Power inverter help please

Discussion in 'General Motoring' started by dogsBollix, Aug 2, 2009.

  1. dogsBollix

    dogsBollix Guest

    i want to put a "spycam" in the car
    it's a computer which draws 60w at 240v

    i have a power inverter rated 150w continuous 300w peak
    but when i switch the computer on the inverter whistles and switches off :-(

    now i know that w=va
    so 150w=240v*a

    the inverter has a fuse labeled "20" (presumably 20 amps)

    so why won't it power my computer ?

    dogsBollix, Aug 2, 2009
  2. dogsBollix

    rp Guest

    Is it a sine wave inverter that gives a proper sine wave output? Some
    don't and that can really mess up a switched mode power supply in a
    computer. Switch on surges can also be much higher than the rated power

    You may be better off getting rid of the inverter and the mains psu in
    the computer and fitting a DC converter instead. Also the computer
    takes a lot of power for a vehicle one and is likely to flatten the
    battery overnight if you use it without the engine running.

    See http://www.mini-itx.com/store/?c=10#dcdc for DC converters. They
    also have a range of lower powered computers that may be more suitable
    and housings for them.
    rp, Aug 2, 2009
  3. dogsBollix

    dogsBollix Guest

    the computer is powered by an external power supply (like a laptop)
    unfortunately i need to power 3 devices: computer, monitor, camera(s)
    the computer+camera works but it won't handle the monitor as well
    the monitor is a small lcd(?) screen

    dogsBollix, Aug 2, 2009
  4. dogsBollix

    rp Guest

    What does the external power supply for the computer output? If it's
    12v you may be able to power the computer directly from the car supply
    but you need to find out if the computer has 12v regulators built in
    since the car will be supplying 14v or more.

    How much power does the monitor use and was the 60W just the computer
    or the monitor as well?

    You could try turning the brightness right down on the monitor and see
    if that helps. Are you switching them all on at once? If so try
    switching the computer or/and the monitor on one at a time in case it's
    just the switch on surge causing the problem.
    rp, Aug 2, 2009
  5. dogsBollix

    dogsBollix Guest

    the psu supplies 12v but the connector to the pc is a 4 pin din thing
    the whole lot uses 60w including the monitor
    i thought about the surge and switched them on seperately without effect
    i'm actually using one of those powerpack things like a portable battery
    that you use to quick start a car ?

    dogsBollix, Aug 2, 2009
  6. dogsBollix

    rp Guest

    Does it have a voltage meter? I know nothing about them but wonder if
    it can't supply the continuous current at the voltage required. Last
    suggestion has to be try it in the car with the engine running.
    rp, Aug 2, 2009
  7. dogsBollix

    dogsBollix Guest

    i got a "heavy duty" Quick start powerpack and that did the trick !
    now all i need to do is see how long it lasts with the engine turned off :)

    dogsBollix, Aug 8, 2009
  8. dogsBollix

    rp Guest


    Well 60watts of 12v is 5 amps and a 70ah battery can thus power it for
    14 hours but car batteries are not efficient for that sort of use so
    you won't get anything like 14 hours. Once the battery is flattened
    it's damaged and won't last for many cycles.

    You can get deepcycle leisure batteries that you can charge from the
    car but even they won't last long being completely flattened.

    Best of luck but be prepared to buy a new battery before long although
    presumably you can switch the monitor off when you are not looking at
    it so that will save some energy.
    rp, Aug 8, 2009
  9. Six hours or less, if you want more than a single cycle out of the rig.

    Brian W
    brian whatcott, Aug 8, 2009
  10. dogsBollix

    dogsBollix Guest

    got 3 hours on the quickstart using a mains "charger" and the monitor
    mostly on standby
    i'll wait for the next long car trip before trying that.

    and i'll take a spare quickstar just in case :)

    dogsBollix, Aug 8, 2009
  11. dogsBollix

    Peter Guest

    Computer may be "60w" but it may not be at power factor of 1 (ie peak
    volts and peak amps not in sync) The inverter may not like this. In
    similar applications I have fixed this sort of problem by adding a
    resistive load to the system. Something like a 15w lamp might be enough
    to stabilise things
    Peter, Aug 21, 2009
  12. dogsBollix

    dogsBollix Guest

    thanks for the info
    i "cured" the problem by running everything from a heavy duty "jump
    start" box

    dogsBollix, Aug 21, 2009
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