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LED Question

LED wing light question

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Tim Flyer03/08/2017 10:32:14
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1011 forum posts
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Hi chaps . I just wired the 2 LED wing tip lights on my 63in span P47. As it is an IC model I chose to use a separate small single cell 550ma LIPO from a small model. I have wired them in parallel using a Y lead radio connector. I am getting flickering on the lights. Is this due to incorrect voltage? And do I need some sort of resistor. I read the piece in this months RCM &E on LEDs but I'm afraid electric wiring & resistors are not really my subject . The kit came with a small dry cell battery holder for two AA batteries in series, so I thought the voltage would not be far out . Is there a simple fix please?

Cuban803/08/2017 11:32:43
2641 forum posts
13 photos

A standard LED will need a series current limiting resistor in order to stop it being destroyed. Some LEDs already have built in current limiting especially if they are 'flashing' LEDs and can be connected to an appropriate battery. Depends what you have - do you know?

McG 696903/08/2017 12:37:47
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2530 forum posts
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C8 is right, Timothy.

With a voltage of 3,7V from your 1S Lipo, you are going to kill your LEDs.

I presume you have a red & a green LED if they are nav lights.

The forward voltage of a red Led is (approx) 2,0V while the forward voltage for a green one equals 2,2V. So, 3,7V is way OTT...

If you're feeding your circuit with 3,7V, you should install a 100ohm (colour code > brown / black / brown) resistor in series with your red LED and a 82ohm (colour code > grey / red / black) in series to your green one. Small size resistors (1/4watt) are perfectly OK here.

By the way, white or blue LEDs have both 3,3V forward voltage and would need a smaller 22ohm (red / red / black) resistor each.

Hope this helps

Cheers

Chris

Tim Flyer03/08/2017 13:29:19
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1011 forum posts
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Thanks very much guys I knew I would get a good answer here. Good job I soon unplugged! I will put in a resistor as above😊

gangster03/08/2017 14:13:22
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941 forum posts
16 photos

Timothy There is a good article on this in the latest rcme

Steve J03/08/2017 14:25:24
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1372 forum posts
41 photos
Posted by McG 6969 on 03/08/2017 12:37:47:

If you're feeding your circuit with 3,7V, you should install a 100ohm (colour code > brown / black / brown) resistor in series with your red LED and a 82ohm (colour code > grey / red / black) in series to your green one.

You can't do the calculation unless you know what the LED is. You seem to be assuming 15-20mA which may or may not be the case.

Steve

Denis Watkins03/08/2017 14:53:35
3811 forum posts
52 photos

Good protection for LEDs can be quickly decided at 75ohms per volt

Then choose the nearest preferred value

So 3v 220 ohm

12v 910 ohm

This took into account students with batteries in various states of charge and unskilled wiring techniques

McG 696903/08/2017 18:18:03
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2530 forum posts
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@ Steve > yes, ideally you should need the exact forward voltage and the current consumption following the manufacturer's specs. But assuming 20mA for 3 & 5mm 'unknown' LEDs is a very safe approach.

The figures quoted above will allow Timothy's diodes not to be killed right away.

@ Denis > how higher the value the resistors have how safer but at the cost of loosing the diodes brightness. If you have a 3V power source & using white or blue LEDs, you don't need any resistor at all as their forward voltage is about 3,3V.

No resistors at all and a source higher than the nominal forward voltage and you very quickly obtain DEDs - aka Dark Emitting Diodes... surprise

Cheers

Chris

Denis Watkins03/08/2017 19:10:17
3811 forum posts
52 photos

Alternately Lads, if you mess with the voltage, ie a small diode will drop voltage, or transistor switch

These are ready built

Denis Watkins03/08/2017 19:10:18
3811 forum posts
52 photos

Alternately Lads, if you mess with the voltage, ie a small diode will drop voltage, or transistor switch

These are ready built

King bright, from Rapid electronics, 5v and 12v LEDs with inbuilt resistor

Edited By Denis Watkins on 03/08/2017 19:14:24

McG 696903/08/2017 22:04:16
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2530 forum posts
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... sorry Denis, but diodes & of course LEDs have nothing to do with 'voltage'. You can NOT find a LED dedicated to say 3,3, 5 or 12V without the use of appropriated resistors.

In the case of LEDs, it is the 'current' that makes them 'react' and light up.

The resistor is only there to 'protect' them by being 'over-amped', to avoid to give them an extreme brightness and then quickly 'flickering' to death. In some cases so 'quickly' that no human eye is able to notice it was 'dying'...

As for an example, the fact of dimming LEDs is only obtainable with a PWM interface bringing the diodes on & off so fast that our eye 'thinks' they are dimmed... remember our 'magical' 25 frames per second...

Sorry for correcting you.

Cheers

Chris

Tim Flyer04/08/2017 16:01:59
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1011 forum posts
172 photos

Thanks McG unfortunately my understanding of electronics is very rudimentary, but you have explained well and I now understand basically that it's the amps they don't like. I have bought a resistors at Maplin to try.

I understand volts and current but was "lost" by the article which I did read in RCM &E.

I don't know if I have already killed the Leds as they did start to flash rather than give a steady light. I will have to replace the wing lights if that's happened. Thanks again all.

Edited By Timothy Harris 1 on 04/08/2017 16:02:32

Denis Watkins04/08/2017 16:19:37
3811 forum posts
52 photos

Tim, you sound jaded by this, and in reality it is not complicated.

Protective resistors just do that job and protect the LED,

If you PM me with an address, even a relative, or works address

I will post you a set of LEDs of different sizes and colours and appropriate resistors

Then you can experiment

Stevo04/08/2017 17:47:33
2699 forum posts
419 photos

"aka Dark Emitting Diodes..."

I have those. I turn them on and the workshop goes black

Re: wingtip leds. Standard LEDS look OK in the confines of a workshop/living room, go to a sunny field and you will struggle to see them, let alone in flight. High brightness ones are a step in the right direction...

I remember getting some dedicated wingtip LEDS from Braincube - and these contain a series resistor and can be seen.. but I don't think they are around anymore. What's the alternative, guys?

Steve J04/08/2017 18:28:04
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1372 forum posts
41 photos
Posted by Stevo on 04/08/2017 17:47:33:

I remember getting some dedicated wingtip LEDS from Braincube - and these contain a series resistor and can be seen.. but I don't think they are around anymore. What's the alternative, guys?

Component shop do 1W and 3W LEDs and driver circuits. Power from 2S or 3S LiPo.

**LINK**

They also do some nice LED strips that take a 12V feed.

Steve

Stevo04/08/2017 19:02:16
2699 forum posts
419 photos
Ah.. I designed my own switch to fade them in and out like a filament lamp. Watchout for a future edition of the Mag 😉
Shaunie04/08/2017 22:05:29
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943 forum posts
78 photos

I have to agree with all that McG has put. It is important to remember that an LED is a current operated device and not a voltage operated one. Difficult for non-electrically minded folks to get their heads around! The higher up the colour spectrum the higher the LED voltage. In the absence of specific data 20mA is a good guideline current for a small LED.

Shaunie.

Tim Flyer05/08/2017 08:57:41
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1011 forum posts
172 photos

Thanks Denis. That is a very kind offer indeed. If I still have difficulty I might well take it up. The two white LEDs work now and I have fitted resistors in each circuit as suggested above. The lights are in the wingtips of my new Seagull P47. They still do flicker a bit after being on for a bit . As mentioned above they are not that bright in daylight, so I may replace them with the component shop brighter ones at some stage. I will have to carefully cut off the light covers first. Luckily they were fixed with cockpit glue (uhu Por) rather than epoxy. I need to get the maiden flight sorted first😊. Unfortunately I'm not getting a chance to fly for the next couple of weeks. I will give the article another read. As I haven't done electronics before it is new for me. The only time i bumped into Ohms was with hi fi speakers but to be honest just fitted what was suggested! I will read up ! Thanks again all. ..& Happy Flying.. Tim

Edited By Timothy Harris 1 on 05/08/2017 08:58:55

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