LED'S what are they and how are they used?

[Sarah Winfield]

I know nothing about LED's so having bought some off ebay it would be useful to know how they are used. Would a member help please?

The description is:-

"L12303W Pre-wired 3mm Bright White LED lamp light set 12v~18v
Forward Current 20mA/30mA"

They comprise a 9" lenght of wire with a tiny see through bulb and a resister.

Thanks.

Sarah Winfield

 

[Greg Elmassian]

I would suggest you google and read, a big topic.

Short answer: a solid state light that works very differently from an incandescent bulb.

Greg

 

[Gizzy]

Looks like you have brought LEDs (Light Emitting Diode, a diode being A device that lets current run in one direction only) with a built in bias resistor.

you should be able to connect these to either a DC or AC supply as specified. However, you will need to make sure they are connected with the positive lead on the positive connection if using a DC PSU, or they will not work. Should this be the case, swap the leads on the terminals, and they should work.

If using several, then connect in parallel and not series....

 

[Greg Elmassian]

Overview | All About LEDs | Adafruit Learning System

 

[ntpntpntp]

Yep, they're much more efficient than good old filament light bulbs and draw less current. Alternatively you can buy really bright ones designed to use more power!

They are polarity sensitive so for DC you have to get the wires connected correctly to positive and negative as has been mentioned. For AC they're only lit for half the cycle (sometimes noticeable on video cameras etc.)

A typical LED only needs a couple of volts in order to light up (it varies by colour, with some needing over 3V). To operate with higher voltages a resistor is needed to drop the extra volts and also to limit the current flow.

If you're not yet familiar with them and how to calculate the required resistor, then you bought sensibly by choosing pre-wired LEDs with a suitable resistor pre-fitted for the expected voltage they'll be used at.

 

[Greg Elmassian]

Endeavor not to connect LEDs to AC without a blocking diode... yes many people will tell you no problems...

 

[ntpntpntp]

Endeavor not to connect LEDs to AC without a blocking diode... yes many people will tell you no problems...

Yes it's best to do as Greg says. LEDs don't have a massively high reverse voltage tolerance.

I'll admit I seem to have got away with it with my control panel LEDs powered from 15V AC and built over 20 years ago. All still working fine.

 

[playmofire]

I'm glad Sarah asked that question as it answered a number of LED questions I was about to ask.

 

[G-force1]

My best advice is, read Greg's page about them. I found it very informative. I'm about to embark on fitting them to my Jackson Sharpe coaches, just got to decide how to mount them.

 

[ntpntpntp]

LEDs can go down to really tiny sizes, much smaller than bulbs ever can.
I used a bunch that are about 0.5 mm square, to fit out this heavy haulage model. A real group effort; a good friend made the model back in the 90s, I added the lights to it in 2016, and we gave the model to a mutual german friend to incorporate in his layout!

 

[Rhinochugger]

Yep, they're much more efficient than good old filament light bulbs and draw less current. Alternatively you can buy really bright ones designed to use more power!

They are polarity sensitive so for DC you have to get the wires connected correctly to positive and negative as has been mentioned. For AC they're only lit for half the cycle (sometimes noticeable on video cameras etc.)

A typical LED only needs a couple of volts in order to light up (it varies by colour, with some needing over 3V). To operate with higher voltages a resistor is needed to drop the extra volts and also to limit the current flow.

If you're not yet familiar with them and how to calculate the required resistor, then you bought sensibly by choosing pre-wired LEDs with a suitable resistor pre-fitted for the expected voltage they'll be used at.

I have frequently googled a programme to calculate the resistor needed - can't remember the link, but just google 'calculate resistor for LED or some such and you'll find it.

One of the biggest advantages of LEDs (apart from their minimal current draw) is with battery powered locos, because, as others have said, LEDs are an electrical one way street, so if you get your wires the right way around you have instant, simple, directional lighting - even I managed to work it out on the first battery loco that I ever built, so it's got to be quite easy

Oh yeah, you cant get flashing ones as well, then you can really have fun This has two LED headlights, and two flashing red LEDs on the roof

 

[ntpntpntp]

This is the one I use
LED resistor calculator

 

[Greg Elmassian]

Thanks for the support G Force!

For the navigationally challenged:

LED Lighting Basics

I have a couple of calculator links there...

Greg

 

[Sarah Winfield]

Thank you for the information.

Please understand gentlemen I have a problem with understanding (I have explained this before during my efforts on the reverse loops).

I'll read the links in the hope I can use my LDE's.

They are fitted with a resistor on one leg.

SW

 

[ntpntpntp]

What uses do you have in mind for them, Sarah?

 

[Rhinochugger]

Thank you for the information.

Please understand gentlemen I have a problem with understanding (I have explained this before during my efforts on the reverse loops).

I'll read the links in the hope I can use my LDE's.

They are fitted with a resistor on one leg.

SW

Sarah, sometimes it seems like a steep learning curve - just take it gently at your own pace.

Looking again at your first post, the LED description says 12v - 18v, so I would say that the resistor that is already fitted would allow you to use them directly with analogue current - say for coach lighting or loco headlights.

They are described as bright white, which could be pretty violent for coach lighting, but then if you want to show off the interiors ...

They could also be used for lineside lighting, buildings lamps etc, but you will need an uncontrolled DC supply - do you have an old H&M transformer / controller from your HO days? That will have an uncontrolled AC outlet on one side and an uncontrolled DC outlet on the other (with the controlled DC being at the back- from memory).

 

[Neil Robinson]

Go ahead and experiment, if obtained in bulk (for example on ebay) they are cheap enough to blow up on the steep bit of a learning curve.

Some really basic starter tips, one, don't connect without a resistor, two, only connect to DC and three, if it doesn't work swap the power supply/ battery wires over.

You'll often get away with connecting the wrong way round for a short time but it's best not to if possible.
After testing a close look can often reveal a physical difference enabling you to identify which side is which. This will allow you to make subsequent connections the right way round first time.
There is a convention but I've sometimes bought cheap LEDs that don't match the convention (probably why they were cheap)!

 

[dunnyrail]

I would always suggest a Blocking Diode to ensure that they will only work if connected up the right way round. Of course you do need to understand the right way round first!

 

[Rhinochugger]

................You'll often get away with connecting the wrong way round for a short time but it's best not to if possible......................

That's strange because all the directional LEDs that I have on my battery locos rely on having the wrong current when running in the wrong direction - i.e. the rear LED will have reverse current (and therefore will not illuminate) when the loco is going forwards and vice versa.

 

[PhilP]

That's strange because all the directional LEDs that I have on my battery locos rely on having the wrong current when running in the wrong direction - i.e. the rear LED will have reverse current (and therefore will not illuminate) when the loco is going forwards and vice versa.

My guess, is you 'under-run' your LED's to get a softer light?
That way you will probably get away with it.. Not considered 'good-practice' though, but as Jon say's, it means working out which is the correct way round, for both LED, and blocking diode!