Mark R. You ALWAYS must use a resistor with LEDs. Mark.
You ALWAYS must use a resistor with LEDs.
Mark.
Thus spake Zarathustra!
Actually the LION did put about 5 in series without a resistor and guess what: They do light up.
But I was told that this is not the way to do it., so now they all get resistors, but sometimes I will use two LEDs with one 510Ω resistor between them. I insert them in a 1" lengths of drinking straw, and now I have something that looks like a florescent light. Not to scale for sure, but you put them where only a little bit of them can be seen such as under a platform canopy, and you have something nice.
Thus Spake the LION.
(Always use the resistors.)
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Your battery charger (I'm assuming car battery charger) shows 20 volts because there is no load on it. Those things aren't designed to be power supplies.
Even those "wall warts" - unless the specifications indicate the output is regulated, a mter reading on the end will be much higher than is marked on the package. Unregulated power sources require a predetermined load on them to provide the proper voltage output. Again, do not use those wall warts if it is not a regulated supply.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
So I tried my "12VDC" charger that really put out about 20+ volts. Even with the 1K resistor it was bright, 2 1K resistors in series tamed thing down some. I think I will try what someone suggested and use one of my power packs and just dial in the brightness. If I use a power pack, do I still need the resistors?
I like the idea of the 9 volt battery with the resistor to test polarity.
Thanks everyone.
LION has a 9 volt battery with a 1KΩ resistor soldered on to it. It is marked + and - and I can test my LEDs quickly and easily.
Bis I took my volt meter to one of the spare bulbs, set the meter to measure resistance. With the positive on one side nothing happened, reversing the probes the led lit up. Can I presume that where I used the + probe with the led lighting is the side to attach the resistor and the + side of the power supply? Ken
I took my volt meter to one of the spare bulbs, set the meter to measure resistance. With the positive on one side nothing happened, reversing the probes the led lit up. Can I presume that where I used the + probe with the led lighting is the side to attach the resistor and the + side of the power supply?
Ken
No, you can't. Some meters have a positive voltage on the black lead when measuring resistance. The best way is to attach a 1,000 ohm resistor to one lead (doesn't matter which) then hook it up to a 12 volt or less power supply. If it doesn't light up, swap the wires from the power supply. Then mark which lead is connected to the power supply's + terminal. Just use a red felt marker. Or use a black one and mark the other side if you don't have a red marker.
..... Bob
Beam me up, Scotty, there's no intelligent life down here. (Captain Kirk)
I reject your reality and substitute my own. (Adam Savage)
Resistance is not futile--it is voltage divided by current.
Ok, I will break them down.
Thanks
Yes, there is a downside.
You do not know what is already attached to the LED.
These sets are wired in series, but some of the LEDs have resistors on them and most do not. Somewhere in the circuit there may be a rectifier.
It is always better to remove the LEDs from all of the wires and sockets. What the heck, once that is done you can mount them on circuit boards if that helps your project:
Thanks, you folks have been GREAT
I am now the proud owner 50 pointed led and 50 cup shaped led Christmas lights. Today I will go to Radio Shack and buy a few 1k resistors just to get things going.
Also is there a down side to leaving the led's in the socket and attaching the resistor to the wire from the socket, other than the size?
Thank for the help.
Keep in mind that running the lights at full power generally doesn't look as realistic as having them at about half power.
If you're going to use a lot of lights, I'd say bite the bullet and go to a model RR fleamarket and pick up an old MRC power pack so you can run variable DC power. I use an old MRC Tech II dual pack. One rheostat controls the building and yard lights, and the other controls the LEDs mounted over the layout to provide a starlight / moonlight glow.
Short answer is yes. I've been using the LEDs form torn apart Christmas Tree light strings since the first year they came out (2003?). Even for loco headlamps. Always been much cheaper than buying LEDs from the electronic store.
No. 1/8 Watt resistors is all that is needed, unless of course if your shack does not have them.
All Electronics has them for far less money. Buy 1000 of them and they will cost about the same as the shipping for them, or about as much as 10 resistors at the shack. You could use smaller wattage on the resistors, but that is a waste of money as those WILL cost much more.
Thanks everyone for all the great inputs.
I have found an old charger, rated at 12 VDC, 200 ma.. so next its off to Wal-Mart for the lights and Radio Shack for some 1K ohm , 1/4 w resistors.
Thanks again for the information.
If you have some old cellphone chargers, check their output voltage and current rating. They are usually DC voltage. There is a simple ohms law calculation to work out the value of the resistor so you get about 20milliamps of current flowing thru the LED. But 1000ohms for 12volt 550Ohms for 6 volt is pretty safe.
The ohms law calculation is R=V/I
ie.Resistor value = the voltage divided by current in amps
eg R =12v/0.020A (20mA)
answer is 600 but 1000 will be fine ie go a bit higher and the current will be a bit lower. The wallwart needs to have at least 3 volts output as white leds need about that much voltage to light up. Red and green only need about 2 volts. But always have a resistor in series with each LED.
HTH
Alan
Alan Jones in Sunny Queensland (Oz)
YUP, the LION has been using them for years and years. This year I bought a coil of 180 LEDs for $22.00 at Walmart.
You can get the 5mm size, or if you buy the kind with the plastic dodads on them, there are the smaller 3mm (T1) LEDs inside. LEDs with round tops will focus light forward like a spot light, LEDs with an inverted cone on top will focus most of the light around the sides of the lamp, more like a flood light.
Check the colors, some are WARM white, like an incandescent lamp, and others are BLUE-White like a florescent or mercury lamp.
Yes you do need 1KΩ resistors, and I buy them by the thousand at All Electronics (an MR advertiser) for about $12.00 or less.
LEDs need to operate on DC and are not very fussy about the voltage, but the current will kill them, that is why the resistor is required. They also operate like a rectifier in that they pass current only in one direction, if it does not light up one way, turn it around and it will work the other way.
Here is a diagram on how I wire two colored LEDs back to back for a signal. Only one will light up depending on the polarity of the circuit. (The colored LEDs at All Electronics are dirt cheap.)
Thanks Hornblower
Tomorrow I have to go to Wal-Mart again :(. I shall pick up a couple of strands of LED lights. I can live with a few 1.5 volt batteries. Leds don't suck that much power so the batteries should last awhile.
Thanks again
Last year at Christmas, I bought several 50 light strings of warm white LED Christmas lights for $6.99 each at Walmart. That works out to about 14 cents per LED. It took a few minutes to disassemble each string but I now have a couple hundred inverted cone tip warm white LED's to use for building lighting, street lamps and such. Must LED's will operate at around 3 volts DC so a couple of 1.5 volt batteries can be used for power. A 3 volt wall wart power supply could also be used. Higher voltage power supplies will require resistors in line with the LED. The inverted cone style LED reflects light out to the sides as much as out the tip. Thus, these LED's are well suited to making street lights or overhead interior lights. However, they also put out a concentrated beam of light straight out the tip so they could still be used for a headlight as long as a separate lens is installed in front of the LED. The warm white color gives my lighting a slightly yellow glow.
Hornblower
Thanks Mark
You say 12 volts, is that AC or DC? I have power supplies that produce 18 volts AC and 22 volts AC ( old supplies) . If its DC where do I get it, besides a car battery charger :)?
Yup - they'll work just fine. But you will need a resistor on each one. If you are running them off 12 volts, a 1000 ohm resistor will work fine.
The "white" ones will have a slight blue cast to them - work well if you are simulating fluorescent lights in your structures ! They also have them in warm white which looks more like an incandescent bulb for color. Painting them white won't alter the color. If you want to eliminate the blue cast of the white ones, you need to tint them orange.
I am working on my first structure and I want to light it. I went to Radio Shack today to price l.e.d.s and try to get info, no luck and high prices. Then I was thinking that all the big box stores are advertising L.e.d. Christmas lights and a string of them would be about the same price as 2 or 3 l.e.d.s at Radiio Shack.
Will they work if I break down the string? What voltage do I need for them? Do I need a resistor in series with each one and what value? Are the white ones to white or do I need to hit them with flat white paint?
Sorry for all the questions, but this is all new to me. Thanks for all the help.
Ken in East Texas