controlling 3 bridge rectifiers

Discussion in 'General Electronics Chat' started by waterbill, Aug 15, 2009.

  1. waterbill

    Thread Starter New Member

    Mar 24, 2009
    4
    0
    I am trying to control 3 bridge rectifiers with 3 seperate inputs of 120vac to control 3 colors on RGB rope light which operate on 120vdc with + neutral. The input comes from a Light-O-Rama controller which is controlled by my PC. My att circuit works OK on control of red & grn but when I use channel 3 for blue all 3 colors come on. The diode that I added (see note 1) allows red & grn channels to operate normally. Without this diode all colors come on tegether no matter which channel I use. I'm sure the good Sgt Wookie or many of you can solve this problem in 3 minutes. I hope so as I'm stumped!
    WaterBill
    PS I apologise for my schematic as I don't know how to draw this on computer so I had to take picture and send it on as attachment.
     
    Last edited: Aug 16, 2009
  2. waterbill

    Thread Starter New Member

    Mar 24, 2009
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    0
    Found out some more interesting facts but still no closer to finding a solution.If I Eliminate all the connections at + side of the FW bridge I get following operation. If I feed + from red rectifier to neutral pin on rope lights, all 3 colors come on. If I power up grn & blu, they operate normally. If I feed + from grn to neutral pin on rope light, all lights come on when I power up grn. Red and blue operate normally. The same thing happens on blue side. The other 2 colors operate normally but all colors light up when I power up circuit 3 for blue. I have tried diodes in many different locations but can't find the winning solution. Any ideas would be appreciated.

    WaterBill
     
    Last edited: Aug 16, 2009
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
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    You probably have a cross feed from the unswitched legs of the AC input to the bridge rectifiers.

    You only really need two diodes (or half a bridge) to feed positive from both legs of the 120V supply to the lamp common.

    You then want diodes from the switched (only!) outputs of the controller to the individual negative R - G - B lamp feeds.

    I've found in the past that if you draw all the input and output connections on something like this, then draw each diode from each bridge separately from the input to the output, you will find one or more diodes feeding where you don't want them.
     
  4. waterbill

    Thread Starter New Member

    Mar 24, 2009
    4
    0
    Robert I thank you for your response and I totally agree with your analysis that I have a cross feed problem. I can't fully understand your solution but I feel you are correct. I thought most 1/2 wave rectifiers only use single diode but you suggest 2. I have found schematic of 2 diodes and I assume this is your recommendation. I don't understand using diode on output of switching AC side feeding the - pins of lights. Is it possible to get a schematic on your solution? Seeing this will answer my questions. Thanks for help from the UK.
    WaterBill
     
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