Cutting Store-Bought Xmas Light Strand to Length - Page 1
Forum section: electronics / general

author: lothian
author_rank: Newbie
timestamp: September 29, 2023, 11:20:48 pm
content: Home Depot sellsHome 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.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 exactly the right spot to get two working sets.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 on 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!

author: IanB
author_rank: Super Contributor
timestamp: September 29, 2023, 11:45:29 pm
content: If you are prepared to reimburse someone to buy a set and figure it out, that will counter your attempts to save money by cutting a strand in half. You might just as well buy two strands instead of one? Unless of course you want to buy and modify lots of them?If you buy lots of them, they can be chained end-to-end, which surely should be fine unless you need small numbers of lights in all sorts of different places?Anyway, what I suspect is they have wired the lights up in some kind of series parallel arrangement, which would explain the four wires, and would explain how they can keep working if one lamp fails. For instance, they might have four lamps in parallel, and then 25 of these parallel groups in series, with one or more resistors in appropriate places. But this is just a guess.

author: lothian
author_rank: Newbie
timestamp: September 29, 2023, 11:53:44 pm
content: uh'mm... anyone else?

author: ataradov
author_rank: Super Contributor
timestamp: September 30, 2023, 12:25:55 am
content: I would agree. Those things cost $20. Just buy an extra set. Nobody is going to waste their time reverse engineering Chinese junk.

author: lothian
author_rank: Newbie
timestamp: September 30, 2023, 04:36:56 pm
content: uh'mm... anyone else?

author: Halcyon
author_rank: Unknown
timestamp: October 01, 2023, 12:40:00 am
content: Quote from: lothian on September 30, 2023, 04:36:56 pmJust a little tip, responses like this can come across as passive aggressive to many forum members and is a good way to get people off-side and ultimately stop people replying to your threads. Something to keep in mind.

author: Brumby
author_rank: Unknown
timestamp: October 01, 2023, 01:32:24 am
content: Since I don't have access to these lights, I can't offer any real assistance other than to echoIanB's comment above about series/parallel connection - but what the groupings would be is an unknown.I do find it curious, however, that we have some conflicting information on the sides and the faces of the box:PanelFaceSideColourCool WhiteWarm WhiteLighted length28'10"33'Max. Sets1730Doing a search on the UPC came up with (for me) 3 hits. Two on eBay and one for Home Depot. Of the two eBay entries, one had them listed for $13.70 + $3.92 shipping for one box and the other had 3 boxes for $49.99 plus $10 shipping.I could not see any technical information - anywhere - not that I ever expected to. Apparently not Chinese, but made in Cambodia.If you want to supply me with a set, I'll be happy to give it a shot.

author: Zbyszek
author_rank: Newbie
timestamp: October 01, 2023, 02:16:35 am
content: Basically HD has very good return policy. Anyone to try...?

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2023, 02:50:23 am
content: They are not available in store (yet?), so not even possible to look at them.

author: Crumpet
author_rank: Newbie
timestamp: October 03, 2023, 12:44:49 pm
content: Typical forum thread... A simple question asked garners useless 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 colour LEDs (yes, the colour 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, add a plug and call it done. You seem aware of some 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. Right. 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 travel 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 travel 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 recombine them after you've sorted things.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; that is, between the lamps that demarcate two isolated segments within the strand.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 must deliver power from the plug-end to the resistor in the next segment. You may have noticed during the detangling phase 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 believe 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 appreciate the terse responses you got.I get you: You simply want to cut a too-long strand of lights in half. Sorry to disappoint but you simply can't with LEDs. I personally think your idea is meritful. But it's impractical to do that for the reasons stated. Truthfully you can makeanylength of LED lights you want with lamps from any LED xmas light strand. And while this would be a project, in some aspects it might be a more practical and inexpensive route for what you want to accomplish. But it'll require learning some important electrical terms, using some relevant formula, doing some simple calculations, and gathering LED specs... and a DC power supply! Perhaps some benevolent electronics forum hobbyists—as opposed to condescending losers who make useless posts to electronics forums as a hobby—will provide you all the whatnots! (...or just PM me if that doesn't happen and I'll help you out.)Anywho... Happy fiddling!

author: Halcyon
author_rank: Unknown
timestamp: October 04, 2023, 03:55:19 am
content: I've banned the above user and the OP in this thread (who are actually the same person).Who would have thought that being abusive to moderators via PM would bring you under notice? I don't know about you guys, but this bloke has been abrasive from the start and really doesn't fit within the community here. Until he matures and starts wearing his big boy pants, I think he'll continue to cause trouble.No doubt he'll be back to have the "final word", trying to hide under various VPNs, browsers etc...

author: ataradov
author_rank: Super Contributor
timestamp: October 04, 2023, 04:11:33 am
content: That's a weird turn of events. What would even be the point of this?

author: Halcyon
author_rank: Unknown
timestamp: October 04, 2023, 04:36:18 am
content: Quote from: ataradov on October 04, 2023, 04:11:33 amPretending to be another person, responding to his own thread, just to "stick it to the mods" and get caught in the process?I'm not exactly sure, it seems like an awful lot of effort to go to. Just one of those "special" users I suppose?

author: IanB
author_rank: Super Contributor
timestamp: October 04, 2023, 04:52:12 am
content: The post is not even sincere.The product packaging clearly says all the other lamps will remain lit if you remove one of them.Yet the post above suggests to count the lamps that go out if you pull a lamp from its socket.So yeah. Just trying to yank everyone's chains it seems.

author: Brumby
author_rank: Unknown
timestamp: October 04, 2023, 05:45:06 am
content: What I find "amusing" is that from the OP's original post (is that a tautology?) those who have some knowledge on the subject will have observed a certain level of technical ability and that it would seem the OP has made their best effort, but to no avail. As such, without some hard reference - such as a sample, a wiring diagram or at least some photos - makes assistance via a text medium pretty dang impossible ...The clincher is the post from the alter-ego which sounds like a detailed description of the actual path the OP had already travelled.I find it hard to believe in their efforts they didn't come acrosssomedetails that may have given us half a chance at working with them towards a solution, but, no. They just threw up their hands and expected to be spoon fed. If someone wants help and makes an honest effort, then I will happily assist as best as my skills and time allow - and I know many members here are the same.But having a tantrum because their expectations are not fulfilled by people who lend their experience and timefor free, just demonstrates their sense of entitlement and lack of maturity.Quote from: Halcyon on October 04, 2023, 03:55:19 amWhile we may hope, from my experience ... don't hold your breath.

author: Halcyon
author_rank: Unknown
timestamp: October 04, 2023, 07:00:30 am
content: Couldn't agree more Brumby.Anyway, I'm not the one losing sleep over it.