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Thread: recommendations on power supplies that WILL not drain the battery

  1. #1
    Join Date
    Apr 2009
    Round Rock, Texas, United States

    recommendations on power supplies that WILL not drain the battery

    Howdy, I'm looking to put a car pc into a 2008 WRX. My main sticking point right now is that it has an Odyssey mini-battery(basically for a motorcycle/ATV) and they have limited Cranking amps compared to a full size battery.

    I just want to make sure that however It's powered, that there is no chance that it will draw down the battery when the alternator is not running. I had always planned to do this, then realized that in going to the race battery, it may now be more complicated.

    I plan to add a touch screen in the factory radio location, and a Small Form factor PC. Probably a Shuttle XPC with the case cut in half.

    The PC itself will be pretty stripped down, M/B, SSD, no Optical drive, but I may be adding an AMP of some sort to power, likely, just the front two speakers. I'll likely remove the rears. I may try to do some sort of mini set of removable speakers, and remove all the speakers, as the type of racing I do, rule number one is take as much weight out of the car as is allowed, so I may not even need an Amp. I'm not an audio connoisseur.

    The PC will run Data Acquisition software of some sort, OBD2 info for digital gauges, and may even run cameras.

    Any info or opinions would be greatly appreciated.
    Last edited by murphyslaww; 12-20-2011 at 02:35 PM.
    08' WRX - lightly prepared for D-stock autocross
    1994 BMW M3/25is - Heavily prepared for SM class autocross
    OBD1 :( no carputer fo the Bimmer

  2. #2
    Constant Bitrate
    Join Date
    Jun 2010
    Vancouver, Washington, United States
    The weight savings from the small battery seems counterproductive to the functionality you want from the stuff you are putting in. Really, if you are stripping things down to that point you don't want to put in an amp, speakers, AC, passenger seats, radio or anything that isn't necessary for driving the vehicle.
    (edit: rereading that, it sounds like I'm being a jerk. Sorry. What I mean to say is, putting a small battery in there should be one of the last options to cut weight. If the car is a daily driver and not a trailer queen between races, I'd say that shouldn't even be an option)

    With the stuff you want, really, just put a standard battery in there. The 10 lbs isn't going to make any noticeable difference, I assure you.

    That being said, Carnetix power supplies, for example have voltage monitoring and auto-shut off. On some models you can adjust this so you can be sure to cut power before it drains the battery past the point of being able to start the car.
    Last edited by Ryven; 12-20-2011 at 03:21 PM.

  3. #3
    Neither darque nor pervert DarquePervert's Avatar
    Join Date
    Apr 2004
    If you're considering a Shuttle unit, most of them use standard ATX power supplies. An M-series, Opus or DSATX will all shut off all power to the PC to prevent battery drain, as well.

    I agree that a minimalist battery is not what you want if you're adding electronic equipment to a vehicle.
    Have you looked in the FAQ yet?
    How about the Wiki?

    Under normal circumstances, a signature would go here.

  4. #4
    FLAC -zip-'s Avatar
    Join Date
    Sep 2004
    1. Make sure its bolted down agressively - have a look at metal strapping. Not sure if you get inspected or not
    2. Forget running cameras from the PC, us a GoPro or Contour if you are considering it
    3. Whatever ODBII software/reader you use make sure the maximum PIDS are supported for your vehicle
    4. Have a swtich between the battery and power supply, that way its impossible to drain the battery no matter what type of power supply you use. Set up the power supply to start shut down sequence as soon as the key is turned off.
    5. I race with air conditioning on, sounds like you are pretty hard core so if you run with it off make sure the PC is vented to the max with fans
    Last edited by -zip-; 12-21-2011 at 01:11 PM.
    2008 350z GT Installed since April 22nd 2011 - Worklog
    2000 Protege Installed Since April 2, 2005 - Intel D201GLY|Fusion Brain|ODBPros ODBII|Engenius|GPS Rikaline|Powermate|Motorized Lilli
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  5. #5
    MySQL Error soundman98's Avatar
    Join Date
    Jan 2008
    on the border of northern IL/IN
    Quote Originally Posted by -zip- View Post
    4. Have a swtich between the battery and power supply, that way its impossible to drain the battery no matter what type of power supply you use. Set up the power supply to start shut down sequence as soon as the key is turned off.
    it is better to use a relay to handle the high draw then a switch-- the switches that can handle that amount of power(10-25A) are less attractive and more expensive then a cheap switch/relay combo.

  6. #6
    Raw Wave
    Join Date
    Nov 2009
    I never like running more than a few Amps (maybe up to 10A in a 16A switch). Plus there are cheaper and more (and smaller) switch options if it merely has to carry ~250mA to maybe 2A for a BIG 250A relay. And all your heavier power wiring stays remote and is probably much shorter.

    The alternator's charge lamp could control a relay that disconnects the load from the battery when not charging, but if needing a supply, the above mentioned 12V-automotive supplies offer far more features (like delayed off or low-volts shutdown).

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