter directly to the 12V battery terminals under the hood.

The DC/DC converter in the car will provide up to 2500W and will keep the 12V battery charged with the car off. I don't recommend doing it all the time, since Tesla could see it and void your battery warranty, but in an emergency, I doubt there would be a problem.

would love to hear more details.

 

[PhysicsGuy]

Wouldn't something like this connected directly to the 12v battery work in an electrical outage situation to at least keep a refrigerator/freezer and a laptop running?

https://smile.amazon.com/dp/B07MS5BY6T/ref=twister_B07PMDVG9X?_encoding=UTF8&psc=1

it might

 

[n2mb_racing]

would love to hear more details.

Sorry, that post was wrong. We've learned since then that you can't draw much power from the Model 3 12V battery. You can do that on the Model S/X, but it is a bit more difficult to reach the 12V battery on those cars, I believe.

 

[PhysicsGuy]

To the OP, if you were sitting there in the dark and had a car with tons of charge in the driveway, why not just turn on the headlights?

I went to a presentation at my local electric car club where they spoke about the ability of the Model 3's charger hardware to act backwards, to convert the battery power into usable 240/120v. It would require a box plugged into the charge port on the car with outlets on it, and a LOT of software changes on the Tesla but there isn't anything in the hardware that would keep you from having 10kW of power that you could plug your devices into.

I would LOVE the ability to tow a trailer and then plug it into the car overnight to run the appliances. To run high power things from the car, like power tools. Perhaps even run a cord to power the fridge and some lights during a blackout. I think it would be too expensive to wire the house so the car could act as a backup generator for those rare occasions that the power goes out, but if I lived somewhere that that happens a lot perhaps even that could be done. Flip an interlocked breaker that disconnects the grid and connects to a cord that goes into the Tesla. Not much in my house uses that much power, even in combination. Maybe the hot tub and the oven, I'd have to interlock all those 240v circuits out too.

That would be amazing

 

[PhysicsGuy]

Sorry, that post was wrong. We've learned since then that you can't draw much power from the Model 3 12V battery. You can do that on the Model S/X, but it is a bit more difficult to reach the 12V battery on those cars, I believe.

That is disappointing. How come you can't draw much from a 3?

 

[PhysicsGuy]

Answering my own question, the DC-DC converter can easily provide more than 1500W with only ~0.1V drop (14.9V to 14.8V) from no load voltage at the DC-DC converter terminals. The voltage at the inverter shows ~0.6V drop mainly due to 1/0 battery cables. It looks like a fully charged Model 3 will be able to provide emergency power to run 1000W+ of essential loads (e.g. lights, fridge, laptops) for a couple days or longer.


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Wow

 

[PhysicsGuy]

Note: None or very little of what I am about to discuss has been confirmed by me.

There is a fairly large red cable running directly from the DC-to-DC penthouse port located under the passenger side rear seat to the 12V Power Distribution Center PDC module mounted near the middle of the firewall in the frunk area. There appears to be a somewhat smaller red cable running from the PDC module to the positive 12V battery terminal. From what I have read in other forum posts, it appears the maximum current delivered to the posts of the 12V battery might be limited to around 6 amps. Not sure if the current delivered to the 12V battery is software fused inside the PFC module? There might also be two current paths to/from the 12V battery that could be software fused independently inside the PDC module?

The 12V cigarette lighter outlet is software fused to around 15A but is only powered when the vehicle is awake and the DC-to-DC converter is active; therefore, it appears more continuous power can be provided from the cigarette lighter port than can be attained from the posts of the 12V battery? If you want to pull more current than 15A, then you need to attach directly to the 12V port located under the rear seat. The power from this DC-to-DC connection point is also only available while the vehicle is awake.

I have monitored the voltage and current at the 12V battery post terminals during sleep and awake modes with interesting results. When the car is asleep, the current draw is only about 0.15A of less. When the car initially wakes up, the current draw is around 0.9A but drops down to around 0.7A after only a few minutes. Not sure why the 12V AGM battery charging current is so low? The car appears to wake up when the voltage at the 12V terminals is around 12.7V so the depth of discharge DOD is approx 12.5%. With this DOD. the battery should have enough cycles to last four plus years.

interesting

 

[cali8484]

What about the switch on the inverter? Does that work? I.e. leave it connected all the time and then turn on the switch after?

The inverter switch works as it should but keep in mind that it has little to do with in-rush current in consumer grade inverters that typically have capacitors connected directly to the battery terminals so as soon as DC power is connected, even with the inverter switch off, inrush current will occur due to discharged capacitors. I use a precharge resistor to charge up the capacitors at low current with the main DC battery cables disconnected via a DC fuse/circuit breaker.

 

[miimura]

Sorry, that post was wrong. We've learned since then that you can't draw much power from the Model 3 12V battery. You can do that on the Model S/X, but it is a bit more difficult to reach the 12V battery on those cars, I believe.

The key point is that the Model 3 is monitoring the current on the battery circuit. If you take too much power from the 12V battery terminals, the car thinks there is a fault. If you take the power directly from the PCS terminals under the back seat, you won't trigger that fault.

 

[PhysicsGuy]

The inverter switch works as it should but keep in mind that it has little to do with in-rush current in consumer grade inverters that typically have capacitors connected directly to the battery terminals so as soon as DC power is connected, even with the inverter switch off, inrush current will occur due to discharged capacitors. I use a precharge resistor to charge up the capacitors at low current with the main DC battery cables disconnected via a DC fuse/circuit breaker.

That sounds important. Can you explain the use of a precharge resistor? I understand capacitors but not what a precharge resistor is or how you implement it. Do you use some sort of auxilliary precharge circuit to charge the capacitors? What is the power source for that? Can you switch over with the capacitors charged?

 

[PhysicsGuy]

The key point is that the Model 3 is monitoring the current on the battery circuit. If you take too much power from the 12V battery terminals, the car thinks there is a fault. If you take the power directly from the PCS terminals under the back seat, you won't trigger that fault.

got it now. Thanks a lot.

 

[PhysicsGuy]

Thanks for the great writeup. You mentioned you were able to run 1300W microwave. Can you elaborate on the DC-DC converter voltage with the microwave load? What was the voltage? How much lower was it than the no load voltage?

Thanks for all your great posts Cali. I am wondering what inverter do you might recommend? Does the Sudokeji 1500 W pure sine wave seem like a good choice?