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total LED mA question

B

boardsportsrule

[H]ard|Gawd
Joined
Nov 27, 2003
Messages
1,107
ok, im running 5 LED's in a parralell...i need to add up the total mA to determin the resistor i need, and to do this i just straight up add the numbers, rihgt??? thanks! :)
 
wait.. how are you gonna wire the LEDs???

remember.. each LED neesds it's own resistor... using one resistor for a bunch of LEDs is not good practice, cause if one LED goes bad.. you can probably fuck up the others too...

just use a 330 OHM resistor for each LED, and use a 5V supply

so you're need 5-330 ohm resistors... i personally like 1K resistors.. i hate my LEDs so damn bright..

in the above configuration, if one LED burns out.. it will not affect the current in he other 4..
 
i cant do that...im running this as a backlight for a LCD screen, and i am VERY limited in space....i cannot have 6 wires running back there for 1...and then the issue of soldering it all like that.. i COULD do that but it would be alot harder...plus LEDs have a long life..right?
 
just put the resistor right next to the led, if there is room for an led there has to be room for a resistor soldered straight to it, then to the parallel running wire
 
boardsportsrule said:
i cant do that...im running this as a backlight for a LCD screen, and i am VERY limited in space....i cannot have 6 wires running back there for 1...and then the issue of soldering it all like that.. i COULD do that but it would be alot harder...plus LEDs have a long life..right?
Click to expand...

I guess.. if i didn't have room to do it.. i wouldn't do it.. but whatever... what exactly are you adding LEDs too?
 
there was this little white box behind the screen where the previous green LEDS where..they were just like surface mounted LEDs tho, not LEDs like we think of them....i could use 3 mm leds and some skinny wire...hmmm...
 
I believe LED with internal resistors may exist...heard a professor talking about them recently I think...Might want to do a bit of search on google or digikey/jameco/mouser's site.
 
Ive only ever seen LEDS with resistors to run at 12V, i imagine so people can put them in cars, and then still have them blow because they cant get over the fact that cars arent 12V all the time. You can however get surface mount resistors pretty easily at any decent parts supplier. Do you mean surface mount? or little square panel mounting ones? The latter will be easier
 
Herulach said:
Ive only ever seen LEDS with resistors to run at 12V, i imagine so people can put them in cars, and then still have them blow because they cant get over the fact that cars arent 12V all the time.
Click to expand...


What are you talking about? LOL

boardsportsrule said:
there was this little white box behind the screen where the previous green LEDS where..they were just like surface mounted LEDs tho, not LEDs like we think of them....i could use 3 mm leds and some skinny wire...hmmm...
Click to expand...

why don't you just use surface mount LEDs then??and put them where the green one's are.. and i don't know what you mean by "not LEDs like we think of them" ??? what the hell does that mean? lol
 
well, they're built into the PCB...there is no glass to bee seen, just some circuitry that lets off alot of light...its an array of a BUNCH of LED's..its really quite amazing...im trying to find it but my digicam's gone, and i might have thrown it out today(cleaning)....ill lettcha know if i can find it...maybe i could just use some surface mount ones and make a little PCB for em...
 
found it..its 11 Leds by 4 leds...they dont look like LEDS, justmetal on a PCB....its so wierd...how hard would it be to solder some surface mount LEDS onto a bread board and use that???(is that even do able on a bread board or woul di need to make a PCB?)
 
boardsportsrule said:
found it..its 11 Leds by 4 leds...they dont look like LEDS, justmetal on a PCB....its so wierd...how hard would it be to solder some surface mount LEDS onto a bread board and use that???(is that even do able on a bread board or woul di need to make a PCB?)
Click to expand...

it's not that hard to do surface mount soldering, you just need a tweezer, and a steady hand.. as for doing it on a bread board.. i think that's a no go.. you would need to make you're own little board for it.. we have these cool machines at my school that can cut out nice little 1 layer copper sheet boards for surface mounting... but yeah lol.. that machine costs a bundle..
 
RancidWAnnaRIot said:
What are you talking about? LOL
Click to expand...
Exactly my point.

When a car is off the electrics are somewhere in the region of 12V (prob just under) because its drawing power from the battery. When the engine is running so is the alternator, which is what powers all the electrics, and runs at 13.8V, which is what is needed to charge the battery.
 
Herulach said:
Exactly my point.

When a car is off the electrics are somewhere in the region of 12V (prob just under) because its drawing power from the battery. When the engine is running so is the alternator, which is what powers all the electrics, and runs at 13.8V, which is what is needed to charge the battery.
Click to expand...


i don't know much about cars.. but i don't see how this applies to an LED.. i mean if you wanted to power an LED with say 5V all you have to do is feed that 13.8V (or just under 12V) to a regulator that can drop the voltage to 5V or any other desired voltage...
 
RancidWAnnaRIot said:
i don't know much about cars.. but i don't see how this applies to an LED.. i mean if you wanted to power an LED with say 5V all you have to do is feed that 13.8V (or just under 12V) to a regulator that can drop the voltage to 5V or any other desired voltage...
Click to expand...

In my original post i was talking about LEDs with inbuilt series resistors for 12V, then happened to coment that it was prob so people can use them in cars, even though they still wont work.
Youre right a regulator would work fine, i was just being a bit OT, while explaining to you why you cant use a 12V LED from a 13 volt source. You asked
What are you talkking about? LOL
Click to expand...
so i told you.

 
Herulach said:
In my original post i was talking about LEDs with inbuilt series resistors for 12V, then happened to coment that it was prob so people can use them in cars, even though they still wont work.
Youre right a regulator would work fine, i was just being a bit OT, while explaining to you why you cant use a 12V LED from a 13 volt source. You asked
so i told you.

Click to expand...


ooohh.. built in resistor LEDs...


jman1 said:
HERE are some calculators and some simple info for use of LEDs http://www.cool-cases-usa.com/design.html
Click to expand...

As i said before.. the method in the website jman provided is not good practice.. if one goes bad.. the whole thing goes to hell.. but i guess the system doesn't need to be robust anyway.. but yeah...
 
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