# Problem with Christmas lights burning out



## asugrads

I have a two small trees that have a short strand of Christmas lights intertwined amongst the branches. The light strand is not removeable. They worked fine for a while and then I noticed that the lights became very bright and hot! Suddenly, they all burned out. I replaced the bulbs and got them working again, but they were again really bright and hot and again they burned out within a few minutes. The fuses are good and I have tried them in my house and my neighbors and I am having the same problem! Can someone please help me!
Thank you!


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## dSilanskas

Sounds like the light bulbs you are replacing them with can't wait the voltage that is being sent to them. Are they the proper bulbs that it says?


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## DangerMouse

how long have they been out there? and why can't they be replaced?

DM


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## dSilanskas

MdangermouseM said:


> how long have they been out there? and why can't they be replaced?
> 
> DM


I think he means that they are part of the tree. One of the fake ones


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## DangerMouse

oh, i get ya.... ive seen those. perhaps a wire is shorting and increasing voltage? are they wired in series or parallel? (if one bulb goes out, do others stay lit or do they all die?)

DM


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## asugrads

Well, if one bulb is out, the others do stay lit. I just replaced every bulb AGAIN and they are still burning like a supernova! They are so bright, they hurt my eyes! I am using bulbs from a regular strand of Christmas lights. By the way, I have two of these small, fake trees and the other one that I fixed is working fine. I just can't figure out why this one is burning so bright! I appreciate your help!


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## asugrads

*Photos of lights*

I added a few photos of what the trees look light when turned on. Obviously, the one on the right is the one that is burning way too bright!


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## jamiedolan

asugrads said:


> I added a few photos of what the trees look light when turned on. Obviously, the one on the right is the one that is burning way too bright!


What watt / volt are the light bulbs you are installing?

Are there transformers in these or do they run right off 120v? 

Have you put the bulbs that are in the left one into the right one to see what happens?

Jamie


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## InPhase277

Alot of Christmas light strands are wired series-parallel. This means that groups of lights are wired in series, say five or six, and each group is in parallel. So, removing one lamp will kill five lights but the rest stay lit. It sounds like there is a short somewhere that would cut across all the groups', allowing a higher voltage to appear across each individual lamp. Perhaps it is in the middle of the circuit, or between just a couple of wires. There is usually three wires at any spot in the string: a hot bringing 120 V to each group, a "neutral", and one series wire for the next lamp in a particular group. If you got short at the right spot, then I could see how the series-parallel balance could be upset.

But what are the chances that the short would have an effect on EVERY light. Seems more likely that some lights would be super bright, and others would be normal, and still others may not burn at all. Are you sure that every single light is doing this?


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## DangerMouse

InPhase277 <---what he said. oh wait, i said it too! ok, he said it better! since these are 'permanent' wired, and probably chinajunk, the only option is to replace the whole thing. could be dangerous. but what do i know? i'm just a mouse...

DM


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## tribe_fan

*I suspect you are using the wrong voltage bulbs - personally I would find a way to put a new string on the tree if possible.*

*http://www.ciphersbyritter.com/RADELECT/LITES/LITESFAQ.HTM*

*I have an old decoration that uses 10 bulbs; can I use modern replacements?*

In these series circuits, the 120V line divides equally across each light. So in 50-bulb circuits, the bulbs run at 120V / 50 = 2.4V. Similarly, 35-bulb circuits use 3.4V bulbs, and a 10-bulb circuit uses 12V bulbs. We cannot expect to replace 12V bulbs with 2.4V bulbs. However, modern, fairly-cheap 10-light, 20-light and 30-light sets and replacement bulbs have been available on the net. My approach would be to get 2 or even 3 new strings each having the same number of bulbs as in the decoration. Then I would replace all the old bulbs with new ones, and keep the remaining string(s) for future bulb replacements.


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## asugrads

Thanks to everyone for your help! I think, after reading everyone's advice, that I may try to find a shorter length of Christmas lights and use those bulbs as replacements. Each bulb is equally as bright as all of the others, so I think the theory that it is a short is less likely. The bulbs that are in the tree now are from a 100 light string and there are only about 25 lights on the tree. If this doesn't work, I will just try to remove the whole string and replace it, which will be more work than it is worth, I am sure. This thing may be made in China, but whoever wired it with those lights did a bang up job! 
Thanks again for all of your help!


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## theatretch85

This is exactly what is going on! Ive fixed thousands of stings of lights over the years, and I try to stay far away from the 10-35 light sting setups. The bulbs for those tend to be harder to find than the standard 50/100 light strings.



tribe_fan said:


> *I suspect you are using the wrong voltage bulbs - personally I would find a way to put a new string on the tree if possible.*
> 
> *http://www.ciphersbyritter.com/RADELECT/LITES/LITESFAQ.HTM*
> 
> *I have an old decoration that uses 10 bulbs; can I use modern replacements?*
> 
> In these series circuits, the 120V line divides equally across each light. So in 50-bulb circuits, the bulbs run at 120V / 50 = 2.4V. Similarly, 35-bulb circuits use 3.4V bulbs, and a 10-bulb circuit uses 12V bulbs. We cannot expect to replace 12V bulbs with 2.4V bulbs. However, modern, fairly-cheap 10-light, 20-light and 30-light sets and replacement bulbs have been available on the net. My approach would be to get 2 or even 3 new strings each having the same number of bulbs as in the decoration. Then I would replace all the old bulbs with new ones, and keep the remaining string(s) for future bulb replacements.


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## tribe_fan

Last Christmas I spent 4 hours and 15 dollars for a tester on one of those [email protected]#$ trees - It was like putting flash bulbs in there ! 

I gave up, bought a strand for 1.99 and replaced the string - was not really that hard........ even if you have to cut the old string off.


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## BigCougarJohn

So within any given series section, one "burned out" light bulb will cause the entire section to not work, is that correct?


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## dmxtothemax

The two most likely problems are !
The voltage is too high,
(ie 110v lights on 120v.)

Or wrong lamps
(wrong voltage)

Please check both !

Check the manufacturers specs.
most are available on line.


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## jamiedolan

dmxtothemax said:


> The two most likely problems are !
> The voltage is too high,
> (ie 110v lights on 120v.)


Really? +/- 10volts on resistance bulbs is going to cause a problem?


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## AllanJ

Replacement mini Christmas tree bulbs also have an amperes rating that is usually not published. Mismatched amperes ratings will also cause some bulbs to be overvoltaged even if all of the bulbs in the string or zone are working.

Because stating amperes rating let along stating the instrucfitons on how to use the amperes rating adds tot he complexity of replacing the bulbs, they odn't publish it and hope that mismatch is not too bad in practice. You can get a hint that the amperes rating is different if the bulbs are labeled "super bright" which means more amperes drawn.

It is actually the lower ampere rating bulbs that will burn out first if you mix and match them.


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## Red Squirrel

Some of the newer series mini lights actually have some kind of bridge mechanism where when the light burns, it activates, so it does not break the circuit. Leave too many lights burn, and the voltage to all the lights will be too high. 

That may be the situation. Which reminds me, one of my lit garlands outside just stopped working, I should probably go check that out, but I'm too lazy. The bridge does not activate 100% of the time, or maybe I left too many bulbs burn... do as I say, not as I do lol.


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## jbfan

Thread is over 3 years old!


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## BigCougarJohn

So the bridging mechanism must be in the mini light base so that when the bulb is removed the series circuit remains connected, correct?


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## McSteve

Nope, the bridging mechanisim, usually called a shunt, is in the bulb itself, and closes when the filament burns out. So a string of lights may work properly with one burned out bulb, but not with one removed bulb.

The gotcha, as mentioned in another post, is that if too many bulbs burn out and shunt themselves, eventually the current in the whole string gets too high, and the rest of the bulbs will all burn out nearly simultaneously.

Not all bulbs have a shunt, though, and the shunts don't always close when the bulb burns. Some of the christmas light tester gadgets have a feature to put a high voltage pulse through the string to get any bad bulbs to close their shunts.


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