Tri-ang R758 to DCC

[Potrail2378]

Hi, I have been gifted a Tri-ang R758 Hymek, but my layout is DCC.

Can it be converted to DCC? I've had a quick look inside and there seems to be quite a lot of pickups/copper. Can the motor be isolated from the track?

Any help or advice you can give me will be very much appreciated.

[ColinB]

The answer is yes, virtually any loco can be converted although Wrenns do present a formidable challenge. I think these are relatively easy, at the moment you should have two brushes on the commutator, one will be insulated one will not. So you insulate the non insulated brush, then you have to break the connection between the brushes and the pickups and insert the DCC decoder. I am sure someone will explain it in more detail. You will need a high current decoder, so the Hornby one is out, but yes it is possible.

[Going Spare]

Although it has two worms, the motor is a derivative of the X04 so the principles of DCC conversion are as per the pinned thread above. As yours is the Tri-ang version of the loco, it is likely that there are not any pick-ups on the non-powered bogie. Downloading Service Sheet 75 from lendonsmodelshop.co.uk may assist by showing the motor bogie in exploded form.

[Chrissaf]

Just to add to G.S's excellent reply. Below is a modified extract from Service Sheet 75 that re-enforces G.S's & ColinB's text.

The X.04 DCC conversion thread G.S mentions is here:

FAQ - Making the X03 and X04 motor DCC fitted the proper way. :: Hornby Hobbies

[Potrail2378]

Hi, GS - it is in an original box, with a plastic molded insert. It does have pickups from the non-driven bogey.

Hope that helps.

[Going Spare]

So you may wish to work from Service Sheet 93, linking the pick-ups on the motor bogie (to which those on the non-powered bogie are wired) to the decoder with the outputs from the decoder going to the brush arms as per Chrissaf's illustration above. But by insulating both brush arms from the brush spring, the contacts above the plastic motor housing need not be disturbed.

As Colin mentioned, you will need to use a decoder capable of dealing with a current greater than the standard R8249 decoder can handle, a 1 amp rating I believe.

[Potrail2378]

Hi, is this the piece I need to isolate?

[Chrissaf]

Even in close up it is hard to see which of the two motor brushes are insulated from the wire spring.

To my eyes when viewed in close up it does look like the one on the left is the one that needs the additional insulating sleeve replicated. The white arrow is pointing to what appears to be the end of the metal spring in contact with the shaped brush with no obvious insulation in sight. Personally I would remove the brown blob capacitor as well. It is only really used when operating DC Analogue, the decoder replicates its function. I would also be looking more closely at the already insulated motor brush [insulated from the wire spring that is]. There must be something connecting to that motor brush that is not visible in the photo that also needs to be removed from the that brush before connecting that brush to the decoder. Any hidden wire or other electrical metallic connection that is connected to either brush will be going to the wheels for track current pickup and if still in circuit and not electrically disconnected when a decoder is fitted will damage the motor control H bridge semi-conductors on the decoder. Both brushes. The one in the red circle and the one with the white arrow need to be electrically isolated from everything else on the motor, including all that sheet brass work moulded to the motor housing and only connect to the decoder orange and grey wires

[Chrissaf]

Addendum,

If it helps, this is my assessment of the brass plating moulded into the housing being used as pickups on that particular bogie. The nut holding down the brush spring is insulated from the blue coloured brass. You can clearly see a black plastic washer under the nut and there is a bridging bar on the left hand side of the nut going to the brown brass. The brown spring electrically connected to the brown nut is isolated from the blue brush on the right by the factory fitted sleeve.

The brown and blue represent the two wheel pickup track rail polarities. It is the connection between the blue brass and the blue brush on the right that needs to be investigated and also isolated as well as the brush on the left which needs to be insulated from the brush retaining spring. The factory fitted insulating sleeve on the right hand brush is only isolating the blue brush from the brown retaining spring. The factory insulating sleeve is not isolating the blue brush from the blue brass, which also needs to be done to support DCC decoder fitting.

[Going Spare]

Looking at the Service Sheets, the only contact that the large blue pick-up has with anything else metallic on the motor bogie is with the two rail wheels on that side, it being insulated from the motor components by the plastic motor cover and the fibre insulating washer beneath the top nut and contact washer.

[Fishmanoz]

Might I summarise the above information and, in doing so, correct an omission in GS’s information, expand on Colin’s explanation so you have enough detail to do what he says, and highlight Chris’s underlined phrase in his Addendum, which fills in GS’s omission.

Let me start with the service sheets 75 and 93. For the purposes of this conversion, they are the same and you can use either. The only differences are the later models using ss 93, have Magadhesion and pickups from the rear bogie.

Next, note that the service sheets show the free ends of the brush retaining spring pointing to the rear while the photos show them pointing to the front, effectively reversing what is left and what is right. I will keep to the photos and confirm the insulted side of the brush spring is on the right.

Now let’s cover those (brown and blue) brass parts which are called collectors on the service sheets but we would call pickups to the left and right wheels. They are insulated from each other as the motor housing to which they mount is plastic. This is maintained by the insulating washer under the brush spring. But then the LH side pickup is connected to the brush spring by the brass washer with the tag sitting on top of the pickup (part S3374).

Finally, where this motor differs from the X03 and X04 is the RH insulated brush spring connects to the RH pickup via an extra tag on the pickup at that end (the L and R pickups are the same part), there is no wire. And importantly, there is no X298 clip on the end of a pickup wire included between the spring and the brush holder on the insulated side of an X03/X04.

Hopefully this description clarifies everything said to date. But how do we do the conversion? It is quite simple as follows:

• purchase 2 X298 clips and solder them to the decoder orange and grey motor connection wires
• remove and discard the capacitor connected between the pickups - not needed for DCC
• insulate the LH side of the brush retaining spring the same as the RH side (you might like to use thinner insulation than used currently - see explanation in the sticky X03/X04 conversion thread)
• bend the tag connecting to the RH brush holder away from the brush holder so it no longer makes contact, and
• insert one each of the X298 tags, on the ends of decoder orange and grey wires, between the brush retaining spring ends and each brush holder

You’ve now both insulated the brushes from chassis and connected them to the decoder. So that’s all there is to it, you are done. QED

[Potrail2378]

Hi, and thanks for all the help and advice you have provided.

The Tri-ang R758 is now converted to DCC.

However, somebody has mentioned that the standard Hornby decoder isn't powerful enough, is this correct? If so, do Hornby have an alternative? So far, all I now need to do is add cab and directional lights - a job in the workshop for my next rest day.

[Fishmanoz]

It’s correct the Hornby R8249 is unlikely to be powerful enough and, no, there is no Hornby alternative. You can confirm what power decoder you need by doing a DC stall test. Unless your motor is in bad condition (weak magnet), a 1 Amp decoder will be sufficient.

And for directional and cab lighting, you will need a decoder with at least 3 functions.

[Potrail2378]

Hi Fishmanoz. Personally, I can't see an issue, but would it double the amperage if I put two decoders in, in parallel? Or is that opening a big can of worms?

[Chrissaf]

Although you can put two DCC decoder INPUTS [black & Red] wires in parallel. You can not put two DCC decoder motor OUTPUTS [Orange & Grey] wires in parallel. You will likely damage the decoders.

[Fishmanoz]

In saying you can’t see an issue, are you telling us that you have installed an 8249 and it’s working without overloading?

One way or another, I still recommend you do a stall test to find out just how much current it is drawing on DC and use that as a guide to the current your decoder must handle.