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Thread: My idea for powering carpc off wall at home (cheaply!)

  1. #1
    Join Date
    Jun 2006
    Calgary, Alberta
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    My idea for powering carpc off wall at home (cheaply!)

    Everytime I want to sync my music, or install stuff, it is a big hassle. The reason is that I do not feel comfortable running the carpc off battery for extended periods of time. Therefore, everytime I want to install something/sync my music/whatever, I have to unscrew everything, take my computer indoors, and use it there. It would be MUCH more convenient if I could just use the computer in the car, but being able to "plug" the car's electrical system into the wall at home so that the battery does not get drained. So here is my idea.

    I came across this site:
    I am mostly interested in the part which suggests connecting the +5 volts of 3 computer power supplies together to obtain 15 volts at a fairly high current (~25 amps). I have a TON of computer power supplies laying around, so this is no problem. To reduce the 15 volts to the ~13.8 volts that a car's electrical system requires, the site suggests connecting one of two high current diodes to drop the voltage to approximately that level. With this ~13.8 volts availiable at a fairly high current, I could then connect the +13.8 volts and -ground in parallel with my car's electrical system, then run my carputer without fear of a drained battery. Before I try something like this out, I would like to hear some opinons. Is this a good idea? Is there anything I have overlooked?

    Also, the most difficult part is where I can find a diode which can handle such fairly high currents cheaply. I would prefer to buy locally and the only store that I know of that carries electronic components is:
    I have not been able to find a suitable diode from looking at this site (maybe I am using the wrong search terms?)

    Or could I go to a car junkyard to find these high current diodes? I know that high current diodes are connected to alternators to convert the AC > DC. But what exactly do automotive diodes look like? I've tried to do a image search, but I couldnt really find a good picture. Where under the hood would I be able to locate these diodes? Are they usually obviously exposed, or are they hidden in something? I am a complete noob when it comes to anything under the hood of cars.

    Suggestions would be welcome. Thanks.

  2. #2
    Confusion Master
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    Sep 2003
    If you go down to the woods today, You're sure of
    Quote Originally Posted by nobb View Post
    Suggestions would be welcome. Thanks.

    Don't do it.

    Unless you do it right you could

    a) screw up your cars electrical system

    b) screw up your house's electrical system (not sure how US supplies are done but if they are not fused properly and fire could ensue)

    c) screw up your person if you touch any of many wrong contacts that will be available to you.

  3. #3
    Join Date
    Jan 2002
    IF you still decide to do it, get an MBR3045PT - SCHOTTKY RECTIFIER,45V,30AMP available at Active.

    Good luck!
    If it ain't broken, open it to see what makes it "tick".

  4. #4
    Fusion Brain Creator
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    Mar 2005

    just use the +12v output from one supply

  5. #5
    Maximum Bitrate Ruffy's Avatar
    Join Date
    Sep 2006
    see, thats the benefit of using a laptop for your setup. if i want to work on my carpc for a lengthy period of time I run a a/c line from the wall to ac connector my laptop came with, then plug the laptop in!


    it's kindof runny looking right now as i have a big orange cable going in through my rear window.
    Car : 00' Chrysler 300M
    Speakers : Rainbow Audio SLC 265 | Subs : Diamond Audio D6 12" Subs X2
    Amp's : Hifonics ZXi 6006 AB | Hifonics BXi 1606 D
    CarPC: HP Laptop AMD Sempron 3000+ | 1.5GB RAM | DVD+RW | 80GB 5400RPM HD | ATI R200 Video

  6. #6
    Join Date
    Dec 2006
    I do have a switch so I can disconnect my car pc from the battery.
    ( )
    On the PC's side, I do have a connection for the 12V (ignition and constant) and the ground. As such, I connect a 12V source (old power supply from a PC case) when playing around with the car pc. Since the screen is powered through the PC's M2-ATX , I do have everything I need.
    No need to uninstall the car pc (which would be quite hard to do avery time).
    2 minutes and I'm set to go.
    Still thinking of creating a type of plug which could make it simplier to connect PC and 12V source.

  7. #7
    Join Date
    Jun 2006
    Calgary, Alberta
    Blog Entries
    Using the +12 volts would not work, because if you connected 12 volts directly to your car battery (and electrical system), then your car battery would slowly be drained. This is because when fully charged, your car battery should be at about 12.6 volts.

    I figure that if I could supply approx 13.8 volts of voltage which a fairly high current availiable (pretty much supplying power like an alternator), then my car battery could be put on floating charge, and all electronics could be powered.

  8. #8
    Constant Bitrate techeros's Avatar
    Join Date
    Sep 2004

    dont do it

    Just get an external hdd kit or something from NewEgg with a usb 2.0.
    Dump your stuff on that and be done with it.
    03' Toyota Tundra T3 Special Edition - Polk Audio speakers - Sony 4ch amp - RF Sub amp
    Carputer Planning |---------*|
    Overall Implementation |---------*-|
    (Stereo complete)
    Computer installed and working

  9. #9
    Newbie v1per's Avatar
    Join Date
    Dec 2006
    Salisbury, NC

    Make an isolator

    I have been planning to do this, too. What you need to do is use the 12 volt rail from one of those old power supplies you have. Just make sure the 12 volt rail makes a high enough current for your computer (old ones don't make a lot). Then make an isolator with a DPDT switch (Dual-Pole, Dual-Throw, make sure it is rated for enough current). I attached a simple diagram. That'll do it. Then you just plug the computer PSU into the wall, flip the switch from battery power to PSU power and you're ready to rock and roll.

    P.S. I hope you can make sense of the schematic, if not PM me.
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    Max Messinger
    Computer Expert
    Car Newbie

    2000 Maxima CarPC Progress: 99%--Basic computer fully installed, full stereo overhaul planned for the future

  10. #10
    FLAC Jahntassa's Avatar
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    May 2005
    Conyers, GA
    What v1per has is the way I would do it, though I would actually use a 12v Automotive relay and install the power supplies in the car. Just running an extension cord from the house.

    Have the power for the computer go through the relay, then when the AC power supplies are turned on, have the 12v trigger the relay to switch from car battery to power supply.

    So, common on the relay goes to the PC, normally closed is car battery, normally open is the AC power supply. The relay is triggered by 12v and ground off the AC power supply. That way it will automatically switch whenever you have AC provided. You can even use a diode or another relay to have it automatically supply power to the ACC wire for the computer, so it'll power on automatically.

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