Electronics Current Limiter as LED Dimmer - Need Advice

Discussion in 'Modding' started by Galgo, 14 Jun 2006.

  1. Galgo

    Galgo What's a Dremel?

    Joined:
    27 Mar 2005
    Posts:
    6
    Likes Received:
    0
    Hello all,
    I'm Using some of my Spare Modding Eq. to Lighten a New self Build Aquarium :dremel:

    I've made Few "WaterProof LED Bars" for the Lighting and they work great on 5V (power is from a Wall DC power adapter that can supply 6V-12V).

    Now i would like to control the light intensity from these LED bars and this is were i need your help! :idea:
    I originaly intend to use a small Rheostat from an old Fan-Bus i have, but, someone told me that since LEDs are Non-Linear Component - i better go with some kind of CURRENT LIMITER instead of VOLTAGE Limiter... (like the Rheo...).

    Can you recommend a simple way to make an efficient and cheap Current limiter (these lights are open almost 24/7) ?


    The LED bars consum 0.8Watt at 5V (i figure around 160mA each) and i want to connect Two of them in parallel to the control unit.

    I did try to limit the Voltage and found that 2V-6V is the range of lighting intensity i'm after.

    Thank you all for the Help :thumb:

    Galgo
     
    Galgo, 14 Jun 2006
    #1
  2. Firehed

    Firehed Why not? I own a domain to match.

    Joined:
    15 Feb 2004
    Posts:
    12,574
    Likes Received:
    16
    Well, rheostats are just going to add resistance, so in a sense I suppose it kind of acts as both. What I'd do is just get a rheostat wired in there so it'll be at the highest brightness you want at lowest resistance, then just raise the resistance accordingly by fiddling with the knob. I think that by the nature of an LED, any form of resistance is going to act as current-limiting rather than voltage-limiting.

    Seeing that it's 5am, this might be totally wrong or make no sense. I think cpemma should be able to do more good than myself on this topic.
     
    Firehed, 14 Jun 2006
    #2
  3. Galgo

    Galgo What's a Dremel?

    Joined:
    27 Mar 2005
    Posts:
    6
    Likes Received:
    0
    Well.. Thats what I originally figured - But i wanted to know if there is a better way....

    In case this is the right way to go - Can you guys advice regarding the Spec. of a suitble Rhe./Pot. ?

    would a conventional PC Fan Rheo. used in a FanBas should work (i'm not sure regarding the Spec. but i know it goes from around 5V-12V with a simple 120mm FAN)

    Gal
     
    Galgo, 14 Jun 2006
    #3
  4. Xiachunyi

    Xiachunyi What's a Dremel?

    Joined:
    3 Nov 2003
    Posts:
    1,404
    Likes Received:
    0
    You probably would have to go the PWM route to achieve what you are looking for. I would suggest, for a cheap and fast way, for you to utilize a 555 IC timer and adjust the duty cycle from there.

    Another way would be build a voltage to current converter utilizing an Op Amp.

    This article is of interesting read that you might find useful.
     
    Xiachunyi, 14 Jun 2006
    #4
  5. cpemma

    cpemma Ecky thump

    Joined:
    27 Nov 2001
    Posts:
    12,328
    Likes Received:
    55
    A rheostat would need to be fairly high resistance (maybe 500 ohm) and a decent wattage, hard to find and expensive.

    The PWM circuit shown here is cheap to build and will work OK on a 5V supply, though I'd change the two 1N4148 diodes to any Schottky types (eg, BAT42 or similar) to give a wider control range on the low voltage.
     
    Last edited: 14 Jun 2006
    cpemma, 14 Jun 2006
    #5
  6. shotgunefx

    shotgunefx What's a Dremel?

    Joined:
    4 Feb 2004
    Posts:
    449
    Likes Received:
    0
    Just to restate what everyone else said.

    Go the PWM route. My first RGB light system used pots, all the noticable adjustment was in like 2 degrees.
     
    shotgunefx, 15 Jun 2006
    #6

Share This Page