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OTS strings on DC

Discussion in 'Lights - Store Bought and Home Made' started by milamber79, Oct 11, 2011.

  1. milamber79

    milamber79 New Elf

    Aug 24, 2011
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    I am new to computer control and would like to use lights that I have already purchased. I have accumulated a number of sets over the years and surprisingly they are all in working order still. All but 1 of my sets are 24v, so I assume that because they are all rated the same I could use 1 powersupply to run them all. They are a mixture of incandescent and LED.

    So I have a couple of questions about that. I would like to run these on DC and use Mosfets to switch them. I am looking at using an Arduino as a controller (If that matters).

    Will these work with just a 24v DC power supply or will I need a higher/lower voltage? If there is a voltage change needed how do I work that out or is there a rule of thumb for this?

    I understand that I will need a supply capable of enough current to drive the strings so I am looking at a 400W supply. But the exact one will depend on the above question.

    Secondly, when the strings have multiple channels (usually different colours), I would like to be able to control each colour group. Are the strings connected as common Positive or common Negative? Or is there no standard and I will need to test each one?

    Unfortunately I don't have a large DC powersupply to test these on, otherwise I would just do some empirical testing. :)

    Thanks everyone.
  2. David_AVD

    David_AVD Bite my shiny metal ass! Community Project Designer Generous Elf

    Jun 12, 2010
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    Victoria Point (Brisbane)
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    Were the LED strings rated for 24V AC or DC ? I makes no difference for incandescent strings, but the LED strings may require the higher peak voltage that the AC would have given.

    You might need to do some testing with a variable DC voltage source one string at a time to determine the wiring and the required DC voltage.
  3. Beacy

    Beacy It's so much better on the dark side

    Jun 10, 2010
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    Where are the LEDS from Big W, Kmart Bunnings ?? - ausming your in OZ
  4. AAH

    AAH I love blinky lights :) Community Project Designer

    Dec 27, 2010
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    Mosfet selection will affect things slightly but as long as it turns on hard at the 5V (?) logic level and has a nice low on resistance you should have few problems.
    The incandescent you can run off 24V DC with no problems. They will typically be 20-30W per string.
    The LED strings will depend on how they are wired. I've seen them with both common +ve and common -ve so you are going to have to check and hope that they are common +ve for N channel mosfets. You are also going to have to check that they have resistors in the strings and not just in the controllers.
    As a cheap short term testing device you could series up 3 9V batteries to test the leds. The batteries will run the leds for a while before they run flat but the extra current for the incand's will flatten the batteries almost immediately.

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