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Re: [nslu2-linux] Rebooting the Slug after power-outage?

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  • CN
    ... I think a capacitor is practical only if the pwr stays off for a fraction of a second, anything past that you would need a huge capacitor. If you put 4 AA
    Message 1 of 8 , Aug 1, 2006
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      On Tue, 01 Aug 2006 22:23:40 +0200, Laurent Gilson wrote:

      > Hello,
      > >
      > > I happen to live in a town where the power goes off every once in a
      > > while for like one second or so. Bigger computers make it through (big
      > > capacitor in the power supply, I figure) but my slug dies.
      >
      > A slug takes like 5w. Get a capacitor for like 30-50 US-cent ...
      >
      > > I would love to have it automatically reboot after a power outage. Is
      > > there a way I can set that up?
      >
      > There is a always-on hack in the wiki (Basicly restarting the slug as soon
      > as the power comes back). But it may fail in your situation if the power
      > comes back too quickly ...
      >
      > cu

      I think a capacitor is practical only if the pwr stays off for a fraction of a second,
      anything past that you would need a huge capacitor.

      If you put 4 AA NiMh rechargeable batteries (about $4 in the USA) in series right
      across the output of your power supply, it will give you as much as 1 hour
      (definitely many minutes ) of operation without any problem. Since at 5 v the
      battery each will be at 1.25 volts, there is no risk of overcharging.

      In this simple arrangement, the battery will never be fully charged, otherwise
      most modern AA batteris (>2300mAHr is very common now) will give almost 1.5 to
      2 hours --- slug takes about 1Amp with a usb 2.5" notebook drive.

      Cordially, Chacko
    • vbgroningen
      ... See this page: http://www.nslu2-linux.org/wiki/HowTo/ForcePowerAlwaysOn I did Alternative 1, and got a free sample from Microchip (very nice of them!).
      Message 2 of 8 , Aug 1, 2006
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        Laurent Gilson wrote:
        > There is a always-on hack in the wiki (Basicly restarting the slug as
        > soon as the power comes back). But it may fail in your situation if
        > the power comes back too quickly ...

        See this page: http://www.nslu2-linux.org/wiki/HowTo/ForcePowerAlwaysOn

        I did Alternative 1, and got a free sample from Microchip (very nice of
        them!). Works well for me.

        PP
      • Frederic Wenzel
        ... That idea is just great. I got the parts and soldered it all together and it works. Now, when I unplug the power, the battery keeps the slug running. I
        Message 3 of 8 , Aug 5, 2006
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          CN schrieb:
          >> There is a always-on hack in the wiki (Basicly restarting the slug as
          > soon
          >> as the power comes back). But it may fail in your situation if the power
          >> comes back too quickly ...
          >>
          >
          > I think a capacitor is practical only if the pwr stays off for a
          > fraction of a second,
          > anything past that you would need a huge capacitor.
          >
          > If you put 4 AA NiMh rechargeable batteries (about $4 in the USA) in
          > series right
          > across the output of your power supply, it will give you as much as 1 hour
          > (definitely many minutes ) of operation without any problem. Since at 5
          > v the
          > battery each will be at 1.25 volts, there is no risk of overcharging.

          That idea is just great. I got the parts and soldered it all together
          and it works. Now, when I unplug the power, the battery keeps the slug
          running. I still have to run a longer test (to see if the batteries
          don't explode ;) or discharge altogether or whatever) but for now it
          works just great.

          Including wire (which was only available as 35 ft. or more), it cost me
          25 bucks now at Radioshack.

          I will blog and wikify that soon (giving you credit for the initial idea :))

          Fred
        • CN
          ... I am reasonably sure the batteries will not overcharge. When they are discharged they have under 1.2 v each (4.8v), and when they are fully charged, they
          Message 4 of 8 , Aug 5, 2006
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            On Sat, 05 Aug 2006 13:57:19 -0700, Frederic Wenzel wrote:

            > CN schrieb:
            > >> There is a always-on hack in the wiki (Basicly restarting the slug as
            > > soon
            > >> as the power comes back). But it may fail in your situation if the power
            > >> comes back too quickly ...
            > >>
            > >
            > > I think a capacitor is practical only if the pwr stays off for a
            > > fraction of a second,
            > > anything past that you would need a huge capacitor.
            > >
            > > If you put 4 AA NiMh rechargeable batteries (about $4 in the USA) in
            > > series right
            > > across the output of your power supply, it will give you as much as 1 hour
            > > (definitely many minutes ) of operation without any problem. Since at 5
            > > v the
            > > battery each will be at 1.25 volts, there is no risk of overcharging.
            >
            > That idea is just great. I got the parts and soldered it all together
            > and it works. Now, when I unplug the power, the battery keeps the slug
            > running. I still have to run a longer test (to see if the batteries
            > don't explode ;) or discharge altogether or whatever) but for now it
            > works just great.
            >
            > Including wire (which was only available as 35 ft. or more), it cost me
            > 25 bucks now at Radioshack.
            >
            > I will blog and wikify that soon (giving you credit for the initial idea :))
            >
            > Fred

            I am reasonably sure the batteries will not overcharge. When they are
            discharged they have under 1.2 v each (4.8v), and when they are fully
            charged, they go to about 1.4 (5.6v). So with the slug power supply at 5.0 or
            very close to it, the bateeries will stop charging at some point in between (the
            voltage vs charge curve is not quite linear). The only downside I see is that
            the batteries will always be only charged to about 30% or so in your normal
            'floating' operation, but even that should provide 10s of minutes of backup.

            As for the cost, 4AA nimh batteries are routinely available for about $5 or less
            on ebay...

            This will have another significant advantage if you are running two usb
            harddrives solely powered off the slug. My observation is that the powersupply
            just does not have enough transient capacity for two drives (when the motor
            starts, or the head moves). But a battery float like this will make the two
            drives operation quite reliable --- this is a conjecture at this point, I have not
            tried this yet, but is planning to do this. In normal idle times in between
            reading or writing, there is enough extra current available form the slug charger
            to keep the battery get the lost charge during the transient heavy loads.

            Keep us posted about your experiences...

            Cordially, Chacko
          • Frederic Wenzel
            ... True, that sounds reasonable. I am done blogging it: http://en.magenson.de/2006/08/05/linksys-nslu2-battery-ups/ Guess I should donate the text to the
            Message 5 of 8 , Aug 5, 2006
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              CN schrieb:
              > I am reasonably sure the batteries will not overcharge. When they are
              > discharged they have under 1.2 v each (4.8v), and when they are fully
              > charged, they go to about 1.4 (5.6v). So with the slug power supply at
              > 5.0 or
              > very close to it, the bateeries will stop charging at some point in
              > between (the
              > voltage vs charge curve is not quite linear).

              True, that sounds reasonable.

              I am done blogging it:
              http://en.magenson.de/2006/08/05/linksys-nslu2-battery-ups/

              Guess I should donate the text to the wiki, too, hm?


              Fred
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