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Making Custom-Length Xmas Lights from Existing Strand

lothian

Jan 5, 2021
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Home Depot sells Home Accents Holiday (HAH) "Super-Bright" 100-ct LED xmas lights. I'm getting an early start on swapping our years-old strands of outdoor lights to these things.

image_58fc3fd1-ed5c-4cc1-b9cd-beca346b7be1.jpg

Each LED strand is ~29ft long, and I'd like to save some money by making two individual strands from one. My problem is I can't figure out the wiring of these things in order to cut the wires at the exact right location to get two working sets.

61UR9hwzpTL._AC_SL1000_.jpg

With previous LED strands, I've been able to get two strands from one, and the trick is to identify the resistor at either end of a some count of LEDs, then determine the two lamps that are adjacent each resistor and cut the wires there. Resistors are apparent as either a comparatively thick lamp socket or a bulbous in-line thing along the wire, but not so much with these HAH strands. I'm also confused by the conductor count: The HAH strand has four conductors between lamps with three conductors at each terminator; my older LED strands have three conductors between lamps and two exiting each terminator. Tracing voltage thru a given wire is frustrating me on a neural level. so I'm posting this S.O.S in the plaintive hope that someone might be familiar with this HAH LED xmas light product and know exactly where to cut the wires.

Better still, buy a set, figure out where to cut the wires in order to get two strands from one and let me know, and I'll reimburse you for your purchase!
 
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Martaine2005

May 12, 2015
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Hi, it may be easier if you give the power supply/adapter specs too.
Also, do the 4 wires come from the supply? Or three from supply and forth ending somewhere near the first LED?.

Martin
 

lothian

Jan 5, 2021
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Maybe I'm misunderstanding you... these are a typical 120vac LED light strand. As for conductors... I need to clarify: my "three wires run from each plug-end while four wires are between each lamp" is a general observation and an oversimplification--and confusing to anyone trying to help me. I'll likely sacrifice an HAH strand in order to identify where the conductors are actually going within the strand and which LED doubles as an inline resistor.

Basically, of the three conductors that leave each plug-end, one wire feeds the nearest lamp, and the other two meander further down the line past some count of LEDs to feed one specific lamp holder. In each instance, the "one specific lamp holder" has three wires while all remaining lamp holders have two wires. Methinks these three-wire lamp holders do double-duty as resistors for their respective "strips" of LEDs, but sorting it all out is difficult.
 

Martaine2005

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Typical AC light strand?
LEDs are DC current driven devices. They are polarised.
Possibly I misunderstand you?

Either way, they probably have a power supply adapter? Rather than a simple mains plug?. You may call it a wall wart?.
24V wall wart seems to fit regulations of low voltage LED strings.


Martin
 

Martaine2005

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OTOH, if the string is really 120VAC, it would probably have some form of rectification.
If these have a plug at both ends for connecting more strings, the forth wire is probably a direct feed through.
That leaves three wires. 2 wires to a series string of LEDs and the third wire going from each series string to the next, connecting them in parallel.
Unfortunately, you’ll have to take your time and work it out as there are too many ways to achieve this. For example, the first 10 or so LEDs might have resistors dropping about 50V. Or simply 2V per LED x 50. Then the two strings of 50 in parallel.

Martin
 

Bluejets

Oct 5, 2014
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Think you'll find the output of the supply is a basic h-bridge and one polarity will give one output set/colour while the other (reverse if you like) gives the other.
 

lothian

Jan 5, 2021
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Perzactly.

There is a tiny bridge rectifier in the plug-end that converts the 120vac mains to DC--I still have yet to read the DC voltage and current. Disassembly of one of these light strands followed by the use of a tracer is inevitable if I am going to make any progress with this project.

The challenge is identifying each segment. Presumably, there are four 25 lamp isolated segments in this strand of 100-ct LEDs. Each segment's LEDs are driven by a constant-current DC feed AND an inline resistor. I should be able to simply cut the wires between the last LED in a segment and the next inline resistor, tie those wires together, et voilà... I've created a strand at some shortened (though fixed) length. I just need two strands from the one!

The difficulty is that each inline resistor has three conductors and this has me stumped.

Even with all four wires splayed out before me and identified--no easy task, btw--after I have cut the wires correctly and created two working strands from the one... the challenge will be to do identify where-and-which-wires to cut within another stand. The problem is the conductors are twisted rather tightly, and not unique nor identifiable as such in any way... and this makes me believe all strands I intend to make into two will require this degree of disassembly.
 
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Martaine2005

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I think you’ll find hundreds on YouTube, but whether they are correct or even dangerous is another matter.
Bigclive on YouTube has many videos pulling these sorts of things apart and drawing the schematic for them.

Martin
 

Bluejets

Oct 5, 2014
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but whether they are correct or even dangerous is another matter.
Yes, all seems a waste of time to me.
These things are as cheap as chips and, in most instances, those with a C tick at least, conform to safety regs.
Amateurs modding things and then stringing them up in public are just asking for trouble.
 

Martaine2005

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To create custom-length Christmas lights from an existing strand, carefully measure the desired length, then cut the strand at designated points, making sure to leave extra wire for reconnecting. Use waterproof connectors to rejoin the cut ends, and seal them for outdoor use. This DIY approach saves money and reduces waste, giving you the perfect holiday lighting solution.
What designated points?
Did you read the thread?.

Martin
 

Holley

Oct 2, 2023
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Typical forum thread... A simple question asked garners responses from the ignorant. Pro tip for those of you who feel compelled to chime in to a forum thread with absolutely no ability to contribute meaningful content: Log Out instead.

Short answer: Yes, you can cut LED xmas light strands to custom length. But it's gonna be challenging. Now for the long answer.

First, the basics...
LED xmas light strands use DC. A widget embedded within the plug-end converts 120vac mains to DC volts, while a specific number of specific resistors limit DC current to the specific number of specific color LEDs (yes, the color of the LED is electrically relevant, believe it or not). For example, your 100-ct LED xmas light strand might contain four LED "segments". Each segment requires a specific current to drive the combined LEDs within the segment to their designed luminosity. This is a simplified reason one cannot simply cut LED xmas light conductors wherever (suggested in a prior post), add a plug and call it done. Judging from your conversation, you seem aware of this already.

Tools:
You're gonna need a DMM and a soldering iron. A benchtop DC power supply would also be mighty handy. You're also going to need some spare plug-ends for each new strand you wish to create. But before you start cutting plug-ends off old lamps, recall that "widget embedded within the plug-end converts 120vac mains to DC volts" thing I mentioned before..? Right. You'll need that exact plug-end with that same embedded widget, else you'll instantly destroy the LEDs in the strand when you plug the thing into the mains. The workaround is not simple. You'll need an external DC power supply. Those things tend to be pricey, they're usually not waterproof, and they must be dialed in somewhat precisely—in both DC volts and current—in order to power ("drive") the mathematically-derived electrical requirements of your strand(s). (Honestly, a DC power supply may be the ideal device for driving all of your strands.) But I digress. Back to your hack...

Unwind the strand:
You must first unwind the LED light strand and separate the constituent conductors (insulated wires). This will be no casual task. The wires are tightly twisted. They will resist your efforts to unwind them and immediately form a Gordian knot. If this thrombosis-inducing frustration doesn't dissuade you from continuing, then you'll soon discover another vexation. Despite appearances, the conductors are not simply twisted the full length of the light strand. A wire may run a few meters, then terminate into a lamp holder or inline resistor (more on these things in a moment) while another wire might originate from a lamp holder mid-strand, travel a few meters, and terminate into another. Yet another wire may run plug to plug. Expect no consistency. You will have to cut wires just to assist detangling the strand in order to make sense of what goes where. Make intuitive cuts, and mark cut ends with colored tape so you can reconnect them later.

Identify segments:
You must determine the location and number of inline resistors servicing the entire strand so you can identify each LED "segment". Every LED xmas light strand contains resistors, one per segment. Resistors are identified as bulbous thingies on the wires or within a lamp socket... perhaps even both 'cause there's never any consistency with these Chinaseum-made things. (Chinese engineers aren't particularly consistent as a rule so expect none, particularly between different brands/styles/configurations of LED xmas light strands.) Confirm a segment by simply yanking any lamp from its holder with the light strand powered ON. Count the LEDs that go out AND mark the lamps on either end within that segment. Repeat this through the entire strand until you've identified each segment and marked segment lamps. You'll eventually cut the two wires between the two adjacent lamps.

Create your first "shortened" segment:
Begin with the segment immediately following the plug-end. Power OFF the strand and cut the wires between the two adjacent lamps you marked earlier. Strip the two wires to copper then tie them together (with solder). Power ON the strand and confirm the shortened strand lights up as expected. Congrats. After an hour or so of unmitigated aggravation you created a segment that is fraction of the whole. This may be the one and only segment you get to work, 'cause making add'l working segments will be difficult.

Where things get tricky:
As long as you ensure 1) each segment has a DC feed with the same voltage and current that 2) immediately goes to an inline resistor, you'll be fine. That means you have to get power from the plug-end to the next segment. You may have noticed the method the manufacturer uses to distribute power to each segment within the strand: via a "pass-thru conductor" either directly from the plug-end or from one of the lamp holders, or maybe some novel method unfamiliar to me (zero consistency). Depending on the configuration of the product you're working with, you might get lucky and one of the three conductors originating from the plug-end feeds the segment adjacent to the one you just made. If the wire is not a power feed, you'll have to tap into the plug-end feeds and run a length of wire all the way to the first LED the segment adjacent to the one you made (I hope this is clear.). You can even use this method to feed power to both segments of your second strand (since the plug-end is powering all the segments in the full strand already!). However, I understand your goal is two independent strands from one. So making that second, independent strand is gonna be real hard without a plug-end with that "widget embedded within that converts 120vac mains to DC volts". Other than that DC power supply thing I mentioned before I have no idea how you can pull this off.

Bottom line:
After hours of frustration and many mistakes, for the effort you'll likely end up with just one working segment of LEDs and only a quarter of the length you desired. Also, you've probably already discovered that you'll never get the conductors to twist back the way they were, so your new strand is a sloppy mess of wires. Also also, because you lack two aforementioned plug-ends you'll have a bunch of LEDs that simply no longer light. That is a LOT of wasted LEDs, amigo—hardly the cost savings that drove you on to this endeavor in the first place. There are workarounds to this, but that's beyond the scope of my already overly-long response. Also beyond the scope of this response, you can most definitely shorten your segment by cutting between LEDs; but doing so changes the cumulative voltage across the remaining lamps (a bad thing) unless you mitigate this electronically.

Wow. After a quick skim of my response and a quick glance at my watch, I kinda sorta understand the terse responses you got. I personally think your idea is meritful though impractical.

Anywho... Happy fiddling!
 
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Martaine2005

May 12, 2015
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Typical forum thread... A simple question asked garners responses from the ignorant. Pro tip for those of you who feel compelled to chime in to a forum thread with absolutely no ability to contribute meaningful content: Log Out instead.

Short answer: Yes, you can cut LED xmas light strands to custom length. But it's gonna be challenging. Now for the long answer.

First, the basics...
LED xmas light strands use DC. A widget embedded within the plug-end converts 120vac mains to DC volts, while a specific number of specific resistors limit DC current to the specific number of specific color LEDs (yes, the color of the LED is electrically relevant, believe it or not). For example, your 100-ct LED xmas light strand might contain four LED "segments". Each segment requires a specific current to drive the combined LEDs within the segment to their designed luminosity. This is a simplified reason one cannot simply cut LED xmas light conductors wherever (suggested in a prior post), add a plug and call it done. Judging from your conversation, you seem aware of this already.

Tools:
You're gonna need a DMM and a soldering iron. A benchtop DC power supply would also be mighty handy. You're also going to need some spare plug-ends for each new strand you wish to create. But before you start cutting plug-ends off old lamps, recall that "widget embedded within the plug-end converts 120vac mains to DC volts" thing I mentioned before..? Right. You'll need that exact plug-end with that same embedded widget, else you'll instantly destroy the LEDs in the strand when you plug the thing into the mains. The workaround is not simple. You'll need an external DC power supply. Those things tend to be pricey, they're usually not waterproof, and they must be dialed in somewhat precisely—in both DC volts and current—in order to power ("drive") the mathematically-derived electrical requirements of your strand(s). (Honestly, a DC power supply may be the ideal device for driving all of your strands.) But I digress. Back to your hack...

Unwind the strand:
You must first unwind the LED light strand and separate the constituent conductors (insulated wires). This will be no casual task. The wires are tightly twisted. They will resist your efforts to unwind them and immediately form a Gordian knot. If this thrombosis-inducing frustration doesn't dissuade you from continuing, then you'll soon discover another vexation. Despite appearances, the conductors are not simply twisted the full length of the light strand. A wire may run a few meters, then terminate into a lamp holder or inline resistor (more on these things in a moment) while another wire might originate from a lamp holder mid-strand, travel a few meters, and terminate into another. Yet another wire may run plug to plug. Expect no consistency. You will have to cut wires just to assist detangling the strand in order to make sense of what goes where. Make intuitive cuts, and mark cut ends with colored tape so you can reconnect them later.

Identify segments:
You must determine the location and number of inline resistors servicing the entire strand so you can identify each LED "segment". Every LED xmas light strand contains resistors, one per segment. Resistors are identified as bulbous thingies on the wires or within a lamp socket... perhaps even both 'cause there's never any consistency with these Chinaseum-made things. (Chinese engineers aren't particularly consistent as a rule so expect none, particularly between different brands/styles/configurations of LED xmas light strands.) Confirm a segment by simply yanking any lamp from its holder with the light strand powered ON. Count the LEDs that go out AND mark the lamps on either end within that segment. Repeat this through the entire strand until you've identified each segment and marked segment lamps. You'll eventually cut the two wires between the two adjacent lamps.

Create your first "shortened" segment:
Begin with the segment immediately following the plug-end. Power OFF the strand and cut the wires between the two adjacent lamps you marked earlier. Strip the two wires to copper then tie them together (with solder). Power ON the strand and confirm the shortened strand lights up as expected. Congrats. After an hour or so of unmitigated aggravation you created a segment that is fraction of the whole. This may be the one and only segment you get to work, 'cause making add'l working segments will be difficult.

Where things get tricky:
As long as you ensure 1) each segment has a DC feed with the same voltage and current that 2) immediately goes to an inline resistor, you'll be fine. That means you have to get power from the plug-end to the next segment. You may have noticed the method the manufacturer uses to distribute power to each segment within the strand: via a "pass-thru conductor" either directly from the plug-end or from one of the lamp holders, or maybe some novel method unfamiliar to me (zero consistency). Depending on the configuration of the product you're working with, you might get lucky and one of the three conductors originating from the plug-end feeds the segment adjacent to the one you just made. If the wire is not a power feed, you'll have to tap into the plug-end feeds and run a length of wire all the way to the first LED the segment adjacent to the one you made (I hope this is clear.). You can even use this method to feed power to both segments of your second strand (since the plug-end is powering all the segments in the full strand already!). However, I understand your goal is two independent strands from one. So making that second, independent strand is gonna be real hard without a plug-end with that "widget embedded within that converts 120vac mains to DC volts". Other than that DC power supply thing I mentioned before I have no idea how you can pull this off.

Bottom line:
After hours of frustration and many mistakes, for the effort you'll likely end up with just one working segment of LEDs and only a quarter of the length you desired. Also, you've probably already discovered that you'll never get the conductors to twist back the way they were, so your new strand is a sloppy mess of wires. Also also, because you lack two aforementioned plug-ends you'll have a bunch of LEDs that simply no longer light. That is a LOT of wasted LEDs, amigo—hardly the cost savings that drove you on to this endeavor in the first place. There are workarounds to this, but that's beyond the scope of my already overly-long response. Also beyond the scope of this response, you can most definitely shorten your segment by cutting between LEDs; but doing so changes the cumulative voltage across the remaining lamps (a bad thing) unless you mitigate this electronically.

Wow. After a quick skim of my response and a quick glance at my watch, I kinda sorta understand the terse responses you got. I personally think your idea is meritful though impractical.

Anywho... Happy fiddling!
Biggest load of ignorant bull crap!.
You certainly know how to start a fire amigo!.
Obviously you watched the YouTube videos of ignorant people like yourself doing it all wrong. This is 120V mains you doughnut!. You can’t just cut it where you want!.
Oh, those little things are bridge rectifiers. You only need one!.
Please educate yourself before posting potentially dangerous things on here. Fine, do it yourself. But don’t pretend you know what’s going on! Amigo!
 
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