In-car 12v UPS

Discussion in 'The Projects Forum' started by YodaTheCoder, Sep 21, 2010.

  1. YodaTheCoder

    Thread Starter New Member

    Sep 20, 2010
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    The problem: I have a portable DVD player which keeps my young son entertained on long car journeys, it runs off the 12v supply. The device has NO internal battery, and the contact the plug makes with the socket is poor so a bump or pothole briefly interrupts power to the device which resets back to the DVD menu screen.

    The solution: A UPS to take up the slack for the fraction of a second the power from the car is interrupted.


    I thought I'd found the answer in this thread but it doesn't have a definite "yes, that'd work" or "no, you need this" post. (Would have bumped the thread but it's too old)


    Can anybody offer any advice. I've done some PIC and Arduino programming in the past, but I don't have the electronics knowledge to know if there is a 10 pence solution to this annoying problem.


    Thanks.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Would it not be more easy to fix the bad contact plug ;)
     
  3. tom66

    Senior Member

    May 9, 2009
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    Do some experiments with supercaps.

    A 1 farad supercap might be able to provide sufficient power to run the DVD player for a few seconds. At 12 volts though you will have to run multiple 2.5V or 5.5V caps in series.

    OR, you could use a lead acid battery and a slow/trickle charge circuit; when power is interrupted it runs off the battery.
     
  4. YodaTheCoder

    Thread Starter New Member

    Sep 20, 2010
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    Where's the fun in that?! :)


    I like the idea of the battery, it's the circuit part I'm struggling with. Is this an off-the-shelf bit of kit or am I assembling it from components?
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    Your car actually do have a UPS system. The car battery. I guess your DVD player use the car cigarette lighter socket. If your car has been used by a smoker. It could be that this unit need some cleaning. Or bad contact in the male plug going into the outlet. As such devices often tend to be cheap massproduced units. Put the device into the outlet, and se if you can reproduce the error. If the error occurs then gently moveing the cable near the male plug, the error is a bad connection in the cable plug interface. But if this is not the case the problem is more likely in the car cigarette lighter outlet. Like dirt or oxidation most probably. I think you should start in that end.
     
    Last edited: Sep 21, 2010
  6. tom66

    Senior Member

    May 9, 2009
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    I have a small portable DVD player. It is rated for 9V to 12V.

    I have found it will operate on as low as 7.5V, but the screen is dimmer than on 12V.

    At 6V it malfunctions (screen shows garbage and flickers. Won't play a DVD.)

    I don't know how you could test yours.

    A 1 farad supercap will power a load drawing 1.5 amps for around 3 seconds, to 7.5V.

    You could perhaps get away with a voltage regulator, but 1.5 amps and dropping 4.5 volts at 1.5 amps can be tricky.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,119
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    Ditto. It doesn't make sense to "fix" a bad connection by adding another component downstream of it. That'll just add clutter into the car. Just fix the connection. They're cheap. I'd even consider a hardwiring solution - maybe a direct plug into the fuse box? - before adding a big cap, another battery or such. These downstream solutions may all work, but as the plug wears the problem will grow.
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    I have to also agree.

    Even if you built a UPS that the DVD plugged into, the plug would STILL be the problem.

    What I would do, is convert your cigarette lighter port to a standard coax type plug.

    Then use a male to male plug to plug it in.

    You could also just bend the springs out on the cigg-plug or, after disconnecting the battery, bend out the friction tensioner IN the outlet.

    Here is one if you need a replacement.. notice the springs on the sides:
    http://parts.digikey.com/1/parts/4958-cord-str-cig-5a-fuse-w-dc-plug-za5073-2-5.html
     
  9. YodaTheCoder

    Thread Starter New Member

    Sep 20, 2010
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    Wrapped a few turns of duct tape around the plug, it's better than it was but still gets upset by a big pothole.
     
  10. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    Nothing like turning the fifty cent solution into the fifty dollar solution. :D Talk about mountains and mole hills.

    I hope your country doesn't have the value added tax ... then again, if they do, you'll be their favorite fixer upper.
     
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