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Thread: Surviving cranking

  1. #1
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    Surviving cranking

    have had a bloody good search and am a little confused.
    I have my Morex 3688 wired directly to my battery via protection fuses yet it still drops out on cranking.
    Do I understand correctly, to survive cranking I either need:
    a) a split charged dual battery system or;
    b) an expensive dc-dc shutdown controller PSU (eg: m1-atx)?
    neither is ideal due to space and funds, is there anything simpler/smaller/cheaper that I can implement?
    thanks
    Richard

  2. #2
    Maximum Bitrate binary.h4x's Avatar
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    try "tank circuit"
    2007 Honda Fit Sport 1.5L SOHC-VTEC

  3. #3
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    yeah searched that, I get lots of ambiguous info about dual batteries

  4. #4
    Maximum Bitrate psyrex's Avatar
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    Your Option (b):
    The M1-ATX and other PSUs are just power converters. It takes a range of input and converts it into +12v, +5v, etc. But if the power coming in is zero volts, there's nothing to convert. Buying some equipment like this won't necessarily solve your problem because your car's setup drops the voltage way too low during cranking. Just throwing cash into option (b) will probably just leave you more frustrated.

    Your option (a):
    The problem is that voltage is near nothing during cranking since the power is going to starting the engine. The solution, therefore, is to give your carpc the voltage it needs. How to do that? Well, what devices are there that gives you voltage? That'll be capacitors and batteries.

    A capacitor is very bulky, and you'll need a really large (in terms of farads and physical size) one to handle the power the carpc will pull during the 1-2 seconds of cranking.

    A battery is smaller, handle the power requirement better, but need a proper circuit to control the charge and discharge.



    Everybody wants it simpler and cheaper, but you have to remember that we're just forcing a computer that's meant for the home with very steady wall power into a very harsh environment. I personally did not spend any time or money into the "survive crank" problem as I didn't think the time or money spent would be worth it.
    Gen 1: Pentium 3 1GHz - ATX - 2005
    Gen 2: Pentium M 1.6GHz - ITX - 2006
    Gen 3: Pentium M 2.0GHz - 5.25" SBC - 2007
    Gen 4: (coming soon: Core2 Duo - 3.5" SBC - 2009)
    ...it never ends

  5. #5
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    so a second battery circuit is the only way,
    is 12v1aH sufficient, or am I going to have to buy a stupidly big battery now?

  6. #6
    Self proclaimed spoon feeder TruckinMP3's Avatar
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    An interesting side note:

    With the same set up in my signature in three different vehicles: One survives Crank and two do not.

    This indicates it is not all about the PS but, the vehicles charging system matters as well.

    95 toyota truck does not make it
    97 Chevy Suburban Does

    We sold them both and now have an 02 Suburban... oddly this does not survive crank. Still the same PS and PC. Weird?
    TruckinMP3
    D201GLY2, DC-DC power, 3.5 inch SATA

    Yes, you should search... and Yes, It has been covered before!

    Read the FAQ!

  7. #7
    Maximum Bitrate psyrex's Avatar
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    TrunkinMP3:

    Well, I remember typical specs like (I'm at work, lazy to search) 6-18v input. If your car dips below the 6v when cranking then the PSU shuts off. I guess your '97 Suburban doesn't dip too far down when cranking.


    r600rkt:

    12v 1AH might be sufficient for just cranking but you're playing on the edge with it. It's always nice to have a big buffer of reserve power especially when you're dealing with lots of inrush amps.
    Gen 1: Pentium 3 1GHz - ATX - 2005
    Gen 2: Pentium M 1.6GHz - ITX - 2006
    Gen 3: Pentium M 2.0GHz - 5.25" SBC - 2007
    Gen 4: (coming soon: Core2 Duo - 3.5" SBC - 2009)
    ...it never ends

  8. #8
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    what's the reccommended? I'm really struggling for space

  9. #9
    Maximum Bitrate psyrex's Avatar
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    How much space do you have to play with? Pictures would be nice. What about budget?
    Gen 1: Pentium 3 1GHz - ATX - 2005
    Gen 2: Pentium M 1.6GHz - ITX - 2006
    Gen 3: Pentium M 2.0GHz - 5.25" SBC - 2007
    Gen 4: (coming soon: Core2 Duo - 3.5" SBC - 2009)
    ...it never ends

  10. #10
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    about 55mm high, and 120mm wide under the drivers seat :-(

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