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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
    try "tank circuit"
    2007 Honda Fit Sport 1.5L SOHC-VTEC

    Comment


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

      Comment


      • #4
        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

        Comment


        • #5
          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?

          Comment


          • #6
            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!

            Comment


            • #7
              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

              Comment


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

                Comment


                • #9
                  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

                  Comment


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

                    Comment


                    • #11
                      Ouch, that's not much. Since this might get a little more involved, I did a little research on the Morex 3688 and here are my thoughts on it.


                      - As I understand it, the Morex 3688 is a prebuilt computer with a very lean DC-DC PSU actually designed for an AC adapter feeding it constant power. It's because this is expecting a constant power that it won't survive crank. One spec I saw says it needs an input of 11.4v-12.6v. This is VERY narrow and no car keeps it in that range. In fact, when your engine is on, you're usually running around 13.8v!


                      - One option is to puchase a PSU like the M1-ATX. However, before you do this, you need to first check how far your battery drops during cranking. You need to use a multimeter (or just a voltmeter) and measure the DC voltage during cranking. If your car, like mine, drops to very low voltages, no PSU can help since there's no voltage for it to use during cranking.
                      Here is a sample list of DC-DC PSUs:
                      M1-ATX: Can handle all the way down to 6v (according to their spec sheet), but is a replacement for the onboard PSU you already have.
                      Carnetix CNX-P1260: Supposed to handle down to 7.5v and is only a 12v supply that regulates the power for your Morex. It doesn't replace the onboard PSU. It's physically large, and might just barely fit into the space you specified.
                      Opus 80w: Similar in function to the Carnetix, but much much smaller, more expensive, and handles 7v input.


                      - If your car's voltage drops too far during cranking, the above does not work and you now need a tank circuit. The space you specified is probably too tight to use. Can you find somewhere else (maybe along the path the power wire as it goes to the Morex) that you can put the battery and subsequent tank circuit? Maybe behind the dash, or in the glove compartment, or even in the trunk?


                      - Last option: Do you really need it to survive crank?



                      I know this was long, but please read it a few times and think about your options. Knowing your battery's voltage level during crank will help deciding.
                      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

                      Comment


                      • #12
                        why not just remove and replace the existing battery in the car with something of the same physical dimensions but with more Cranking Amps? That to me would be the easiest solution, and would cost roughly the same as a 1Farad Capacitor.. I'd say around $85 bux...
                        Sell me your stuff.. please see what i'm looking to buy
                        http://mp3car.com/vbulletin/showthread.php?t=75182

                        Comment


                        • #13
                          Originally posted by psyrex View Post
                          Ouch, that's not much. Since this might get a little more involved, I did a little research on the Morex 3688 and here are my thoughts on it.


                          - As I understand it, the Morex 3688 is a prebuilt computer with a very lean DC-DC PSU actually designed for an AC adapter feeding it constant power. It's because this is expecting a constant power that it won't survive crank. One spec I saw says it needs an input of 11.4v-12.6v. This is VERY narrow and no car keeps it in that range. In fact, when your engine is on, you're usually running around 13.8v!


                          - One option is to puchase a PSU like the M1-ATX. However, before you do this, you need to first check how far your battery drops during cranking. You need to use a multimeter (or just a voltmeter) and measure the DC voltage during cranking. If your car, like mine, drops to very low voltages, no PSU can help since there's no voltage for it to use during cranking.
                          Here is a sample list of DC-DC PSUs:
                          M1-ATX: Can handle all the way down to 6v (according to their spec sheet), but is a replacement for the onboard PSU you already have.
                          Carnetix CNX-P1260: Supposed to handle down to 7.5v and is only a 12v supply that regulates the power for your Morex. It doesn't replace the onboard PSU. It's physically large, and might just barely fit into the space you specified.
                          Opus 80w: Similar in function to the Carnetix, but much much smaller, more expensive, and handles 7v input.


                          - If your car's voltage drops too far during cranking, the above does not work and you now need a tank circuit. The space you specified is probably too tight to use. Can you find somewhere else (maybe along the path the power wire as it goes to the Morex) that you can put the battery and subsequent tank circuit? Maybe behind the dash, or in the glove compartment, or even in the trunk?


                          - Last option: Do you really need it to survive crank?



                          I know this was long, but please read it a few times and think about your options. Knowing your battery's voltage level during crank will help deciding.
                          I could really do with it surviving a crank, as I intend to leave it running most of the time as a node on our network, obviously it'll get shutdown at night. space is tight, the glovebox is going to be my USB hub and power distribution block, the dash is already full with aircon stuff, condenser etc so that's out of the question, the bay may be an option, however the boot is too far away, I'd have to run power all the way there and then back into the car again. I'm seriously considering just fitting a second car/leisure split charged battery in the boot and be done with it, will that work?

                          Foo, a larger battery won't work as it'll still drop out to below the PSU's operating window, in order to maintain a 11v cranking voltage I think you'd need a battery the size of a vault.

                          Comment


                          • #14
                            Wouldn't a CarNetix be cheaper than a new battery?
                            2007 Honda Fit Sport 1.5L SOHC-VTEC

                            Comment


                            • #15
                              What about those surge protectors that store power in case of power out. Would that work?

                              Comment

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