6 pin DCC wiring

[ColinB]

Do anyone know how to wire up the front and rear lights on a 6 pin DCC module? I know how to do this on a 8 pin one, but on my 6 pin Bachmann one that I fitted to a non DCC ready class 08, there is no blue wire, as obviously there are not enough pins. Some modules I gather have a blue flying lead, but the bachmann does not. So where do you get the supply from, as all the module does is switch grounds (open collector output drivers)?

[Howbi]

This may shed some light.......... https://dccwiki.com/6_Pin_DCC_Plug .........HB

[Chrissaf]

When a loco is built DCC Ready but with a 6 pin socket rather than an 8 Pin socket. The loco usually has an internal PCB that generates the 'positive' (blue) power rail. When you are 'hard wiring' a 6 Pin decoder into a loco without a DCC Ready 6 Pin socket, then you have to generate the positive supply rail yourself away from the decoder.

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The easiest way to do this is to add two silicon rectifier diodes. Suitable diodes are from the 1N4000 series. So anything in the 1N400x range where x = a number between 1 & 7. So that would be 1N4001 to 1N4007.

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In order to get the diodes the right way round, the black bar at the bottom of the triangle is denoted by the 'bar' on the physical diode device.

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How it goes together is shown in my schematic drawing below. The F & R in the 'Red' and 'White' LEDs denote loco Front & loco Rear. The boxes with the R in them, denotes the LED current limiting resistors. Typically these would be values between 1,000 & 2,200 ohms at 1/4W rating. But in this case, the supply voltage is full DCC track voltage (28 volts peak to peak). So for this circuit I would recommend increasing the overall resistor range to 1,800 to 4,700 ohms. The actual values ideally need to be arrived at through experimentation to get the most optimum brightness balance between 'Red' & 'White' LED colours. Note that the 'Red' LEDs might need a higher value resistor compared to the 'White' ones.

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HB posted whilst I was drawing my schematic.

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[ColinB]

Great, thanks, I never thought of that. No issue, now I know, before I retired I was an elecronics design engineer, although I did mostly software (embedded stuff). I bought a load of bridge rectifiers for coach lighting so I will use those. The thing that does facinate me though is I use SMD LEDs for smokebox glow and internal lighting and to get the right light level I have been using 33k resistors which means the current must be incredably low (about 0.3 mA), if I use 1 k resistors which would mean they are flowing about 10 mA, I need sunglasses. I am surprised they work with that low a current. Individual diodes though may be easier to fit, funny in my job I used to use 1N40001 or 1N4148, must be very popular diodes.

[Chrissaf]

You cannot easily use a bridge rectifier unless you propose to only use half of it and leave the negative rail of the bridge open circuit. The negative needs to come from the switched decoder outputs, not the bridge.

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I would have thought that a couple of 1N4xxx diodes compared to a bridge would be far more space efficient, particularly within the limited space of a Class 08.