DCC Decoder installation query.

[ShavingtonIan]

The Hall class loco used in the Harry Potter and the Order of the Phoenix set is easy to take apart, but when I have done this, I can see that the DCC ready socket  and the small circuti board used to connect the front light mean that the space available to fit the decoder is extremely limited.
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Can anyone offer advice on the best / correct way to install the decoder into this model?

[SteveM6]

A smaller 8 pin direct fit decoder would probably be a better fit. Hatton’s own brand is the one I would look at as a start.

[jane1707819582]

perhaps fitting a sleeve on the decoder and laying it above the socket ,

the capacitor is not needed ,so you can create a little space there ,and there seems to be a few wires going up to the cct board are these needed ? from the colour coding you appear to have pick up wires ,motor wires and directional lighting wires is the lamp a led or incandesent bulb ?.

[96RAF]

Direct plug decoder won’t fit as the socket is athwart ships.

 

Not sure what that 4-legged IC is on that circuit board in the body top. Its marked on two legs as track.

Rob

[SteveM6]

Rob, the decoder socket is longitudinal not side to side. I have fitted many direct fit decoders in locos with lengthways sockets with no issues at all but whether it works with all that rubbish in the boiler is another question.

[2e0dtoeric]

Four legged chip looks like a rectfier (for the lights?)

[Rog RJ]

I would say that the small PCB just isn't needed for DCC so would be best removed completely.

[RDS]

... isn't needed for DCC so would be best removed ...

 

I have just fitted a DCC decoder to a Heljan Class 05.  It is 00 gauge but I consider this Loco to be tiny.

It is 6 pin DCC ready and requires the usual removal of the dummy board but this still leaves another PCB that has to remain in place.

 

The first Decoder I tried was a Hatton's 6 pin but this was to big to fit in the space available, so I have fitted a Gaugemaster 6 Pin Decoder.

[Fishmanoz]

Having played with this one but not completed an installation as the body is broken in mine, I can confirm the PCB in the body is for the LED light in the smoke box door, two wires running through the slot in the weight that otherwise fills the smoke box.  The PCB function is just to ensure the LED gets the correct polarity on DC.

 

So for DCC, yes you can remove it and power the LED from a function wire plus series resistor.  Doing that will give you plenty of room for any reasonable size 8-pin decoder like an 8249, noting it must be a 4-function type so you can use green or purple wire plus blue for the light.

[ShavingtonIan]

Thanks for all the good suggestions. It looks like the "DCR-8PIN-Direct 8-pin" from Hattons is the first option I'll investigate.If I were to remove the circuit board driving the light and use the decoder instead, someone above suggested that I would need a series resistor in place. What value of resistor would be needed? Can anyone point me a circuit diagrams to detail the connections in full ?

[Fishmanoz]

Not a criticism, in fact the opposite ........ I said “you can .... power it from a function wire plus series resistor.”  And what does Chris do.  He produces a whole project worthy of his Certificate IV in Model Railway Electronics!

 

I trust that Ian and all subsequent users who ask about lighting and how to use decoder functions will be grateful for his efforts. 

[Chrissaf]

Just for the record, I chose the Green function wire independently as my own conclusion because the headlight on the Harry Potter steamer can still be on when the loco is in reverse. The bridge rectifier (highlighted by others in this thread) would be doing that under DC analogue control, so using the green function wire just replicates what was there already.

[96RAF]

For clarity in case the OP or any other using Chris‘s diagram isn’t already aware, the decoder functions so labelled are actually switched by function buttons on the controller with different numbers...

 

Controller F0 controls both decoder functions 1 and 2 (fwd and reverse directional lighting).

Controller F1 controls decoder function 3 (also known as aux 1).

Controller F2 controls decoder function 4 where present (also known as aux 2).

 

Rob

[Chrissaf]

What value of resistor would be needed?

Can anyone point me a circuit diagrams to detail the connections in full?

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The absolute minimum resistor value is 470 Ohms, but I recommend a minimum value of 1,000 Ohms (1K) at 0.25 Watts. If the LED(s) are still too bright then increase the value of the resistor until you get a brightness you are happy with. This could be as high as 3K to 6K (experimentation is required).

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I have added a FULL circuit diagram. Note: so that this post can also be used by someone who wants to wire up a Diesel Loco with front and rear directional lights I have included (in dotted lines) the wiring for those as well. As you are only concerned with a front Harry Potter light you can just ignore the Function 1 and Function 2 wiring in the drawing below.

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I have chosen to put your front Harry Potter light (assuming it is an LED) on the Green Function 3 wire. When using the R8249 decoder it is the F1 DCC command that switches the third function on and off (the appropriate F button number may be different on other decoder brands / types).

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Note that LEDs are polarity sensitive and have a positive and negative side. The positive side of the LED must go to the positive blue wire via the resistor in the drawing above. The LED will not light up if the polarity is reversed.

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The 8 Pin plug and socket are drawn separately above, but the plug will connect pin for pin with the socket pins in the drawing when coupled together.

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The White wire is drawn with a very light grey colour.

The R8249 Purple wire is a flying lead and does not go via the 8 Pin plug and socket.

The Blue wire is the common positive return wire for all functions.

The White, Yellow, Green & Purple wires are negative polarities switched on and off under DCC decoder control.

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Note: If someone is contemplating this mod with a Steam loco that has a bulb rather than an LED for the front headlamp. Then either replace the bulb with an LED or use a resistor with a much lower value. Somewhere between 10 and 50 Ohms but with a much higher 0.5 Watt rating. Using a resistor with the bulb will reduce the current and stress the decoder function output less.