Help with LED wiring

[beemer]

To all those electrical experts out there. Is there an alternate way to wire LED than in parallel with each LED having its own resistor? This is very time consuming and bulky way of doing things. Isn't there some component that I can just wire all the LED into and it will regulate the power? I just started working with breadboards but again those are fairly bulky.
Thanks every one
Jerod

[caseyz]

Just match your power transformer to the LED's input requirement and you do not need a resistor. Mine is setup something like this:

*******************
** 3.5V **
** Transformer **
** **
*******************
+ -
| |
| |
| |
-----LED------
| |
| |
-----LED------
| |
| |
-----LED------
| |
| |
-----LED------

[caseyz]

Grrr, ASCI art. Think of the "-" side being on the right, not over on the left.

[caseyz]

Here, like this:

[sfsuphysics]

Ok here goes my shot, although Casey's drawing is better than mine.. did we forget a resistor casey? or is your transformer prematched to the diode setup?

Anyways I did mine as a series connection, only 1 resistor is needed for either case. This is an example of a 3 led setup.

please ignore the bad drawing, I did it in MS paint just now.

http://www.physics.sfsu.edu/~mbolling/leddiagram.bmp

[sudsy]

caseyz how many volts are you leds rated at, how do you ise on 3.5v transformer for 4 leds, could you elaborate on that, please
Thanks MIke

[caseyz]

They are 3V I think and they pull 20ma each. It pulls it pown to about 3.1V. The transformer puts out 200ma. I had a EE in my office bless it and it works fine.

btw, I got the LED's off of www.digikey.com. We use them all the time.

[sumphead]

Quick question: Seems easy enough but electricy is not my strong point. I have an adjustable output transformer from radio shack. 300ma. I was told (at radio shack) that they wouldn't work for the LEDs at 20ma. Do I need a resistor? If so which one do I look for? or strait away like caseyz?

Thanks.
R-

[Heavydc2]

if your trying to mimic moonlight I would put a resistor on, I got the same transformer at RS, and I also got resistors there, · ½ watt, 150ohm, 5%resistant Resistors, and the moonlights came out superb! If you put too much power to the led it will be too bright and won't be a real moonlight effect.

[caseyz]

The transformer that I use is a radioshack model. I checked before I came to work and it is set at 5V 200ma.

Here is the link to the didgikey part I used http://rocky.digikey.com/WebLib/Chicago%20Miniature/Web%20Data/Blue%20LED%20Lamps.pdf

Here is a link to calculate the resistor that would be required

http://www.luxeonstar.com/resistor-calculator.php

You can see that 4 4.9V nominal led's pulling 20ma each is the same as 1 80ma LED. So theoretically, you should use a 1.5 ohm 1/8 watt resistor. In reality, it is not required. You are talking about so little power that it is not going to hurt anything.

By the way, if you have a multimeter, just plug the transformer into the wall and then use your multimeter to see what it is putting out. It will almost always put out more voltage than what it says.

Anyway, if you are just lighting LED's and it is within a few 10ths of a volt or so, it isn't a big deal.

[sumphead]

Thanks all. It was the mA that had me a wee bit confused.

[sfsuphysics]

An easier thing to do instead of buying a transformer, is just to use one you might have around the house. Have any old phones, battery chargers you dont use anymore? Anything with those big black plugs? Well guess what that'll turn the AC out of the wall into DC current for your LEDs. And IMO resistors are not only useful, they're necessary to stay within the optimal conditions, I use a decade box and start with a high resistance and tune down to find the optimal resistance, but if you dont have there there are a multitude of calculators online (although alot of them are crap because they assume only 1 LED!). Here's a good one that does both series & parallel, and more than 1 is possible.

http://www.projectx.com/Kits/LEDNotes/

Just remember series connections your voltage drops across each LED, so with 12Volts you can't have any more than 3 3.3v leds in series. But with parallel, you only need a 3.3Volt source, its your current that'll drop off, and since most LEDs are 20 mA usually you have more than enough current, but same rules apply with current in parallel, if you have a 100 mA source, no more than 5 (although you can get away with it, they'll be dimmer than normal).

Also if you go my route and cannibalize things, check the volts of the plug, I know I yanked a nice thin one off an old cordless phone I never use, it said it was rated at 12V & 300 mA, and when I put a voltmeter across the leads, it said closer to 16V.. still gotta figure that one out.

[xrunner1234]

Originally posted by sfsuphysics
...phone I never use, it said it was rated at 12V & 300 mA, and when I put a voltmeter across the leads, it said closer to 16V.. still gotta figure that one out.

Probably an unregulated source such as an AC stepdown transformer fed into a rectifier bridge and cap. Output voltage will vary with load, so at 300mA, it's 12V, but at no load it may be 16V, like you measured.

[marm64]

The only problem with going with one resistor with multiple LED's in parallel is if you have a LED that has a lower forward voltage will be the easiest path for the electricity so if it is a lot lower it could just burn out, this is why most people go with a resistor on each LED. Also when you hook it up you will probably notice that some of the LED's are brighter or darker than others, this is baecause the forward bias is diferent for each one.

[sfsuphysics]

Very true, LEDs are not exact on their voltage requirements, although they do have a tolerance threshold, so while you will get them of varying intensities, as long as they are somewhat close you shouldn't have a problem. I know the blues I use have a 20 mA optimal current, up to 30 mA max. So that's a 50% output increase if your LEDs are that badly mismatched, you should find ones that are closer matched then do parallel & series combinations. Might be a little time intensive sorting through them, but hey its something to do :)

xrunner: Oh yah duh, should of thought of that, all the junk in the cordless phone (including a battery that is constantly pushing back) would change the voltage.

[TroyPierce]

A famous person once said that free advice is worth what you pay for.

I've worked in electronics for many years and agree that having a current limiting resistor for each LED can be a royal pain, especially if you're building an LED array. I can also tell you that NOT having one is courting disaster. I've seen transformers/power supplies go up in FLAMES because of this.

The resistor has two basic purposes, one it to limit the current going to the LED and the other is to drop the voltage so that what the LED sees is within it's specs.

DO NOT, UNDER ANY CONDITIONS, LEAVE THE RESISTOR(s) OUT.

I'd also councel against putting ONE resistor on a bank of parallelled LEDs. There are some complex rules about current when you do this.


The LED is about $3, the transformer about $5 to $10. A 25 cent resistor is cheap insurance.

Having said all of this, I go back to my original comment about advice. get yourself a book on electronics or find someone you trust to give you good advice or buy a pre-wired device.

[sfsuphysics]

Originally posted by TroyPierce

Having said all of this, I go back to my original comment about advice. get yourself a book on electronics or find someone you trust to give you good advice or buy a pre-wired device.

I have my old copy of Hayes & Horowitz for sale if anyone wants to offer enough :)

[caseyz]

TroyPierce,

I see your point, but it is not like he is designing a intrinsically safe circuit. As another option if you are worried about an LED failing open and cooking the transformer, you could just put a single fuse inline and that would work as well.

Not trying to start a war here, just saying…

Now I am going to go home and look at my LR!

[beemer]

Thanks for the info guys. So it seems that you do have to have resistors for each LED. Or don't at your own risk. That being said is there any easier way than soldering each LED and resistor? I know a bread board will work but I am still working out the kinks on that. Fried 4 LED so far.......Thanks again ya'all
Jerod

[TroyPierce]

Originally posted by beemer
Thanks for the info guys. So it seems that you do have to have resistors for each LED. Or don't at your own risk. That being said is there any easier way than soldering each LED and resistor? I know a bread board will work but I am still working out the kinks on that. Fried 4 LED so far.......Thanks again ya'all
Jerod

There's two challenges in soldering these things: Holding the wires steady and in contact with each other and not using too much heat.

For the first problem, you can bend the leads to be joined into a hook and interlock them (like links of a chain). Then squeeze the bend of each to apply pressure to the other wire.

Another way to hold everything is with a gadget that Radio Shack sells. It's two roach clips on a stand. There's even a magnifying glass on it if you want to use it. Just slip them in the clip and solder away. BTW, this type of 'clamp' also helps with the overheating problem.

For the second, use a heat sink. If you have a pair of needle nose pliers (they come in handy for the above bending and crimping), you can simply hold the LED wire and apply solder to the joint. Radio Shack also sells inexpensive 'tweezers' that open when you squeeze them.
http://www.radioshack.com/images/ProductCatalog/ProductImage/276/276-1567.jpg
They cost $1.59. Clip them on the LED lead.

The heat will transfer to the tweezer or pliers before moving on to the LED.

Troy

[sfsuphysics]

Originally posted by beemer
Thanks for the info guys. So it seems that you do have to have resistors for each LED. Or don't at your own risk. That being said is there any easier way than soldering each LED and resistor? I know a bread board will work but I am still working out the kinks on that. Fried 4 LED so far.......Thanks again ya'all
Jerod

Well I wouldn't say LED on each resistor, unless I was misreading Troy, he only suggested that you DONT use a single resistor for parallel combinations, serial setup should work fine (but then again you dont get as many LEDs off a single serial connection.

Fried the LED? apply too much heat? Or did you have them hooked up wrong? There is a specific direction for current to flow and that will fry your diodes (in through the long wire, out through the small). I use a old fat industrial soldering iron that has a cord wrapped in cloth (to age date it) and I usually have no problems. You could use a breadboard if you wish, then you just cut little pieces of wire to use as connectors, but that doesn't give you much leway for space. What you'd want to do if you have trouble soldering, is make sure your iron is good and hot (so solder melts like WAM instantly) then make sure to precoat your iron or else the solder will stick to it and not your connections, put a little dab of solder on the end of the resistor you're going to hook to the LED then just put the led arm next to it and remelt the solder and when it flows (it should do it quick so you dont burn your led or resistor) pull back and let it cool.

Also pre-tin any copper wires you're working with.

[marm64]

I would say if you fried them that you had too much current going through them. I saw somebody fry a whole LED array by just chekcing the LED's with 5 volts and no resistor, all he did was just quickly put the 5 volts to the LED to check if it worked and moved on and when it was hooked up nothing worked they were all fried. You have to have a resistor to limit the current as well as to drop the voltage.

[mjw357]

yes you may get lucky with a 'wall wart' transformer and find one with 3.2v output and 150mA current, and then use just the right number of LED's so that it works well, but you are taking a chance. Diodes not only act like a check valve, but can also actually change the voltage in a circuit due to the bias. A transformer showing 3.2v out of circuit may increase or decrease because of the electrical characteristics of the diodes, depending on how they are wired (one resistor or individual, series, parallel etc.)

[beemer]

I am mainly looking for a way to make the LED units as compact as possible. I have made a few LED units encased in the ultraslim project box made by radio shack. There is very limited space. I guess I was hoping to find some control module that I could just wire in line and limit the power going to the LEDs without individual resistors. Maybe I will just wire them in serial since I will only put about 4 LED in each unit. Thanks ya'all for the help. Wiring in parallel is very easy and I have made several for people on this board. Just looking for other ways of doing things
Thanks again
Jerod

[beemer]

I am mainly looking for a way to make the LED units as compact as possible. I have made a few LED units encased in the ultraslim project box made by radio shack. There is very limited space. I guess I was hoping to find some control module that I could just wire in line and limit the power going to the LEDs without individual resistors. Maybe I will just wire them in serial since I will only put about 4 LED in each unit. Thanks ya'all for the help. Wiring in parallel is very easy and I have made several for people on this board. Just looking for other ways of doing things
Thanks again
Jerod

here is the link for the project box incase any body wants to put these on their tank. Great for small tanks
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=270-288

[sfsuphysics]

Well if you want it as compact as possible you're going to need to solder some wires to the LEDs and then just bring the wires out one side and have the transformer/resistors outside of the tank.

listen to mjw get a transformer thats rated higher than what you mathematically need, you can always use resistors to step down any voltage. My 16V transformer dropped to 15.5v when I put LEDs on there, luckily I only have 2 so its not a big deal.

[Heavydc2]

I am looking into lighting a fowlr tank with white leds. The tank is a 60 hex that is 26 inches deep, would super bright LEDS work you think? I was also thinking about super bright Cold Cathcode lights too. Does anyone have any expereince with LED lighting other then moonlights?

[sfsuphysics]

No experience with daytime lights... YET! I'm planning on getting a white LED setup, they make some nice 5500k-6500k whites that probably would do the trick. And if you want a little more bluer you an always just pair them up with some blue LEDs. Of course I need to find a cheap supply of them, I just snatched up a batch of 470nm blues (30 deg) for .29 cents a piece and I only had to buy 50. Trying to find a similar deal, as it is, $1.50 is the lowest I've found, that might be a little too much for my tastes, of course I still need to find out how bright an individual one is, converting mcd to lumens or whatever is too much of a pain.

[beemer]

I got mine from Ebay. They were very inexpensive. They come out of china. They come with the appropriate resistors and free shipping. I had good dealings with them. I can't remember the name of the seller. I think it is Chi Wing ind....maybe
Jerod

[sfsuphysics]

That's where I got my 470nm blues. The only problem is the ebay ones only specify the mcd rating they dont say what the color temperature is. That and the few that have many auctions think they're fooling someone by having a low initial price then $15 shipping & handling. Although the cost per unit is a lot lower than $1.50 each.

[beemer]

I e-mailed them directly to get the Kelvin rating and also just orded through their store not off the aution. They will even mix and match for you as well as give what ever resistors you ask for.
Jerod

[Heavydc2]

beemer Was that Blues or whites?

[sfsuphysics]

Originally posted by beemer
I e-mailed them directly to get the Kelvin rating and also just orded through their store not off the aution. They will even mix and match for you as well as give what ever resistors you ask for.
Jerod

Happen to recall the store (er website) name?

[beemer]

don't have access to ebay at work but I just went to their auction and clicked on the link to their ebay store. I think it was Chi wing inc. If you just look for blue LED on ebay they should come up.
I orded the blue ones so far but originaly got info on the whites as well. Unfortunatly I have since lost the info
Jerod

[sfsuphysics]

Hmmm, the blues I ordered were from Wai Chi Lau, similar? besthongkong.com?

[marm64]

I bought some LED's from besthongkong and I emailed him to get the data sheets for the blue and the red. His blue are 470 - 475 nm.

[beemer]

I will look up the company tonight and get back here
Jerod

[lurch694u]

How about this setup? I am going to try this setup. Will all you electronic buffs out there let me know if this setup is safe? I don't want to burn the house down.

DIY LEDS (http://www.kaotica.com/frag/diy/moonlight/)

[sfsuphysics]

Yup, that's the parallel combination where the voltage stays doesn't drop except by what the resistor does for each LED. Its current that you need to add up.

[beemer]

ok here is where I got my LED from http://www.stores.ebay.com/id=70930951
Like I said I had a good experience with them. Prices for whites are between 25 cants and 18 cents per bulb depending on quantity. That includes resistors suitable for 12V and free shipping. No this isn't an add for them :)
Speaking of lighting I wonder how 25 of these over a nano would work. These would be perfect for a small 1 gal tank huh?
Later
Jerod

[lurch694u]

blue led:

Wavelength: 468 nm (typ.), Type: T-1-3/4 (5mm), Lens Color: Clear, Viewing Angle: 30°, If mA: 20 (max.), Vf: 3.7 (volts typ.), Vf: 4.5 (volts max.)


power supply:


6VDC/300mA AC-to-DC Adapter


Can anybody solve for me what resistor I need?

watt? ohm?


:confused:

[sfsuphysics]

Ok first thing, when you have your adapter use a voltmeter across it to make sure it is really 6 volts, if one isn't available then skip that and hope it really is :)

if you put one resistor across the entire connection, it's going to depend upon how many you have in parallel, but since I was chastised about giving that kind of advice *grin* you'll probably do good with about 120 ohm resistor attached to each LED.

But again if you have access to a voltmeter, double check, 3.7 is the "typical" voltage(sounds like you got the super expensive radio shack kind & 468nm), you can operate fine in the 3.3V range as well. So dont worry too much if you're under but a little, just try not to go over.

[lurch694u]

ok radio shack has a 1/2 watt 150 ohm resistor would that work?

[Heavydc2]

I did Fabios moonlight project also. I wrote an article for our reef clubs newsletter on it to explain it a little easier. The resistors I used were: ½ watt, 150ohm, 5%resistant Resistors. The spread on the led was 15 degrees which is good for moonlight, you should not really be able to see your fish with the lights, the 30 spreads the light more.

I am very interested in finding out more about the whites and anyones experience using them.

this one is ok http://www.servangle.net/reef/led/
Does anyone else have any other articles that have been written?

Here is thelink to my article:

[sfsuphysics]

Lurch: 150 ohm will work fine, you might have your bulbs tad dimmer, but it'll prevent them from burning out, I still say everyone who's working with electronics should have atleast one cheap multimeter around, and things like variable resistors (or better yet a decade box!) just for these testing purposes.

Heavydc: you wrote that article? I read that a little while ago, nice job. I especially like how you specifically mention the cluster vs spread out effect of the LEDs.

[Heavydc2]

Opps no I did nto write that article, thats one I found, I forgot to add the link to this article:
http://www.chandev.com/reef/Led-Moonlighting-Project.pdf
That one is the one I wrote.

[sfsuphysics]

Nice article, although I would note the gauge of the wire used and not just speaker wire, I certainly wouldn't use the thin crap that usually comes with most systems to wire any large setup.

You mentioned a 1.5~12 volt transformer, that is definately overkill since its adjustable you're probably paying for more than you want, and the lowest setting wont work very well (if at all), and infact with the resistor you put in 12V is the only setting that you're going to get optimal results.

Also you mentioned soldering the resistor wire on the goldband side, this isn't necessary as resistors dont have any sort of polarity to worry about, either side will do.

A note on transformers though, you do NOT need 12 volt transformers, at the very least you need a transformer that's capable of putting out 3.3volts (probably a little more just in case) if in parallel (or just 1) and N x 3.3volts if you hook in series. The reason so many do the 12 volt route is because originally people with cars hooked these up, and thats the voltage of the car battery, and guess people just couldn't do the math associated with any different voltage (although its good to note that there are plenty of resistor calculators out there where you can punch in whatever voltage load you want.)

[bzzbee2]

Beemer.. how compact... here is what i have done.

http://bertagnoli.home.comcast.net/fish/light1.JPG

i would say its pretty compact... and i can make it bigger or smaller depending on my needs. im gonna test this out for a couple weeks and see if it fits my needs.. if anything i may put a larger resistor on it to dim the lights a bit..they are insanely bright right now.

Sys - (or anyone else)
i was looking at potimeters today. I am assuming that these would just replace the resistor, as they have ohm ratings just like resistors?

[sfsuphysics]

yah pots are variable resistors. It'll serve as a dimmer with LEDs, but the ones I've seen you physically turn a knob on it, meaning that unless you wanted to stay up all night to dim it yourself its not an option. Good thing to use if you want to find the optimal resistance for any particular setup though.

[bzzbee2]

very well. I might still get one, so that i can find the proper dimming level. thanks!

oh.. total time involved above.... 40 minutes.

[MartyDW]

Heavydc, great artical, I am looking into setting up something like that over a refuge to see how the Macro reacts. One modification I plan on using is to include a few UV LEDs for extra UV radiation. Also a quick not on using Variable Resistors (POTS) one way to use them would be to place one in siries with the parallel circiut layout so you could use it as a dimmer to get your setup to the brightness you need it. make sure you resistors on your led's are at optimal level and place a POT so you can dimm from max to off. then place the pot in a place where you can number from 1 to 12 and adjust each night to simulate moon phases. (just a thought).

[8BALL_99]

Just incase anyone wants it. This site has pretty good prices and I've ordered from them before. They don't have the right kind of blue leds, but if your looking for uv or ultra bright white leds they have good ones. www.superbrightleds.com:bum:

[ONAGI]

Good reference material. Thanks