Help LED's and wiring please!

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avbat

Active Member
I have been trying to read up on this for some time now, but most references that I find are too advanced i guess for me.

I have to make a string of two white, wide-angle leds, and then connect them to a regular red one. My problem Is that the white ones appear incredibly bright sometimes, and other times they aren't. I DO NOT want them to be so bright.

How do I do this? Any help would be appreciated.
 

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DrewSmith007

Sr Member
RPF PREMIUM MEMBER
Do you mean you want to have 2 white LED's and 1 red LED on and off at the same time, but make the white ones less bright?
 

exoray

Master Member
You need to limit the current further on the white ones...

What battery voltage and type of battery are you using? What are the specs for the LEDs?
 

Delmustator

Sr Member
Most LED forwarding voltage ranges from 1.5 vdc to 3.7 vdc. If your using non-high power LEDs, you can drive these with a couple AA batteries.

If your using Cree, SSC, Luxeon, P7 high power LEDs, you need a minimum 3.7 vdc between 300 mA to 3000 mA current. Most Li-Ion rechargeable batteries produce 3.7 vdc and push up to 2000 mA of current. So watch it! If you push too many milli-amps, you'll fry the LED instantly. Get a good buckpuck to limit the current to under 1000 mA. READ THE DATA SHEET FOR THE LED TO DETERMINE AMPERAGE LIMITS.

To dim the white to be less than the red, just add a resistor in-line with the white LED. A 5-10 ohm resistor is probably all you need. There are calculators on the web that can help you figure out exactly what ohm'age you need.
 

DrewSmith007

Sr Member
RPF PREMIUM MEMBER
You'll want to run the white LED's separate from the red, or you'll dim the red LED too.

EDIT: Not separate as in whole other circuit, but parallel with with each other.
 
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DrewSmith007

Sr Member
RPF PREMIUM MEMBER
Here's a schematic for what you need to do. I can't really help further without knowing your battery voltage or info about your LED's.

Change the value of resistor 2 to change the intensity of the white LED's. The higher the resistance, the lower the intensity. Hope that helps!
 

avbat

Active Member
Yea I feel like what I am doing is not that hard:

Having two white, wide-angle LED's turn on the same circuit as a standard run-of-the-mill red LED.

The wide-angle white ones are too bright though.

Here are the specs for the White LED's:

5mm Straw Hat White LED With Wide Angle

Emitted Colour : White

Size: 5mm

Lens Color : Water Clear

Forward Voltage (V) : 3.0~3.2

Forward Current (mA):20

Viewing Angle: 160-180 degree.

Luminous Intensity: 18000mcd

I figure I can experiment and go from there with help from you guys lol
Thanks so much for the help thus far guys I appreciate it!
 

exoray

Master Member
What is your battery source, and what is the specs on the red led? If you are trying to bring a 18000mcd LED inline with a standard 15mcd red LED it's going to be a challenge, depending on the white LED it might cut out before it dims that much...
 

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avbat

Active Member
I have a 9V and a 6V power source and I can use either, but I dunno which is best to use for what I am doing, and no I have no specs on the red LED, but none of them can be super bright.
 

modeljag

Active Member
White leds need to be run in parallel with the red, and a large enough resistor needs to be installed in series with the whites to dim them to your liking.

edit: drewsmith007's diagram is exactly what you need.
 

avbat

Active Member
I am seriously a novice when it comes to resistors and what they do, as well as where to get them lol . . .
 

exoray

Master Member
Well if you don't have any resistors laying around get some tomorrow, a few packs from Rat Shack will do, get the 100 Ohm ones for this experiment...

I stole DrewSmith007's circuit, see attached...

This is a test circuit because predicting how the LEDs will dim is guess work... And this test circuit is setup to use all 100 Ohm resistors to help narrow down what values you actually need, this allows you to purchase one value resistor and then experiment, keeping it simple...

So using 100 Ohm resistors, wire it up like shown in picture #1, see what happens, this is for a 6 volt battery source... If the white LEDs are still too bright, one at a time remove a resistor on the White LED side, the standard Red LED should be happy as shown... If you get down to one resistor on the white LED and it's still too bright, then refer to picture #2, and repeat the process of removing one resistor at a time, except this time, remove them one at a time from staring at column 1... Example remove a resistor from column one, then remove another from column one, until there is only one left, then start on column 2... Not the most 'efficient' method to figure this out but a straight forward one...

If all works out you will find the sweet spot then, it's just a matter of working a little simple match to see what the final resistance is...

I know "what a hassle" but unfortunately you are the only one that can see the relative brightness of the LEDs and short of using a pot or variable resistor and measuring it after the fact this is the most straight forward way to narrow it down...
 
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avbat

Active Member
oh wow thanks exo. This will be great. I am going to give this a go tomorrow and see what happens. I have the day off for the most part so I am stoked to try this out.
 

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exoray

Master Member
oh wow thanks exo. This will be great. I am going to give this a go tomorrow and see what happens. I have the day off for the most part so I am stoked to try this out.

No problem, as long as the white LEDs just don't go out before they get dim enough (sometimes they do) doing the trial and error hack above will allow to calculate the final circuit values... Not an elegant solution but it will get the job done...

Tomorrow if you get happy results, post up the number of resistors left in whatever circuit and where they are located and I (or someone else) can push the numbers and give you a single resistor that will do the job...
 

DrewSmith007

Sr Member
RPF PREMIUM MEMBER
Also, with the forward voltage of each white LED being 3.0-3.2, you might not be able to use the 6V source with both LED's inline with each other, because the added forward voltages could be over 6 volts. So, if you're sure it's wired correctly, and the LED's don't come on, it could be due to not having enough voltage. If this is the case, up the voltage to 9, but make sure you've got enough resistance to keep the current to safe levels with 9V where you used to have 6V.

Are you getting anywhere with this?
 

avbat

Active Member
Hey guys. I discovered yesterday that I have an old, made up circuit board with resistors already in place. I do not know what type of resistors they are, but I figured i would mess around with it and put my lights on it to see what they looked like. They actually didn't look too bad at all, but it got me thinking if I am even using the proper type of LED. The white LED's are replacing ones that look like this:

IMG_4827.jpg


I have had no luck at all finding these or anything like them, so that is when I just got the wide-angle white ones I am using now.
 

jasonw2112

Sr Member
RPF PREMIUM MEMBER
I have to say I have never seen a LED like that before! That does'nt mean you still can't find them! If you can, check the circuit board for the output voltage. This will not help you check current, but it will at least give you something! You could also check the resistors ( by the color bands on them ) to determine what ohm's the resistors are in the circuit. Are you sure that the old LED was white? It looks like it could have been a frosted green.
 

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