Currently available suitable LEDs for DIY blades?

[SparkyMJ]

Hey HF,

I am looking to build some night blades for a few rigs, and I've got the copper strip tapes, wire bits, and batteries. But there are a ton of LEDs out there and I have no idea what is good and what works well for this application.

Could any of you recommend ones you have used with success or ones you know for sure would work? Id hate to buy a hundred LEDs to find out they won't work well for this application.

Any links?
Thanks in advance.
-Mike

[JWeber]

I used these 0805 LEDs

https://www.amazon.com/gp/product/B00AV4EL9Q

Then I used 100 Ohm 0805 SMD Resistors

They are nice and small.

[smittylube]

Are you using a resistor on each led or will one resistor work for 6-8 leds?

I do know the green is super bright and needs a bit more to looks similar brightness to the others. Based on the resistors I stole from an adhesive strip led while waiting for my 100ohm ones to arrive..

I used just one on the power strip, but then added one for the green by itself.

[JWeber]

Every LED has it's own resistor.

Here is a link to the LEDs I bought most recently.

https://www.amazon.com/dp/B01LYX8FBF..._G1.zEbASY1PW7

[smittylube]

I bought those as well I think from your previous link.
These things are tiny tiny. I found most will work with one 25 ohm resistor on the ground, but green was super bright so I add one additionally there. I used some from a led tape strip for now. I Ordered some 100 ohm and am waiting for those.

Trying to figure out mounting options going forward.
Thinking of notching the blade at the leading tip forward edge corner and sticking one in there with clear epoxy to handle/send light both sides.
Possibly even drilling onto the blades and put the LED in there then clear epoxy.

[smittylube]

Originally Posted by JWeber

Every LED has it's own resistor.

I see this is important due to the fact we are using Diodes that have very little resistance or no resistance one direction so if no resistor it is almost shorted and pops really easily.

[smittylube]

Working on my second set. This time my 0805 100 ohm resistors arrived.
This set is much better, but the next set will be killer.

Dang these 0805’s are small. Glad I found my tweezers to help mount them.
I have some 0603’s arriving tomorrow. I hope I can get those mounted properly. They are going to be super tiny. I hope I can see them well enough.

[smittylube]

I was able to get the 0603's to work. These are so crazy small. about 2/3's the size of the 0805's.

I think I might have found the sweet spot. I put a slight notch in the front corner blade tip,(dab of ca to hopefully avoid shorting in the carbon fiber) and was able to get an LED mounted, then some 5-minute clear epoxy. Hopefully, I will have the results I'm after.

I put the top and bottom LED's on the trailing edge this time. NO other notches this time.

[smittylube]

I’ve been reading and playing around now and see how the calculators agree for some smled 100 ohms is pretty much right on. But I do see how proper calculating can get the proper resistance for that particular color.

However in reading I see that say the red being a lower voltage might actually work with no resistors if I do 2 in series. (One cell Lipo obviously)
Red being 1.7 volts. So 3.4v total I wonder if 3.8-4.2 would kill them.
Then I thought how about a red and say green that total 4.0 so then 4.2/4.1/ 4.0 Would light, but when it goes out I’ll know to charge.

On my RT blades if one color led goes out (green I think) it is an indication of low cells. This set used a double nickel cell setup.

I don’t see my setups using much current at all, but might this give me an indication of a low battery maybe? Am I thinking right?


EDIT.
This absolutely works.! I had a charged pack 4.15 and one at 3.85v with the right combo I can get yellow and green to light with the full pack (not quite as bright as the led/ resistor combo) and barely if any light from the 3.85 pack. What an excellent way to tell the pack voltage!

[kavic5150]

tl;dr its always safer to use resistors along with leds to avoid the risk of an overcurrent situation.

It might work out temporarily but the problem with running leds with no resistors is you always run the risk of feeding them too much current.

I might not be explaining this correctly, keep in mind I'm not an EE, but without a resistor there is nothing to limit the current going through an LED. From what I understand the resistors are there to limit current and as a result that lowers the voltage. And even those tiny lipo cells are capable of a whole lot of current.

Using just 2 red leds in series may not keep the flow of current in check.

Something I've also noticed is the online led resistor calculators will give conservative resistor values at about 80%.

Our tiny lipos may have an open circuit voltage of 4.2v, but when you load them up with 3 or 4 leds, the supply voltage quickly drops to 4.15v or lower. And for the duration of a flight that voltage doesnt sit at that 4.15v for very long.

While the LED resistor calculator might say 100 ohms, its generally safe to drop down to a 91 or even an 80 ohm resistor without significantly reducing the lifespan of the leds.

[myxiplx]

Yup, always run a resistor is my understanding too. I'm no EE, but from what I've read as the LEDs warm up their resistance drops.

If you don't have a resistor in the circuit as the LEDs warm, and that drops, current flow starts to increase, warming them more, etc, etc.... Eventually you blow the LEDs from over current.

A resistor in the circuit limits the maximum current that can flow to a safe level for the LEDs, typically 20-30mAh.

Sent from my SM-G970F using Tapatalk

[smittylube]

OK the heat makes sense, but since the LEDs are rated a voltage if you put 2 in series you add those together for the voltage. The same effect as a resistor- I think..

I found a green and white or yellow, not sure exactly since they just have a swipe of color on the tape, will light with a full charge pack, but almost not at all with 3.85v.
I believe this is how they get away with one resistor, 3 diodes on the LED tapes. The LED drops the voltage as a resistor does.

If the LED is rated at 2v then a 4 volt supply would work for two in series.
so the result is when the voltage drops the LED's go out giving you a voltage warning...

[smittylube]

More research says not a good idea, too much current after all. I hate saying it, but Google is your friend.......... sometimes.

>>>Forward Voltage<<<<

I’m going to try experimenting to make a voltage indicator with more resistance instead.