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NEW to Forum

Hello, I'm trying to build an array of led turn signals for my motorcycle using 31 leds. At the bottom is the specs of the LEDS. Now, I am placing them in a circular pattern and was wandering if is best to use a resistor per LED or per 3 or 4? Also, when I put the LEDs in series can I run a continuous link attaching the resistors between the sets or each LED til I get to the to make my Negative Ground. Or do I have to make a sort of Positive and Negative buss? Thanks for and advice and feedback

Forward Voltage (V) : 3.2~3.5

Forward Current (mA): 20

You should use 1 resistor for every 3 or 4 LEDs, although with 4 LEDs in series you may not need a dedicated resistor at all.

Is that 20 mA the absolute max, or the recommended current?
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Wacky Races 2012!

I went back and took a look and it didn't say. It just stated 20ma. But I can run the continous series of 31 going 12v +, resistor, led,led,led,resistor,led,led,led,resistor,led,led,led, 12v neg.

You mean: "+12V resistor LED LED LED GND" 10 times?

Yeah, you'll probably have to make a kind of buss..

Like aurgathor corrected, you'll probably have to "Batch" the LEDs. Positive to resistor, resistor to 3 or 4 LEDs, then to neg. repeat said set-up until all the Leds are powered.

Powering LEDs in series can get weird, not to mention the load on the current limiting resistor you use,,, If you really want to power the LEDs all in series, then a current controlling LED driver would probably be a better option than a simple resistor.

And, theres an argument to be made for powering the LEDs in 3 or 4 LED strings, rather than all off a single driver.. They're important signals on your vehicle.. If a single string fails, or even a couple stings, no big whoop.. Your turn signalling still works, allbeit not pretty.. If theyre all driven off a single circuit, (especially one designed, and built by hand) once theres a single failure in the circuit, no signal.. no light.. no love...

I'm a big fan of reducing work, and component count, but in this case I think that the redundancy of a series of 3-4 LEDs attached to power with a limiting resistor is a better option here.. Better fault tolerance.
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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Thanks alot. I just hate paying a high price for somthing I know I can do easily myself. I have a Harley and they want $70 a set for led turn signals that just retro fit in your turnsignals. I know I can do this I just want to do it right the first time. I looked at using the mini PWM to turn the leds down a little for the front turn signals due to the do stay on until you turn the turn signal on.
THen my next project will be the brake light. THey want $150 for them boys. I figured I could do it for $20 to $30 using 50 to 100 leds.

Curious, do you have a link to the LED you are using? Does a turn signal have to be a particular color, 3.5V sound like a white or blue LED? Have you tried these LEDs at 20 mA in the bright sun to see if you can see them?

questions questions

Notwithstanding of bluish headlights, usually only police, emergency, etc., vehicles are allowed use blue lights, so he should be using white LEDs. Which are just blue LEDs with phosphor.
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Wacky Races 2012!

4 LEDs won't work. 4 x 3.2=12.8V, very close to the battery voltage so a very small resistor would be needed. However the battery voltage is variable and can easily reach 14V and that may lead to smoke.
3 LEDs would drop 9.6 - 10.5V so the ~2-4V difference can be handled better by a resistor. 3V @20mA yields 150 ohms.

Thanks for the help

Being in the EMS industry in parts or services I am pretty sure you are right.

Forgive my ignorance, I was taught that regarding DC flow, it is from – to + so should not the resistor like so negative > resistor > led?

From what I gather you imply the opposite...thanks just curious. Cus I have LEDs running on battery with the resistor like so...

+[____]- resistor > LEDs > back to positive

is it the same like this....

-[____]+ resistor > LEDs > back to negative

thanks.

I went ahead and put the resistor on the positive side