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class 66 headlights and marker lights


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Hi can I have some help I got a Graham farish 66 i wanted to add marker lights to its detailed end so i removed the fiber optics for the tail lights and plastic dividers but left the lenses i then added an LED to the factory fitted head light all this worked well for about an hour, then the loco slowed down stopped flickered the lights and gave of some smoke,

any ideas why this happened?

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How did you connect the extra LED electrically? Was it in series or in parallel with any of the existing LEDs and did you add any resistors? Did you connect via the existing wires from the PCB? Are you using DC, and if so would the LED be subject to track voltage when running backwards?

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yes I connected the legs of the LED to the existing wiring of the lighting PCB where the factory soldered wires are which go to the headlight I did not add any extra resistors because the main PCB already has them, I thought adding just 1 more LED shouldn't effect it much if anything make all of them slightly dimmer, and yes I am using DC to test them on before adding DCC

 

the loco works fine with all original lighting at other end working but only the top light on the faulty end

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I think this means you are connecting the new LED in parallel with an existing LED or possibly two (I don't recall if the existing ones are in series or parallel and I'm not clear whether you have removed one of them). This is a bad idea because each type of LED essentially needs a fixed voltage across it and as your new LED is different from the existing ones then it probably needs a different voltage. Since the parallel circuit puts the same voltage across each LED then it is quite likely one of them will be getting too many volts and sooner or later will blow.

 

When connecting LEDs in parallel, unless they are of exactly the same type, then always include a resistor in series with each individual LED. You can usually connect different types of LEDs in series without any problem as long as they are not vastly different.

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I think this means you are connecting the new LED in parallel with an existing LED or possibly two (I don't recall if the existing ones are in series or parallel and I'm not clear whether you have removed one of them). This is a bad idea because each type of LED essentially needs a fixed voltage across it and as your new LED is different from the existing ones then it probably needs a different voltage. Since the parallel circuit puts the same voltage across each LED then it is quite likely one of them will be getting too many volts and sooner or later will blow.

 

When connecting LEDs in parallel, unless they are of exactly the same type, then always include a resistor in series with each individual LED. You can usually connect different types of LEDs in series without any problem as long as they are not vastly different.

 

thank you so much for that I think I will make a new lighting board with all the same LED's, please can you tell me more about LED's being subject to track voltage when running backwards on DC as i thought even a brand new model straight out of the box would have that problem but i've never know anything to happen before

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Basically you can't just connect a LED, even with a resistor, across a DC supply and expect it to turn on when the polarity is one way and turn off when the polarity is the other way. When the reverse voltage is applied across the LED it doesn't draw any current, so the resistor doesn't reduce the voltage, so the whole track voltage is across the LED. Most small LEDs can't cope with 12V across them and will blow up either straight away or after a while. You need an ordinary diode or another LED connected the other way round in such a way that they share the same resistor.

 

However in your case I think you are OK. The PCB includes some sort of circuit to stop this happening when running on DC, and as you are still connecting your lights via the PCB this should still be working.

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