OTS strings on DC


New elf
Aug 24, 2011
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.


Grandpa Elf
Community project designer
Generous elf
Jun 12, 2010
Victoria Point (Brisbane)
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.


It's so much better on the dark side
Jun 10, 2010
Where are the LEDS from Big W, Kmart Bunnings ?? - ausming your in OZ


I love blinky lights :)
Community project designer
Generous elf
Dec 27, 2010
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.