Need to convert AC monitor to 12v

Discussion in 'The Projects Forum' started by trader007, Oct 6, 2014.

  1. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    I am looking to run this monitor off 12v. Its a Dell 1908FP 19" Monitor (ultrasharp model)

    It will be installed with a touch panel inside a Kiosk, and I want to run the monitor off the computer power supply instead of running an AC wire up to it (seems redundant to have two inverters in the system anyway, not to mention the inverters that run for the monitors backlight)

    Basic questions need not be asked. I am fairly savvy with electronics, I just want to make sure I am not missing something. And for the record- I have done this in the past with a TV, but it was obviously doable the way the board was laid out.

    My plan is (when I get home tonight) to find what voltage is coming off the primary transformer. I hope to simply remove the transformer and feed in 12vdc where the transformer otherwise would. I plan on leaving the opti-coupler and everything else in place.
    IMAG0503.jpg IMAG0504.jpg

    Has anyone done anything like this before? Would love some insight.
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
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    120
    It's a switched mode power supply with possibly multiple taps on the secondary side. I don't see how this can work?
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,980
    744
    No, its a switch mode psu, unless its giving out 12v, 5v, it wont work.
     
  4. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    well, at least in the tv i did, the secondary side taps were all 12vdc. Yes, multiple taps, but they were all fused together. Obviously just a board design used in many different applications. from there it broke down to 5v and 3.3v as needed.

    I was hoping to find the same logic in this board and do the same thing. I know its a SMPS, but after it rectifies the incoming AC voltage, and then transforms that down to 12v (or whatever pressure it goes to), from there is essentially a DC-DC converter. Only when it hits the backlight inverters does it turn back into AC.....
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    You're right in principal, but the devil is in the details. A service manual for the monitor would provide those details - the voltage test points.
     
  6. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    19
    Well best I can tell the whole secondary side is run off 5v! I don't see 12v anywhere... surprising.

    You're right about the details... I get -5v on the output of the transformer... on all pins. even when the unit is off, all outputs are shorted together.

    Thing is, they don't seem to be directly bridged anywhere... as all the pins lead to their own trace routes. And because they are negatively biased, it makes me wonder if parts of the board are designed to turn off for specific reasons.

    I'm tempted to just try it anyway and see what happens. I have 20a or so on the 5v rails of the computer, so it should power the monitor fine. wish me luck
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Why on earth would someone attempt to do all that work when they can simply run an extra power cord?
     
  8. trader007

    Thread Starter Active Member

    Feb 27, 2010
    222
    19
    It's going inside a kiosk. We only want one power cable out the back. Monitor needs to run off the computer.
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    So, an outlet strip inside the kiosk, with the computer and monitor plugged into it. Only one cord out the back then. Or, are there other details we don't know?

    Ken
     
  10. trader007

    Thread Starter Active Member

    Feb 27, 2010
    222
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    the kiosk was custom designed to fit only the computer case. a power strip won't fit, and we are looking for a more elegant solution.

    right now, i take apart the computer power supply and add in a power socket i solder right to the switch inside. this works, but i think it would be a lot better to eliminate the ac cable going up to the screen. Would be very cool to just run 5v up there....
     
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