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OK to modify light strings?


LORi P
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I am using C7 LED strings from Holiday Creations to outline my roof and gutters.

To do the roofline and gutters as they are will require a lot of blacking out bulbs with electrical tape, so I don't double-up (or triple up) on lights in some areas.

I know that it is a bad idea remove lights from a string, because the rest of the bulbs will get too much voltage, but is this OK:

1) Cut the strings in the sections where I would be blacking out bulbs,

2) splice in some wire (say 16 or 18 guage) to connect up the three wires on the string again?

3) Then seal up with the shrink wrap.

I know it is extremely important to connect the right wires on the light string again. I would paint each wire.... one red, one white, and leave the 3rd the green color that the wire already is. Then when splicing, connect the red painted wire to the red painted wire, white to white, and green to green - to make sure I don't screw up and connect the wrong wires to each other.

Is this a bad thing to do? Will it damage the light strings in any way? Does the wire I would splice with have to be any particular guage?

I know there are a lot of electricians on the forum, I hope someone can help.

Thanks! - LORi

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testraub wrote:

Never Mind Your asking about LED strings I just saw c7.

Tom Straub


So Tom, does this mean, yes, I can do it, or no I should not, or I don't know???

Thanks!
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Lori,

As long as your do as you state and connect the wires back to the same wire that was cut. I think you should be find. Of course make very good connections, such as soldered and then shrink tube. I have heard you can actually get shrink tube with a sealant inside that when it shrinks will seal the connection from any penetration.

To be honest, most people just want to remove lights. You are charting new area as far as I know. But I do not see any major issue. How far are you looking to extend? The one issue I can see might be voltage drop. Use at least the same size wire or larger to help keep down on voltage drop.

Chuck

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cmoore60 wrote:

Lori,
How far are you looking to extend?
3-5 feet in most cases

The one issue I can see might be voltage drop. Use at least the same size wire or larger to help keep down on voltage drop.
What guage is Christmas light wire? 18?
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DO NOT DO IT!

Each LED in the string makes up a specific voltage that equals out to the voltage you are using.

If you were just splitting an LED string, say a 100 LED string into 2 50 ct LED Strings, this is doable in most cases, but NOT all. It depends on the string and the make up.

All light strings, whether LED or Incandescent ONLY USE 2 WIRES, NOT 3! That 3rd wire is a pass through wire straight to the female plug at the end of the string, YOU DO NOT NEED TO CUT THAT WIRE!

The reason you don't want to just cut out a LED bulb from the string, is as stated above, the voltage requirment for the string, say you have a string of 50 LED bulbs, the String operates on 120V ~AC~, therefore to be sure those 50 LEDS are equal to the input voltage, 120 volts in this case, make each LED's voltage at 2.4 volts, so each LED you remove will increase that same voltage to all the other LED's in the string. So if you took out 8 LED's at 2.4 volts, you just increased the voltage to that all the other LEDs by 19.2 volts. So now you have a string of 42 LED's with each LED now receiving 2.9/3 volts, you are now feeding every LED on the string an extra .5 to .6 volts, now that may not seem like much to you, but it can cause premature failure (burn out) of the remaining LED's on the string.

Even though it may be a hassle, blacking out the unused or un-needed LEDs is your best option for a long life string, otherwise, you may be replacing your strings long before the season ends.

I've been using LED's for a very long time in many hobby applications, so if you do remove those LED's, you'll need to calculate for a voltage dropping resistor to put in series with the LED's to keep the voltage at their required voltage. Don't remember the formula for calculating the resitor value, but sure someone here knows what it is and will post it for you.

But, no, you really DO NOT want to just cut out LED's and then re-splice the string unless you really know what you're doing and how to compensate for the new voltages the string will be getting after the modification.

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As long as you match up the correct wires, you should be OK. I've extended strings that way before without problems. Use cheap nail polish in two different colors; smear it about 1-2 inches then when dry, cut in the middle. Match up colors as you reassemble.

Shrink tubing is normally "2x" which means it shrinks to half of it's original diameter. You can also get "3x" tubing, which shrinks to one third of its original diameter and many of those tubes have an inside sealant to prevent water from seeping inside. See http://www.heatshrink.com/w3b2.htm

The final product will be quite nice, but it's tedious work, with all the soldering, shrinking and stuff.

If you only need to blackout a few bulbs, reach for the heat shrink tubes again, slide it over the bulbs to blackout, cut with scissors about 3/8 longer than the bulb and use the heat gun on it. While it's cooling down, squeeze a needle nose pliers on the 3/8 extra and you will have a quick, cheap blackout. If you change your mind, get a sharp knife and cut the heat shrink stuff off.

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With the LED strings you won't have to worry about the voltage drop from 5 extra feet, because the current is typically only 20mA. Most strings are only something like 20 gauge, so 18 would be more than plenty..

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From reading your post over - sounds like you just want to extend your strings in several sections. as long as you cut/mark/splice everything correctly, that will work fine.

But if it were mine, I'd just look for something larger to blackout several bulbs at once. (I also dont follow how a string across roof outline needs anything blacked out.. but thats ok)

If I have a rather large area where I dont want to see lights, and I dont want to cut the strand (like a big bundle at the end of my roof outline) I zip tile the left overs into a small bundle, then cover it with tinfoil. and just to stomp out anyone going off a bout an electrical hazzard - if you want lay some plastic over the foil first.

If you go to a theatre / lighting supply store, they actually sell a product called "Black Wrap" its heavy duty foil with a black coating. theatre folk use it to stop light from creeping out into areas (like a curtian above the stage) they dont want light.

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LORi P wrote:

Orville wrote:

But, no, you really DO NOT want to just cut out LED's

You are right. I DON'T want to cut out LEDs from a string. Please re-read my post.


Oh okay, somehow I got the impression you were wanting to cut out some of the LED's. If you're extending the string, yes, you would need to cut all 3 wires to splice it in. Sorry, I misunderstood what you were wanting the first read through.

So yes, if you can find an old non working Christmas light string, you could actually cut your splice wire from it, I keep old non working strings for sockets, wire and their male/female and female plugs and receptacles I use to build extension cords from too.

So yes, you should be fine just splicing in those pieces of wire to lengthen the string.

Now here's how I do that {without needing paint or color coding the wires}

Cut your shrink tubing at least a 1/2" (inch) longer than your connections, so that when it shrinks it will not leave any exposed solder or wire, I usually cut mine at least 1-1/2" (inches) longer than I need just to be sure. For the larger piece to cover all wires, cut it about 2" (inches) longer than your longest smallest piece so that when it shrinks it will cover the entire small shrank connections. You'll understand this more from the information below. NOTE: I also use BLACK heat shrink to black out bulbs, shrink the tube over and then pinch it together while still hot.

Cut the first wire, then add the length of wire I am going to extend it, put on a large piece of shrink wrap that will cover all wires, sliding it over the current cut wire, then put on the two smaller pieces of shrink wrap over each end on the light string wire, strip, solder, slide the small shrink wrap over the connections, shrink, plug string in and test to make sure connection works, now cut the 2nd wire, run it through the large shrink tubing, repeat process as for 1st wire, cut 3rd wire run it through the large piece of heat shrink, repeat process as for 1st and 2nd wires.

Also have a magnifying glass and good lighting handy, you want to examine your heat shrink after each process to make sure you have no stray wire strands poking through the heat shrink that could create a short.

Sometimes you can tell this just by running your fingers lightly back and forth along the tubing, but best to check with good light and a good magnifcation lense of some type, a Jewelers Eye Loop magnifier is really useful here.

Now once all your connections are soldered and heat shrink tubing has been shrunk and verified you have no stray strands poking out anywhere, now slide the one large piece over these connections and shrink it over them. This will hide all your connections under one shrink tube.

Hope that helps you get the strings extended!
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Lori,
If you ever want some of that heat shrink tubing that has the sealer in it. There is a place not to far from where I work called Gateway Electronics near West Port Plaza (270 and Page)in St. Louis. I use this stuff a lot. I have converted over displays that had been wired with Icans and now I have LEDs in the string. I put a Full wave bridge and resistor in-line and cover with this type of tubing.
Well anyway, if you ever need some. I can purchase and snail mail to you. Although be it known, a 4' piece might run between 3 or 7 bucks. Depending on diameter.

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LORi P wrote:

cmoore60 wrote:
Lori,
How far are you looking to extend?
3-5 feet in most cases

The one issue I can see might be voltage drop. Use at least the same size wire or larger to help keep down on voltage drop.
What guage is Christmas light wire? 18?


I have done exactly that with LEDs (as well as with incandescents in the old days...)

The current draw of LEDs is much lower than incandescents, and I would not worry about voltage drops over an additional 3 - 5 foot extension!

LED wiring is typically not 18 gauge, but usually is smaller (which means a higher number) Yours might be 20, or even 22 gauge. You can tell once you cut through one of the wires. You need to see the actual diameter of the conductor, and not just judge it by overall diameter, as insulation thickness varies between manufacturers.

Take a short piece of cut off wire to your local R Shack store, and compare it to the wire they have spools of. They have 16, 18, 20, and either 22/24 gauge as I recall.

20/22 should be more than adequate. 18 of course will work, but it is just a waste of $$ for your intended purposes.

Greg
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In some places I use LED strings I don't need to use the socket on the end to extend the string because I am only using 1 string. To make the string less bulky, I "harvested" the female socket and the excess wire. If you will never use the socket on the end, cut it off and unwind the wire that connects to it. I got over 10 feet this way.

This will only work if the string has the rectifier on the plug end (two wires in, two wires out), or on half-wave strings. Don't try it if the blob near the female end has 3 wires in, 2 wires out.

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