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Pre-lit Popup Tree

Pre-lit Tree

I bought a couple of these from Deals Direct as I wanted a simple lit tree to go on either side of my front door.

Powering the tree using a DC power supply set to 29V gave the same light level as the supplied 24V AC plug pack. At 29V DC, the set draws approx 120mA (3.5W).

So that I can use these LED trees with the same (30V DC) power supply as my Big W strings, I had to do a simple modification. I also wanted these trees to be plug compatible with the other Big W string based items I have, so used the 3 pin plug from a dead string of lights.

First I cut off and discarded the controller / switch box from the Deals Direct tree. I then soldered the common +ve wire of the Big W plug to the +ve of the Deals Direct string. (I had already used a 30V power supply to determine which wire was +ve on the tree’s string)

Resistor Mod
Resistor Mod

Next I soldered a 22 Ohm, 1 Watt resistor inline with the -ve of the string and the channel 1 wire of the Big W plug. (Plug pinout is in the wiki) The channel 2 wire was cut back a little shorter as it’s not used here.

After a quick test (to make sure it worked!), I slipped the pieces of heatshrink over the connections and resistor and shrank it down being careful not to overheat the shrink or wires.

So, how did I come up with that resistor value? I actually wound up the power supply to where it indicated the string was drawing 120mA (approx 12mA per LED) and noted the voltage (27.3V in this case). That meant I had to drop approx 2.7 Volts across the resistor.

Using Ohms Law, that calculated to 22 Ohms (2.7V / 0.12A). The wattage dissipated by the resistor is about 0.3W (2.7V x 0.12A), so I selected a 1W type as that will handle the 0.3W continuously and is also mechanically sturdier than a 0.5W type.