Extending Xmas mini-light string

I read in sci.electronics.design that GJWK wrote (in ) about 'Extending Xmas mini-light string', on Sun, 5 Dec 2004:

Yes, but it's not very safe. Over 1200 ft, the wire could easily be damaged and not noticed, and someone could get a bad electric shock.

See below.

No. More wire resistance reduces the voltage and current.

No. In a series circuit, the current is the same everywhere. All the lamps might be dim, but none will be if your wire resistance is low enough.

Running off 120 V? I doubt you have lamps rated 0.8 V 0.5 W. We can't advise you further because of lack of key data, and we need to know either the rated voltage of one lamp or how many there are in a 120 V string.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

You seem to think that a "single string of Xmas mini-lights" has

150 bulbs in it ("twelve hundred feet or one light every eight feet along a fence line") instead of the usual 48.

Here is a refresher on how the lights work:

Here is the wire data you need to know:

I could walk you through the math, but there is a simpler way given your skill level.

Here is how you do it:

Keep the wiring exactly the same, but replace each short length of wire between bulbs with an eight foot length of 12AWG stranded lamp

That's it. It will work fine.

Safety is another issue, though. Some person could be shocked by the mains AC voltage anywhere along the line. Especially if the OP adds his or her own bogus splices at every bulb.

To do this safely, one would need to use properly rated wire with some kind of outdoor rated lights and junctions and so on.

Maybe it would be better for the OP to just use short strings of LED's, with alkaline battery packs powering them. Maybe 10 LED's per battery pack of 4 D batteries.

At least there will be no fire or risk of shock.

--Mac

Unfortunately

to

a I

plus

It would need more information to answer that. The main item being the supply voltage. IMHO it would not be wise to use mains in that situation but of course with an extra low DC supply the current would occasion the need for heavy (read expensive) cable. If the lamps are 0.5watt x 150 gives 75watts, by putting your supply voltage into the formula "Watts/Supply volts" you will get the current required (With the lamps in series this will need a high voltage, see comment 1). If you put the lamps in parallel, (which would not be your average "Xmas string" for the tree) using the same formula you will see that the supply at

24v will need cable that will support about 3.2 amps. If you can source cable of about 18 guage for that length it would probably suffice, since the dimming effect would be gradual along the length IMHO it wouldnt be all that noticeable. Personally I would connect such a string as a 'ring' if at all possible and that would reduce any dimming to minimum. One can not simply 'extend' mini lights in series since the number of the lamps determines the voltage that is applied to them. Remember when posting to always add the voltage, lamp power and supply volts to get a better answer !

-- Regards ..... Rheilly Phoull

Thank you all for your help. I'm sorry for the delay in my response I was at a birthday party and didn't get back till late. So what I have is this. I am aware that a 150 light strand is in fact 3 strands but did not realize why until I followed Guy Macon's links. So I think what Rheilly, Guy and Mac's advice boils down to is that if I am very careful to splice safely I can do it but I will need to create 3 sets of fifty lights. And if I'm right each set will draw about 50 watts at 120v .42 amps? The first set can use 18 AWG wire. The second set 16 and the third will need 14. (See below)

0 400ft 800ft 1200

14 AWG __________________________________________

18 AWG__x__x....x__x__| | |

16 AWG ________________x__x....x__x__| |

14 AWG ______________________________x__x....x__x__|

If the above diagram shows up correctly I think it shows my intentions.

Leaving the following parts list:

2400ft 14 AWG

800ft 16 AWG

400ft 18 AWG

100 each 14, 16 and 18 AWG splices (I can't remember what they're called).

1 150 light mini-light set.

Many hours of cutting, striping and splicing

Leaving two final questions can I use the original fused plug from the mini-light set or do I need to pick something up at Radio Shack? And can I get away with lesser gage (cheaper) wire.

I just called a supply store and priced all this wire a about $200. This is not totally unacceptable but does mean that it will have to be something I prepare for next year. Any suggestions, cautions or better ways to place 150 some lights on 150 some fence post will be eagerly read.

Thanks again

Geoff

Unfortunately

to

a I

plus

I had a "Well D'oh!" moment. I don't intend to sequence the lights so I'll just string the lights with 18 AWG and have 3 strings in parallel fed by 14 AWG. I might drop the strings to 40 bulbs to make them brighter.

0 400ft 800ft 1200ft

14 ________________________________________

18 x__x__x__x_| x__x__x__x__| x__x__x__x__|

14 _|____________|______________|

I'm not sure about LED's. This setup would require 15 4packs of D cells(10LED's each). How long would they last? It could get very inconvenient and rather expensive.

Unfortunately

to

a I

plus

Check the prices for overdesigning it by using 16/14/12AWG instead of 18/16/14AWG. Also check the prices for using nothing but 12AWG.

That seems high. Did you specify lamp cord with your length divided by two (because each length has two wires)?

You can do it with wire nuts or crimped barrel connectors.

A thermal stripper is a great tool for this sort of project.

Should be fine.

How much loss of brightness and golden rather than white color are you willing to tolerate?

Use blobs of RTV to keep the weather out of your connectors.

Consider whether LEDs will do the job.

Consider using much smaller wire and reducing the number of lamps per series circuit so that the lamp voltage is the same.

My office "tree" (more like a collection of long twigs in a nice pot) has mini-lights on it. I replaced one of them with a 1N4007, so the bulbs last a few years 24/7.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Minilights are a poor choice if you want reliability. The brighter you run them the more likely a series section will fail completely. I've rewired and re-lamped strings for 60% stress - resulting in yellowish (read 'golden') light, but they run longer, if not mechanically banged around. These are used all year round.

The expense of these things is in your labour and in your liability. The lamp bases are constructed with crimped soffit terminals that are reasonably safe. You are still warned to remove power before replacing lamps. I expect few people do. 1500 feet of wiring is about 50x the liability, regardless of the number of lamps involved.

Rope lights that use similar hardwired incandescent series strings are also available off the shelf. These are imbedded in flexible transparent vinyl that provides some mechanical protection, though the vinyl degrades visibly with time. Wiring your strings in sections of clear tubing might produce similar mechanical and electrical protection, providing they were sealed against moisture.

Series 120vac LED strings are now marketed commercially. These have non-replacable, molded-base bulbs and plastic envelopes (which could theoretically be cut away). They are not prone to mechanical damage. Obviously a different effect when illuminated - depending on the envelope for dispersion effects - but demonstrating that there is a more reliable solution on the horizon.

RL

Instead of the good kind? ;-)

Its a simple matter of measuring the length of an existing light loop and determining its total resistance based on original length * ohms/ft AC reactance for the original wire size. Then, select a wire size that gives the same overall reactance for 1200 feet. Be sire to add in a few milliohms for each splice you will be making. Cut the lamps out of the existing loop and splice them into the new wire. Make sure your home owners liability insurance is paid in full and plug it in.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Telemark:  If it was easy, they'd call it snowboarding.

As long as they don't get banged around, which seasonal decorations tend to, there's only environmental and operating stress to deal with.

Protected from the weather and running at half power, I imagine your office tree will survive quite nicely, until it gets knocked over.

Enjoy.

RL

I think I'll see what a 120 v LED string looks like. The string I'm putting up is alongside a long driveway and is not likely to be a danger to anybody unless the deer decide to nibble of it.

Thanks again

Geoff