Shortening LED icicle lights

Submitted by Dave-L on Tue, 01/11/2022 - 04:14



I have a set of outdoor Christmas icicle LED lights that I’d like to shorten and wondered if anyone could help me please with the way to do this? I thought it would be a simple job but there's something odd about the way it's wired.

The lights are 22 meters long and I’m wanting to shorten them to 20M, it’s an 800 LED string so I’d be losing about 40 LED’s. The set is low voltage (31v PSU). Running along the main “backbone” are 3 wires, then there’s lots of drop-down strings to give the icicle effect. 

I marked the 3 wires and cut each in turn with differing results -

Wire A cut = small section dies.

Wire B cut = entire lot dies.

Wire C cut = entire lot dies.

So having read that these type of lights are normally wired in series/parallel arrangement I’m puzzled why the whole lot dies when I cut either wire B or C, as I’d obviously expect the ones prior to mostly all stay on. It almost seems they’re all in series, but guessing with a volt drop of about 4v per LED (white) then the PSU voltage should be 3.2Kv! I expected a small section to die when cutting wire A, as this would suggest a sub-parallel section, but I just can’t figure why ALL go out when cutting B or C. Several of the LED’s also have 5/6 incoming wires connected.

Once shortened I was planning to add several 1N4148’s in series at the cut points to overcome the additional voltage presented to all the remaining LED’s.

My feeling is that these are some kind of “smart” LED being used - possibly addressable as the power pack has options for various chasing sequences, yet is connected to the set with just 2 wires. Could this be true?



Many thanks !