DCC Control System for N gauge.

From time to time over the last 20 years, DCC systems seem to have come into vogue. It has always seemed to me a control system most useful for modellers of town tramway layouts where there are a lot of tramcars running together and it is nice to have the interior lights on when the tramcar stops. And least useful on a branch line layout where the usual operation was "one engine in steam". It must also be remembered that although there is a full voltage AC carrier current present through the track, this does not mean that locos will not stall on dead sections of track nor that you do not need clean, level track for reliable operation.

Another factor to consider for the established modeller is the cost of converting an existing, perhaps large, fleet of locomotives to DCC. The cost of the small module needed for N is normally in excess of £20 per loco assuming you are competent to do your own fitting. Another problem is finding room for the module. This can usually be managed in tender locos by one means or another but tank locos are quite another matter. Mine have every available space filled with lead to give enough weight for reliable running and even if they did not, there is rarely enough space in a tank engine to fit even the smallest module. So do be sure that all the locomotives you want to use, even small tank types, are able to be converted.

If none of the above has put you off, how do you convert a Union Mills locomotive to DCC control?

Two ways to hide your module. -

Minitrix, Kato and Micro-Ace German and Japanese N models all feature large motors entirely filling the interior of the cabs. Many modellers seem content to live with this state of affairs. if you are one of these, then why not fit your module in the loco cab, it is much smaller than a motor and nothing like as visible. All Union Mills locos have enough space to fit a small Lenz Silver Mini decoder (10310-02) or the smallest Hornby size in the cab.

If you don't like this idea then it is possible to fit the module directly above the motor in the tender. Drill four holes in the corner of the tender body coal heap and with a fretsaw join up the holes to cut out the coal heap. The white metal alloy cuts easily. Clean up the corners with a file. You can then fix your module with double sided adhesive tape to the top of the actual motor. These can motors run quite cool so you won't have a heating up problem. A piece of Plasticard of 112 mm thickness (0.020" or 20 thou) can then be cut to size to make a new false floor for the tender coal heap. A little real coal can be crushed and stuck to the plastic with PVA adhesive and the whole lot painted matt black to bring to one colour. Although a bit more work it does not take too long to do and avoids the 'module in the cab' look.

Wiring up.

On some locos (Graham Farish in particular) one of the brush housings is earthed by being built into the chassis structure. This can cause particular problems for DCC module installation needing a bit of engineering to insulate this brush. No such problems exist with Union Mills locomotives. I use a can motor the casing of which is electrically isolated from the two brushes. All that I do is to solder a wire from one brush to the motor casing to make the electrical return through the tender wheels. If you cut this wire and then unsolder it from the brush terminal, you can then solder up your motor connections in whatever manner your module 'calls for. I wire a 0. 1 u capacitor across the brushes to kill any sparking on the newest locos. Your module fitting instruction will give advice on whether this should be left in or removed, if they say remove it, then do so, for many years I never fitted capacitors with no apparent ill effects.

I do not have time myself to fit DCC modules to locos myself, nor do I have the test equipment to ensure the performance has been optimised. However I can recommend a good man who is able to fit modules in either of the ways described and I can recommend his work as being satisfactory and reasonable in price. Here are the contact details:

Mr. Douglas Stewart,

Wickness Models,

6, Greenlea Crescent,

Collin,

Dumfries and Galloway

DG14PR

www.wicknessmodels.co.uk

e-mail: wicknessmodels@gmail.com

Tel: 01387 738175

Many people have fitted DCC modules to Union Mills locomotives with every success in the operating sense, so if you wish to go down that route, you can do so with confidence. At the moment I make no special provision for module fitting as I. reckon the great majority of my customers use and prefer analogue DC control systems.

If you have any questions you would like to ask, then please feel free to contact me with your queries. I have some further information sheets that are available for the asking which go-into more detail about wiring and fitting.

Colin Heard,

Union Mills Models Ltd.,

Unit 5,

Union Mills Trading Estate,

Braddan,

Isle of Man

IM4 4AB

Tel: 61624 852896 e-mail: cohin.h@manx.net

First posted on RMweb on 24th October 2018

Fitting a decoder to a Union Mills loco turned out to be a lot easier than I expected. I had seen a guide somewhere but that involved milling out the inside of the tender under the coal load. This was, apart from plugging a decoder into a DCC ready loco, my first conversion.

The first thing to do is separate the loco and the tender. Note that there is a connecting wire between the two, it is trapped by the drawbar screw on the loco. Pick up is simple, the loco is live to the right hand rail and the tender to the left hand rail. This actually makes the DCC conversion very easy in my view. Simply undo the tender drawbar from the loco and the wire will pull out:

The next step is to remove the drive unit from the tender. Again just undo the drawbar screw but note the thin washer between the chassis and the body, don't lose it! The wiring is simple, a resistor from the tender pick ups (the motor body is used as a proxy for these as it is live to the track) to one motor brush and a wire direct to the loco from the other motor brush:

Dean Goods tender mechanism

Because of the way this is wired all I did was remove the resistor completely and unsolder the wire from the other motor brush. For those who want to retain the resistor in circuit just unsolder it from the motor body, use some small heatshrink to insulate it when reassembling.

At the time that this DCC conversion was done - the advice was to remove the resistors as well as any capacitors and then modify the appropriate CV in the decoder - to limit maximum voltage to the motor to 9 volts for the early models.

Now this is where it can all go wrong. I was lucky as I bought, a while ago, a pair of CT Elektronic DCX77zD decoders specially for my Dean Goods. Unfortunately these don't seem to be available at the moment but the DCX77L is; this is the same decoder but with the connections on the short side of the board instead of the long side, it is a couple of mm longer and a mm narrower as a result. I've measured the available space under the coal load and the DCX77L should fit without a problem. For comparison I've shown below (from left to right) a DCX77zD, a DCX74zD and Gaugemaster DCC22.

Decoder comparison

I've then fitted the decoder soldering the red wire to the motor body and the decoder motor output orange and grey wires to the motor. The black decoder wire is left at full length. If anything I've left the wires to the motor a bit long on this one. you can also see that I have left the yellow and white auxiliary outputs in place but cut back and then covered by a short length of heatshrink to insulate them. The tape on top of the motor is original, it is actually put there by Union Mills.

Decoder fitted

At this point strip and tin about 8mm of the black decoder wire. Refit the drawbar to the loco fitting the decoder black wire into the small hole above the drawbar from which you removed the original Union Mills wiring. Place on your programme track and set up and test. If all is OK refit the tender body and drawbar making sure the wires are clear of the tender wheels and, most importantly, the tender drive gears. That is why shorter decoder leads are more desirable for this conversion.

The only external difference is a slightly finer wire from loco to tender:

All finished

Overall I found this a very easy conversion, the only downside is that it requires, ideally, a very slim chip and they are a bit dearer than most and difficult to find. I've found the DCX77L in stock in the UK today at £32.00. I've recently dealt, in person, with the shop selling these and they are really helpful.