Need help with LED wiring

[Diggs]

Hey all.

I have a big stack of LEDs and a bunch of 100ohm resistors. I want to wire up a few planes for SEFF and need to get rolling. Pulled up the LED calculators here
http://led.linear1.org/led.wiz to determine how I should proceed. Well, I quickly found that my specs for my LEDs are different and that I don't know enough about electronics to figure out what to do.

My goal is to wire in a few strands of LEDs to my RX. I really want to avoid another power source due to the weight required for a second or third battery. I also don't know what happens when I have multiple values of LEDs in my circuit.

Blue LEDs with minimum \ typical \ max values per the vendors site
Forward Voltage \ 3.0 \ 3.5 \ 3.8 V
Forward Current \ ~ \ 20 \ 30 \ mA

Now Red
Forward Voltage ~ 1.9 2.3 V
Forward Current ~ 20 30 mA

Can I wire these in a parallel circuit? My guess is that would be a bad idea, but then again the current seems to be the same.

Does anyone know of a circuit builder type tool online where I can plug in all these values and get a recommendation on how to make this work the best? I will have 2~4 channels available for powering the LEDs from my RX since most of the planes are pretty simple. One being a superfly which will only use throttle elevator and aileron with delta mixing enabled. This will leave me with rudder aux and gear to use, but I have never plugged into one of the control surfaces outputs either. So what will rudder do as a power source? I assume hitting the rudder stick will change some value, but don't know what.

Any suggestions for a site for reference material on this? I looked through the threads here, but didn't see anything related that was this advanced.

Thanks in advance!
Diggs

[EP Dean]

When I did my LED's I had a similar issue. I chose to run a secondary battery and run in strands in parallel (whites in series of 5 and coloured in a series of 4 if I remember right). With the draw of the LED's and the fact that I wasn't running with a seperate BEC, I didn't want to overload my primary circut and felt a secondary power source was a necessity.

I know this isnt what you were looking for but I couldn't find what your currently searching for either.

[anatoly]

Diggs,

For 5v receiver power, the blue LEDs can be run in parallel with the 100 ohm resistor. They won't be as bright as with the recommended 82 ohm resistor (which is what I use on my 3.6v bright white LEDs) but it will work. For the red LEDs, because they have a lower forward voltage you will need more resistance. The LED wizard recommends 180 ohm, but you can use 2x100 ohm resistors in series and it will give you 200 ohm. Then you can run them all in parallel. You can also run two red LEDs in a series, but you need a 68 ohm resistor. I run all of my LEDs in parallel, I think it's easier.

As far as amp draw on the primary battery, I have a plane with 13 LEDs on it and I don't notice any significant reduction in flight times; I land before the battery is depleted anyway and don't push my batteries to LVC.

-Anatoly

[David Hogue]

Diggs,

The voltage off any of the rx channels will not change with stick movements, except due to servo loads. The signal is on the white or yellow wire, and the red and black are just power and are bused across all the pins. You can even power a servo from a separate battery and run only the signal from the rx,

does that make sense?

[Diggs]

Awesome info guys! I have my SS wired up with 8 white LEDs with 56 ohm resistors all of them in parallel. Seems to be happy on my RX, but don't remember the specs on those LEDs. I have some 56ohm resistors, but just a few.

So, if I run say 2 100 ohm resistors on the leg of a red LED and one 100 ohm on the leg of a blue LED, I can run all these on the same parallel circuit? Just want to make sure I understand that correctly.

Thanks again. That is exactly what I needed to know about he RX output David :) OH and on my Mini Mag, I intend to wire up probably over 100 LEDs, and that one will have a different power source. Likely go with just another BEC or a small 7.4 or 11.1 lipo pack.

Diggs

OH and another question. I have a multimeter sitting around somewhere. I haven't used one since the 80's :o How could using one help me with these projects? After I wire up a circuit with various LEDs and Resistors, what should I check?

[TommyB]

I've run led's off the rx and the flight battery. I prefer to run them off the flight battery in case the rx fails for any reason. At least that way you can find the plane if something goes wrong.

With a 3s pack, I use 330ohm resisters for all led's. I've found there's only a minor deviation in brightness that is negated by the ease of only using one resistor type.

Doing it this way, you put a resistor on every led, then just wire them up in parallel. Extremely simple method.

Another tip to get some pretinned, non insulated bus wire from Radio Shack. Run a pair of bus wire around the plane secured from shorting with hot glue or whatever. Then you just need to solder both legs of the resistor/led combo to the bus wire.

For the wings, you can just use a length of piano wire to drill a pair of holes the length of the wings through the ribs. Then run the buss wire through the holes. For the fuse, I have taken a balsa stick with bus wire on both sides, then presolder the led's at intervals along the stick. Then you can just insert the whole stick into the fuse lengthwise, and wire up the bus leads.

Make a harness with micro deans in a convenient spot on the fuse, and plug in the wing lights, fuse lights, etc. From there, make an adapter with a pair of regular dean's soldered back to back, take the leads from the harness and solder in between the two dean's, shrink wrap, and plug in between the flight pack and the esc.

I think I have like 50 or so lights on a mountain models j3 cub, and the whole thing glows. You can fly it like its daytime. Total cost about 5 or 6 bucks.

YMMV

[Bryan Davison]

Id highly recommend wiring them in parellel. That way if one LED fizzles or breaks or something....the rest of them will still work.

[Diggs]

Hey guys, thanks for all the help. This is what came from it.

http://www.rcgroups.com/forums/showpost.php?p=9620741&postcount=76

Thanks again!!

Diggs

[TommyB]

That's awesome Diggs, and the minimag is a fantastic plane that you won't outgrow.

Listened to ATTF the other day, good show! I'm subscribed on itunes.

Thanks,

Tom

[Diggs]

Thanks Tom!!

I love the Mini Mag. That is my second one. After flying the first one I knew it would be a great first night flyer with ailerons. Glad you are enjoying the show!!

Diggs

[Xptical]

@Tommy

You use a 330-ohm resistor on every LED and then wire the entire bus to a 3-cell LiPo?

Or are you saying you wire every LED for a 5v bus and then use the 330-ohm to drop the 11.1v down to 5v?


My application will be 4 LEDs in each wing, 4 in the fuse, and one on each side of the tail to light that up. So, four busses.

[davidsons]

I've run led's off the rx and the flight battery. I prefer to run them off the flight battery in case the rx fails for any reason. At least that way you can find the plane if something goes wrong.

With a 3s pack, I use 330ohm resisters for all led's. I've found there's only a minor deviation in brightness that is negated by the ease of only using one resistor type.

Doing it this way, you put a resistor on every led, then just wire them up in parallel. Extremely simple method.

Another tip to get some pretinned, non insulated bus wire from Radio Shack. Run a pair of bus wire around the plane secured from shorting with hot glue or whatever. Then you just need to solder both legs of the resistor/led combo to the bus wire.

For the wings, you can just use a length of piano wire to drill a pair of holes the length of the wings through the ribs. Then run the buss wire through the holes. For the fuse, I have taken a balsa stick with bus wire on both sides, then presolder the led's at intervals along the stick. Then you can just insert the whole stick into the fuse lengthwise, and wire up the bus leads.

Make a harness with micro deans in a convenient spot on the fuse, and plug in the wing lights, fuse lights, etc. From there, make an adapter with a pair of regular dean's soldered back to back, take the leads from the harness and solder in between the two dean's, shrink wrap, and plug in between the flight pack and the esc.

I think I have like 50 or so lights on a mountain models j3 cub, and the whole thing glows. You can fly it like its daytime. Total cost about 5 or 6 bucks.

YMMV

Do you see any loss in brightness as the 3s pack is discharged and the voltage drops? The voltage under load could dip down to between 9-10 volts.

Steve

[Diggs]

Do you see any loss in brightness as the 3s pack is discharged and the voltage drops? The voltage under load could dip down to between 9-10 volts.

Steve

The only time I notice the LEDs dimming is when I hit full throttle on a pack that is almost done. It is actually a good way to tell when it is time to bring it in and change packs. One night I grabbed a pack out of the wrong stack, or a pack that wasn't charged but in the right stack, either way it didn't have a full charge on it and noticed it as soon as I did the throttle test in my flight check. Lights really dimmed so I changed packs before flying it. They never dim enough for it to be a problem though. And again, it is only at WOT. Once you drop back to half throttle, they are back to their normal brightness levels.

Diggs

[davidsons]

Thanks Diggs!

Steve