Shortening Christmas Light Strings

[bad_idea]

I am putting some mini led Christmas light strings outside. I would like to cut the strings to custom lengths to get rid of that remainder that hangs down. These are the typical multi-color mini led light strings you get from Lowe's, Home Depot, Wal-Mart, etc. For instance, I have a string that is 4 bulbs too long. I would like to cut the string down and put a resistor in line to take up the difference so that the remaining bulbs are still supplied the appropriate voltage. I have watched a bunch of YouTube videos on it and people have interesting methods to identify the needed resistor size. Seems to me, I can cut the unwanted portion of the string off and measure the resistance through it with my multimeter (have a quality Fluke) and install a resistor with the same resistance. Sound about right?

 

[Shiftless]

I had the same problem with a string that was too long for the area I wanted to decorate. I just unscrewed the unwanted bulbs and put tape over the sockets. Easy peasy.

I don’t think you can measure the resistance on a string of LED bulbs. Incandescent yes, LED no.

If you are bound and determined to shorten the string, just cut it and splice the ends together. As far as I know, LED’s aren’t that sensitive to voltage variations. If youve got a string of 100 bulbs, will 4 fewer make a difference?

Let’s wait for some actual electrical engineers to chime in. I’m not one of those by any means.

 

[whateg01]

I am putting some mini led Christmas light strings outside. I would like to cut the strings to custom lengths to get rid of that remainder that hangs down. These are the typical multi-color mini led light strings you get from Lowe's, Home Depot, Wal-Mart, etc. For instance, I have a string that is 4 bulbs too long. I would like to cut the string down and put a resistor in line to take up the difference so that the remaining bulbs are still supplied the appropriate voltage. I have watched a bunch of YouTube videos on it and people have interesting methods to identify the needed resistor size. Seems to me, I can cut the unwanted portion of the string off and measure the resistance through it with my multimeter (have a quality Fluke) and install a resistor with the same resistance. Sound about right?

Are you sure that are all wired in series?

 

[u2slow]

Are you sure that are all wired in series?

Yeah, I don't think so.
Common for half a string to dim or go dead. Hint: look for the spot(s) in the string where it changes from 3 wires to 2.

 

[bad_idea]

Yeah, I don't think so.
Common for half a string to dim or go dead. Hint: look for the spot(s) in the string where it changes from 3 wires to 2.

They are indeed wired in series. Depending on the strand, they will be wired 20-30 in series and then the next set will be 20-30 long. Thats why a bulb going out will take out just a section.

I tried pulling the last couple bulbs, but then that section of the string went dead.

 

[u2slow]

They are indeed wired in series. Depending on the strand, they will be wired 20-30 in series and then the next set will be 20-30 long.

That's not fully/all in series (as I thought was the question).

 

[PCustoms]

I tried pulling the last couple bulbs, but then that section of the string went dead.

They used to sell "dummy" incandescent bulbs to blank out a section of lights

 

[bad_idea]

https://grayhousestudio.com/how-to-shorten-string-christmas-lights/

This article outlines how to cut the strings down. The article has some good diagrams at the bottom showing how the lights are wired. The article mentions the change in voltage each bulb will see, but doesn't cover adding a resistor. The article is working off of the same assumption Shiftless makes, that a few bulbs removed won't impact the voltage enough to burn the bulbs out. I'm a bit obsessive about details, not very good at 'good enough' - I would prefer to measure the effects and assess from there.

 

[PCustoms]

Delete

 

[mm08822]

Determine the number of series strings in the overall string. Then the number of bulbs in each series section.

Measure the current of the entire string with your fluke in series with it and the power cord.

Let's say you measured 1 amp total and there are 4 series strings. That means 0.25 amp per series string.
If 20 lights per series string, then each bulb/driver requires 120/20 = 6v.

Each resistor for each removed light needs to handle 6v*0.25a = 1.5w minimum.
R= 6v/0.25a =24 ohms. (In my example!!)

Don't burn the place down. It would safer to remove an entire series string than making little heaters that would become unattended and forgotten until that "oh ****" moment rudely surfaces!

 

[dave*99]

I don’t think you can measure the resistance on a string of LED bulbs. Incandescent yes, LED no.

You can't use an ohmmeter to measure the resistance of an unlit LED or incandescent light. Well you can, but the numbers are meaningless.

Resistance changes dramatically when the bulb is illuminated.

You can, however, determine the "ON" resistance using the methods described above in post #10.

 

[bad_idea]

Determine the number of series strings in the overall string. Then the number of bulbs in each series section.

Measure the current of the entire string with your fluke in series with it and the power cord.

Let's say you measured 1 amp total and there are 4 series strings. That means 0.25 amp per series string.
If 20 lights per series string, then each bulb/driver requires 120/20 = 6v.

Each resistor for each removed light needs to handle 6v*0.25a = 1.5w minimum.
R= 6v/0.25a =24 ohms. (In my example!!)

Don't burn the place down. It would safer to remove an entire series string than making little heaters that would become unattended and forgotten until that "oh ****" moment rudely surfaces!

Thank you! I'll do the math and some figuring to see how much resistance is being removed from the circuit. Then I'll look into the wattage range the bulbs can handle, I'm sure there is room for a little fluctuation. I have one string in particular that I wrap around the eaves of the kid's playhouse that is 4 or 5 bulbs too long. Would be nice to trim it down, but not the end of the world to wrap those bulbs in tape and tuck them out of the way. I had not considered the heat generated by the resistor on the light string.

 

[dave*99]

Also, look carefully at the parts you intend to amputate.

Some strings have a molded resistor inline with each of the series strings.
Some have a single LED base that is larger and holds the resistor serving that section.
Some have a resistor in every LED.

 

[Leaflessshadetree]

Why not just space the bulbs a little closer as you hang them?

 

[bad_idea]

Why not just space the bulbs a little closer as you hang them?

Because it's a nuisance. I clip them on the edge of the shingles with the cable stretched snug. Would need to stretch cable, then pull back 0.285" to maintain even spacing with each bulb. I know I am being excessively **** retentive, but I feel like it's simpler to modify the string once than to mess with the spacing every year. Don't mean to come across condescending or anything like that.

 

[CJ7VFR]

Why not just space the bulbs a little closer as you hang them?

This is what we do when the light strings are a few bulbs too long. That and we sometimes just wrap those last couple of bulbs back over and onto the end of the main part of the light string to shorten the length. It does kind of double up the last few bulbs but if done right it does not look too bad.

Or you can do what my neighbor does. He paints those last few bulbs with some black paint so the light does not shine thru. This leaves the bulbs in the string so it does not mess with the voltage of the remaining bulbs while making those last few bulbs not visibly lit up. He also does this for those few bulbs that he wants not to be seen on the string of lights that go between his front door and two front windows.

Jim

 

[Fav Onefour]

Relevant topic. Squirrels shorten our strings quite often. It seems like a waste to toss them just because they are shortened with a little help from natures furry tailed rats.

 

[bad_idea]

Also, look carefully at the parts you intend to amputate.

Some strings have a molded resistor inline with each of the series strings.
Some have a single LED base that is larger and holds the resistor serving that section.
Some have a resistor in every LED.

I've seen that molded resistor. I'm out of town for work right now, so I don't have access to the light strings. Killing time in the hotel and doing some research for when I get home. I assume that resistor is there to soak up extra voltage in the line to avoid overdriving the leds? If so, figure I could swap the resistor for a larger one after removing a couple bulbs? Is the resistor typically at the start of the line or at the end? Appreciate the info.

 

[kbuhagiar]

Or you can do what my neighbor does. He paints those last few bulbs with some black paint so the light does not shine thru. This leaves the bulbs in the string so it does not mess with the voltage of the remaining bulbs while making those last few bulbs not visibly lit up. He also does this for those few bulbs that he wants not to be seen on the string of lights that go between his front door and two front windows.

Jim

^^^This is what I did years ago, except instead of painting the bulbs I used sections of heat shring tubing to mask the light bulbs.

 

[bad_idea]

Relevant topic. Squirrels shorten our strings quite often. It seems like a waste to toss them just because they are shortened with a little help from natures furry tailed rats.

For your issue, I would buy some solder sleeves and just repair the string. I bought the below kit to replenish my stock recently, haven't used them yet - should be fine, simple enough item. If you haven't used them, they are really simple. Strip both wires, slide the solder sleeve on one side, twist wires together in line, slide sleeve over and shrink with a heat gun or lighter. You'll see the solder melt into the wires. Be careful not to overheat them and melt the shrink tube. The colored bands on each side is a glue that seals the connection from moisture.

https://www.amazon.com/dp/B0CR881Z9L?tag=atomicindus08-20

 

[bad_idea]

^^^This is what I did years ago, except instead of painting the bulbs I used sections of heat shring tubing to mask the light bulbs.

Not the worse plan, better than the electrical tape I have been wrapping them in. The tape unravels by January when I take them down.

 

[mm08822]

I've seen that molded resistor. I'm out of town for work right now, so I don't have access to the light strings. Killing time in the hotel and doing some research for when I get home. I assume that resistor is there to soak up extra voltage in the line to avoid overdriving the leds? If so, figure I could swap the resistor for a larger one after removing a couple bulbs? Is the resistor typically at the start of the line or at the end? Appreciate the info.

Doesn't matter where as long as it in the same series string that is modified. I would assume at the end of the last string modified is the end of the entire set of lights.

 

[dave*99]

There is some wiggle room. Let's say you remove 5% of the total number of LEDs I suspect you can do that without an additional resistor. Just be sure you didn't chop out the original resistor.

Also, consider working backwards from the end of the string at install. If you have a few bulbs leftover at the plug end, maybe the heat shrink on bulb suggestion is palatable. Since you have a joint to an extension cord there it may be easy to just hide that whole assembly.

 

[kbuhagiar]

Not the worse plan, better than the electrical tape I have been wrapping them in. The tape unravels by January when I take them down.

I used the same strings for seven consecutive holiday seasons and the shrink stayed put.

 

[mm08822]

Colored cables ties/tape to match wiring.

 

[Higgins]

I am putting some mini led Christmas light strings outside. I would like to cut the strings to custom lengths to get rid of that remainder that hangs down. These are the typical multi-color mini led light strings you get from Lowe's, Home Depot, Wal-Mart, etc. For instance, I have a string that is 4 bulbs too long. I would like to cut the string down and put a resistor in line to take up the difference so that the remaining bulbs are still supplied the appropriate voltage. I have watched a bunch of YouTube videos on it and people have interesting methods to identify the needed resistor size. Seems to me, I can cut the unwanted portion of the string off and measure the resistance through it with my multimeter (have a quality Fluke) and install a resistor with the same resistance. Sound about right?

do the led lights get hot??

What about putting shrink tubing around them shrink the tubing?

 

[bad_idea]

There is some wiggle room. Let's say you remove 5% of the total number of LEDs I suspect you can do that without an additional resistor. Just be sure you didn't chop out the original resistor.

Also, consider working backwards from the end of the string at install. If you have a few bulbs leftover at the plug end, maybe the heat shrink on bulb suggestion is palatable. Since you have a joint to an extension cord there it may be easy to just hide that whole assembly.

You might be a genius. Hadn't considered stringing the lights from the end and working back. The extra at the start of the strand won't be an issue at all in this situation. Sometimes I worry I might be a dumb ***.

 

[dave*99]

You might be a genius. Hadn't considered stringing the lights from the end and working back. The extra at the start of the strand won't be an issue at all in this situation. Sometimes I worry I might be a dumb ***.

Ask your wife - they usually know. Good luck.

 

[tarmy]

Ask your wife - they usually know. Good luck.

Usually?

If you EVER want positive affirmation from any woman…especially my wife…ask, “dear, am I a *******?”, or “ am I (enter anything related to what we idiot male types often do)?” And you will get that affirmation.

been married near 45 years…I got all kinds of affirmation…

 

[dave*99]

Usually?

If you EVER want positive affirmation from any woman…especially my wife…ask, “dear, am I a *******?”, or “ am I (enter anything related to what we idiot male types often do)?” And you will get that affirmation.

been married near 45 years…I got all kinds of affirmation…

So, positive reinforcement from your bride. We all strive for that. Kudos.

 

[rsanter]

For 4 lights too long?
coil the end up and use a zip tie.
then wrap the part with the extra lights and tuck under the eve

 

[bad_idea]

For 4 lights too long?

This is Garage Journal, a forum dedicated to going over the top. If good enough were the option we all wanted, we wouldn't be on the forum.

 

[Thorold]

You might be a genius. Hadn't considered stringing the lights from the end and working back. The extra at the start of the strand won't be an issue at all in this situation. Sometimes I worry I might be a dumb ***.

He is indeed a genius. Glad i read this before starting this morning.

 

[rsanter]

This is Garage Journal, a forum dedicated to going over the top. If good enough were the option we all wanted, we wouldn't be on the forum.

Good enough is fine for little **** so I can get back to my real projects in the shop