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Dimmer for 12volt AC LED strip

Discussion in 'LEDs and Optoelectronics' started by bvz, Nov 19, 2015.

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  1. bvz

    bvz

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    Nov 19, 2015
    Hello everyone,

    I am new here and a relative newbie to electronics in general. I am fairly handy, having rewired my entire house, but I have no experience with electronics other than having once soldiered together an electronics kit given to me as a gift.

    I have a low voltage (12 Volts AC) outdoor lighting system to which I am connecting a strip of LED's (cabled lighting system by cabledlighting). These LED's are way too bright and I would like to dim them. The company that makes them (optiled) sells a dimmer but it seems kind of badly designed. Specifically, every time it loses power - i.e. when the transformer's timer says "Daytime! Everyone off!" - the dimmer resets itself to the brightest setting again.

    Being completely new to electronics, I thought I would ask here: Is it possible to create my own dimmer for a 12 Volt AC LED strip? Is it a general kind of thing or would I have to know how the actual driver(s) in the strip work? The driver's must be inside the led strip because there are no housings between the LED strip and the wires that connect directly to the transformer.

    Thanks!
     
  2. brevor

    brevor

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    Apr 9, 2013
    Can you get the electrical specifications for the led strip?
     
  3. cjdelphi

    cjdelphi

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    AC 12v? They're usually DC, maybe a bridge rectifier on input...
     
  4. bvz

    bvz

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    Nov 19, 2015
    I just looked a bit closer and You are correct cjdelphi... They are 12 Volts DC and not AC. I will have to put an AC to DC adaptor in there somewhere. Does that make it any easier to make a dimmer? I remember a while back when i was playing with an arduino I used PWM to dim an LED. Would something similar work here?

    @brevor:
    I'm not sure I can. It is a sealed package with little info and the manufacturer is not giving out much info other than that they are cree LED's.

    Thanks everyone for the quick replies!
     
  5. Colin Mitchell

    Colin Mitchell

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    Just put a 22R to 47R resistor in series with one lead.
     
  6. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I assume 12 Volts will produce maximum brightness. What about running them from say 9 Volts?
    Adam
     
  7. bvz

    bvz

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    Nov 19, 2015
    @colin:

    I'll give that a try. Now that I know it is actually DC it means that I am more comfortable with how to mess with it.

    @Arouse:

    Is that basically the same as putting in a resistor? I know V = IR. I assume the current draw from the LED is relatively constant, so putting in the resistor that Colin suggests would effectively reduce the voltage, yes?

    Thanks again for all your help.
     
  8. Minder

    Minder

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    Apr 24, 2015
    If you use a transformer use a dimmer or triac control before the bridge that feeds the LED's.
    You can also use a dimmer on the primary if needed, this is the way many control their Nichrome wire cutter.
    M.
     
  9. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    It depends on the power supply you use. The resistor will dissipate some of the energy as heat thus reducing the amount for the LEDs. If you use a switch mode power supply then this is more efficient than using a resistor. Both options will accomplish the same thing at the end of the day.
     
  10. bvz

    bvz

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    Nov 19, 2015
    The power supply is a standard outdoor lighting 12 AC power supply which (I assume) is some sort of a transformer that converts the main power down to 12V AC. I will then be buying a 12V AC - DC converter to make that a DC system. I assume putting the resistor inline after that converter will drop my voltage and give me a reduced brightness.

    The other alternative is to buy a PWM dimmer switch from Amazon or something. They seem to be fairly cheap and it would save me from accidentally doing the wrong thing...

    (don't know if I am allowed to post links but here goes: http://www.amazon.com/SUPERNIGHT-Al...TF8&qid=1447970881&sr=8-5&keywords=12v+dimmer)
     
  11. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Yeah the dimmer looks good but it does mention certain LEDs I think, maybe just marketing stuff. Give it a go, I will be interested how you get on.
    Adam
     
  12. bvz

    bvz

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    Nov 19, 2015
    Thanks for all your help everyone! I'm most likely going to go the PWM dimmer route. I'll try to remember to post back here with my results for anyone else in my same boat.
     
  13. cjdelphi

    cjdelphi

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    Oct 26, 2011
    PWM seems a good idea, better than heat loss via a resistor...

    A 555 could be an option for pwm?
     
  14. Minder

    Minder

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    Apr 24, 2015
    The 555 based PWM controllers on ebay go for aropund $5.00.
    M.
     
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