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Sulzer B101 wiring LEDS.

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Kirley
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I’ve just finished wiring my Sulzer and on testing only the white LED’s (supplied by Express Models) worked. The Red LED’s from Des had one wire shorter than the other and he advised connecting the resistor to the short wire but none of them worked.

 

B101Sulzer002-2.jpg

 

When I had wired LED’s before I always connected the resistor to its long leg and they worked. A quick trawl of the Web suggested “we find the LONG LEG of the LED which is POSITIVE and attach the proper resistor to it. Connect the ground to the SHORT NEGATIVE lead.”

 

B101Sulzer003-1.jpg

 

Before I disconnect all the red LED wires and investigate further can anyone confirm it is always the “long leg/wire” that is connected to the resistor or does it differ from LED’s to LED’s or does it matter?

 

Any advice would be welcomed.

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Hi Kirley,

 

The resistor should always go to the LONG or POSITIVE leg on the LED.

The power will not pass through the diode from neg to pos so putting resistor on that leg is no use.

 

Hopefully that helps.

 

It actually does not matter, the resistor will break the circuit regardless of which side it's wired.

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It doesnt matter which leg (annode/+ or cathode/-) the resistor is connected to. Its purpose is to drop the current flowing through the LED. V=IxR where V=voltage which is a fixed value so if R (resistance) increases then I (current) will be decreased proportionally.

 

The polarity is important though, an LED wont light up if the current is flowing through it in the reverse direction.

 

The annode/+ (long-leg) must be connected to the positive side of the voltage supply, in the case of DCC the Blue is a common positive so the Long leg side of the LED must be connected to Blue with the short leg connected to the appropriate function negative which could be white/yellow/green depending on the Function button to be used.

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Just in case anybody is confused, the polarity of the LED does matter, as above, but the resistor is the same whichever way round it is connected, and in whichever leg it is - so, just get the resistor somewhere in series with the LED, have the LED the right way round ( long leg is positive ) and all should be well.

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It actually does not matter, the resistor will break the circuit regardless of which side it's wired.

 

It doesn't matter what side, the main purpose of the resistor is to limit the voltage drop across the LED to below the max specified value (typically 2volts), as well as limiting the circuit current.. Otherwise it fries.

 

Example:

Rated LED V =Vled=2V

Supply voltage =Vs=12v

1800 ohm resistor

 

Vs(12)=Vled(2) +V resistor=

12-2=8 Volts = Voltage across resistor= Current * 1800ohms

Current = 8/1800=4.4mA

Edited by Weshty
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Thanks Guys for all your imputes, I was never really clear on which side the resistor went.

 

I picked up on MRHD’s comment as the most informative:

The polarity is important though, an LED wont light up if the current is flowing through it in the reverse direction.

 

The annode/+ (long-leg) must be connected to the positive side of the voltage supply, in the case of DCC the Blue is a common positive so the Long leg side of the LED must be connected to Blue with the short leg connected to the appropriate function negative which could be white/yellow/green depending on the Function button to be used.

 

The key phrase here is polarity is important. I have connected all the red LED’s via the short leg to the resistors which would explain no red LED’s working.

 

There’s nothing for it but to unsolder all the red LED’s connections and reconnect to the long leg/wire.

 

O happy days..........

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Thanks Guys for all your imputes, I was never really clear on which side the resistor went.

 

I picked up on MRHD’s comment as the most informative:

 

 

The key phrase here is polarity is important. I have connected all the red LED’s via the short leg to the resistors which would explain no red LED’s working.

 

There’s nothing for it but to unsolder all the red LED’s connections and reconnect to the long leg/wire.

 

O happy days..........

 

 

 

 

As everyone has said K you don't have to put the resistor on the long leg of the LED any one will do. You've probably got the polarity wrong.

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Props to Herr Scahalane as the first to put up a schematic, but here is my own version that I hope helps things along the way. :D

 

I will include this in all future versions of relevant instructions. The resistors are a standard 0.25w so with a current draw of 7-9mA per LED, a single 1800Ω resistor should handle two LEDs ok.

 

 

wh.gif

Edited by Weshty
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