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Puzzled about MFC

Discussion in 'Lights - Store Bought and Home Made' started by diyer, Apr 15, 2018.

  1. diyer

    diyer Full Time Elf Generous Elf

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    Over the last few years I’ve swapped out many mfc’s, but today I struck one that has puzzled me. It’s on a set of 24v icicle lights, three wire, one positive, two negative 21.3v out of the mfc.
    Ok wires identified, cut them off and apply the same voltage from a bench power supply - nothing, reconnect the mfc, they work? Has anyone come across this before? The mfc is labeled HP-408-24E
     
  2. AAH

    AAH I love blinky lights :) Community Project Designer Generous Elf

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    It's possible that they won't turn on until they get a higher voltage. If it was on a 24VAC plugpack then the peak voltage that could be produced is about 33V. Depending on what's inside the controller you could have something like halfwave rectified 24VAC being sent to each channel. Measuring with a meter will show something like the RMS voltage.
    Slowly wind up the voltage until the leds turn on. There's every chance that they will need to be ran from somewhere between 27 and 31V to match the original brightness.
     
  3. OP
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    diyer

    diyer Full Time Elf Generous Elf

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    Thanks Alan,
    Yep 30v worked
     
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    diyer

    diyer Full Time Elf Generous Elf

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    I busted the controller open, it does in fact contain full wave rectification diode bridge?
     
  5. David_AVD

    David_AVD Bite my shiny metal ass! Community Project Designer Generous Elf

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    Correct, almost all MFC have a full wave bridge that converts the incoming 50Hz AC into 100Hz pulsed DC.
     
  6. AAH

    AAH I love blinky lights :) Community Project Designer Generous Elf

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    Photos or it didn't happen
    The output voltage depends on whether it has capacative filtering or not. It's likely there's not a real lot.
     
  7. David_AVD

    David_AVD Bite my shiny metal ass! Community Project Designer Generous Elf

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    There's no filtering on the output of an MFC with AC input. The output switching is done with SCRs so needs to drop to zero every half cycle.
     
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    diyer

    diyer Full Time Elf Generous Elf

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    See pictures, the capacitor is a 2.2uf
     
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    diyer

    diyer Full Time Elf Generous Elf

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    The photos
     

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