TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

12-volt Accessory Plug - Switched? Unswitched? Other?

Discussion in 'Roadster' started by Habious, Nov 4, 2014.

  1. Habious

    Habious Member

    Joined:
    Sep 30, 2014
    Messages:
    408
    Location:
    Springfield, VA
    OK, so I'm very confused here.

    I have a 2011 Roadster 2.5.

    I've connected a head's up GPS-based speedometer to the 12V accessory port (I'm 6'1" and, between the steering wheel and the glare from the sun, I can see exactly NONE of the 3 speedometers in the car).

    The HUD works great...I've installed them in another car of mine. At some point, I plan to hard-wire this sucker in at the fuse panel but, for now, it's hooked to the accessory port. My question is on this 12V port;

    It doesn't seem to be switched, or unswitched.

    I plug the doo-dadd in, and it's on. I turn the car off...it's still on. I lock the car...it's still on. I look in on the car a few hours later...and it's off.

    I can't be 100% sure but, it seemed like it was on 100% for the first few days. Did I drain the 12V accessory battery (I know there's one up front somewhere but, I assume this gets charged by the PEM somehow as the car does its thing)? Maybe it turned off after a while initially, and I just didn't notice (this is possible).

    Does anyone think it's a problem leaving something plugged into the accessory port 24/7 (it's a very low-current draw...but haven't measured the exact rate)?

    When I unlock the car in the morning, the accessory port comes on (along with the interior light).


    Also, quite possibly completely unrelated but, maybe I'm causing my own problem here...so I'll ask along with my original question...Is it just me, or does the range on the key fob absolutely stink? I've checked the battery, and changed the battery, in the key. But, I can only get it to work if I'm standing within about 2 feet of the driver's side door.
     
  2. Doug_G

    Doug_G Lead Moderator

    Joined:
    Apr 2, 2010
    Messages:
    15,848
    Location:
    Ottawa, Canada
    When you "touch" the Roadster the battery cooling pump runs for a while. As long as it is running, the 12V socket has power. When it switches off, so does the socket.
     
  3. shrink

    shrink Member

    Joined:
    May 21, 2013
    Messages:
    555
    Location:
    Phoenix, AZ
    I remember last year I was in a holiday parade with my Roadster and ran a strip of flex LED's off the 12V socket. When the car was running there was obviously power, but I remember during the prep stage, I'd get of the car with the lights on to take pictures and talk to folks, after about 10 minutes the lights would go out. Once I opened the door, lights were back on and power to the socket was restored.

    So in my experience, it seemed to cut out after about 10 minutes, but looks like Doug_G had the more technical explanation.
     
  4. markwj

    markwj Moderator, Asia Pacific

    Joined:
    Apr 10, 2011
    Messages:
    3,655
    Location:
    Hong Kong
    The accessory socket power on 2.x cars is provided by a 12V converter in the main battery pack.

    This power will be on when the car is 'awake'. That typically means when the car is driving, charging, or actively trying to condition the battery (if the hottest battery brick is >31C). The simplest way of determining whether the car is 'awake' is that the coolant pump is also on that circuit. You can hear it in the rear right corner of the car.

    If the car is off, not charging, and the hottest battery brick is <=31C, then the car will go to sleep after approximately 5 minutes.

    You can wake up the car by pressing on any door handle, waking the VDS, unlocking the car, opening the charge port, etc.

    It sounds like your HUD would be best hardwired to the switched 12V line, rather than the accessory socket.
     
  5. Habious

    Habious Member

    Joined:
    Sep 30, 2014
    Messages:
    408
    Location:
    Springfield, VA
    That makes total sense, thank you for that explanation.

    That is my eventual plan. The 12V accessory port was just something to get it working. Once the weather turns to crap (which is very soon), I'll have plenty of non-driving time to tap into switched power, and route the wiring properly (it's currently splayed across the dash).

    And, by the way, I have to say that the HUD speedo makes the car so much easier to drive! I'm not constantly worried about how fast I'm going, or squinting/squatting in the cabin, trying to read one of the other speedometers.

    In the DC metro area, the Beltway speed limit is 55 MPH. Of course, everyone routinely does 75 MPH. The problem is, cops around here don't seem to think that "keeping up with the flow of traffic" is a valid excuse for doing 20 over, so I like to know exactly how fast I'm actually going.
     
  6. markwj

    markwj Moderator, Asia Pacific

    Joined:
    Apr 10, 2011
    Messages:
    3,655
    Location:
    Hong Kong
    100% agreed. The analog speed gauge is unreadable, and speed display on VDS is in the wrong place for the driver. That is why I worked on developing the OVMS digital speedo feature. That puts the speed in the little orange display in the instrument cluster.
     
  7. sethr

    sethr CPO Roadster #1089

    Joined:
    Mar 24, 2013
    Messages:
    152
    Location:
    Fairfax, VA
    Also connected the same way: the trunk light. When the battery cooling pump turns off, so does the trunk light. I suspect this was done to keep the 12 volt battery from being run down.

    P.S. - I agree, the range on the fob is poor. In some long ago thread, someone rerouted and lengthened the wire that serves as the antenna for the receiver. It sits behind the trunk release button. I got the nice people in Rockville to add a wire and run it along the door sill. Not a huge change, thanks to the carbon fiber, but definitely better.
     

Share This Page