How to wire LEDs

[heyok]

Originally Posted by BigGuyJT

Thanks for the great write up Heyok. Now lets see if I can get the pics posted...

Well done!

You're welcome.

[powercat]

This is a great write up. Can I just wire up the resistors and LEDs to the wires I already have on my Wraith RTR and use the existing plug at the ESC?

[heyok]

Originally Posted by powercat

This is a great write up. Can I just wire up the resistors and LEDs to the wires I already have on my Wraith RTR and use the existing plug at the ESC?

I can't really answer that because I have no idea where your existing plug and wires go.

[powercat]

Sorry, the lighting on my wraith is the stock simple axial lighting. I wondering if could just wire in a few extra lights and resistors on the wires that lead to the other lights. And since the BR-XL that I have installed has all the channels full right now, I don't have anywhere to plug another strand of lights in anyways.

thanks

[heyok]

Originally Posted by powercat

Sorry, the lighting on my wraith is the stock simple axial lighting. I wondering if could just wire in a few extra lights and resistors on the wires that lead to the other lights. And since the BR-XL that I have installed has all the channels full right now, I don't have anywhere to plug another strand of lights in anyways.

thanks

I found this picture. Pretty sure this is the one you have.


You could solder onto the red and black wires that go to the receiver and wire your LEDs into there, using the proper resistors, of course.

If you are worried that you have used up all your connections on your receiver, you could also get yourself a Y cable.

[BigGuyJT]

Heyok, could you use one fat resistor to run all of the leds of the same color? Say like a 1/2 or 1w resister (if those are even a common size) for 5+ white leds? Or does the parallel'ing of the leds change something?

[powercat]

Thats what i've got. Hadn't thought of the Y cable til you mentioned it. Probably the way i'll go. Thanks for the input and again, great info.

[heyok]

Originally Posted by BigGuyJT

Heyok, could you use one fat resistor to run all of the leds of the same color? Say like a 1/2 or 1w resister (if those are even a common size) for 5+ white leds? Or does the parallel'ing of the leds change something?

It would be nice, but no, that's not the way to do it. Skip this if the theory lesson bores you!

The LED is a semiconductor junction that has a certain "forward voltage". It is also has a maximum current it can use or it will have a shorter life.

I was going to go on, but did a google search instead and found a great answer. I want to quote from:
LED center » Why do I need a resistor with an LED?

Why do you need a resistor with an LED? The short answer: to limit the current in the LED to a safe value.

The long answer: LEDs are semiconductors, diodes in particular. The current flowing in an LED is an exponential function of voltage across the LED. The important part about that for you is that a small change in voltage can produce a huge change in current. That is the most important concept of this article. Resistors aren’t like that. The current and voltage in a resistor are linearly related. That means that a change in voltage will produce a proportional change in current. Current versus voltage is a straight line for a resistor, but not at all for an LED.

Because of this, you can’t say that LEDs have “resistance.” Resistance is defined as the constant ratio of voltage to current in a resistive circuit element. Even worse, there’s no real way to know exactly the relationship between current and voltage for any given LED across all possible voltages other than direct measurement. The exact relationship varies among different colors, different sizes, and even different batches from the same manufacturer. When you buy an LED, it should come with a rating that looks like this: 3.3V @ 20 mA typical. That gives you one point along the operating curve. Usually that’s a safe operating point. You may get a maximum rating in addition. It may be in the form of either a voltage or current. For example, a lot of people report buying “5V blue LEDs.” These are really not rated to operate continuously at 5V in most cases.

The other thing I’d like you to take away from this article is the idea that it’s more useful to talk about driving an LED with a current of a particular size, instead of a voltage. If you know the voltage across an LED, you can not determine the current flowing in it, unless you are operating it at the exact point along the curve that’s described in the specs. Worse, being “off by a little” in the forward voltage can have a drastic effect in the current. So the approach I prefer is to select a current-limiting resistor in order to achieve a target current in the LED.

Most 3mm and 5mm LEDs will operate close to their peak brightness at a drive current of 20 mA. This is a conservative current: it doesn’t exceed most ratings (your specs may vary, or you may not have any specs–in this case 20 mA is a good default guess). In most cases, driving the LED at a higher current will not produce substantial additional light. Instead, the junction (the working parts of the LED) has to dissipate the excess power as heat. Heating the junction will decrease its useful life, and can reduce the output of the LED substantially. Heating it enough will cause catastrophic failure (producing a dark emitting diode).

and he goes on to show a graph that helps explain this. I encourage you to visit the page.

Hope that answers you

[heyok]

Originally Posted by powercat

Thats what i've got. Hadn't thought of the Y cable til you mentioned it. Probably the way i'll go. Thanks for the input and again, great info.

You're welcome!

[BigGuyJT]

Wow that's a h3ll of an explanation. Thanks for the info, sounds like I should just stick with plan A.

[KJ10]

Meh, I still wired two additional white LEDs in parallel to the white side of one of those axial kits. Robbed 'em from the kit I used to light my son's truck. I'm running 6 white, he's got 2 white. No reds connected to either. About 3 months now and neither of them have had any issues, yet. They're cheap enough (to me) that I'm not too worried about it, though.

[kwonchoba]

Got everything to do this!

[BigGuyJT]

Originally Posted by kwonchoba

Got everything to do this!

Awesome! Please post pics of your project!

[dieselmudder]

this was linked into a thread i started on another forum. handy little widget for designing LED systems

LED series parallel array wizard

didnt realise this link was already provided earlier in the thread. i missed it on my read through.

[BigGuyJT]

Originally Posted by dieselmudder

this was linked into a thread i started on another forum. handy little widget for designing LED systems

LED series parallel array wizard

And this is the thread that I learned from! I did exactly what he said and used the calculator he posted.

[badhoopty]

maybe its been discussed...

is there any way to have just one resistor and run the leds in series after it?

it'd be awesome to cut down on the amount of resistors and wiring.

[dieselmudder]

i actually just pm'd heyok about that this past weekend. in series the voltage necessary adds up. heres the original message and subsequent replies.

Quote:
Originally Posted by dieselmudder
Quote:
Originally Posted by heyok
Quote:
Originally Posted by dieselmudder
need a little help here. wanting to try some LED wiring in series, tried to research but still coming up a little confused. wanting to run a 7 LED setup on my exo terra, either 2 or 3 S. ive figured out 7 LED's divided by 7 volts is 1 volt drop per LED so will i need (7) 1 volt LED's? everything i see uses a resistor, just not sure how to determine what size resistor to use. ive tried searching some LED calculators but its not helping much. hoping you can give me a simple equation to make the figureing easier.

Hi,
First, I have to ask what colour LEDs you are going to run?
The reason is that different colours have a different voltage drop.
White and Blue are about 3 volts, red is about 1.7 volts.

Let's say you have 7 white LEDs.
7 x 3 volts = 21 volts .... 3S lipo is only about 12 volts so we are out of luck there. We need to exceed the LED voltage by at least a couple of volts because white LEDs are actually 3.?? volts. I meant that they are sometimes slightly higher than 3 volts.

Let's try 3 white LEDs:
3 x 3 volts = 9 volts

We want to feed them 20 mA, so we need to find the resistor value, but to do that we need to know how much voltage is across the resistor. We know that we have 3 of 3 volt LEDs and the they are being fed by about 12 volts. The voltages of the LEDs add together and will be the "Load Voltage":
Resistor Voltage = Source Voltage - Load Voltage
Resistor Voltage = 12 volts - 9 volts = 3 volts

Now we really get to calculate the resistor value:
Resistor value = Volts / Amps
Resistor value = 3 volts / 0.02 amps = 150 ohms

I hope I didn't leave anything out here.


So, on with my sermon... Why not just plug into the receiver and get 6 volts to run your lights? The lights really don't use much power and the power from the receiver is regulated and protected. By protected, I mean that most likely it comes from a BEC with a Lipo Cutoff so it will help keep you from over discharging your battery. Then you just connect all you lights in parallel.
That's just my feeling - hook them up in series if you want instead.

Good for you for making your own lighting! Hope you post up for others so that they might give it a try too!

Cheers,
Al


okay thank you! that helps clarify a lot. my reasoning behind series was to try and keep the wiring simple. i also didnt make the connection that the colors were different voltages.shopping around last night i could build basically a plug in system from axial factory parts but it was going to be expensive. thought maybe trying to build my own personal set would be a fun project. youre welcome to use my question in your LED wiring post to help others grasp it if its not already there. and if it is and i missed it i apologise for the redundancy. thank you again

You're welcome.
I hope I didn't discourage you.
Maybe I should do an addition to the LED page and show three white LEDs in series running from a 3S lipo for those that want to try it.

[BigGuyJT]

Hey Diesel, I sent those pics you asked for over on RCSC.

[Olle P]

Originally Posted by badhoopty

... is there any way to have just one resistor and run the leds in series after it?

Yes!
Provided that a) the voltage feed is higher than the combined voltage drop of all LEDs and b) all LEDs do well with the same amount of current.

The LEDs on my rig all want (no more than) 30mA, so in theory I could couple them all i series as long as I feed them more than 5x3.1V + 4x2,8V = 26.7V through one resistor limiting the current to <30mA. (An 8S LiPo setup with 20ohms resistor should do the trick, with built-in cutoff at 3.3V/cell!)

[rdl77]

Im planning to run 2 white led and 2 red led, and i have a bunch of 1/4w 1k resistor, is 1k to high for a 6v power source? Or can i use 1 resistor to run my 2 headlight in parallel?