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hey there ...
I wired my dc-dc power supply to the car. and tested it with a multimeter . i get all the voltages +5 -5 +12 -12. I connected a fan to it and it worked . again -5 +5 +12 -12
it was it got on the multimeter , however when i connect it up to the motherboad .. i get +5 -5 -12 and the +12 reads +1V ... what could be wronge ???? any ideas would help ???
Well mate it could be your DC converter is not powerfull enough to power your MB. What dc->dc are you using?
it also could be your MB faulty ( like short circut). alsp the wiring from the power source to the converter could be too thin ( the wires i mean).
Or after all it could be your DC converter faulty!
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Fosgate
Since I don't know what DC-DC converter you are using I can only guess.
I think there is a regular voltage regulator IC in the DC-DC converter. Depending on the type these regulators need about 4V more input voltage, thus about 16V input. If the input voltage drops below this, the regulator is not able to regulate anymore, resulting in possibly 1V output.
Since I don't know what DC-DC converter you are using I can only guess.
I think the MOBO draws too much current and 12V regulator falls into some safety condition. Since you have a multimeter, try measuring how much current it draws. If you know what regulator type is inside the converter you can lookup how it behaves when you draw too much current.
Also harddrives can draw a peak current of about 2.5 Amps upon motor spin up. Try disconnecting this, or use a 2.5inch HD, they use much less power.
After a discussion with macphisto it appears that the DC-DC is not able to supply enough power to the 12V line.
It sounds like the DC-DC is using a switching converter for the 12V. A linear regulator would be more likely to get hot an shutdown completely if it is overloaded.
A few checks in the 12V current draw will reveal more.
It is not one of my designs
yeah that could be the problem too...
the +12v rail is comon problem in DC converters when used in the car (with 12v input).
With liner regulators even with low drop out
you need at least 0.5-0.75v over the output voltage which is 12v in this case.
so if the Input voltage goes below 12 volt your regulator will fail to supply the output 12v and will go down i guess even to 1v (when there is a load on it). So what you need in this case is a flyback regulator which has input voltage range from 8-16.
But again you might be using a flyback regulator and it could be faulty.
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Fosgate
hummm .. i'm not into electronics ... so i dont understand a word ya'll are saying ..
by the way just to correct myself .. when i measure the 12v .. i actually get 12,5v...
any other sugestions ???