hello everybody hope you can help me

Discussion in 'General Electronics Chat' started by zad, Oct 5, 2008.

  1. zad

    Thread Starter New Member

    Oct 5, 2008
    hi everybody... just joined the forum as you can tell.

    i have signed up as im starting to build a few projects and this looks like the site to help me out.

    i have recently build a mood lighting panel using rainbow led's ( hxxp://www.rapidonline.com/netalogue/specs/55-1904e.pdf spec sheet)
    i have 50 of these in series with a 11watt 4.8k ohm resistor. this in turn is connected to the mains via a high power bridge rectifier.

    the leds all illuminate however some of them are not colour changing (the leds are fine as i have tested them directly with a 3v button cell).
    this problem also seems to be a bit random as sometimes only a few will stay on red (the first colour they go) and sometimes it it other leds that stay the same.

    i have also noticed if i switch on my soldering iron on the same 13a extension socket a lot of the leds reset back to red then go on with the colour change.

    due to this a assume it is a power spike thats causing the issue but i have no idea on how to fix it, there is no need for the leds to change colour all at the same time however it would be nice to have them all change

    thanks in advance
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Apart from the usual comments about non-isolated mains powered equipment....

    Because these are flashing LEDs I doubt they will work when connected in series without interacting with each other, also, they will need a smoothed DC supply to work properly.
  3. zad

    Thread Starter New Member

    Oct 5, 2008
    yeah i wa thinking i needed to smooth it, i dont mind the random patternt its creating so them interacting with each other is not a factor however i do think i need to smooth things.
    any idea on what rating cap i will need over the recitfier to make things a little more stable
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    What you need is a 1:1 isolation transformer so your mood light string isn't a lethal shock hazard.
  5. SgtWookie


    Jul 17, 2007
    It's not going to work very well having them in series. The current demands will change depending upon what color or colors are lit at any point in time.

    What you need to do is to wire them all in parallel, and supply them with 4.5v DC.

    Since the current drawn by each LED will change continuously, you should really use a regulated DC power supply.

    Connecting items up directly to the mains is strongly discouraged, as it is very unsafe.

    You could start off with a "wall wart" transformer capable of around 1.5A output at 7V to 12V, and use a filter capacitor (around 1000uF) a voltage regulator IC such as a LM317, with a couple of resistors to set the output voltage.
  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Use a transformer, any transformer (not auto) that can supply enough current for all the LEDs and ideally one with a non-lethal secondary voltage. A few thousand uF at a sensible supply voltage should be sufficient, it's not critical.
  7. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    If the colours brighten and fade then the current changes a lot. Then they will not work properly when in series and they might be destroyed.