Why Three Wires in Xmas Light Strings?

strangelove · Post by **strangelove** » Thu Sep 17, 2009 2:15 pm

I pose this question, in a rather muddled way, via video. What is the purpose of the 'third' wire in a typical string of outdoor LED xmas lights?

Johnnycrash · Post by **Johnnycrash** » Thu Sep 17, 2009 2:38 pm

Does it have an AC outlet on the end?? If so, then the third wire runs power from one end to the other so you can plug another set into it. Think of it as a regular extension cord, and the lights are wired between the two normal wires, like a lader, or in electronic/electrian speak, in parallel. If one light goes out, the rest will still work. As well, it will not kill power to the second string.

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OK. It's a little more complicated than that. But it is hard to explain without 27 8x10 glossy photos with circles and arrows and a paragraph on the back
of each one. But that's the gist.

mhvink · Post by **mhvink** » Fri Sep 18, 2009 1:48 am

"OK. It's a little more complicated than that. But it is hard to explain without 27 8x10 glossy photos with circles and arrows and a paragraph on the back
of each one. But that's the gist.
_________________
John Fleming "

You can get anything you want at MMI's restaraunt, 'cepting Johnny.

Stu Pidasso · Post by **Stu Pidasso** » Fri Sep 18, 2009 2:23 am

You're wrong.

THERE. ARE. FOUR. WIRES!

strangelove · Post by **strangelove** » Fri Sep 18, 2009 5:58 am

But which one do I cut? The red one or the blue one? Red? Blue? Red? Blue? Tick tick tick . . .

DaveVan · Post by **DaveVan** » Fri Sep 18, 2009 7:23 am

The string of LED Christmas lights I bought were 4 volt lamps. Thus the lights were wired in a series so the total was 120 volts. When I cut them up I cut them up into group of 3 as I use old 12 volt wall mounted power supplies to power the LED's. The combination of wires 'controls' the voltage in a way by having the correct number of bulbs together. More confused???

strangelove · Post by **strangelove** » Fri Sep 18, 2009 7:36 am

These LEDs are 35 in one string. The listed specs are: 120V, 60 Hz, 0.02A. 2W.

Each string of 35 lights totals 2 watts. The strings may be joined together for a total of 420 or so watts. As I only need about 120 lights I will not come close to the allowable limit here.

After brief experimentation and one short (which thankfully did not blow any lights or kill me ...) I have eliminated the 'third'. Now I simply 'splice' more lights on top the string as I build each section of the model and thus keep everything in one long closed circuit. In other words, I'll have 120 LEDs on one wire that loops throughout the inside of the model and out again to the plug (one wire, two ends of the loop . . .).

Not ideal but ...

See my blog for related visuals.

seam-filler · Post by **seam-filler** » Fri Sep 18, 2009 8:01 am

And when one LED blows the whole lot will go dark. That's the problem with series.

strangelove · Post by **strangelove** » Fri Sep 18, 2009 9:43 am

Drat, I should have thought to test that before sealing the saucer... I just smashed one light in the series and yes, the whole string went dark. I was told by someone else that each bulb had an internal bypass, but that must be the function of the third wire. Oh well, the lights are rated for three years use. This was a test 'learning build' anyway ... lesson number 26.

strangelove · Post by **strangelove** » Fri Sep 18, 2009 10:47 am

There are some very narrow sections at the rear of the shuttle bay in which I would like to insert some lights. The xmas lights are much to big, even after wittling away unneeded plastic.

Forgive my extreme ignorance here, but given the LED string's specs -- 120V, 60 Hz, 0.02A. -- I assume that I could add a bulb that is rated for 0.02A at 60 Hz. Is this correct?

What should I be looking for here at my local Circuit City?

brt · Post by **brt** » Fri Sep 18, 2009 10:49 am

Are the pink domes on the LEDs removable?

Johnnycrash · Post by **Johnnycrash** » Fri Sep 18, 2009 10:51 am

strangelove wrote:I was told by someone else that each bulb had an internal bypass, but that must be the function of the third wire.

The third wire is there JUST to supply power to the extension cord function. And yes, the bubs do have a shunt for when a bulb goes out. But, they almost never work. Hey! What to you want for $3.99.

(or whatever the cheap price that was paid)

strangelove · Post by **strangelove** » Fri Sep 18, 2009 11:11 am

Johnnycrash wrote:
strangelove wrote:I was told by someone else that each bulb had an internal bypass, but that must be the function of the third wire.
The third wire is there JUST to supply power to the extension cord function. And yes, the bubs do have a shunt for when a bulb goes out. But, they almost never work. Hey! What to you want for $3.99. (or whatever the cheap price that was paid)

I did quite a job of smashing the bulb, so I probably destroyed whatever element was to act as a shunt. Good news none the less.

The bulbs were not that cheep. 20$ CNC for a messly string of 35, on sale at Sears for around 12$ (still pricey...).

Bad news that the shunts almost never work -- can anyone else confirm this?

strangelove · Post by **strangelove** » Fri Sep 18, 2009 11:14 am

brt wrote:Are the pink domes on the LEDs removable?

Yes, I just discoveredso this morning. This still leaves the very bulky plastic molding below the bulb in which the wires are buried. I will be able to sand and cut this down quite a bit but not enough.

tetsujin · Post by **tetsujin** » Fri Sep 18, 2009 5:33 pm

Never understood why anybody would want to go buy a string of "white" christmas LEDs just to cut them up, and hopefully pull them apart sufficiently just to get their hands on 30 or so blue LEDs...

strangelove · Post by **strangelove** » Fri Sep 18, 2009 7:37 pm

tetsujin wrote:Never understood why anybody would want to go buy a string of "white" christmas LEDs just to cut them up, and hopefully pull them apart sufficiently just to get their hands on 30 or so blue LEDs...

That is not what I get nor what I am doing . . .

DaveVan · Post by **DaveVan** » Fri Sep 18, 2009 8:12 pm

Never understood why anybody would want to go buy a string of "white" christmas LEDs just to cut them up, and hopefully pull them apart sufficiently just to get their hands on 30 or so blue LEDs...

60 white LED's for $1 at close out last year seemed like a good deal. And the fact they work so well for me.....worth every penny!

strangelove · Post by **strangelove** » Mon Sep 21, 2009 2:13 pm

Could a string of xmas LEDs be rewired to prevent a single bulb failure form cutting power to the whole string? See the attached diagram, where an xmas light string is turned into a single loop, with two connecting wires branching off the loop for each blub. Keep in mind that I have zero wiring knowledge . . .

en'til Zog · Post by **en'til Zog** » Mon Sep 21, 2009 7:01 pm

Whatever you do, guys, do not ever put 110 or 120 volts into a model - full power line or mains current. That puts LETHAL power into a breakable model which could cripple or kill someone.

Always use 12 volts or lower from batteries or a "wall wart" or power converter like you would use to recharge a battery powered gadget.

strangelove · Post by **strangelove** » Mon Sep 21, 2009 7:54 pm

While I agree that a breakable model is a hazard, so too is a lamp, an aquarium, xmas trees, and many pieces of electronic art -- all running on 120 volts, all breakable. So as a piece of electronic pop art, I do not see the rationale for excluding 120 volts as a source.

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