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Old 08-28-2008
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LED Cluster Idea Thread for LED whiz kids only...

So I am going to add individual component LED's in my cluster to add light where it is not supposed to be directly under the needles...

The problem is, I'm not sure what is safe. I know the truck should run at about 14 volts when the engine is running.

The LED's I'm looking at are 360 degree LED.

The specs are:
Continuous Forward Current: 20 milliamps
Voltage Max = 3.4 V
Voltage Nominal = 3.2 V

The question I have is would It be completely safe to run 4 of them in series with no resistor?

When I check on the "series LED resistance calculator" it says I should be using a small 25 ohm resistor. This is VERY tiny. I wonder if no resistor would work just fine. On a 12V system, you would not need a resistor, but I'm not sure about when the engine is running and it typically is at what you would guess is 14V.

Does anyone have more experience with this?

I just think it would be nice to run enough LEDs in series to not need a resistor. I think if I only used 3 in series it would put too much current into the LED's and shorten the life of them. At the same token, 5 of them in series is probably WAY overkill and they wouldnt light up as bright.

Shane - you might know this one.. you or trev.
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Old 08-29-2008
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nobody knows? Shane where are you?
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Old 08-30-2008
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I think you -have- to run a resistor on LED's no matter what, even if you add up to 12 volts + to use all the power coming in... it cleans up the current, or else you'll start popping random bulbs.
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Old 08-30-2008
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I would run the leds in parallel with a single 470 in series( say 4 leds per resistor).

The resistor is there to limit current and adjust voltage.


Either method you choose you need the resistor. They cost what a few pennies a piece pending your source.
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Old 08-30-2008
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Try this simple NFET source-follower circuit. It will give the LEDs a constant voltage, independent of the number of LEDs you use, and only 3 parts!


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Old 08-30-2008
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I believe it's a 510ohm 1/4w resistor that runs in line before each cluster of 3 leds per resistor... Anything more and only 3 will come on. So far I've found 3 is the max... with that size resistor. That's what I have in my dash and that's what I ran in shane's when I did his as well...

You may be able to play around with different sizes, I would probably say smaller resistance to run more in the same cluster, but I'm not sure...
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Old 08-30-2008
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Quote:
Originally Posted by TrePaul86 View Post
I believe it's a 510ohm 1/4w resistor that runs in line before each cluster of 3 leds per resistor... Anything more and only 3 will come on. So far I've found 3 is the max... with that size resistor. That's what I have in my dash and that's what I ran in shane's when I did his as well...

You may be able to play around with different sizes, I would probably say smaller resistance to run more in the same cluster, but I'm not sure...
The big advantage of my source-follower circuit, its the voltage will be constant, independent of load. This isn't the case with resistive voltage
dividers.
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