Hey guys, just bought some loose LEDs from ebay and I am stupid to the electrical thing. If I put one resistor in the main power wire(12 volt), can I run multiple LEDs directly from that wire downstream of the resistor ? Or does each LED need its own resistor and direct connection with an unrestricted 12 volt wire ?

I hope someone understands this question, because its hard to explain. Also, is the longer lead pos. or neg. on the LED ?

 

The short side is negative. Also there's a flat spot (looking down) on the negative side.

Here's what I came up with for 1 to 6 LEDs (parallel - not in series).

You can either get a tiny box from radio shack to hold the resistors or you can put it all on a board.

If you're gonna run more than 6 LEDs on this circuit then you'll need less resistance -- just make sure the divided value would be the same: 150/390 = .385 So if you wanted to run 10 LEDs on this circuit you might try 120/312 = .385 Doing it this way will keep the voltage the same but raise the amperage a bit. A bread board is a beautiful thing for trying different combos out.

Good luck.



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Thanks for the reply chain, but I`m sorry to say that I have no idea what the 150/390=.385 thing means or how you come up with that... I have the most basic knowledge of electronics and thats it. So let me ask this, how many LEDs (vf 3.2 - 3.6) can I run off of a 510 ohm resistor ?

 

O.K. the "=.385" is the value of R1 / R2. It must remain constant in order to maintain the voltage. If you lower the value of R1 then R2 must be lowered proportionally. The voltage will remain the same but lowering the resistance will increase the amperage (what ya need to run more LEDs and keep 'em bright).

Not sure how you intend to use the 510 ohm resistor -- hooking up that resistor parallel before the LED's will probably cook it unless it's a ceramic coated bad boy. Hooking it up in series will kill the amperage and I doubt the LED would light at all.

 

It will light with the 510 in series. But it won't be very bright. I just hooked up a crude set up with a 680 ohm and a LED. Voltage was at 12.2 V (battery without resistor was at 12.5V) but amperage was reduced to 22 MA at the leads. Not sure how long the LEDs would last with 12V hitting them all the time.

 

That makes a little more sense to me. The LEDs were bought as a 100 pack with 100 resistors to make them work off 12 volt, so I figured it would be cake. Stupid me. Thanks for the help, man !