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New to LEDs - help please!


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1 hour ago, Junctionmad said:

See other replies to clarify that I meant the application of model railways. 
 

You  need to specify resistors. One value isn’t enough 

That 'model railway' seller on eBay, has almost certainly made the assumption that the supply is going to be a regulated 12 Volts DC and the supplied resistors are likely to be around 1000 ohms or 1k. If that is what's being used, then there will be no issues.

 

Problems arise when people dig old power supplies/controllers/unmarked equipment out of junk boxes. These voltages could be anything.

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2 hours ago, kevinlms said:

That 'model railway' seller on eBay, has almost certainly made the assumption that the supply is going to be a regulated 12 Volts DC and the supplied resistors are likely to be around 1000 ohms or 1k. If that is what's being used, then there will be no issues.

 

Problems arise when people dig old power supplies/controllers/unmarked equipment out of junk boxes. These voltages could be anything.

I have two boxes, one is 'unspecified' and has random transformers, both open frame and 'unreadable' sealed units, the other has old chargers and power supplies from long gone equipment.

Personally I wouldn't dream of using any of them without first testing their output.

For multiple LED's it is just as important for a supply to deliver enough current (milliamps).

 

Edited by d00m
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On one YT site I saw a variable resistor (potentiometer) used on a workbench to adjust the brightness of LED's.  Upon the desired dimness is achieved the resistance was measured so that a normal resistor could be used instead.

 

Many will start with a 1K Ohm and also have a variable one to adjust the brightness similar to the Just Plug system from Bachmann.

 

Subject to the lighting type to be represented you might like to look at various online retail outlets as many do "flicker" to represent way that flames move in the wind. 

 

Many LED projects are available from https://www.layouts4u.net/

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On 01/09/2021 at 08:42, kevinlms said:

That 'model railway' seller on eBay, has almost certainly made the assumption that the supply is going to be a regulated 12 Volts DC and the supplied resistors are likely to be around 1000 ohms or 1k. If that is what's being used, then there will be no issues.

 

Problems arise when people dig old power supplies/controllers/unmarked equipment out of junk boxes. These voltages could be anything.

In general I find I need to tweak the brightness so I always calculate my own resistors 

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  • 2 weeks later...

The electronics calculator I find most useful is Electronics Assistant found here;

 

https://www.electronics2000.co.uk/

 

It does a lot of things but as far as LEDs are concerned it can be as simple or detailed as you want. Simple is enter the number of LEDs in series, their colour and the supply voltage. The result tends to be the minimum resistor value so the LEDs tend to be quite bright. If you want dimmer use the starting value and increase the resistance until you are happy.

 

Richard

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