wiring up LED's

[BigBen2k]

"In series" won't work here, because the current to the two types of LEDs isn't the same (you'd end up with a white LED at less-than-half brightness).

Here's what you do: use my advice as above for the white LEDs, and run a separate chain for the red ones. Each chain will have its own resistor.

The supply voltage from the receiver should be the same as the battery you've got hooked up to it (If you're running a BEC/ESC, assume 6.0 volts).

[BigBen2k]

Oh I see... 4 whites at 3.2 volts, and 2 red at 1.85. That complicates things a bit.

You can't run more than one white LED, because you won't have enough voltage for them:
2 * white LED require 6.4 volts, and your supply only has 6.0 .

The two red LEDs in series will be fine, with the right resistor.

Ok, time for a new design.

4 white LEDs in parallel, will drop 3.2 volts, and run a total current of 80 mA, so the resistor will be:
V = 6.0 minus 3.2 = 2.8
I = 0.080
V = R * I
R = 35 Ohms or higher.

There you go (this assumes that all 4 white LEDs are *exactly* the same, and were manufactured from the same batch. Otherwise some of the LEDs might appear slightly brighter than others. To get around this, treat each white LED separately, with its own resistor, like Diego suggests).

[ozboater]

ok.. now i m really confused... RPM, in the first original attachment i used specced 4 X 3.2v LEDs to run off the rx... these are for the front set of 4 canister white LEDs..

is that even possible ??

ben, you think diegos schematic won t work ?? reckon you could sketch me out one that will work ?? if possible i d like to power all 6 LEDs from the rx... if thats even possible...

thanks again for the help from you blokes... i ve definately learnt something here... i m not sure what it is, but i ve learnt something...

[BigBen2k]

Yes, Diego's diagram will work. Mine's just a bit different.

Give me a bit of time, and I'll draft up something.

[Diegoboy]

My design is simple but effective (like old Vacuum tubes)

Ben's desgn will probably be more efficient with less components (like integrated circuits or IC's)

[BigBen2k]

I borrowed Diego's pretty diagram

For the two red LEDs, I calculated 230 Ohms:
6.0 - (2 * 1.85) = 2.3 volts
V = R * I
where I = 0.010 A (10 mA)
so R = 230

Now there's no such thing as a 37 Ohm resistor, but the next up, standard value, is 39 Ohms. You'll also find a 240 Ohm resistor to be standard.

To answer your other question: no these LEDs won't have any significant impact on your run time: they only draw 30 mA, which is insignificant compared to whatever electric motor you use. Just remember to turn them off when you're done though; they will drain your battery pack, in a few days. A 3'000 mAh pack will provide 3'000 mA (or 3A) for one hour, or 30 mA for 100 hours.

Diego: no, I'm not going to go into switching regulators here :) but I'm working on one for myself.

[ozboater]

great... looks like the project is moving forward... i owe you lads a cold one

thing i ll pick up the stuff to build it up today...

you fellas recommend 22 AWG stranded for wire ???

thanks a million you guys..

cheers

oz

edit - bigben2k, i m assuming your schematic takes into account the largish 'mcd' rating of the white LEDs i figure... i see you listed the specs of the red LEDs (2 x 1.85), but not for the whites... sorry to second guess ya but is this diag. all go for the white LEDs with a rating of: 3.2 Vf @ 20mA w 3200mcd...

[BigBen2k]

22 AWG ought to be just fine.

Measure twice, cut once

The mcd rating has nothing to do with how much power it draws. However... this is a significantly brighter LED (160x) for something that draws 4x the power. Maybe you could double check the mA that the white LED draws?

I have a couple of white Luxeon LEDs, and they are nothing like a standard red LED: they're mounted on a tiny board, and draw a lot more power than 20 mA. Is this what your white LEDs look like? It would draw at least 200 mA, and that's a whole different situation.

Maybe a picture?

[ozboater]

unfortunately i don t have anything yet... the white LEDs were recommended by RPM for their light canisters and i only have the part numbers... Linrose manufacturer, part # bcmd204uwc

this is them:

http://www.frys.com/product/1681761#detailed

i checked the linrose webpage and located the same LED part number...

http://www.linrose.com/

i clicked LEDs and scrolled down, they are listed just over 1/4 of the way down the page... available as single and in a five pack...

cheers again bigben2k, this project would be a pipedream without the help of kind folks like yaself and diegoboy

[BigBen2k]

Oh, ok, then everything's all right, cheers!

The Luxeon LEDs I have are similar to these:

http://www.luxeonstar.com/

They draw at least 300mA

(I'll be using them on my plane, as landing lights).

Diego: this is the kind of LED that could really use a switching regulator

[ozboater]

awesome, thanks mate... really appreciate ya help... diego too, great forum and some good folks around here... stoked

gonna cost me about $4 for each damn white led... little steep, but i hope it turns out good... i ll post some photos of the finished product !!

cheers

oz

ps - australia is gonna rip it up in vancouver in 2010