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Need Technical Advice For Xmas Light Mods - 11/21/2009 1:18:36 PM

ThatDaveGuy69

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I've been taking advantage of some beautiful late-fall weather over the last few weekends and have been hanging Christmas lights. One of my strings came up about 3' short and wouldn't ya just know it, no one sells a 3' string of lights! So I decided to cut down a 6' string. It's a 2-wire set (as opposed to the better, 3-wire type) so the cut/splice was easy. The problem is that the remaining lights are way too bright and after only 10 minutes they have already left burn marks inside the bulbs. I'm thinking a resistor will solve this but I don't know what size. Can one of you electronics types out there offer some advice?

Thanks!

~Dave

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RE: Need Technical Advice For Xmas Light Mods - 11/21/2009 4:01:21 PM

MasterG2kTR

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Don't use the modified string!! The bulbs are essentially resistors and must all work together to achieve the appropriate resistance. They act in a closed loop circuit to do this. Not enough resistance and you will get what you see, bulbs burning too bright and also overheating their wires potentially causing a fire. When you buy (yeah right like anyone ever does....lol) replacement bulbs for light strings, they are always rated for a certain size light string (35, 50, 75, 100, 150, 200, 300).

You could however use your modified string IF you substitute the proper bulbs for the number of sockets you have on it.

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RE: Need Technical Advice For Xmas Light Mods - 11/21/2009 5:12:01 PM

GreedyTop

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I think I just puddled.

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RE: Need Technical Advice For Xmas Light Mods - 11/21/2009 5:39:00 PM

rockspider

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Well there really is several ways of doing it.
The one needs a socalled variac, which unless you do have one handy probably set you back more than 10 new lightchains. I got some laying around but then i am a pro who often experiments.
Another is using a light dimmer if you got one of those handy.
The resistor as you mentions needs a multimeter to measure the current. As the voltage is given it is Ohms law U= I * R to calculate resistor. But as this is a resistor more than ,5W it is often a bit tricky to get.
Really if you don't have an electrical workshop containing all sorts of crap collected over the years, those chains so cheap it isn't worth the hasle. Even i would probably just buy one that fit.

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RE: Need Technical Advice For Xmas Light Mods - 11/21/2009 5:57:03 PM

DarkSteven

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I think dollar stores sell strings of Christmas lights. For a dollar.

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RE: Need Technical Advice For Xmas Light Mods - 11/21/2009 6:42:12 PM

Rhodes85

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Shush Steven....we're trying to be technical here

Though I used to buy those dollar store lights....half the time they never worked right and one time I nearly electrocuted myself on a string of them.

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RE: Need Technical Advice For Xmas Light Mods - 11/21/2009 7:56:22 PM

pahunkboy

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Gosh- I am still searching for my Christmas lights.... from last year! hehe

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RE: Need Technical Advice For Xmas Light Mods - 11/22/2009 10:37:49 PM

Termyn8or

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Not that hard if you get the volt and watt rating off the bulbs. What you describe indicates the bulbs are in series. As such first, how many are you using and how many not ? If you are using half of them it is the same thing as plugging them into a 240V supply instead of a 120.

Now let's say for example that the original whole string had 12 lights in series. Now assuming they are say five watts each, you know they are in series so they must be 10 volts, with those figures you can extrapolate the current drain. Then it is a simple matter to just use a resistor except for a few things. For one it is a waste of power, and for two because of the waste of power it will dissipate significant heat.

Even if you do this, note that resistance measurements will do no good. You need to know what the resistance is when they are lit up, and it is quite a bit different than what you would read on an ohmmeter. But the whole idea sucks.

What I would do is go get the cheapest light dimmer I could find, at a DIY type store or even a dollar store in some cases. Just turn it down until the brightness matches. Much easier and more energy efficient.

A modern light dimmer works by subtracting voltage, and when dimmed any fluctuations in line voltage show up more prevalently. This is the only disadvantage. I mean when your compressor starts this string will dim more than the other strings. For a small fee I can design something to eliminate that effect, but really, why not just hide the bulbs you don't want seen ? Clear it up all in one fell swoop.

T

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RE: Need Technical Advice For Xmas Light Mods - 11/23/2009 6:20:19 PM

trappedinamuseum

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quote:

ORIGINAL: DarkSteven

I think dollar stores sell strings of Christmas lights. For a dollar.

Steven, I think I love you.

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RE: Need Technical Advice For Xmas Light Mods - 11/23/2009 7:28:31 PM

Hierodule

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I'm not a super technical person but cant he just jimmy rig some kind of variable resistor at the spice? Isn't that what a dimmer switch is? Put it at the splice with some connector nuts, a little electrical tape and then adjust the resistance. Is that asking for an electrical fire? If the lights are in series (one gets pulled they all go out) the resistances ad up to one value don't they? If it was parallel I could see it being complicated but I have a very basic grasp of electronics. I would try it but I circuit bend. :-)

A new string or lights might be a better idea. Esp. If this is on the roof or some where dangerous.

< Message edited by Hierodule -- 11/23/2009 7:29:41 PM >

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RE: Need Technical Advice For Xmas Light Mods - 11/23/2009 8:30:06 PM

Hierodule

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I really want someone to tell me why this wouldn't work. I'm not saying it would. I just want to know why it wouldn't.

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RE: Need Technical Advice For Xmas Light Mods - 11/24/2009 7:12:26 AM

Termyn8or

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Hier that is a potentioneter. The one in the picture won't work because it is not a high wattage type. Even a high wattage type will simply waste the extra power in the form of heat.

A light dimmer on the other hand works by turning the power on and off very fast, and thus dissipates very little power.

The only other reasonably efficient way to accomplish this would be with a step down transformer. Not quite as efficient but would be easier on the bulbs because it would output a sign wave, while a "chopping" type dimmer does not.

T

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