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Why won't my "mini-Sproggy" work?

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  • Why won't my "mini-Sproggy" work?

    My setup is using a bit too much power at certain times for a standard Sproggy and I decided to build another scaled down version, just to supply +5v and +12v.

    I did some chopping on the full sproggy schematic, and came up with this:



    I chopped the relay section out, as I am using a shutdown controller.

    I built this circuit, and the outputs are fine (i.e. +5V, and 12V), but when I plug it into a hard drive, the drive won't spin up! I know that the drive is working, as when I plug it into a standard supply (or my full sproggy) it spins up just fine.

    I am not using low ESR capacitors, but did not think this would make much difference.

    Could someone please tell me if I have missed something obvious here! I can't understand why the voltages are all correct, it will power a fan, but not my hard drive!? I am guessing that I have made a mistake somewhere, but I just can't see it.

    Please let me know the obvious (or not so obvious!), so I can put myself out of my misery!

    This is the final hurdle for me before my install is finished! Really frustrating........

  • #2
    Have you measured the voltages with the hard drive plugged in?

    Comment


    • #3
      Thanks mp3hombre, but I have managed to solve the problem... my mistake (or actually the Renco T6's fault!) It's the pin 7 and 8 switch around thing that caught me out. Strange though, as the voltages were all correct, but obviously the T6 was not supplying enough current with pins 7 and 8 the wrong way around. I was just wanting to check whether anyone else could see anything wrong with the schematic. The 12 volt rail dips to around 11.6V when the drive is starting up, and stabalises at around 11.90. Is this acceptable?

      Its all working now, but I think my drive is overheating in the case now! If I do a defragment of the drive, and then re-boot, the drive is not detected. Leave the machine off overnight, and try the next morning, and it detects fine again.

      I have an IBM 20GB desktop drive encased in a dense foam rubber housing. Has anyone else had problems with overheating drives? Maybe the drive is just faulty? Well I will keep testing and see what happens.

      Thanks again.

      Comment


      • #4
        Originally posted by LDO
        The 12 volt rail dips to around 11.6V when the drive is starting up, and stabalises at around 11.90. Is this acceptable?

        That's fine, well within tolerances.


        Rob
        Old Systems retired due to new car
        New system at design/prototype stage on BeagleBoard.

        Comment


        • #5
          Originally posted by LDO
          I have an IBM 20GB desktop drive encased in a dense foam rubber housing. Has anyone else had problems with overheating drives? Maybe the drive is just faulty?
          Although IBM drives are notorious for failing, keep in mind that they do generate a lot of heat even under normal circumstances, and "dense foam rubber" = "thermal insulator" = "cooked HD" = "bad idea"

          Take off the housing and just mount it directly, it's been shown time and time again that you don't need shock mounting for your hard drive. If it still gets too hot, pass a small fan over it to help cool it down.
          IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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          • #6
            Thanks for the feedback guys.

            I have since established that the drive is not at fault here. Since I sorted out the T6 pinout changes, the drive spins up intermittently. I have tried another drive, and have the same results, so the problem is not heat related or drive specific.

            I have replaced the T6, and LM2587 in case they were damaged by the pinout changes, and also checked the MUR120, SA28A, and MBR340, and they all checked out fine, but the problem persists. Both voltages are fine, but it still won't source enough current. I have checked my PCB layou a hundred times, and it is correct.

            Is it possible that the fact that the caps are not low ESR could cause this type of strange behavior? They are the only thing left that could be at fault IMHO (on the 12v side of things anyway). Or maybe one of them is a bit dodgy? The 5v rail seems fine, as I plugged a laptop drive onto this rail, and it spins up happily....

            Grrrrrrrr..............

            Comment


            • #7
              what drives are you trying to use (specifically)?

              Will a CD-ROM power up and eject the tray?

              Keep a voltmeter on the +12V rail at all times, and tell us what happens when you try to spin up the hard drive.
              IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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              • #8
                OK, just tested again. When the drive does actually spin up, the voltage dips to around 10.6V for a split second as the drive kicks in, then while it spins up it rises to around 11.8V. Once the drive is spinning it recovers to 12V exactly.

                When the drive does not spin up, it drops to around 11.86V for a second, then recovers to 12.09V. This recovery happens much quicker.

                I am about to try a CD-ROM drive now, but it seems to be in a "working" phase right now, so am guessing that the CDROM will work perfectly. I will post result shortly....

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                • #9
                  CDROM works fine, the voltage ony dips very slightly starting up or ejecting the CDROM drive.

                  One thing I have noticed though, is the LM2587 seems get get much warmer when the circuit is in the "non functional" state. When the drive is functioning correctly, the chips does not even get sligtly warm, whereas when the drive won't spin, the 2587 seems to feel warm to the touch.

                  Oh, also forgot in the first post to tell which drives I have tried:

                  IBM DTLA-305020 (20GB IDE Desktop drive)
                  Western Digital WD Caviar 12500 (2GB IDE Desktop drive)

                  Edit: Just noticed something else fairly important.....

                  When the drive spins up and I cut the power, the voltage immediately drops to around 2.3Volts and bleeds off slowly to zero. When the drive does not spin up, the voltage bleeds off slowly from 12V to zero, and takes about 30seconds before reaching zero. Significant? Sounds more and more like caps to me?

                  Comment


                  • #10
                    Low ESR caps are not a requirement, but more a niceity.

                    The slow dropoff that you are witnessing is from the caps, but that is the intended behaviour. Basically it looks like the LM2587 is sensing an overload and shutting off, so the cap slowly discharges into the +12V rail until there is nothing left.

                    Do you have an ammeter?
                    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

                    Comment


                    • #11
                      Yip, I do have an ammeter, and have tested on the input side of the circuit.

                      When the drive does not spin up, the current drawn from the supply starts at around 100mA for about a second, then jumps up to around 1.5A for a second, then stabalizes at 140mA and stays there. It does not always jump up as high as 1.5A initially. Sometimes it only rises to 850mA or there about.

                      When the drive does spin up, the current starts at around 1.7A for a second. then drops to around 750mA while the drive completes the spin up, and stabalises at around 450mA once the drive is spinning.

                      Man, I don't know! I thought I knew a bit about electronics, but this one has me stumped!! The only thing that remains that could be faulty is one of the caps, as I have either tested or replaced everything else in the damn circuit! I will try to change the caps tonight, and see if the results change at all.......

                      Any other advice greatly appreciated.....

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                      • #12
                        Well, now I am totally baffled! I have replaced all the caps (except the small value caps 0.68uF, 10nF, and 100nF), and am still getting exactly the same results!

                        Unless someone has any suggestions, I have pretty much run out of ideas! Ijust can't figure out what is wrong here.

                        Comment


                        • #13
                          The sproggy design can only put out 1.2A on the 12V rail.

                          It is not rated to putting out 1.7A.
                          IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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                          • #14
                            but the same drive was working on my full sproggy.... thats the part that frustrates me. The only reason that I built the second one was because my mainboard has onboard everything (LAN, Sound & VGA), and the machine would act strangely sometimes by re-booting, so figured that the 12v and 5v rails were maxing out sometimes causing the mahine to reboot. Since I removed the CDROM, and hard drive from the full sproggy, the machine is fine....... Why does the mini sproggy not like the drive, and the full sproggy has no problem starting it up (as well as the mainboard stuff) every time???

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                            • #15
                              are you using a renco on both? It's possible that the different components between the two are causing the problem. I think that I heard that the renco transformer can't handle as much current, but I could be wrong.

                              how often do you use the computer with the car turned off?
                              IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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