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Thread: M1-ATX and heavy 12V rail

  1. #1
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    M1-ATX and heavy 12V rail

    Hi

    I got an nForce2 motherboard (very unique mobo from jetway, the one from their twin 765 small form factor PC), Athlon XP 1700+ and an M1-ATX.

    My net power requirements (measured on the ATX when powered off a desktop PSU, running two WinXP consoles both showing MPEG-4 streams, both graphics outputs active, two sound cards actice (one is USB) obviously box at 100% CPU, ):

    5V Rail 5A
    12V Rail 0.5 (main ATX plug) +3.5A (auxillary 4-pin ATX rail)
    3.3V Rail 0.5A
    -12V Rail 0.1A
    5Vsb Rail 0.5A

    The M1-ATX specs are:
    5V Rail 10A
    12V Rail 2A (INSUFFICIENT!)
    3.3V Rail 10A
    -12V Rail 0.15A
    5Vsb Rail 1.5A

    I actually measured all of these only *after* having bought the M1-ATX. (Prior to purchase I only measured the gross power consumption of the box when using a desktop PSU, which was ~86W, and assumed any 90W PSU would do. Ignorance is bliss, or so they say, at least to the point where reality runs you over. I also missed the bit that said the 12V rail feeds off the 5V.)

    I'm currently weighing my options and would very much like to hear opinions. I like the M1-ATX because it's really-smart (tm) and I already have it. All other PSU's I checked can't facilitate 4 amps on the 12V (morex 80W, OPUS-120W, Minibox PW-80). The only two that can are the Minibox PW-200-M which lacks any switch logic and has a miserable input tolerance (11V-14V, -16V with mod that invalidates warranty) and OPUS-150W which is the only one that has a big 12, and whose input tolerance isn't a find either (8-19V)

    Another option is assemble Maestro's Mk-4, which also has a big 12 and also doesn't tolerate too many battery jolts.

    A third option I'm currently very inclined towards is to feed the aux 12V rail on the mobo using an external (regulated) source, such as a Minibox ITPS.

    So
    1. Any suggestions anyone?
    2. Is there anything like the Minibox ITPS, that lacks all the logic (which I don't need as I'll be using the M1-ATX for logic, thus cheaper and simpler), and preferrably with a more decent input power tolerance (ITPS has 9-19V I think)
    Thanks!...

  2. #2
    FLAC evandude's Avatar
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    ITPS is crap. it's only a linear regulator, so it requires 13.5v input to produce 12v output; anything lower and the output won't stay at 12v. You can buy a separate linear regulator for like $5 if you don't need the logic, but the input voltage range is just worthless... only really even works if the car is running.

    Have you seen my DC-DC converter design? My weekend project...

    it outputs ONLY 12v so it would probably work well for your application... and I think it would be fine at 4 amps output. I don't know the input voltage range yet, but I do know that it survives engine crank in my car... And I've put less than $20 into it.

    On another note, might I ask why you don't think the 8-19v input tolerance of the Opus is good enough? 8v is enough to survive crank, which is about all that matters on the low end, and 19v is quite high, definitely higher than you'd ever see continuously in the car (not counting short spikes, which would generally be decently absorbed by caps and inductors in a supply anyway) I can't see any reason to need more than that on either end. After all, the more specific you can make something, the more effective you can make it... making a DC-DC work with a gigantic input voltage range would probably mean it wouldn't be as efficient... there's tradeoffs for everything.
    But don't take it from me! here's a quote from a real, live newbie:
    Quote Originally Posted by Viscouse
    I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
    eegeek.net

  3. #3
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    Opus is currently default way to go

    9-19V is good enough, it just doesn't make the warm fuzzy feeling that a 6V-30V ranged makes. The OPUS 120 has 6.5-30, but only 3.5V on the 12. Also, it's very expensive.

    I drive a 4WD, and intend to put a second battery with big fridge and other stuff hooked up to it at some point, so I'm designing around a very moody electrical system.

    Thanks for pointing out the ITPS will not help due to lousy input tolerance.
    Your design looks nice, but I'd prefer buying something ready to putting one together. Last time I welded circuitry was in highschool, which was a over 10 years ago. I'm neither properly equipped (no proper welder, PSU, dunno where they sell components here, etc) , too inclined or very enthusiastic about doing it today (will if must, will avoid if can).

    Any commercial alternatives?

  4. #4
    FLAC evandude's Avatar
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    what about the are two power supplies right in the mp3car.com store that output only 12v? both of them exceed the ~4A you need...
    But don't take it from me! here's a quote from a real, live newbie:
    Quote Originally Posted by Viscouse
    I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
    eegeek.net

  5. #5
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    Nice. Much more suitable.

    Quote Originally Posted by evandude
    what about the are two power supplies right in the mp3car.com store that output only 12v? both of them exceed the ~4A you need...
    So I buy the OPUS 80W (12V model, as it supports 6 amps, not the 12V/5V model) and feed the 12V rail off that. 7-30V input range.

    Sounds reasonable.

    Any useful ideas as to how to properly chain it to the switch-on logic on the M1-ITX?

    I want the 12V off when the M1-ITX shuts the machine down. Somehow hook it up to the "ground-me-to-energize-the-PSU" green wire on the ATX connector?

    Thanks!

  6. #6
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    miki,

    One other combination you may want to consider is the CarNetix P1900 in conjuction with one of the Travla 120W PSUs. Either the P4-120 or C4-120 may fit your needs and they are cheap ($45) at DC2DC.com.

    Hope this helps!
    MikeH

  7. #7
    MySQL Error Scouse Monkey's Avatar
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    Quote Originally Posted by MikeH
    miki,

    One other combination you may want to consider is the CarNetix P1900 in conjuction with one of the Travla 120W PSUs. Either the P4-120 or C4-120 may fit your needs and they are cheap ($45) at DC2DC.com.

    Hope this helps!
    know anywhere cheap to get that P4-120 in the UK? Wonder if it would run off a 120W laptop 19V DC-DC. Running it off the p1900 would be cool though.

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