Christmas Lighting

[DRAYCO]

Ok, first I'm not sure that this is the best place to ask a question about this,

But this is the only place I know where there are smart ppl in electronics, and well I've always get many good answers to my questions in the past, so thanks for that.

Well, alright, the one thing that is related to this site, is that I'm saving allot of power to go with LED Christmas lights only, this year and last, so all my displays are so cheap in running that its about 2 dollars (CDN) I figure I'm spending on running them.

Well, you may or may not know, but LED Christmas lights are fixed, they cannot be removed and switched around like the traditional ones, so that brings me to my problem, I've got some of those spinning things and light up little figures that used to use. Besides other then just putting one string of traditional to solve that, I'd rather not do that.

So, I figured that, each light, most introduce a voltage drop as the more you put on, If say I have a set of 50, and 25 of them are dead or just weird to bypass the light part, the rest of the set becomes allot brighter,

I took apart a set, and cut out a section, leaving only 5 lights, and as soon as I connected it, it all blew; they became real bright for a sec, and then died completely.

So I figure I need to create some sort of dummy load to give the impression that there are 45 lights that are not there, so that the remaining 5 will work normally, and allow me to connect up my little tree figures, with out blowing them up

now I know this is likely AC power, on a string of Christmas lights, so I'm not sure, if you can connect up those, um forget their names, to it to create that load or not

That is what I want to know, what I'll need to pull this trick off?

If anyone can suggest or help me in this question, I'd appreciate it.

p.s. I'd think that next year, someone will create a consumer product similar to what I'm trying to do, I can see it now, but I don't want to wait

[Nando]

DRAYCO:

Short to the point : LEDs run from 1.8 ( Red, green, yellow) to 3 volts ( white)

The do not need voltage they need current so the voltage source needs to have a resistance in series to protect them.

Regular diodes use around 20 milliamps.

If you have a string of 5 LEDs: 1.8 * 5 = 9 volts and if you have 12 volts dc then

(12 v - 9 V)/20 milliamps = 150 OHms in series with the string,

Power = (V^2)/R = (3*3)/150 = 0.06 watts is the dissipation of the resistor, therefore you need to get one that is at least 3 times higher wattage,

Use 1/4 Watt 150 ohms resistor and you will be safe.

Regards

Nando

[LEXX]

I think what nando is trying to say is this: If you have a string of lights that needs a certain amount of current then your resistance has to be of a certain value.  If you have cut out 45 of the 50 lights then then voltage across each one will be 10 times as high as it should be and the current will also be 10 times as high resulting in a POOF!  What you need to do is measure the resistance across the 5 LEDs that you have remaining, lets say for the sake of arguement that it is 10 ohms, that would mean that you need to have a 90ohm resistor for a total of 100 to get the voltage and current to the proper level.  like he said a resistor in the 150 ohm range would be big enough for sure but it might be too big, just measure the resistance out, multiply by 9 and that will be the value of the resistor that you need.  Remember that resistors create heat as their way of dissapating energy so don't cover them with anything very flammable, it will only be a very small amount but still, be on the safe side.

LEXX

[nothing to lose]

The other guys gave more detailed info but this is simple and what I do many times.

Take a few 1.5v batteries like AA, C, D ect.. and try one led. If it lights nicely and does not burn out then 1.5V is what to use. So wire 8 leds in series for 12Vdc  or 4 leds for 6Vdc ect.. If they don't light then take one out.

 If the leds do not light at 1.5v then I connect 4 leds in series and 3 batteries, That's about 6Vs of leds on 4.5Vdc source, if works nicely I use that, if not I take out 1 led and see if that works, if not I take out another.

Nice to know that a color LED is 1.8V and white is 3V, you can add that up for close to the correct volts then go an extra led or two for safty. Then if not working take out 1 led or two if needed. 12vdc source with all color leds then should be 6.66 leds, 7 should work nicely and not fry them. Myself I would rather heve the extra light instead of wasting the power with a resister.

For all White at 3V that would be 4 leds even at 12v.

I would like to point out that as I recall the leds Christmas lights I used "SEEMED" to be a little different than normal ones. They may be the same 1.8V for colors but I think they seemed to be a little over maybe. Been a year, so not sure. This year I can't find them, I have 1/2 a string I never used yet  but where did they go?? Any way I think the ones I had worked fine at 1.5-2v each.

Also

"but LED Christmas lights are fixed, they cannot be removed and switched around like the traditional ones"

Either I read that wrong or you have something a bit different than I had. My string was exactly like normal little twinkle lights except they were leds instead. They had they little sockets, pull them out and the led leads were bent around the sides same as the twinkle lights. Just pull the leads straight and pull them out of the holder. I could put any light in any holder, mine were all color leds. No whites.

[wooferhound]

 Here is a handy series resister calculater for LEDs

http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm

[richhagen]

I would recommend placing resistance in series with the LED's as when they fail, they often do so by shorting.  If you have nothing to limit the current, your whole string would likely fail with the first LED.  I like Nando's evaluation.  If you can get an efficient switching 12 volt (or other low voltage) supply, like from an old lap top or such, use that to provide your 12 volts, and then run your LED's in series with a resistor off of that (V = I*R).  

The color of light given off by an LED is generally a function of the voltage drop.  Blue light has a higher frequency than red light. The energy in a photon of light is equal to the frequency of the light times a constant value or ratio, which is called Plank's Constant.  Since the speed of light is the same for all frequencies, the energy could also be described as being equal to Planck's Constant multiplied by the Speed of light and divided by the wavelength.   Thus a photon of blue light has more energy than a photon of red light.  Energy is conserved across the P/N junction.  so the voltage drop for a red LED is less, often about 1.7 volts compared with a blue, often about 3.6 volts.  White LED's are actually blue or ultraviolet leds with a phosphor coating which absorbs most of the generated wavelength and re-transmits the energy as a combination of wavelengths of lower energy.  Think of a rainbow, the light wavelengths have more energy as you travel from the red to the purple side.  LED's follow the exact same pattern, with highest voltage drops on the ultraviolet end and lowest on the infrared end.  The differences with LED's are that there is internal resistance in the LED itself, the amount depending upon how it is made, which can cause a higher voltage to be required across the leads than is actually required to generate the LED's light frequency for any practical amount of current.    Rich Hagen

[nothing to lose]

Hmm, you may have a point, I don't like those "IF one goes out they all go out" old time Christmas lights, don't want the leds to all fry if one goes out, so maybe the resistor would be a good saftey measure for that. SO far I haven't needed it, YET.

As for the led colors. I don't know what he has for the light string, but mine were colored plastic and most likely all the same led inside. Maybe all whites shining though red or green or blue plastic. Really just a little glowing light inside plastic is all they were, but all one piece, not like an led with a plastic cover over it.

I do have real leds that all are clear when off, then some are UV, red, ect.. when lit.

Kinda hard to tell whats what if they get mixed unless I put power to them. Definantly not the same thing as the Christmas lights leds I had but more like whats being mentioned here probably.

[ghurd]

You are 'mixing apples and oranges'.

it will take a balancing act to get the parts to work in series.

One is current driven, one is voltage driven. Simplified.

G-

[DRAYCO]

actually, i wasn't totally talking about what everyone answered my question to about.

I was talking about, how the fact i've got LED lights, and that they are fixed bulbs, so there is no putting in those spinny things or those additional light up thingys for the tree,  only the traditional lights can do that,  and i was wanting to know what to do, to take a traditional set, and cut it down to only having 5 bulbs on it, 5 outlets more or less, becasue i'll be putting those spinny and lighty up things into them, and spreading them around the tree

so i figured someone here could tell me, what i would need to do, i figure personally i need something to make a load so that those only 5 bulbs feel as if there are 45 more, but there isnt,  there is some sort of dummy load thing there instead.  

does that clear things up a little ?

[nothing to lose]

OH.

Well I don't know what you would do then for a dummy load?

If your talking the standard mini twinkle type lights everyone normally uses, they are usually 1.5V or the super brights I think are 2V.

I think if it were me I would just run those 5 lights on rechargable batteries or a wallwort transformer. They sell those strings of about 5 and 10 lights that run on batteries.

 The little spinning motors to rotate ornaments are the same volts also since they plug into the light sockets normally.

I don't have any handy to test with but I think you could just cut off 6 sockets/lights already wired in a row and use a 12V wallwort transformer wired to the set. If you try that, run it for several hours (or all day) laying out safe and check for any heat problems with wires or the wallwort. I do that kind of stuff all the time with twinkle lights but not exactly what your doing so test first. You might want to try 8 lights first incase you have the 1.5V bulbs, if they are dim then cut off one at a time till you get the correct brightness. Or just test 1 bulb first on a 1.5v battery and see how bright it lights.

Of course the wallwort transformers come in all kinds of powers. If you have one laying around from a junk scanner or printer it should probably work ok, just match the volts for the lights to the transformer in case you have 9V or 12V, if it can run a scanner/printer it should have the amps to run a few lights. Beware of those wallworts for things like cheap speakers and such, they are often low power and may NOT run the lights. It should have the amps  or miliamps listed with the volts on it.

Anyway that's what I would do, either rechargable batteries or a good wallwort transformer.

[tawa]

First, LEDs run on DC not AC. So plugging in LEDs into a standard XMas light string may have bad consequences. For my LED projects I got an AC to 12vdc convertor from this guy on ebay (gongadealz): http://stores.ebay.com/id=16792258  

Only $8 including shipping.

Then from www.allelectronics.com I got a cig adaptor with bare wires, plus some resistors. Now I have 12v to play with for my LED projects. Not a lot if I start using those high brightness LEDs which take up to 4vdc, but it's a start. Allelectronics has great prices on stuff but their shipping is $6 I think, so it pays to make a bigger order.

[tawa]

I should probably add that the convertor converts 110vac to 12vdc. But they have other convertors too.