adjustable dc regulated kit not working

Discussion in 'The Projects Forum' started by ninjaman, Apr 28, 2016.

  1. ninjaman

    Thread Starter Member

    May 18, 2013
    306
    1
    hello

    i bought this,
    http://www.ebay.co.uk/itm/PCB-LED-0...054158?hash=item43de84cd8e:g:dIYAAOSwBahVf9Qv

    put it together following the schematic and it doesnt work. i am using a 19v 3A laptop supply though. and it says 24v input.

    is that why? i thought that you could use any dc supply, the output would be limited though if not 24v.

    also, i am not to sure how to test this to find where the fault may be. any suggestions on testing a circuit?

    thanks
    simon
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Post the schematic.
     
  3. TheButtonThief

    Active Member

    Feb 26, 2011
    219
    38
    It appears the project is based upon a linear voltage regulator so you're not going to get a higher output than what you put in. Also, the module takes an AC input, not DC. Rectify 24VAC and you'll get something close to 32VDC, feed 32V to the regulator and you'll get a max output of 30V (with all linear regulators, there's loss). You could feed a DC voltage to the input but remember if it's lower than 32V then you're not going to get 30V at the output, if you feed 19VDC then you're only likely to get around 17V max at the output.
     
  4. TheButtonThief

    Active Member

    Feb 26, 2011
    219
    38
    Also...
    When testing a PSU, always do it with a load. Test & measurement equipment lies to you if there's no load.
     
  5. ninjaman

    Thread Starter Member

    May 18, 2013
    306
    1
    what would be best to use as a load, i am guessing a high power resistor would be best. i have no experience of this. i have a book that shows how to design and build a power supply. all i need is a 0-30v dc supply the current does change from 0.5A to 1A and thats all.
     
  6. TheButtonThief

    Active Member

    Feb 26, 2011
    219
    38
    Your load doesn't need to draw very much current if it's just for the purpose of testing. I'd draw about 200mA, just use a resistor.
     
    Last edited: Apr 28, 2016
  7. ninjaman

    Thread Starter Member

    May 18, 2013
    306
    1
    at the moment with a 19 volt 3 amp dc supply i get 400 millivolts at the output. my reasoning is that output voltage over the 200 milli amps mentioned above gives 2 ohm resistor(?) would this be right?

    thanks
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    The silkscreen on the board indicates input is 24VAC. That appears to be the input for the 7824 regulator, so you need to provide at least 27-28V DC. With less than that the regulator won't function.
     
  9. ninjaman

    Thread Starter Member

    May 18, 2013
    306
    1
    cool, cheers dl324 and button thief. im thinking of just getting a dc dc step up booster for a few pounds. it wont change current but should provide the 30 volts.

    thanks
     
  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,544
    1,251
    Putting a switching boost converter in front of a linear regulator seems like a lot of unnecessary complexity. If you are going to buy something, what about getting a 24 Vac output transformer and connecting it to the board as the instructions suggest?

    ak
     
  11. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Pretty nonsense these don't normally need extra standby load. Put a led if it doesn't Have one.

    Bypass the bridge rectifier. It's not clear if it works even with lower DC.

    Otherwise need to look item description

    24 volts AC

    Anyway it could be bad if the transformer goes down under load and you don't receive 30v anymore.

    I'd try bypassing the bridge rectifier
     
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