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Powering a PC from a Car Without an Inverter?

Posted by Cliff on from the hardware-hacks dept.

(H)elix1 asks: "Without using an inverter, what is the good cheap way to power an ATX motherboard from a DC source? I have a mini-itx based computer I'm looking to use in the car and house. I'm looking for something like a laptop uses, with an AC-to-DC brick that feeds a DC-DC internal connector. Linitx.com has one, but it is a bit pricey after shipping to this side of the pond, googling turned up even more expensive industrial PSU's. Am I missing a simple hack? I have a soldering iron and am not afraid to use it..."

9 of 80 comments (clear)

  1. Maybe I'm missing something here... by gklinger · · Score: 3, Informative

    Have you considering using a DC power supply?

    1. Re:Maybe I'm missing something here... by CyberDong · · Score: 2, Informative
      Ummm... I think the part you're missing is this stat from the linked page:

      Input Source:
      -42v ~ -56vDC
  2. Don't skip the inverter. by Bastian · · Score: 3, Informative

    The DC power supplied by your car only in the region of 12v. It's riddled with power spikes that will be damaging to the motherboard's electronics. This is the main reason why you're supposed to use a power inverter on anything that wasn't specifically designed to be powered by a car's DC outlet.

    A DC adapter can't effectively smooth off the spikes. On the other hand, switching the current to AC using an inverter and then converting it back to DC with an AC-DC adapter will supply power that isn't dirty.

    You can get a decent 300 watt power inverter at a truckstop for 30 or 40 bucks if you look around. It would certainly be a lot cheaper than having to replace a fried motherboard.

    1. Re:Don't skip the inverter. by AnimalSnf · · Score: 2, Informative

      Absolutely true. Although I stick to the computer/physics end of electrical engineering I've seen the tolerances for the 12V bus and there is absolutely no way a motherboard will survive the spikes and voltage swings that automotive componenets are designed to withstand. Of course you can always try to design your own conditioner, but that will take more than just soldering knowledge. I would think for efficiency sake 300 watt inverter maybe a bit much, but a personal descision.

  3. Thoughts by Futurepower(R) · · Score: 1, Informative

    The DC directly from the car's battery terminals is almost completely clean. This is because of the low internal resistance of a charged car battery. There are IC regulators that output the other voltages, using a +12 Volt input.

  4. Try .. by .milfox · · Score: 4, Informative

    http://205.147.44.194/store/commerce.cgi?product=S olarPC

    There's a 12V DC/12V DC/ATX inverter there. :P

  5. A few sources, and a site for more info by TwoStep · · Score: 4, Informative

    DC-DC Power supplies:
    The best one is Opus Solutions
    Another good one is Keypower

    You can find a lot more info at MP3Car.com, and especially at the forums there.

    Twostep

    --
    There are 10 different types of people in this world... those who understand binary, and those who don't.
  6. Yes, It Can Be Done by Anonymous Coward · · Score: 2, Informative
    Moderators - please mod this up as this is a serious reply.

    Your task can be done, but a certain degree of care needs to be applied or you will end up with a fried motherboard. An ATX psu generates five different output voltages and these must be considered on an individual basis:



    +12 volts - This is the most difficult so we will consider it first. Your options will either be a switched-mode regulator with a wide input range (say 11v-15v) or a parallel regulator which uses a low value resistor in series and a power transistor wired across the load in parallel. Excess voltage in this circuit will be disappated as heat which means that it can get damn hot !!



    +5 volts - Use any regulator circuit you can find but switched mode will be the most efficient.



    +3.3 volts - Wire as for +5v but change values. An alternative source is an old ATX supply which may have the 3.3v regulator as a seperate board inside the case



    -5 volts - The load on this circuit will be low so any switched mode circuit will probably do the job. You need a switched mode in this application because of the voltage inversion.


    -12 volts - again a switched mode circuit must be used but the load on this might be a little higher.



    With all circuits you MUST have some form of surge protection or you WILL kill both the supply and the PC. I don't think you can get varistors as low as 12v and 5v so your only option will be to wire the biggest zener diode you can find across the outputs. I suggest using 5.3v for the 5v lines and 12.5v for the 12v outputs. The 3.3 volt circuit needs special attention as this supplies the CPU, use the closest zener you can get to the output voltage. You should also seriously consider isolating the whole thing from the car electrics until the engine is started. A Google search for 'switched mode regulator' should help you find the circuits you need.



    Hope this information helps.



    Edward Almos

  7. You are missing something here... by Anonymous Coward · · Score: 1, Informative
    Have you considering using a DC power supply? [amtrade.com]
    Input Source:
    -42v ~ -56vDC

    Now all he has to do is figure out where to get a 12VDC to 48VDC converter.

    This kind of DC power supply is intended for telecom sites that have 48VDC power sources. Phone company central offices have huge banks of batteries to supply the 48 volts. That's why the phones work during a power blackout.