wiring LEDS

[computerman]

ok well i'm getting a bunch of LEDs with just the two leads... is there a certain amount of power that i can only use like if i use to much can i ruin them or anything like that? i know nubi question let me know would ya gues thanx

[linlin]

You will need to calculate the right size resistor (ohms) for the job.

Many on-line calculators available for this.

EDIT: Here it is I found the one that everyone uses
Linear's LED Calc (http://linear1.org/ckts/led.php)

[zeLupin]

Yes...LEDs are sort of complex for beginners. You're going to need to learn two things. Ohm's Law and The Resistor's color code bands.

Ohms law is (Supply Voltage - Forward Voltage)
---------------------------------------
(Amperes)

that basiclly means the voltage of the original source like 12v, 5v, 3.3v from a psu minus 3 volts, 2 volts (depending on the led) divided by the number of amperes (or commonly mA ÷ 100)

Here's (http://linear1.org/ckts/led.php) a calculator if you don't feel like doing all that. Yet i recommend you to memorize it because you wont always be at a computer or have one avalible.

Second is the Resistor color bands. those basiclly equal the final result of the equation that you used above. the more the number is, the more voltage is resisted. the color codes go as follows:

First and Second Color Bands
----------------------------------
Black - 0
Brown - 1
Red - 2
Orange - 3
Yellow - 4
Green - 5
Blue - 6
Violet - 7
Gray - 8
White - 9

Third Color Bands
---------------------
Black - x1
Brown - x10
Red - 100
Orange - x1k
Yellow - x10k
Green - x100k
Blue - x1 Meg
Silver - ÷100
Gold - ÷10

Fourth Color Band
---------------------
Gold - 5%
Silver - 10%
None - 20%


Now i know that is alot but it actually easier to memorize after a while getting used to it. Again it's not necessery but recommended to memorize.

The first and second color bands are simply the first 2 numbers. Those two values will change with accordance to the third color band. The third color band basiclly multiplies the resistance or reduces the resistance. The fourth band is tolerance. The tolerance of common resistors is 5%.

That's all you need to find out the proper resistor you need to get the LED NOT to blow in your face. The other thing you need is how much the max voltage the LED actually tolerates. Usually 3.3v is enough. The usual ampers needed is .02 (20 mA)

[linlin]

Thats why we have the calculators. :wub:

Resistor color codes useful though.


O look I found a use for that face

[zeLupin]

bah im wiped...that took me like 10 minutes to write trying to remember everything. and dont worry the color codes are right i double checked in my little Led and resistor notebook i made after i wrote everything.

[mwbrooks42]

Originally posted by Lupin_Modder@Aug 2 2004, 02:31 AM
Again it's not necessery but recommended to memorize.
The old mnemonic for resistor colors was much less PC than this:
"Brave boys resist overt young girls, but Victor goes willingly."

If you want star spectral classes I think I remember that, too.

Also it's easier for me to remember the third band as just the number of zeros, rather than a multiplier.

To calculate R if you're really lazy, breadboard in a 470-ohm pot (or so) and twiddle it until you measure 3.3 V (or whatever is correct) across the LED, then measure the pot's resistance. If you're even lazier than that, just crank the pot up until the LED starts to smoke, then back off a bit. <_<

[computerman]

thanx for all the feedback.. i guess i'm not the only one up at odd times of the morning

[computerman]

wow after re-reading everything it sounds like i'm getting in over my head... i dont understand the hole Ohms thing and all.... oh well thanx guys
forgot to tell you... this is not going into a computer so i guess i kinda posted in the wrong spot but oh well

[benjamin1254]

heh... ive been up since 3 am yesterday!

[computerman]

ok i went to the calculator and well i wasn't to sure what to type in...

Supply voltage 3.2 V [3-24 V]
Diode forward voltage 3.2 V [2-4 V, or more for series combinations]
Diode rated current 2 mA [10-50 mA, or more for parallel combinations]

Calculated resistance value 0 Ohms
Next standard 5% resistor *1 Ohms
Resistor color markings Brown Black Gold
Power dissipated in LED**0mW
Power dissipated in resistor**0mW

ok i just kinda used the numbers Lupin_Modder said were usually the right for the LED... see i'm looking to get about 15 LEDs or so different colors but on the site they dont say anything about voltage or any of that
if any1 would be nice enough to take a look and maybe let me know this is the linkLEDs (http://www.mouser.com/?Ne=400&handler=data.listcategory&N=63803)

[linear]

Originally posted by computerman@Aug 2 2004, 08:44 AM
ok i went to the calculator and well i wasn't to sure what to type in...

Supply voltage 3.2 V [3-24 V]
Diode forward voltage 3.2 V [2-4 V, or more for series combinations]
Diode rated current 2 mA [10-50 mA, or more for parallel combinations]
&nbsp;
Calculated resistance value 0 Ohms
Next standard 5% resistor *1 Ohms
Resistor color markings&nbsp; Brown Black Gold
Power dissipated in LED**0mW
Power dissipated in resistor**0mW

ok i just kinda used the numbers Lupin_Modder said were usually the right for the LED... see i'm looking to get about 15 LEDs or so different colors but on the site they dont say anything about voltage or any of that
if any1 would be nice enough to take a look and maybe let me know this is the linkLEDs (http://www.mouser.com/?Ne=400&handler=data.listcategory&N=63803)
You need to put your supply voltage in the supply voltage field--like if you are using the red wire from a molex connector, supply voltage would be 5V. Yellow wire would be 12V.

You should probably be using 20mA for the current most of the time also, not 2mA.

[computerman]

ya i had no clu at all with any of that stuff... there the thing lets say i'm just gonna use 2 AA batteries since this isn't going into a computer.. then how would i?

[mwbrooks42]

Originally posted by computerman@Aug 2 2004, 10:44 AM
... on the site they dont say anything about voltage or any of that
if any1 would be nice enough to take a look and maybe let me know this is the linkLEDs (http://www.mouser.com/?Ne=400&handler=data.listcategory&N=63803)
Those LEDs don't all have the same specs, so what you do is get the "MFG Part No." from Mouser's table for each LED you want, then go to the manufacturer's website (http://www.everlight.com/en_product.asp?g=26) and search for the part number. You'll get a table with all the parameters you need.

Don't freak. This stuff is really pretty easy. It just takes time.

[linlin]

2 AA batterys should be the perfect voltage for most LEDs.

I dont think it will blow it out.

[linear]

Don't use the calculator when you use batteries as power. They have an unknown internal resistance, so you can't really get an accurate calculation.

You can try just using 2AA cells with no resistor, and rely on the internal resistance to limit current, but in a lot of cases, 2 AA cells won't even light your LED (for example, 2 NiMH cells only develop 2.4V, which won't light up most white or blue LEDs).

[computerman]

oh ok so if i do it just with batteries its ok i dont have to worry about the current and all.? thanx soo much guyz i appreciate all the help i'm 14 and well i like to think i know a lot but i dont know everything so its nice to know that people r thre to help

[linlin]

Ya pretty sure you wont burn up an LED with 2 AA batteries.

No prob. We live to serve :ph34r:

[RedXray]

Just remember all standard round batteries (AAA, AA, C, D) are rated at 1.5 Volts
so the more you add just add 1.5 volts... So two AAs = 3V... Three AAs = 4.5V... Four AAs = 6V etc.
Try not to exceed the LEDs max forward voltage.

[computerman]

ok i have been looking and i think i'm going to go with a 9 volt battery... will that work fine with about 15 LEDs that have a current of 20Ma? for the forward volt at the site it just says 2.0 at IF=20mA now i'm guessing that means that if its 20Ma then it takes 2 volts? just a guess if u want the site http://www.everlight.com/prd_list.asp?lang...g=en&g=26&p=421 (http://www.everlight.com/prd_list.asp?lang=en&g=26&p=421)

[linear]

Originally posted by RedXray@Aug 2 2004, 10:55 AM
Just remember all standard round batteries (AAA, AA, C, D) are rated at 1.5 Volts
so the more you add just add 1.5 volts... So two AAs = 3V... Three AAs = 4.5V... Four AAs = 6V etc.
Try not to exceed the LEDs max forward voltage.
Two big exceptions to keep in mind:

a) rechargeables are 1.2 Volts
B) batteries that have been used a while are 1.x volts, where x < 5.

Decent quality LED flashlights have circuitry that attempts to overcome the general suckiness of batteries as a voltage source.

computerman, for your 9V battery example, you can run up to 4 of your 2V @ 20mA LEDs in series from it. To do more, you have to combine series strings of LEDs in parallel. Each parallel string will draw an additional 20 mA from your battery, so with 16 LEDs you'd need about four strings of four LEDs, putting an 80mA load on your battery.

9V batteries are rated in the neighborhood of 150 mAh (milliamp-hours) so you can enjoy the light show for a little less than two hours before you drain the battery with this scheme.

Edit: to clarify what I mean by the "general suckiness of batteries as a voltage source," check out the datasheet on a duracell (http://www.duracell.com/oem/Pdf/MN1604.pdf) and in particular the discharge curve. The voltage will sag enough after a several minutes, that you probably won't be able to light your LEDs at all.

[computerman]

ohh umm ok well then should i just stick with the regualr 1.5volt batteries and do like wat Redxray said and just for every volt i need add another battery?
oh and what do you mean by string?

[zeLupin]

don't say anything about wacky times cause i was up since.....2 p.m yesterday :D

ok to say it simple its like this

supply voltage is the ORIGINAL voltage you are putting into the LED.
forward voltage is how much you WANT to go into the LED
Ampers you should leave at .02

so it would be 12(from psu) - 3.3 (typical rating for white,blue,green and such leds)/.02

remember red LEDs share a different voltage maximum than every other color.

[anode]

Just a few notes.

I rememeber the color ccode by
bad Boys rape our young girls but violet gives willingly

But thats fine for US color codes. The Euros use a 5 band color code (forgot that one in a hurry!)

The voltage of using multiple batteries. Voltage is summed when in series, and amps is summed when in parralell. (You can combine differnet banks to get desired results)
Batteries are considered 'good' when at or above 80% of rated voltage

The resitors neened for a LED is not that big a deal. Rule of my thumb, if going off 12V I grab a 1k If off 5V then somwhere in the 330ohm to 470 ohm range. You can use a bigger resitor with no problem other then it being a little dimmer and wasting a little current. No resistor tends to turn them into "smoke emitting diodes" Done that!

Luppin said:

" supply voltage is the ORIGINAL voltage you are putting into the LED.
forward voltage is how much you WANT to go into the LED
Ampers you should leave at .02 "

Going IN? I guess. I have my resitor on my breadboard on the ground side. Gives me 5.1 V in and the nominal 3.1 on the cathode before the resistor. 6 of one, half dozen of the other. ( do keep in mind, electron flow *from* ngetive to positive. That always screws me up when designing)

[dworld]

well i have one question related to this on my case when they hooked up leds they just ran them into a molex conector so like how come mine dont blow up

[zeLupin]

Originally posted by dworld@Aug 2 2004, 07:52 PM
well i have one question related to this on my case when they hooked up leds they just ran them into a molex conector so like how come mine dont blow up
there might be a resistor somewhere along the way. check the connections. also see how much power is in the connection with a multimeter.

[anode]

Originally posted by dworld@Aug 2 2004, 07:52 PM
well i have one question related to this on my case when they hooked up leds they just ran them into a molex conector so like how come mine dont blow up
What are these LEDs for? Molex, like a HD or Floppy connector? Or do you mena like HD and power that are being plugged into the mobo? If they are shrinkwrapped, there *might* be a resistor under there.

[dworld]

well i cant see one unless it is the wire soemhow


well no these are leds they stuck on the case just for looks they go into a molex conector

[mwbrooks42]

Originally posted by dworld@Aug 2 2004, 07:52 PM
well i have one question related to this on my case when they hooked up leds they just ran them into a molex conector so like how come mine dont blow up
Did they hook two or more up in series? I've had luck running two LED's in series with a 4.8 V supply and no resistor. Drop is drop. Or the LED's might have a built-in series resistor. Maybe even a voltage regulator, I don't know--some of these new super-bright LEDs get pretty fancy.

[anode]

Originally posted by mwbrooks42@Aug 2 2004, 10:49 PM
Did they hook two or more up in series? I've had luck running two LED's in series with a 4.8 V supply and no resistor. Drop is drop. Or the LED's might have a built-in series resistor. Maybe even a voltage regulator, I don't know--some of these new super-bright LEDs get pretty fancy.
I just tried running them in series (3) and it drops at each stage. Not surprising. I just would never have thought to run them in series. Loose one and they all go out. Then go fish to find the bad one. (not that LEDs fail often) But its a nice cheap/easy trick.

Been thinking of lighting my bedroom with just LEDs (have a 120watt solar cell on the way) Series idea, might be part of the trick there.

[linear]

Originally posted by dworld@Aug 2 2004, 05:52 PM
well i have one question related to this on my case when they hooked up leds they just ran them into a molex conector so like how come mine dont blow up
It depends on the LED--some can handle a 5V drive voltage, but the current the LED draws makes it fail much earlier than typical.

An LED typically has a 100,000 hour service life, about 11 years. You shorten that significantly when you overdrive them.

[dworld]

welll ok one mine they have 3 leds on the conector and i had some bare wire so i checked and it has 5.13 volts so could i hookup up 4 more leds

[dworld]

well mine arent in a chain they all divide off of 2 central wires

[fryguy]

[QUOTE=linear]Don't use the calculator when you use batteries as power. They have an unknown internal resistance, so you can't really get an accurate calculation.QUOTE]



You can calculate the internal resistance of a battery by shorting it through a high current amp meter briefly and getting the peak amperage then you can calculate the internal resistance of the battery with R=V/I. To get a more accurate reading you can compensate for the resistance of the amp meter.



When taking the reading don’t short it too long, this will cause the battery to get hot fast. No damage will happen with temporary shorting it but don't do it to all your batteries. Big batteries produce a lot of current so don’t try this for them! It’s not necessary to know this for most purposes anyway! So why bring this up when powering LED's ?

[Sportnskater801]

good luck