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ac voltage regulator

Discussion in 'General Electronics Discussion' started by scientifico, May 8, 2014.

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  1. scientifico

    scientifico

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    Mar 13, 2012
    Hi, I'm trying to build a circuit to regulate the ac voltage of my moped lights to 6v since it has peaks as high as 18v so i followed the circuit in the picture that is supposed to short the generator after the zener works but I get about 3.4v stable instead of 6, could you help me? What's the easiest way to stabilize an ac current ?

    [​IMG]


    th1 = scr 12A 600v
    r1 22 ohm
    d1 Ba 159 like diode
    dz1 6.2V zener diode

    Thanks
     
    Last edited: May 8, 2014
  2. duke37

    duke37

    5,344
    753
    Jan 9, 2011
    You need to stabilise voltage not current.

    AC has a varying voltage, the zener will pass current when there is 6.2V across it and short the supply. Thus the peaks are trimmed as is also the rest of the cycle.

    You will need to raise the zener voltage.

    I am not sure of the effect of only limiting the positive half of the waveform. Perhaps you should drive your circuit after a bridge rectifier or use another circuit for the negative part of the waveform.
     
  3. scientifico

    scientifico

    62
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    Mar 13, 2012
    The problem is that the lights configuration is up to 15W so the rectifier diode or zener would get too hot and burn. Is the gate of scr connected to the ground pin in some way ?
     
  4. duke37

    duke37

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    Jan 9, 2011
    You are only dealing with an amp or two. You can get 5A diodes cheaply.
    The zener will not get any hotter, when it passes current. it turns on the SCR so drops the voltage to a volt or so. The zener will dissipate very little.

    An SCR normally has a resistor gate to ground to stop false turn on. If you use a fat SCR with a low sensitive gate, this may not be a problem.
     
  5. scientifico

    scientifico

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    Mar 13, 2012
    Do you think the solution in the second example could work well enough ?

    [​IMG]
     
  6. duke37

    duke37

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    753
    Jan 9, 2011
    The second circuit will work to clip the peaks so will help to extend the life of bulbs.
    The trouble may be to find zener diodes which can handle the power. I have not looked up what is available.

    If you use a bridge rectifier to get a unidirectional supply, then a single zener can be used. To get the power handling, the zener could drive the base of a power transistor. The transistor would need heat sinking

    The idea of shorting the output is to use the inductance of the generator to limit the current. Power generated is low. If you clip the peaks, the power generated will be considerable and will need to be dissipated somewhere.
     
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