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K9-70 · Boiler Cleaner Joined: 17 Aug 2008 Posts: 49

Converting the Hornby Class 110 Dmu for DCC operation isn't as hard as it looks, or is it ?

Hornby used the 3 pole X940 Ringfield short wheel base motor for their Class 110 Dmu. No problems with that except it's a poor runner compared to todays modern motors and also uses the motor as the live chassis to transfer power from the track to the lefthand brush cover.

If you wire a DCC decoder to the motor, and turn on the power, the end result will be a blown decoder. This is because the lefthand brush cover is live as well as the motor. So how do you get round this ?

Hornby X940 Ringfield motor as removed from the Class 110 Dmu. The brown wire connected to the righthand brush cover connects to the rear bogie. The rear bogie takes the power from the righthand rail to the righthand brush cover. So far, so good.
The lefthand brush cover is held in place by a screw which also secures the cover plate to the motor. There may also be a short wire X1193 connecting the motor to a tab on the lefthand brush cover. This takes the power from the lefthand rail to the lefthand brush cover and completes the circuit for DC operation.
The problem with this is, when you connect the red or black wire from the decoder to the chassis and either the orange and grey wire to the lefthand brush cover. A short circuit will occur and you will end up blowing the decoder.

I removed the cover plate and using a 3.5mm drill bit, reamed out the lefthand existing screw hole and also drilled the hole a wee bit deeper. Don't drill through the back of the chassis, otherwise when you fill the hole with Araldite Epoxy Resin, it will run out the other end.

I then mixed up some Araldite Epoxy resin and filled the hole and left it to set. When the resin was tacky, I refitted the cover plate inserted the screw and left it to harden overnight.

The brush cover plates have now been refitted, and to test that there was no short circuit between the lefthand brush cover and motor body, I connected up my old DC controller, turned on the power, took the two track feed wires from the controller, and touched the motor body and lefthand brush cover, no short circuit occured and the motor didn't spin. To be safe, I also did the same with the righthand brush cover. The two wires where then connected to the left & righthand brush covers and the power turned on resulting in the motor spinning without any problems.
Now that the motor totally insulated from the metal chassis, I then had to get the power from the metal chassis to the decoder in order for it to work. This was done by drilling a 1.5mm hole through the cover plate and the body of the motor that allowed me to attach a screw and brass tab washer so as I could solder either the black or red wire from the decoder.

The final photo shows the motor now back in it's Class 110 chassis, and the decoder wired in and ready for testing which it passed with flying colours.

There is another method I could have used to save time and a lot less work, is to fit a fibre or cardboard washer below the screw on the lefthand brush cover to insulate it from the motor. The only problem with this method is, if the brush cover moves slightly it can short out against the screw and result in a blown decoder.

K9-70

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