12v LEDs

D

Daifeichu

[H]ard|Gawd
2FA
Joined
Mar 16, 2002
Messages
1,864
Where's a good place online to buy 12v leds. I'm looking for white ones, 3mm. I don't want them in strips or clustered together. I've googled and cannot find one 3mm white 12v led.

I don't want to spend $5 for a single led either.

LSDiodes doesn't have any at the moment. That's where I usually get mine from. They are dirt cheap and of course robots kill, but they don't have the largest selection.

twatt
 
I've never heard of a 12V LED. Most work at very low voltage around 2.2-2.5.
 
webbee said:
Here are some places to look:

http://www.allelectronics.com/cgi-b...egory,INVENTORY.brand,INVENTORY.model&start=0

http://superbrightleds.com/leds.htm

http://www.123leds.com/
Click to expand...


Thanks for the sites webb. Unfortunatly they don't have them either.
I agree drizz, resistor it is. I just like keeping things simple.
You're right dino, most do. But if you search around you'll find 12v leds. The local tronix shop near me has them but no white ones, just green and yellow.
 
really 12v LEDS are just ones with pre-soldered resistors in them.
 
However he does bring up a good point that LED's should be a different voltage :D It's a pain having to wire up only a max of 5 led's in a string. I should be able to wire up 12 in a string (1v each)
 
I'd imagine IOke is right.. a "12v led" for sure just has a resistor built in already..

Also stringing LEDs in series is considered very bad practice.. it would work.. but once one burns out.. you're fucked.. all of them get fucked up.. Also.. you will need at least one resistor.. you never wire LEDs without resistors.. NEVER...

last.. if you're gonna do multiple LEDs what you should be doing is wiring them all in parrallel along with each parallel set having it's own series resistor for the corresponding led...

in other words.. every LED should have it's own resistor... any other way is just bad practice..
 
What if you're using a large number of led's in tight places? Find another lighting solution?
 
But sometimes it's impractical to use lots of resistors for LED modding. I mean, if you need 5 LED's that are all of the same type, what is more inconvenient... stringing 5 together, and running them off the 12v line, waiting the 50 000 MTBF hours until one burns out, and re-doing the string, or soldering them all with their proper resistors, onto a board if needed... Not to mention the extra heat emitted by reducing down the voltage...

Also.. you will need at least one resistor.. you never wire LEDs without resistors.. NEVER...
Click to expand...

How is this true? if you're running 5 (or even 4) led's in series off of the 12v line, each LED will recieve 2.4v (or 3v, respectively)... Most 5mm led's have a maximum forward current of at least 3v, white and blue leds can usually work up to 3.5v without burning out. Customs be damned, it's not like you're putting together some sophisticated circuit!

having said this, lots of car mod products are 12v leds... as cars are restricted to 12v output... Try a wallmart/Canadian Tire, etc.
 
Arcygenical said:
But sometimes it's impractical to use lots of resistors for LED modding. I mean, if you need 5 LED's that are all of the same type, what is more inconvenient... stringing 5 together, and running them off the 12v line, waiting the 50 000 MTBF hours until one burns out, and re-doing the string, or soldering them all with their proper resistors, onto a board if needed... Not to mention the extra heat emitted by reducing down the voltage...



How is this true? if you're running 5 (or even 4) led's in series off of the 12v line, each LED will recieve 2.4v (or 3v, respectively)... Most 5mm led's have a maximum forward current of at least 3v, white and blue leds can usually work up to 3.5v without burning out. Customs be damned, it's not like you're putting together some sophisticated circuit!

having said this, lots of car mod products are 12v leds... as cars are restricted to 12v output... Try a wallmart/Canadian Tire, etc.
Click to expand...

the resistor's purpose is to limit current.. there is no telling what the current is without the resistor.. the resistive properties of a diode change easily therefore it's hard to get a nice consistent (and safe) current through the LEDs

without a resistor your current can easily spike up (due to some other component turning on or off.. say in a car for example.. you get voltage spikes when some electric motor or something else turns on.. the current can easily spike up just due to noise..).. then who knows how much currect will flow.. you can burn your LED out prematurely.. the forward voltage to current curve of a LED (actually of diodes in general) increase exponetially..

i'm not saying it won't work.. it's just very very bad pracice.. you can burn out LEDs easily..

as i said.. i'm sure the single "12v LED" has a resistor built into it.... you need that current limiter... show me a 12v LED with a foward voltage of 12V.. i'd like to see that..

Also.. how the hell can you have a forward current limit of 3V?? that doesn't make sense...

you sure about that.. a CURRENT limit of 3 VOLTS??? since when is current measured in volts??

That is why you need a resistor per LED.. every LED has a different forward drop.. (usually in the range of like 1V - 3V).. putting them all in series is just asking for trouble.. wiring the LEDS all in series along with a series resistor is alittle better.. but you're gonna have a fun time finding the right resistor to get just the right amount of current through there..

one thing that can be done.. is use one resistor, tie one end to 12V, and then the other end to all your LEDs (anode.. and then the cathode to ground).. that would work.. but that is also a bad idea given the different foward voltages.. you just won't be able to control the current well.. plus. once one of the LEDs burns out due to the poor wiring scheme.. all the others are more likely to burn out.. especially because all the LEDS are not exactly the same ( No two LEDs are ever the same due to manufacturing tolerances.. it is impossible to make identical LEDs. that's why we have tolerances. )

here's food for thought...

the ideal LED is a short circuit when forward biased.. let's assume these LEDs are ideal.. you're telling me you want to create a short between power and ground??? LOL.. ridiculous.. trust me on this man.. you want resistors.. at least one.. but even then that's a bad idea.. you really should have one resistor per LED in parallel. if you put them in series.. you still need a resistor.. but it will be a bit tricker and getting the current you want (whatever the forward current should be for a given forward voltage)
 
Yeah, I meant voltage. I edited that post like 3 times adding stuff to it, I guess I got lazy by the third revision ;). It's 2am here too :).

I never thought that would be a problem with a good quality PSU, as, voltage and current fluctuations (like, during a HD startup) could royally screw up your box, I figured that would be properly filtered. Good information nonetheless.
 
Arcygenical said:
Yeah, I meant voltage. I edited that post like 3 times adding stuff to it, I guess I got lazy by the third revision ;). It's 2am here too :).

I never thought that would be a problem with a good quality PSU, as, voltage and current fluctuations (like, during a HD startup) could royally screw up your box, I figured that would be properly filtered. Good information nonetheless.
Click to expand...

Like i said.. you can do that stuff.. but i would never risk wiring anything like that.. whether the circuit is important or not...

this is what i'm trying to get at.. this is the proper way

http://www.ngineering.com/parallel.gif

Also..

this is okay too

http://www.ngineering.com/series_LED.gif

but i wouldn't do it like that .. i'd recommend the parallel way.. because once one burns out in series... everything gets all fuxored... You would also have to make sure that resistor can handle a decent amount of power.. just in case something shady happens when that one LED burns out.. you don't want to fry everything else..

so yeah.. hehe that's all i was trying to say.. you should do it one of those two ways..

last, i cna't find a picture.. but another way you can do.. which would work.. but i don't recommend is using one resistor, and then off that resistor wire all your LEDS in parallel.. so you use only one resistor.. but i really don't recommend that.. if you're gonna do that.. make sure the LEDs are as matched as possible.. DO NOT do it with different types of LEDs..

Just as i thought.. here's 12V and 5 V leds that don't need resistors.. because they're designed with a resistive load inside

http://www.elexp.com/opt_3330.htm

sorry for previous grammar errors and typos..

also.. sorry if i came off as a dick
 
Here's another question. Why are LEDs shaped the way they are? Why not square? Why not in large sheets?
 
Qtip42 said:
Here's another question. Why are LEDs shaped the way they are? Why not square? Why not in large sheets?
Click to expand...


This is the most "Sqaure" LED i've ever seen

http://news.thomasnet.com/fullstory/464985

my guess is it has to do with how the light gets emited from the P-N junction.. light only comes out form a limited angle.. so the cone shape helps expand the viewing angles. A square wouldn't really spread the light out well...

as for a sheet. i'm not sure what you mean by a sheet.. but the same reason would apply...
 
Qtip42 said:
Here's another question. Why are LEDs shaped the way they are? Why not square? Why not in large sheets?
Click to expand...

Most led's are shaped the way they are because the case acts as a lens/filter. The actually diode is significantly smaller and square or rectangular in most cases. Surface mount leds are rectangular or square.

I don't know why they couldn't be produced in large sheets, the larger dimensions of silicon would probably be cost prohibitive.
 
Qtip42 said:
What if you're using a large number of led's in tight places? Find another lighting solution?
Click to expand...


No.. you just have to think like an engineer.. be alittlre more creative... solve the problem of space!!
 
TheTMan said:
Most led's are shaped the way they are because the case acts as a lens/filter. The actually diode is significantly smaller and square or rectangular in most cases. Surface mount leds are rectangular or square.

I don't know why they couldn't be produced in large sheets, the larger dimensions of silicon would probably be cost prohibitive.
Click to expand...


true that.. i forgot that surface mounts are actual rectangular....

i guess there aren't good reasons to make them as sheets either...??
 
RancidWAnnaRIot said:
No.. you just have to think like an engineer.. be alittlre more creative... solve the problem of space!!
Click to expand...

... like using led's with integrated resistors??? haha
 
Get some FETS, build a constant current power supply, then you can put a bunch of LEDS on a sting if you want.
 
Whatsisname said:
Get some FETS, build a constant current power supply, then you can put a bunch of LEDS on a sting if you want.
Click to expand...

you could build a current mirror with FETs.. that would work well too.. but.. the LED with built in resistor will probably take up less space..
 
Whatsisname said:
Get some FETS, build a constant current power supply, then you can put a bunch of LEDS on a sting if you want.
Click to expand...

Or just use a voltage regulator as a current regulator - one piece simplicity.

Right now I'm working on a large LED outdoor lighting project. There are 4 white LEDs on a circuit board wired in parallell. There will be 60 of these circuit boards. This means the voltage drop is about 2.2 volts and I'm aiming for a current draw of 60ma per board. This way if one or two of the LEDs burn out, they will still be in spec. I have several options -

1. run them in six parallel groups of 10 in series
2. run them all parallel

and then the wiring challenge - wire each to its own line that runs back to the power supply or wire groups in series to minimize the amount of wire used?

Hard wiring 10 in series means I can use a higher voltage power supply and less resistors, and also means less wiring runs and clutter. Wiring them in series at the power supply means 10x more wiring and clutter, but the ability to swap a failed one out more easily.

Wiring in parallel means a 5v supply (probably) at 3.6+ amps which means that over half my power will be lost as heat, lots of resistors and wiring, but does give the advantage of diagnosing (and replacing) each circuit board individually. I know that this is the better design electrically, but running 60 lines through conduit is NOT fun.
 
Each line is four strands of 24ga wire with a PVC jacket. About 1/4" diameter, but that adds up quickly. Using PVC conduit, I could probably get 10 in a 1" pipe, but it would take a 2.5" pipe to get all 60. These need to be run underground so conduit is needed.
 
Going on 2 years, and no problems yet. No resistors in the entire string.

Server031.jpg


Server018.jpg
 
You must log in or register to reply here.
Back
Top