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Thread: Opus 150W - input voltage drops to 2V

  1. #1
    Constant Bitrate Caitlin's Avatar
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    Opus 150W - input voltage drops to 2V

    Heya, I've got this supposedly lovely lovely psu wired up to a 20A circuit in the car (ciggy lighter) the switched 12V down there is admittedly triggered by the headlights, not the ign, but I don't see how that would make a difference, 12v is 12v when all it's doing is activating the main circuit.

    The second I hook the psu up to the feed, the voltage across the + and - leads falls to 0.5V and climbs back to around 2V over a second or two, then sits, like a sulky wet crappy dog that won't power my computer.

    I get nothing at all from the PSU, no LED flashes, nada.... I can't find a short, and none of the fuses are blowing.

    I am, to say the least, confused.

    Any thoughts? The whole system works fine when powered from a psu in my house, and has also worked from the same feed circuit in the car using a 300W inverter and a normal psu.

    Heeeeelp

    Merci.
    Cat
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  2. #2
    Raw Wave
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    Hey Cat,

    Give the PSU a go connected directly to the battery but with a fuse inline with the positive - I have a feeling that the lighter socket isn't delivering enough current to power the PSU

  3. #3
    MySQL Error Scouse Monkey's Avatar
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    Quote Originally Posted by Caitlin
    Heya, I've got this supposedly lovely lovely psu wired up to a 20A circuit in the car (ciggy lighter) the switched 12V down there is admittedly triggered by the headlights, not the ign, but I don't see how that would make a difference, 12v is 12v when all it's doing is activating the main circuit.
    Eh????? I am confused.

    Why would it be switched by the headlights. Sounds as though you have take the power from the circuit to light the ciggy lighter when you turn the lights on not the power for the ciggy lighter which should always be on in a 306 (my inverter runs with no key in).


    EDIT: hang on misread your post, i see you are switching the ign line off the lights are you? ahhh. in that case i am puzzled. Try running from the battery as UKmp3car suggests. There maybe something screwy with the 12V down there.
    Andy

  4. #4
    Variable Bitrate
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    Caitlin, the problem is that while 12 v is 12v, the wires in the dash are not sufficient to run a PSU or inverter. You need at least 8 gauge wire for an inverter, and may be able to get away with 10 or 12 gauge for the Opus.

    Too small of gauge wire is why voltage drops on the OPUS soooo much. The wire in the dash has too much resistance because it is too small, which makes the wire have voltage drop, which makes the wire hot, which could melt insulation and cause fires.

    Addressed to everyone doing this sort of quick-fix: Do NOT use the cigarette lighter for powering an inverter or an opus! It is Dangerous. (yes yes, there is a fuse on that line, but it's best not to rely upon it, and there are many cases where the wire insulation melts for high current draw, but the fuse still doesn't blow.)

    KyferEz
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  5. #5
    FLAC
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    Quote Originally Posted by KyferEz
    Too small of gauge wire is why voltage drops on the OPUS soooo much. The wire in the dash has too much resistance because it is too small, which makes the wire have voltage drop, which makes the wire hot, which could melt insulation and cause fires.
    I second this. That's why you're seeing that voltage drop.

  6. #6
    Variable Bitrate Curly_cat's Avatar
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    Get some suitable 8AWG wire and run it directly from your battery to the OPUS with an inline fuse.

    You can find all the bits you need HERE

    : Jetway J7F2 1.5Ghz Mainboard : Cubid 3688 : CarNetix CNX-P1260 :
    : Netgear 802.11g PCMCIA : 2 x LinITX 7" Screens :
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  7. #7
    Raw Wave rando's Avatar
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    Like they said, using too small of a wire presents a fire risk and also causes a substantial voltage drop as current flow increases. Still, in the case of a fully loaded Opus powered by something crappy like the 18G you might find on a lighter circuit, you'd only expect a ~2-4V drop max. Either you've got an extremely long power run, exceptionally thin wire and/or numerous poor connections; or you've got something else strange going on here.

    Either way, do what they said. Hook the thing up correctly first to rule out any problems with your Opus and computer.

  8. #8
    Constant Bitrate Caitlin's Avatar
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    I'll give it a try straight from the battery terminal, but the wire is as fat as the stuff in the opus leads, and it's not going to get thinner back through the loom...

    I *hate* finding bulkhead holes and routing crap behind the dash...
    Cat
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  9. #9
    Raw Wave rando's Avatar
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    OK, you're still missing half the point. The wire that comes with the Opus is 14AWG. That's more than capable of carrying the maximum current the Opus can use. It cannot however carry the maximum current over any appreciable distance without a significant voltage drop. That's why Opus recommends you run 10-12G or larger ... depending on how far away your battery is from your Opus.

    If you need to run regulated voltage wires back to your accessories (5V for example) then the same situation applies. Even though standard Molex PSU connectors are typically wired with 18-20AWG which can safely handle in the 2-4.5A range, that same wiring won't work for runs 10-20ft round trip. At that distance, 18G wire will have about 0.2 Ohms or more resistence (not counting the connectors). At 5A you will lose 1V and many of your accessories will fail to operate correctly/reliably. In short, use bigger wire!

  10. #10
    Constant Bitrate Caitlin's Avatar
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    How come the same wiring is fine running the 'efficient' load of an inverter, a 300W psu and my whole system without a similar voltage drop - this should be far more draw than this psu? I'm not arguing trying alternatives at all, I'm just confused on this score.
    Cat
    Woot, or something.
    Epia M10000 (less rubbish than the 800) :: LCD touchscreen
    GPS :: 80G drive :: Not enough ram... Never enough..

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