I have several sets of led Christmas lights. 60 bulbs 3 wires with 120 ac plug.
How much extra wire can I add to the set before it blows? I don't want lights below the train board but they are only 5 inches apart. I want to add wire between some bulbs. How much is safe?
iwander I have several sets of led Christmas lights. 60 bulbs 3 wires with 120 ac plug. How much extra wire can I add to the set before it blows? I don't want lights below the train board but they are only 5 inches apart. I want to add wire between some bulbs. How much is safe?
GACK!
Are you working with a 120 volt set? LION would not play with those.
The LION takes the LEDS out of the wires and holders. He keeps the LEDs and discards the rest. Now he has pile of LEDs on his counter. One leg is (+) the other leg is (-). Add a 1000 ohm resistor to the circuit and you can light the led with 12 volts from your train transformer. If it does not light one way turn the lamp around and it will work the other way.
LION uses these for signals, for station lighting, for the control panel, and for car lights.
Here is one of my stations.
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Break them up and use them like indivdual LEDs. Do NOT try to splice in extra wire then plug the whoel thing in to a wall outlet. Too dangerous. The only thing plugged in to wall outlets for your layotu should be UL listed transformers and power supplies. Only LOW voltage strung around the layout, please.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
To answer the question: If you know what you are doing, any reasonable length is fine.
If you don't know how to make safe splices or what gauge wire to use or have ANY question about how to do this then you shouldn't.
Be aware that by modifying the string you will invalidate the UL or CSA "listing".
The mind is like a parachute. It works better when it's open. www.stremy.net
Those LED strings are a combination of series / parallel wiring - if you mess up the sequence they are wired in, you could be in trouble.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
The 120V is likely stepped down and rectified somewhere, LEDs don't like 120V and they don't work on AC. The 3 wires are so that you can have an LED blow out and keep the others lit. You can take a meter and check for voltage and polarity within the string where you want to add wire length to verify, then splice in according to what length you want(within reason, not like adding 100 feet to the string). These splices IMHO should be soldered and shrink wrapped to support the string weight. But, if the string truly has 120V(which I doubt) throughout its' length--I wouldn't put it around the layout where accidents can happen. Also, are you sure the lights are LEDs, mine are bulbs and run on 3.5V.
Seriously though, the fact you're asking this question and it being a 120V system makes me nervous.
Richard
LEDS work fine on AC. They just light every half cycle, 60 times a second.
Train Modeler The 120V is likely stepped down and rectified somewhere, LEDs don't like 120V and they don't work on AC. The 3 wires are so that you can have an LED blow out and keep the others lit. You can take a meter and check for voltage and polarity within the string where you want to add wire length to verify, then splice in according to what length you want(within reason, not like adding 100 feet to the string). These splices IMHO should be soldered and shrink wrapped to support the string weight. But, if the string truly has 120V(which I doubt) throughout its' length--I wouldn't put it around the layout where accidents can happen. Also, are you sure the lights are LEDs, mine are bulbs and run on 3.5V. Seriously though, the fact you're asking this question and it being a 120V system makes me nervous. Richard
There are no transformers. They are wired in series, and there are a few resistors so small you can hardly see them. There may be rectifiers either in the plugs or in a wart on the line, or they can just be on AC, you will see them flickering more.
The LION throws away the wires and sockets and keeps the lamps.
ROAR
nedthomas LEDS work fine on AC. They just light every half cycle, 60 times a second.
I guess that depends on your definition of fine.
Train Modeler nedthomas: LEDS work fine on AC. They just light every half cycle, 60 times a second. I guess that depends on your definition of fine. Richard
nedthomas: LEDS work fine on AC. They just light every half cycle, 60 times a second.
Using the appropriate resistor, try an LED on 12vdc and 12vac - I bet your eye cannot dicern the difference. Remember bi-color red / green leds - forward bias dc gives you green, reverse bias dc gives you red and applying ac would light both the red and green due to the ac voltage providing an alternating bias cycling at 60 times per second giving what appeared to be a yellow indicator. This was done in an MR article probably twenty years ago !
There's no transformer or rectifier in those LED light strings. The simpel expeient of having 2 LEDs wired back to back makes them work fine on AC - that way neither LED sees a high reverse voltage, which would otherwise quickly destroy an LED - instead it sees teh forward voltage of its partner LED as the reverse voltage. The, string enough pairs together in series and it'sll work on 120VAC.
BroadwayLion Train Modeler: The 120V is likely stepped down and rectified somewhere, LEDs don't like 120V and they don't work on AC. The 3 wires are so that you can have an LED blow out and keep the others lit. You can take a meter and check for voltage and polarity within the string where you want to add wire length to verify, then splice in according to what length you want(within reason, not like adding 100 feet to the string). These splices IMHO should be soldered and shrink wrapped to support the string weight. But, if the string truly has 120V(which I doubt) throughout its' length--I wouldn't put it around the layout where accidents can happen. Also, are you sure the lights are LEDs, mine are bulbs and run on 3.5V. Seriously though, the fact you're asking this question and it being a 120V system makes me nervous. Richard There are no transformers. They are wired in series, and there are a few resistors so small you can hardly see them. There may be rectifiers either in the plugs or in a wart on the line, or they can just be on AC, you will see them flickering more. The LION throws away the wires and sockets and keeps the lamps. ROAR
Train Modeler: The 120V is likely stepped down and rectified somewhere, LEDs don't like 120V and they don't work on AC. The 3 wires are so that you can have an LED blow out and keep the others lit. You can take a meter and check for voltage and polarity within the string where you want to add wire length to verify, then splice in according to what length you want(within reason, not like adding 100 feet to the string). These splices IMHO should be soldered and shrink wrapped to support the string weight. But, if the string truly has 120V(which I doubt) throughout its' length--I wouldn't put it around the layout where accidents can happen. Also, are you sure the lights are LEDs, mine are bulbs and run on 3.5V. Seriously though, the fact you're asking this question and it being a 120V system makes me nervous. Richard
LED Christmas light strings are wired in the exact same manner as the bulb variety. Depending on the material the LED is made from (which designates the color) white LEDs require 3.4 to 3.7 volts to operate at full potential. In the case of the OP's light string of LEDs, there would be 30 LEDs wired in series (30 LEDs X 3.7 = 111 volts) parallelled with another series string of 30 LEDs - hence the third wire. No wall warts, rectifiers or resistors required. If there is a resistor with each LED, it would be a minimal value like 10 ohms to help account for variations in line voltages which are common in rural areas.
Good points.
Look, I'm not an electrician or electrical engineer like a few of you, and, although I was in Jesuit formation for four years I am no brother in a monastery like the LION, but I don't get it........
Why is a string of Christmas lights that is perfectly safe plugged into the wall and running around your tree and house perfectly safe, but the same string of lights (even extended with a little of the same wire) is somehow dangerous because it's plugged into a wall and used on a mrr layout?
Seriously, am I missing something here???
The St. Francis Consolidated Railroad of the Colorado Rockies
Denver, Colorado
[quote user="Mark R."]
Train Modeler: nedthomas: LEDS work fine on AC. They just light every half cycle, 60 times a second. I guess that depends on your definition of fine. Richard
[/quote
Good point that it will work, but even though you won't look at Christmas lights as you do a computer screen, after a while that flashing is not good for your eyes(even though you can't discern it--you're right at least I can't). Also, it is not optimal for LED life. But, running them on AC seems more efficient.
IF you ran the line UNDER your layout and extended the individual lights up through the benchwork, you should be ok. I think what the previous concerns have been, would be the routing of the 110 volt line ON the benchwork where there might be a danger to driving a spike or something into the line !
Two important factors you need to adhere to .... use the same gauge wire to extend any leads, solder them and cover them with shrink tubing. When cutting the socket from the set, make certain your extensions re-attach in the exact same orientation as is was to begin with.
Lastly, DO NOT add or remove the number of LEDs in the string. They are designed with a specific number of LEDs to function properly on line voltage. Adding more LEDs, and they probably won't work .... take any out, they will all self destruct.
St Francis Consolidated RR Why is a string of Christmas lights that is perfectly safe plugged into the wall and running around your tree and house perfectly safe, but the same string of lights (even extended with a little of the same wire) is somehow dangerous because it's plugged into a wall and used on a mrr layout?
Two possible answers:
1) You still have 110 Volts AC in the wiring, and having a lot of splices in that wiring leads to more chances of electrical shock if they are not done properly.
2) If one of the wires is not spliced properly because you cut all 3 at the same spot and get them mixed up, you could cause a fire.
If you've never been near an LED that exploded because an improper voltage was applied to it, you haven't lived. The shattering plastic could very easily put an eye out. They also give off a very noxious smoke.
St Francis Consolidated RR Look, I'm not an electrician or electrical engineer like a few of you, and, although I was in Jesuit formation for four years I am no brother in a monastery like the LION, but I don't get it........ Why is a string of Christmas lights that is perfectly safe plugged into the wall and running around your tree and house perfectly safe, but the same string of lights (even extended with a little of the same wire) is somehow dangerous because it's plugged into a wall and used on a mrr layout? Seriously, am I missing something here???
For me, the concern is to cut and splice between all of those bulbs and end up with accidentally exposed/weakened wire. Also, given the nature of working under layouts with many wires, you would not want to accidentally cut into 120V live wire. Just a few reasons that quickly come to mind, there are others I suspect.
If you wanted to hang a string of lights up out of the way where they won't be rubbed or accidentally cut, etc that is what their designed for.
Many people *can* see that 60 Hz flicker. I have one computer user who could never look at a regular computer monitor without getting a headache from the flicker. I never could see the flicker. I stopped short of telling him it was in his head, and simply bumped up the monitor to 85 Hz.
As for "why not" extend the wires... The danger comes in your reassembly of them, one solder joint not perfect will cause 120 volt arcing at that point, and will lead to heat and fire. I have had some small 'fires' on my layout at 12 volts since my track circuit can put out 15 amps. I will have to install a fuse to limit it to 3 amps, since I know now that 3 will be sufficient for my requirements. But I can have as many as 12 "locomotives" potentially running at once on this layout.
I agree with the monitor refresh rate - I can't see it, but my wife can !
With an LED, I think the brightness tends to overcome the pulsations. If you put about a 20,000 ohm resistor on an LED hooked up to a 12vac source, the LED is dim enough that you can detect the pulsations.
Well, then.....your responses prove once again that there is no such thing as a stupid question. I won't be modifying Christmas light strings any time soon.
Thanks.
Mark R. I agree with the monitor refresh rate - I can't see it, but my wife can ! With an LED, I think the brightness tends to overcome the pulsations. If you put about a 20,000 ohm resistor on an LED hooked up to a 12vac source, the LED is dim enough that you can detect the pulsations. Mark.
This is correct. AND modern high intensity LEDs do get quite hot. They are off about 1/3rd of the time, but we are talking severaly hundred cycles per second. Here are two photos. Your eye cannot see the difference, but if your camera is too fast, it sure can!
BTW: You want to know if your TV remote is working... Just look at it through your camera, you will see the light!
There's nothing wrong with cutting upt eh strings and using them as indivudual or groups of LEDs - with low voltage and the appropriate resistors. White LEDs with 12Volts are goot with a 1K resistor - if you plan and wire them all the same, instedof having numerous resistor values you can buy a whole box of oen value - in such quantities they are 5 cents or less each, when purchased from an electronic supplier like Mouser. Thus adding the resistors does not really negate any savings from picking up the cheap string of lights.
Heh heh heh. If you run LEDs on AC, you don't have to worry about polarity.
Actually, running LEDs on AC should not harm them, so long as the voltage is not excessive. After all, they are.................ta da, DIODES, used to rectify AC into DC. They are light emitting diodes, but still diodes, just like those in a rectifier. Just make sure you use the right resistor.
hobo9941 Heh heh heh. If you run LEDs on AC, you don't have to worry about polarity. Actually, running LEDs on AC should not harm them, so long as the voltage is not excessive. After all, they are.................ta da, DIODES, used to rectify AC into DC. They are light emitting diodes, but still diodes, just like those in a rectifier. Just make sure you use the right resistor.
Actually they are a little different in that they don't tolerate reverse voltage very well and need provision made to handle that.
Joe
hobo9941 Actually, running LEDs on AC should not harm them, so long as the voltage is not excessive...
Actually, running LEDs on AC should not harm them, so long as the voltage is not excessive...
This is true, emphasizing the "so long as the voltage is not excessive" part(more on that later).
hobo9941 After all, they are.................ta da, DIODES, used to rectify AC into DC. They are light emitting diodes, but still diodes, just like those in a rectifier. Just make sure you use the right resistor.
After all, they are.................ta da, DIODES, used to rectify AC into DC. They are light emitting diodes, but still diodes, just like those in a rectifier. Just make sure you use the right resistor.
Unfortunately, I often see this advice given on forums. As Joe mentioned, LED's are different than rectifier diodes. Here is the data sheet for some common rectifier diodes: http://www.fairchildsemi.com/ds/1N/1N4001.pdf. Here is the data sheet for a random white LED: http://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTW-2S3D7.pdf. The rectifier diodes in that data sheet have a reverse voltage rating from 50 to 1000 volts, where the LED has a reverse voltage rating of 5 volts. If you try to power that LED with 12 volts AC, then you will likely kill it.
Many LED's will actually withstand a higher voltage than rated, especially the red, green, amber, and yellow ones; however, white LED's tend to be much less tolerant of reverse voltages. Also note that excessive reverse voltages do not always kill the LED quickly, but will often drastically shorten the LED's life.
.... But if the resistor is safely keeping the forward operating voltage at 3.4 volts, does not that same resistor also keep the reverse voltage at the same level ? In other words, the resistor keeps the upper ac sine wave (positive bias) at 3.4 volts, wouldn't it also keep the lower sine (negative bias) at the same 3.4 volts ?
That being said, the reverse voltage rating of any given LED is usually around a couple volts higher than the forward voltage. Based on that, wouldn't an LED running on AC be destroyed on the forward bias before the reverse bias is even attained ?
Mark R. .... But if the resistor is safely keeping the forward operating voltage at 3.4 volts, does not that same resistor also keep the reverse voltage at the same level ? In other words, the resistor keeps the upper ac sine wave (positive bias) at 3.4 volts, wouldn't it also keep the lower sine (negative bias) at the same 3.4 volts ?
No, the voltage drop of the resistor depends on the current through the resistor. No current, no voltage drop. The full reverse voltage then falls across the diode.
That being said, the reverse voltage rating of any given LED is usually around a couple volts higher than the forward voltage. Based on that, wouldn't an LED running on AC be destroyed on the forward bias before the reverse bias is even attained ? Mark.
A diode is a non-linear device. In the forward direction, there is a small almost linear operating region, followed by a near constant voltage drop across the diode, regardless of current. Which is why LEDs need resistors to limit current whenever supplied voltage is equal to or higher than the forward voltage drop.
When reverse biased, the junction inside the diode fails when the reverse bias voltage exceeds the rated reverse voltage. And the diode is no longer a diode.
hope this helps
Fred W
Thank you everyone who responded so far. It was a little overwhelming and sometimes TMI. I have 43 buildings for my downtown and the 60 lights will be distributed to most of them. I will cut one wire at a time and reatach them before going on to the next cut. The total will remain 60 and I am not afraid of 110 or120 AC under and on top of my train board. No more than the extension cords and power pack cords under the table. This won't take place for awhile but I'll let you know what happens. Thanks again to everyone.
Ok - the logic sounds reasonable .... but under what circumstances will this happen ?
I know numerous people who run AC into the bi-color LEDs (red / green) to achieve a simulated yellow indicator - and have been doing so for years with no adverse effects. Is this a case where practice trumps theory ? .... "it shouldn't work - but it does !"