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Author Topic: HELP!! Surface mount LED : Forward voltage?  (Read 3390 times)

carlmt

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HELP!! Surface mount LED : Forward voltage?
« on: March 23, 2013, 11:42:05 AM »

HI all,

I hope someone with LED knowledge here can help:
 
http://www.maplin.co.uk/side-looking-leds-10382#specification
 
I am hoping to use these on the ferry, but what is the forward voltage for them? The website says between 4 & 5.2V.
And what resistor?
And which leg is positive?
 
Completely confused - even rang Maplins store.....and they have no idea.  The guy was just reading what I was reading on the website!!!
 
Yours confused...
Carl

Tug-Kenny

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #1 on: March 23, 2013, 12:04:49 PM »


I couldn't get on this site this morning.  %)   All I can tell you is the

positive lead on a LED is the longest wire.

If you look into the glass top you will see that it is connected to the thinnest part of the assembly. the other lead has a block of material on it.  (useful to know)

Cheers

Ken
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tigertiger

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #2 on: March 23, 2013, 12:42:40 PM »

Forward voltage. They will only work wired on way. The other way and you get no light.


4v is the minimum to get one LED to emit light, and this will be dim.
5.2v will give you maximum light intensity. Not sure how far you can overdrive them.


If you wire two in series, then you need minimum 8v, 3 you need 12v.
Because some uses of LEDs use multiple LED they are wired in parallel circuits, or multiple parallel circuits.
The resistor is used to step down the voltage. This can be on each LED or on each circuit. As such you need to do some math V=IxR or summat like that. Depending on your battery and how the LEDs will be wired.


This might help.
http://www.electronics-tutorials.ws/diode/diode_8.html


In short, it is a bit complicated, but not difficult.



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david48

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #3 on: March 23, 2013, 02:03:17 PM »

I am on with the same issue I found this web site just about every thing we need t know
http://www.hobby-hour.com/electronics/resistorcalculator.php
I am trying to do a circut  for the mast lighting for my tug and make a shopping List  I think I might try Technobots thy seem to have a fair choice.
Trying to help.
david
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david48

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #4 on: March 23, 2013, 02:26:39 PM »

I have just found this   http://www.rapidonline.com/Electronic-Components/Optoelectronics  there is a lot on here to confuse us even more
David
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david48

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #5 on: March 23, 2013, 05:11:47 PM »

Yet another LED link http://www.rapidonline.com/downloads/dynamic-mailers/2012/M0078/#/1/  This is page one there are six pages in the catalog
David
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Netleyned

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #6 on: March 23, 2013, 05:26:20 PM »

Talk to Component shop who do very competitive prices.
You will also get top class advice from Ian

Ned
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Stan

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #7 on: March 23, 2013, 07:37:16 PM »

Component shop for me very good on price and advice.
 
Stan :-)) :-)) :-)) :-))
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cos918

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #8 on: March 23, 2013, 09:29:48 PM »

The Component shop does not do these LED I have all ready asked.

john
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Steve Dean

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #9 on: March 23, 2013, 10:50:34 PM »

The type of LEDs you are referring to are primarily designed for the side lighting of LCD screens and I'm not sure they are ideal for your application. Maybe you can give some further input into how you intend to use them.


These LEDs have a forward voltage in a range between 4 to 5.2 Volts. Therefore the series resistor if fed from a 12 Volt battery would be between 360 ohms and 430 ohms. Given that LEDs are often brighter than needed I would suggest you start with 430 ohms and if you need them brighter go down to 390 ohms or 360 ohms. If you need them to be less bright then increase the resistor value.


I don't want to complicate matters for you ...... therefore, if you want to use a battery source other than 12V, then put a note on this thread and I will help you some more.


For your info, I wrote 2 articles in Marine Modelling International during 2012 about using LEDs and explaining the math involved.


best regards


Steve Dean



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carlmt

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #10 on: March 23, 2013, 11:16:53 PM »

Cheers for the replies guys...
 
And Steve - Many thanks!!! The intention is to use them as deck lighting.  They are the perfect size to represent miniature flourescent strip lights found on the outside decks of passenger ships (in this case, car ferries).
 
The intention is to run them off a 12v battery. As I understand it, dependent upon the bightness emitted, I can run up to three units on one series circuit at a time. As the three will be divided into the 12v - they would each pull 4v? Therefore no resistor needed? If 3no off 12v was not bright enough, then two in series off 12v - requiring a resistor to bring the forward voltage down to 5.2v each - would be brighter?  I am not looking for Blackpool Illuminations type brightness, but noticeable at dusk.
 
The other problem we have with these is that there is no obvious +ve and -ve leg.  I assume (from the poor diagram on the Maplin site) that the left leg (when looking at the light emiting face) is the +ve?
 
Carl - obviously taking a crash course in electronics here!!!!

grendel

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #11 on: March 24, 2013, 12:39:44 AM »

looking at the drawing with dimensions one pin is shaded for a greater distance up the leg, corresponding to pin 2, all I need to remember now is which direction the current flows through as far as the symbol depicts..
Grendel
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RAAArtyGunner

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #12 on: March 24, 2013, 10:01:59 AM »

The type of LEDs you are referring to are primarily designed for the side lighting of LCD screens and I'm not sure they are ideal for your application. Maybe you can give some further input into how you intend to use them.


These LEDs have a forward voltage in a range between 4 to 5.2 Volts. Therefore the series resistor if fed from a 12 Volt battery would be between 360 ohms and 430 ohms. Given that LEDs are often brighter than needed I would suggest you start with 430 ohms and if you need them brighter go down to 390 ohms or 360 ohms. If you need them to be less bright then increase the resistor value.


I don't want to complicate matters for you ...... therefore, if you want to use a battery source other than 12V, then put a note on this thread and I will help you some more.


For your info, I wrote 2 articles in Marine Modelling International during 2012 about using LEDs and explaining the math involved.


best regards


Steve Dean

Steve,
 
Any chance of posting it, or something similar as a tutorial thread. :-)) :-))
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cos918

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #13 on: March 24, 2013, 10:15:10 AM »

Cheers for the replies guys...
 
And Steve - Many thanks!!! The intention is to use them as deck lighting.  They are the perfect size to represent miniature flourescent strip lights found on the outside decks of passenger ships (in this case, car ferries).
 
The intention is to run them off a 12v battery. As I understand it, dependent upon the bightness emitted, I can run up to three units on one series circuit at a time. As the three will be divided into the 12v - they would each pull 4v? Therefore no resistor needed? If 3no off 12v was not bright enough, then two in series off 12v - requiring a resistor to bring the forward voltage down to 5.2v each - would be brighter?  I am not looking for Blackpool Illuminations type brightness, but noticeable at dusk.
 
Hi Carl
I wound not do that. Tou might find one led is weaker that the other and might blow. If ones shorts the other might blow + the resistor drops the voltage and limits the power . Ie a small 1/4w resistor will only let a little power throught. X3 lED in series can draw diret from the battery and there is nothing to limit them . A 12V ah can deliver some big power.
Do each LED/resistor in Parrel and you will have no problem.

John
The other problem we have with these is that there is no obvious +ve and -ve leg.  I assume (from the poor diagram on the Maplin site) that the left leg (when looking at the light emiting face) is the +ve?
 
Carl - obviously taking a crash course in electronics here!!!!
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malcolmfrary

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #14 on: March 24, 2013, 10:43:06 AM »

Quote
As I understand it, dependent upon the bightness emitted, I can run up to three units on one series circuit at a time. As the three will be divided into the 12v - they would each pull 4v? Therefore no resistor needed?
The purpose of the resistor is not to drop the voltage, but to limit the current.  Maplins Q&A bit on the link also suggests this.  Further reading of the spec from Maplin reveals that - A range of side-looking LEDs in a very low profile package, designed to be used for illuminating LCD displays (usually mounted at each end of the display glass). Available in yellow, yellow/green and orange/red. Each package contains two LEDs, giving a forward voltage of 4 to 5.2V.[/size][size=78%] - [/size]which indicates that these are not white LEDs, but the regular colours.  The different colours have different specifications for the same brightness, hence the uncertainty in the spec.  Bi-colour LEDs are usually 2 different colour LEDs connected in a sort of "69" configuration, so that current one way lights one, current the other way lights the other, and both protect their mate against over voltage in reverse.
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tigertiger

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #15 on: March 24, 2013, 12:46:34 PM »

With forward voltage of 3 LEDs in series, requires minimuym 12v. That will give you little light, until the battery voltage drops below 12v, which could happen quickly, then no light.
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Stan

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #16 on: March 24, 2013, 05:07:00 PM »

I got this piece of kit from Maplins some years ago. I am not sure if they still stock them. It is ideal for testing L E D before fitting them in your model and making sure they all work before final fitting. The unit runs of a 9 volt  PP3 battery  it will not give you the resistor value you need for the L E D you intend to use.
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Stan

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #17 on: March 24, 2013, 05:17:09 PM »

Just checked Maplins site they still stock these units. They are priced at 8.99. You will see on the unit marks AN this is the postive terminal and KA this is the negative terminal. I do not use the M/A markings at all hope this helps.
 
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inertia

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #18 on: March 24, 2013, 07:38:57 PM »

The other problem we have with these is that there is no obvious +ve and -ve leg.  I assume (from the poor diagram on the Maplin site) that the left leg (when looking at the light emiting face) is the +ve?
Just connect a battery pack across one (I'd use 3 x 1.5v Alkaline cells). If you get the polarity correct then the LED will light. If you don't then you haven't broken it - it's just done its job as a diode.
DM
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Stan

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #19 on: March 24, 2013, 07:52:17 PM »

HI Dave got my tester a along time ago price was right.The battery idea would be a lot cheaper but you pays your money and make your choice all the best.
 
Stan
 
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malcolmfrary

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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #20 on: March 25, 2013, 10:08:13 AM »

Just repeating - the ones listed in the maplin link are not white, so unless the deck is to have disco lighting, red, yellow, orange and green lights will probably not do the job anyway.
The bicolour ones are in fact 2 LEDs connected in reverse parallel, the colour depending on which way round they are connected.
There are plenty of references to white side view LEDs on the web, but they are all SMD types and the references are all techno descriptions from manufacturers, so probably only available by the truckload to us civilians.
http://sharp-world.com/products/device/newproducts/GM4BNx53C0A/index.html
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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #21 on: March 27, 2013, 01:16:25 AM »

I got this piece of kit from Maplins some years ago. I am not sure if they still stock them. It is ideal for testing L E D before fitting them in your model and making sure they all work before final fitting. The unit runs of a 9 volt  PP3 battery  it will not give you the resistor value you need for the L E D you intend to use.

http://www.rapidonline.com/test-measurement/kemo-led-tester-32606/
 
Still make them!!
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Re: HELP!! Surface mount LED : Forward voltage?
« Reply #22 on: March 27, 2013, 01:18:32 AM »

Just repeating - the ones listed in the maplin link are not white, so unless the deck is to have disco lighting, red, yellow, orange and green lights will probably not do the job anyway.
The bicolour ones are in fact 2 LEDs connected in reverse parallel, the colour depending on which way round they are connected.
There are plenty of references to white side view LEDs on the web, but they are all SMD types and the references are all techno descriptions from manufacturers, so probably only available by the truckload to us civilians.
http://sharp-world.com/products/device/newproducts/GM4BNx53C0A/index.html

Thank you for that!! Ive been plowing around trying to find something..
Now if only I could find a Fixture to plug it all in..
 
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