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Is it safe to connect a large inverter to the 12V battery?

Discussion in 'Model S: Battery & Charging' started by BrettS, Sep 8, 2017.

  1. BrettS

    BrettS Member

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    I’m a bit north of Orlando and getting ready for Irma. Last year after hurricane Matthew I was without power for three days. I have a large saltwater fish tank that can go for a few hours without power if necessary, but the less time without power the better. I have a large portable generator to power the house and the fish tank if (when) the power fails, but it occurred to me today that if the power goes out toward the beginning of the storm I could have a long wait before it’s safe to put the generator outside and I could potentially still be without power for some time. Luckily with Matthew my power failed at the very end of the storm.

    I happen to have a 700 watt 12V to 120V inverter that I was considering connecting to my Model S and using it to power the fish tank and maybe a light or two in the event that the power fails before I can safely use the generator. Luckily I have a 2015 Model S with the 12V posts behind the nose cone, so it would be pretty easy to pull the nose cone and connect the inverter and run an extension cord though the garage door into the house.

    However that inverter can draw a decent amount of power (the fish tank pumps and such probably draw about 200 watts to 250 watts as they run). I know that the car will top off the 12V battery as it drains even as the car is off, but how quickly will it do so? I’m afraid that I may be drawing more power than it can provide to top off the battery and eventually I’ll wind up with a dead 12V battery. Alternately I could start the car and leave the door open a bit so hopefully it would stay on which may provide more power to the 12V system.

    Has anyone tried anything like this? Do you know if the car will be able to keep up with my power draw for hours?
     
  2. Lloyd

    Lloyd Well-Known Member

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    How about a UPS for the tank essential systems?
     
  3. Blup85

    Blup85 Member

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    Hopefully someone knows the current capable of the on-board 12v battery tender. I would imagine it has to be cable of 200-300 watts. Your idea seems sound. Maybe the safe bet would be to just cycle the circuit you want to run off the 12v battery and allow the 12v battery to charge back up every 3-4 hours or so, if you have a battery tester you could always test the battery to see if its drawing more than the battery tender is capable of producing (constant voltage drop from 12.5-13v)

    Seems like a fun experiment, if you weren't in a nasty situation. Be safe and take care!
     
  4. BrettS

    BrettS Member

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    I’ve had reasonably bad luck with UPS’s in the past... it always seems that their battery is dead and needs to be replaced when you actually need it. In any case it’s too late for that option now... the storm is supposed to hit this area on Sunday and pretty much everything is closed tomorrow.

    It may be something to consider for the future though. Maybe I just need to go with a higher quality UPS and keep a better eye on the battery health.
     
  5. BrettS

    BrettS Member

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    I do have a volt meter and that’s a good idea. I can check the voltage before and just after I connect the inverter and then check it again periodically... if it seems to be dropping that’s a bad sign.

    I did do a bit more research after I posted this and discovered that apparently the DC-DC converter is actually rated at 2500W, so I should be good there. However it also appears that the 12V posts in the front of the car are connected through a 50amp fuse. At 12V that’s only 600W. It sounds like I should be fine for my aquarium, but I’ll have to be careful not to put on too much other stuff and max out the 700W inverter.
     
  6. tpham07

    tpham07 Member

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    it is not a good idea at all, the system was never designed for such a purpose.
     
    • Like x 1
  7. gregoryg

    gregoryg Member

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    The Model S Manual indicate a much lower safe draw level:

    The 12V power socket is suitable for accessories requiring up to 11A continuous draw (15A peak) or a maximum of 150 continuous watts (180 watts peak).​
     
    • Like x 1
  8. Terry_B58

    Terry_B58 Member

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    A Powerwall may do the job.
     
  9. BrettS

    BrettS Member

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    That’s for the 12V accessory socket though, which has a much smaller fuse. The 12V posts should be able to provide more power.
     
  10. n2mb_racing

    n2mb_racing Member

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    The 12v battery charger should just kick in more often and recharge the battery. It seems to cycle on at some minimum voltage and turn off when it reaches some Max voltage. If you draw enough power it might actually even keep the high voltage battery on continuously and try to charge the 12-volt continuously.

    I'm not sure if there's a 50 amp fuse on the 12 volt jump posts in the front of the car. It seems people are able to jump start other cars using those posts. If there was a 50 amp fuse it would probably blow.

    All of this is not recommended by Tesla and they might decide to void your warranty if you do it too often since it is extra we're on the main battery and the 12 volt battery. But in an emergency I don't see any problem.
     
    • Like x 1
  11. OBX John

    OBX John Autonomous Driving Enthusiast

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    Doesn't using the car as a stationary power source void the warranty?

    I think it's crazy we don't have a nice 15 amp 120 volt Outlet standard though.
     
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  12. copyhacker

    copyhacker Member

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    I have a 1000W inverter I attach to my Volt's 12V battery for just this sort of thing. Ran a portable PA system off of it for about 6 hours today with no problems. If the Volt can handle it surely the Tesla can.
     
  13. FlatSix911

    FlatSix911 918 Hybrid

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    Great move by Tesla ... Tesla remotely extends range of vehicles for free in Florida to help owners escape Hurricane Irma

    A Tesla Model S 60 owner in Florida reached out to us with almost 40 more miles than in his usual full charge and a new ’75’ badge in his car software. While he didn’t ask for it nor knew why it changed, Tesla had temporarily unlocked the remaining 15 kWh of the car’s software-limited battery pack option to facilitate the owner’s evacuation.

    We reached to Tesla and a representative confirmed that the company has put in place the emergency measure to temporarily extend the range of the vehicles of Tesla owners in the path of Hurricane Irma.

    The company says that a Tesla owner in a mandatory evacuation zone required another ~30 more miles of range to optimize his evacuation route in the traffic and they reached out to Tesla who agreed to a temporary access to the full 75 kWh of energy in the battery pack, an upgrade that has cost between $4,500 and $9,000 depending on the model and time of upgrade. Considering the 15 kWh (30 to 40 additional miles) could also be useful to other owners affected by Irma, Tesla decided to also temporarily unlock other vehicles with the same software-lock battery packs in the region
     
    • Like x 3
  14. David99

    David99 Active Member

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    The 12 Volt socket has a 15 Amp breaker so that's your limit using that. I have seen the DC-DC converter provide 60 Amp (looking at CAN bis data) so the 12 Volt system is definitely capable of much higher loads. You just can't use the normal cigarette lighter outlet. You'd have to go into the jump start terminals or directly from the 12 Volt battery which isn't a big issue. The DC-DC converter is active all the time. If doesn't matter if the car is on or off, parked or running.
     
    • Informative x 1
  15. Blup85

    Blup85 Member

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    This is awesome info. 60 amps is plenty of power to keep some stuff running. I miss Macgyver..
     
  16. David99

    David99 Active Member

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    The DC-DC converter is also liquid cooled so it can sustain that power.
     
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  17. tga

    tga Supporting Member

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    How is the DC-DC converter active when the car is off? When the car is off, the contractors are open and the HVDC bus is de-energized, so the DC-DC converter has no input power.
     
  18. n2mb_racing

    n2mb_racing Member

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    When the 12v battery charge level drops below some minimum, the contractors close and turn on the hv to charge the 12v battery. It does this about 5-6 times a day, if you don't have the computer power saving features turned on.
     
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  19. David99

    David99 Active Member

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    The DC-DC converter is not active 100% of the time, only on demand. It will activate automatically as soon as the 12 Volt battery drops below a certain level. This system is active at all times regardless of the car being on or off. That means you can draw power from the 12 Volt system without having to worry about draining it.
     
  20. tga

    tga Supporting Member

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    Right. The DC-DC is "available" all the time, but it's not really active all the time. To me, anyway, "active" implies powered up and actively powering the 12V bus. Semantics, I guess.
     
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