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Controlling multiple dimmers from one potentiometer

Discussion in 'General Electronics Discussion' started by deathbybear, Aug 4, 2011.

  1. deathbybear

    deathbybear

    3
    0
    Aug 4, 2011
    Hey everybody!

    I'm working on a weird little project, and I've hit a wall. There are five lights inside a box, all of which I want to control from a single master dimmer. I'm using 12v auto lights and sockets for the lights themselves - like these - http://tinyurl.com/4yefsg7

    For power, I am using a 500w computer power supply, which is supposedly capable of pushing up to 32A at 12v.

    I got this 12v dimmer, which was rated for 8A - http://tinyurl.com/3vb6abd - though I paid about 3x as much for it. :x

    So, I wired everything together using a configuration like the attached image below. Basically: Power => Dimmer => Hub => 5 Lights/Switches

    [​IMG]

    This didn't work. If I have the dimmer turned all the way up, all of the lights turn off and on with the switches, and all juice seem to flow fine. The problems come when I start trying to use the actual dimmer. If one or two lights are on, it will dim them from 0 to 100% without problem, but as soon as I attempt to dim 3 or more lights, something fails (presumably the dimmer) and the whole power supply shuts off. Not ideal!

    My assumption is that the dimmer itself is just not capable of handling that much power. I tried to track down a 12v dimmer that would be able to handle more juice, but the only one I could find is $100 and you have to use a SPDT toggle. I really want to keep the rotary potentiometer for the dimming, and I really want to keep it set up so one dimmer is controlling all five lights.

    So I came up with the idea I diagrammed out below, where basically I would use five separate dimmers, each controlling its own switch/light, but that each of the dimmers would be controlled using a single potentiometer. To accomplish this, I would just wire together the "like wires" from each dimmer's potentiometer, and wire each cluster back to a single master potentiometer. Hopefully the diagram will make this make more sense.

    [​IMG]

    I guess my question is - will this work? Before I go spending $50 on four more dimmers and start cutting up the wires, I wanted to make sure this was even reasonable. Logically it seems to work for me, but there are usually factors i'm not considering. If it isn't obvious already, I'm already messing around in an area well beyond my knowledge level with all of this stuff, and just trying to figure it out as I go.

    If I can't do it this way, are there any ideas for how I might be able to accomplish what I'm trying to accomplish.

    Thanks for your time and any help you might be able to give me!

    Jason
     
  2. shrtrnd

    shrtrnd

    3,670
    453
    Jan 15, 2010
    It's probably the TYPE of dimmer you're using. Most of them are thyristor controlled,
    they have a voltage point that must be reached to switch on, and conduct current.
    With multiple loads, I would guess that as each voltage is energized, your trip-voltage
    point is changing, and the dimmer is not reacting well to it.
    Just as guess, as there are many different circuits available for dimmer applications.
    Is it possible to contact the dimmer manufacturer, and ask if your application is what
    their dimmer application was engineered for?
     
  3. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Do you have the detailed spec's of the power supply? Not many of them are too happy about being loaded a lot on the 12V with no load on the 5V.
    The Amazon page doesn't say how much power those lamps draw, and the link to the dimmer didn't work for me.
     
  4. deathbybear

    deathbybear

    3
    0
    Aug 4, 2011
    Thanks for your responses...

    Here's some better specs on the parts i'm using...

    Dimmer - Working temperature: -20-60 ? ? Supply voltage: DC12V ?Output: 1 channel ? External dimension: L89 ? W59 ? H35 mm ? Packing size: L96 ? W64 ? H65 mm ? Net weight:8 5 g ? Gross weight: 10g ? Static power consumption: <1 W ? Output current: <8 A ? Max. output: 96 W

    Power Supply - DiabloTek 550Watt ATX Power Supply; Diablo is a direct manufacturer of power source solutions, producing high quality power supplies. DiabloTek power supplies feature High efficiency, Low Noise and Ripple Output, Over Voltage protection and Short-circuit protection at any DC output. Fans: 80mm fan; Main Connector: 20+4Pin; SATA Power Connector: 2; Input Voltage: 115/ 230 V; Input Frequency Range: 50/60 Hz; Output: +3.3V at 28A,+5V at 30A,+12V1 at 24A,+12V2 at 0.8A, -12V at 0.3A,+5VSB at 2.0A; Connectors: 1 x Main connector (20+4Pin) 1 x 4-Pin ATX 12V 4 x Peripheral 2 x SATA 1 x Floppy

    Bulbs: 26.88/6.72 watt - 2.1/.48 AMP - 12.8/14 vol

    I know now that trying to control five of these bulbs with the 8A dimmer was going to run into problems... it's designed to control LED ribbons. it's strange to me though that it begins failing with even three bulbs, which seems like it should be pulling 7.5A max

    Resqueline - your point about the power supply having no load on the 5V is interesting - I tried running power directly to a few other 12V components outside of the dimmer - a fan and another light bulb - thinking even if the dimmer failed it might keep the power supply functioning, but this didn't work. I can try running some things on 5V and see if that helps.

    Any thoughts on the single potentiometer for multiple dimmers route? I can't seem to find a 12V dimmer that can do what I need.

    Thanks again!
     
    Last edited: Aug 4, 2011
  5. BobK

    BobK

    7,632
    1,657
    Jan 5, 2010
    I have a theory of why it might fail with what looks like it should be < 8A output. The dimmer is probably actually a PWM device, that is it is turning the voltage on and off rapidly rather than varying the voltage. The filament of a light bulb increases its resistance with increased temperature. So if it is being supplied with12V half the time, say, it will not be as hot and therefore be lower resistance than it would if was supplied with 12V continuously. Which means it would draw more current during the period when the 12V was on that it would if the 12V was on all the time. It seems plausible to me that this effect could raise the peak current from 7.5A to over 8A.

    Bob
     
    Last edited: Aug 4, 2011
  6. deathbybear

    deathbybear

    3
    0
    Aug 4, 2011
    This makes sense, and you're right, it is a PWM dimmer - here is a working link to it - http://www.amazon.com/Dimming-Contr...KKF2/ref=sr_1_1?ie=UTF8&qid=1312494178&sr=8-1

    Someone else suggested I should slave additional transistors to the dimmer, but i have literally zero idea how i'd do that, or how i'd even go about determining what kind of transistors i would use, hence my idea to just use multiple dimmers and wire together the potentiometers.
     
  7. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Bob is right about the peak currents, but if it was the dimmer failing it wouldn't shut down the PSU anyway.
    1st try to load the 5V, 2nd try to post pic's of the dimmer guts (I'm sure it's easy to mod.).
     
  8. poor mystic

    poor mystic

    1,059
    28
    Apr 8, 2011
    I have an alternative which may work for you.
    You could power the lights directly from a 12V transformer, and use a normal commercial lamp dimmer in the mains supply to the transformer. This'll work fine, for as long as the load is resistive; the circuit will power light bulbs.
     
  9. BobK

    BobK

    7,632
    1,657
    Jan 5, 2010
    Whoops, I missed the fact the it was the power supply that was cutting out.

    Bob
     
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