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Car Computer

Discussion in 'Automotive Electronics' started by dreamproject, Jun 28, 2005.

  1. dreamproject

    dreamproject New Member

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    Hi all,

    I am fixing up a computer for my car . The following are its specs:


    I am using a Gigabyte Motherboard hosting a AMD 2400+ processor , the board's SMPS is powered by a 400w off-the-shelf inverter (1.3 A max.)(running on the car battery) . The Computer's VGA output is fed to a VGA-AV converter and then to a 8" LCD-TFT monitor (NecVox)(Accepts only AV input). The monitor is driven directly by the battery . All ports present in a normal desktop are available (USB , Parallel , Serial , Etc..) . My doubts are:


    1. A warning on the inverter says " The output is not purely sinusoidal " . Is this cause for worry ?

    2. When I start my car with the computer running , will it restart due to the voltage drop that occurs during a start ?

    3. I have noticed waves on the monitor display , Is this due to the inverter being on the same line as the monitor or due to the inconsistencies in the refresh rates of the PC , VGA-AV converter and the Monitor ? . The waves become more prominent when the car is running.


    Thanks
     
  2. zachtheterrible

    zachtheterrible Active Member

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    With a big enough capacitor it wouldn't :lol:
     
  3. MARINE1142

    MARINE1142 Member

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    What kind of plans do you have for a onboard pc in your car> Why cant you just put a laptop in there and call it a day?
     
  4. dave

    Dave New Member

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  5. tansis

    tansis New Member

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    The output of the inverter should not be a worry,
    what is cause for concern is why you are using it in the first place?

    For this application a DC/DC converter would be more efficient
    in terms of both electrical losses and space as it replaces the computers SMPS

    http://www.mpegbox.net/products.html
     
  6. Oznog

    Oznog Active Member

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    1. Don't think so. The SMPS rectifies it out anyways. The rectifier won't charge to the same peak voltage but I think it's ok.
    2. Yeah, and a cap won't help here because it will instantly drain into the starter. You need a second battery and battery isolator to keep current from flowing backwards out of it. Or a UPS. The thing to watch out for is charge current. If you run a small secondary battery down and start the vehicle, it might put out a 50 amp-100 amp charge current to it.
    3. Probably ignition noise or maybe the alternator's AC peaks are coming through.

    Be aware your big issue here is vibration and shocks. This is very harmful to desktop drives. Much less so to laptops. It may also present problems for card connections, etc.
     
  7. dreamproject

    dreamproject New Member

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    points

    Hi all ,

    Thanks for taking the time to discuss this issue . I could have gone in for a laptop but I considered these points:

    1. A laptop would have looked like an after-market fitment.

    2. I already had a 8" LCD-TFT screen in the car , Connecting the computer to this made it look really cool the primary purposes being music and movies.

    3. All that is visible is the DVD-ROM drive in the dashboard , a couple of USB ports and a RJ-11 Ethernet jack for data transfer.

    4. A cordless trackball completes the setup for total wirless use .


    5. The total cost of the setup was less than 60$ , but a comparable laptop would have cost more (2.4Ghz , 80 Gb , 512 Mb)

    6. A Laptop screen's hinges would definitely be damaged during vehicle movement.

    7. A DC-DC converter is possible but using an inverter simplifies things and avoids messing with power wires inside the CPU. we have to contend with four voltage levels (+12v,-12v,+5v,-5v)

    Thanks
     
  8. Someone Electro

    Someone Electro New Member

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    Yea an 400W PSU from scratch wod be prety complicated.

    btw: You forgot the +3.3V rail That rail is probobly the most inportant since it powers the CPU (The modern CPUs went to 3.3V to reduce the heat produced and so making the cooling problem well... less a problem)
     
  9. Jay.slovak

    Jay.slovak Active Member

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    Well most modern CPUs have even lower voltage (I think 486 had +3.3V Core), for example my AthlonXP has Vcore of 1.65V. Motherboards use step-down converters to lower +3.3V to Vcore of procesor that is installed.
     
  10. Someone Electro

    Someone Electro New Member

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    I thnink his CPU is 3.3V (mine P4 is too)
     
  11. dreamproject

    dreamproject New Member

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    thanks

    Hi all,


    Thanks for your views
     
  12. checkmate

    checkmate New Member

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    There are many car PC project on the web. A Google search yielded some interesting results. I was particularly intrigued by this. :D
     
  13. Optikon

    Optikon New Member

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    1.2, 1.3, 1.25, 1.5, 1.8 core voltages are common these days.
    3.3V & 2.5 are mainly used for I/O. and in most cases, 5V is out of the question altogether.
     
  14. Thunderchild

    Thunderchild New Member

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    i think most modern cpus get the power from the 12 v rail that has a switching power supply on the mobo. this is more efficient as less amps have to go thru the power transistors per watt of current needed making less heat and power loss
     
  15. Someone Electro

    Someone Electro New Member

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    12V are they nuts !?
     
  16. Thunderchild

    Thunderchild New Member

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    no if u had to convert 100 watts of 3.3v to 1.65v then ud get thinking about using 12 too. whats the deal u use 220 volts to power the pc but it is reduced by the psu. on the motherboard there is another psu that reduces 12v to 1.65v. this would also solve the problem of unstable crapy psu's as te mobo one has probably special attention payed to it to ensure stability and reduce interferance from other parts:
    open ur pc case and look at the mobo u will see near the cpu (probably between it and the paralel port) many power transistors and coils that is the onboard power supply for the cpu. intel also use another one on a small board plugged into the mobo as modern intel chips take 100 watts easy
     
  17. mstechca

    mstechca New Member

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    Why do you care?
    How long is the voltage drop? that needs to take into account. You can get away with a ridiculously large value capacitor (1F +) in most cases, but if you want to save money, you may want to measure the resistance of your load (computer), and then if you use the simple RC equation, you can roughly determine how long it takes for a capacitor to charge up.
     
  18. dreamproject

    dreamproject New Member

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    calc

    hi,

    how do I calculate the load , R=V/I , Is this right , by measuring current drawn ??

    :wink:
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    That's right. If the computer draws 20A from the 13V battery, then its resistance is only 0.65 Ohms.
    The capacitor discharges into the computer and therefore powers it while the engine is cranking and the capacitor will need a diode between it and the battery to prevent the capacitor from also powering the starter motor.

    The voltage on the 1F capacitor will drop to only 4.44V in only 0.65 seconds! Ridiculous. :roll:
     
  20. shamikrudra

    shamikrudra New Member

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    Hi
    i have gone through your problems

    as u want to install a pc in your car and want to use a inverter
    my first sagesion will be use a UPS in between PC and Inverter
    if output is not purely sinusoidal then then ups will solv your problem of heating of SMPS.
    and if u can modify the UPS then there is no need for inverter but there may be a problem when starting your car
     
  21. dreamproject

    dreamproject New Member

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    thanks

    Hi shamik,

    Thanks for your input . I think this is just what I needed. Okay , is a 400 w inverter with a maximum continuous current capability of 1.3A good enough to charge the UPS batteries . Also , Did you notice waves on the display screen (TFT) , I have also connected a CCTV camera in the rear for rear vision . The waves appear even when the diplay is switched to camera mode from the computer mode , thus there can be no inteference from the computer . Could the inverter be causing changes in the Power Factor , causing this ????

    Kindly advise.
     

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