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Converting R850/5 to DCC


Pnosferatu

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Hi,

I'm a complete novice to all of this. Ive recently converted a little 0-4-0 to DCC with ease, but have just been given an R850/5 Flying Scotsman with a glowing fire box and want to convert that too. I have a decoder and have run it for an hour in both directions on DC to check it runs ok, which it does. 

The problem is that I can't find a guide on how to do this conversion anywhere. I can't even make heads or tails of how the thing is wired up.

Could anyone help?

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Yes indeed, a standard decoder or the TTS decoder wouldn't cut the mustard stall current wise.

 

Unless you want to keep the loco original I would also suggest making a small pcb to fit in the glowing fire box, it is possible to fit a bridge rectifier, resistor and orange or yellow flickering 3mm LED on a tiny pcb in the glowing firebox to replace the old power hungry firebox glow bulb.  The feed wires for this can simply be passed through the hole the old bulb used to sit in and connected to the first function output.  Being an LED means the load on the function output will be a lot less than a bulb.

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Forgot to add... If you opt to use the decoders Function outputs you do not need a bridge rectifier or any other rectifier or diode. As a decoders Function output is DC.  You would of course need a series resistor fitted into one lead to the LED.   See below re 12 volt rated LEDs..

You would only need a bridge rectifier if using the DCC power directly to the LED (Ideally use a fast recovery rectifier or make one from four Diodes e.g. UF4001)) and feed the rectifiers input (AC) from the DCC power and its output (DC) to the LED one lead via the series resistor. 

Ohm rating of the resistor will be best at around 1K to 2k2  (1000 to 2200 Ohms) Higher ohm if you want to reduce the brightness of the LED.   A 1/4 (0.25) watt or higher wattage resistor will be fine to use with a single LED.

Note: LEDs are polarity conscious and need to be connected the correct way around to illuminate and also have a series current limiting resistor fitted (unless the LED is rated at 12 volts then it will have a built in resistor). Never connect a 'standard' 2 to 3 volt rated LED directly to the DCC or a decoders Function output without a series resistor. 

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Ok... so to clarify if i were to get a sapphire or similar decoder and wire an led with a resistor directly to function 3/4 and the blue wire it would work without a pcb?

 

Correct - just get the led the right way round as previouslymadvised - anode to blue wire. Resister can be in any leg. If you want flicker then you will likely need additional components or a flicker led. Some folk have used a flashing yellow with a steady red for firebox glow. Having said that if you are usng a Sapphire it has the ability to set special effects for lighting, such as strobe, flash, flicker, etc. via CVs.

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Brilliant. Now having followed the guide on a different loco with a x.03 motor, ive got everything in place and can read the cvs on railmaster but... if i try to run the loco it won't move at all. If i squeeze the motor brushes towards the motor it runs constantly in reverse and wont respond to any commands.... any thoughts?

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My first thought is as you are now talking about a problem with DCC operation of a different loco, not converting the original loco to DCC, you start a new thread with a descriptive heading including loco type and you are far more likely to get useful replies.  Hidden at the bottom of this thread, many may miss it.

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