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Thread: How much power from 12 V power outlet?

  1. #11
    Roadster 919, S 2006 Doug_G's Avatar
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    Quote Originally Posted by smoothoperator View Post
    I am pretty sure the ABS & SRS & VMS use that 12V battery and are not run off the ESS.
    I'm pretty sure those systems are backed up by that battery. In any case the primary power to keep that battery topped up comes from the ESS.

  2. #12
    Roadster 472 - S 440
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    Most cars have a 120W limit on the accessory 12V plug - the connector can't safely handle more than that.

  3. #13
    smoothoperator
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    Quote Originally Posted by Doug_G View Post
    I'm pretty sure those systems are backed up by that battery. In any case the primary power to keep that battery topped up comes from the ESS.
    Yea that is pretty obvious that the 12v battery gets replinished by the ESS, the 12v battery serves a larger purpose than just being there for backup. It actively powers electronics in the cabin.


    Quote Originally Posted by Doug_G View Post
    The Roadster's battery is a small sealed lead-acid battery used for backup power if the ESS goes offline. It keeps the headlights and wipers working until you can pull over. It's normally not used.
    I am referring to this, the 12V is indeed normally used.

    Check this thread out:

    12 volt accessories?

    Post 5

    Quote Originally Posted by scott451 View Post
    I believe there are two 12V power systems in all Roadsters, Vaps and Vsb. Vaps appears to be used by the major EV systems in the car (PEM, HVAC, etc). The Vsb (secondary battery?) seems to be used for all car critical systems (VMS,ABS, SRS, doors, alarm, etc). Some systems (like the VDS and possibly the VMS) appear to have the ability to draw power from either, if one should fail.

    I'm not sure which one the radio runs on, but I'll check (when I get back on 1/7/11).
    Last edited by smoothoperator; 2012-04-18 at 11:32 AM. Reason: added link and reference

  4. #14
    Roadster 919, S 2006 Doug_G's Avatar
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    Yes, but I expect the 12V battery is constantly fed power while the car is operating. So the power comes from the ESS. At most the 12V battery is acting like a (super)capacitor.

    We actually manufacture a motor control system that runs that way. It has a 12V sealed battery - identical to the one in the Roadster - that is essentially trickle charged all the time. It doesn't really provide power to the electronics except in two situations. If the mains power goes out, it provides emergency backup power, so everything can shut down safely. Also if the control system is hooked to a larger DC motor, the battery essentially acts as a capacitor and absorbs the motor startup surge.

  5. #15
    smoothoperator
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    Quote Originally Posted by Doug_G View Post
    Yes, but I expect the 12V battery is constantly fed power while the car is operating. So the power comes from the ESS. At most the 12V battery is acting like a (super)capacitor.

    We actually manufacture a motor control system that runs that way. It has a 12V sealed battery - identical to the one in the Roadster - that is essentially trickle charged all the time. It doesn't really provide power to the electronics except in two situations. If the mains power goes out, it provides emergency backup power, so everything can shut down safely. Also if the control system is hooked to a larger DC motor, the battery essentially acts as a capacitor and absorbs the motor startup surge.
    The ESS charges the Lead Acid battery when it falls under a certain threshold (not continously)... I know that certain electronics operate exclusively off the ESS, certain electronics operate exclusively off the 12v Lead Acid battery (regardless if ESS is "charging" the lead acid battery or not) and electronics that operate off both. Do you have any technical documents or logs (from Tesla or your Roadster) which corroborate your theory with regards to the ESS and 12v (that you claim is only used in emergency situations i.e. Failed ESS)? I am just curious because I have never heard of the 12v battery on the Roadster working in the fashion you describe.. Thanks!

  6. #16
    S85 - VIN:P05130 - 3/2/13 jerry33's Avatar
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    Hopefully Tesla will have a better 12V battery monitoring system than the Prius (or the Leaf from what I've read on the forums). The problem with the 12V battery is that because there is no starter motor, there is no warning when it starts to get weak. in the Prius this can cause odd behaviour and sometimes cause it to throw codes. In one case the Toyota dealer told the owner that they would need a new traction battery, new transaxle, and new inverter. Fortunately the owner posted this in one of the groups and followed the groups instructions to replace the 12V battery and see if the codes didn't go away. They did. On my 2004 at five years I replaced the battery and found that it had two dead cells. I never had to do a jumpstart nor was there any odd behaviour.
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  7. #17
    mod squad TEG's Avatar
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    Keep in mind that 1.5's seem to have a different arrangement for the aux 12v compared to 2.0 & 2.5's...

    For the 2.x's it is my understanding that the aux 12v battery is primarily there to keep things like the headlights and door locks working for a while if the ESS / DC->DC should stop providing power. This could be due to it failing, running out of charge, or being disconnected such as in an accident. If your ESS got damaged in an accident it might be good for the headlights and door unlocks to keep working - so, for instance, someone could see the car, and open the door to help you out.

  8. #18
    smoothoperator
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    Quote Originally Posted by TEG View Post
    Keep in mind that 1.5's seem to have a different arrangement for the aux 12v compared to 2.0 & 2.5's...

    For the 2.x's it is my understanding that the aux 12v battery is primarily there to keep things like the headlights and door locks working for a while if the ESS / DC->DC should stop providing power. This could be due to it failing, running out of charge, or being disconnected such as in an accident. If your ESS got damaged in an accident it might be good for the headlights and door unlocks to keep working - so, for instance, someone could see the car, and open the door to help you out.
    If you disconnect the lead acid 12v the door lock switch works, if you disconnect the ESS the door lock switch does not work....I know this much from my own personal experience (2011 Roadster)...

    Scott451 in this thread:
    12 volt accessories?

    Listed a comprehensive list of electronics that work off the ESS and ones that work off the Lead Acid battery. Quote below:



    Quote Originally Posted by scott451 View Post
    The battery for the 2010 is located behind the right headlamp. I believe this battery is there because of DOT requirements. The door locks do not appear to run off this battery (b/c when the Vaps is off, the locks do not work). ABS, SRS, VDS and VMS do appear to run off this battery. The VDS can run off either Vaps or Vsb because it can be use to turn off the primary +12V supply (Vaps) while running off of (Vsb). The techs always turn off Vaps via the VDS whenever they are working on anything electrical in the car. (that would imply that all the 400V contactors are controlled by Vaps not Vsb/small battery)
    Please advise?

  9. #19
    Roadster 919, S 2006 Doug_G's Avatar
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    Quote Originally Posted by smoothoperator View Post
    Please advise?
    It could well be true; however, I don't believe every detail of technical information I get on the Roadster, because I have heard too many contradictory things from different people. So you might very well be correct. Or not.

    Scott has certainly dug further into the Roadster than any non-Tesla (uh, formerly non-Tesla) person I know of. But saying it "runs off the battery" might really mean "runs off the Vsb bus", and depending on how things work it might not draw primary power from the lead-acid battery.

    Basically I'm saying I'm not convinced either way at this point.

  10. #20
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    Quote Originally Posted by VolkerP View Post
    One Roadster was damaged by using an inverter, Tesla claimed that line noise destroyed some 12V circuitry and initially it looked like the customer had to bear the cost (they changed their mind afterwards and handled it under warranty)
    WARNING: Do not plug an AC inverter into your 12VDC socket!!
    Any updates on this topic?

    Specifically, is it safe to use something like:

    Amazon.com: BESTEK 150w power inverter car dc 12v to 110v ac inverter dc adapter laptop charger notebook adapter dc charger ac adapter usb charger Dual USB 3.1A 1511C: Cell Phones Accessories

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