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DCC Conversions: On-track Plant






Bachmann OWB8 self-powered Crane .. 5 August 2018
Lilliput Plasser and Theurer ballast tamper .. 23 October 2018



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Bachmann OWB8 Self-powered Crane


The OWB8 has only four wheels and I chose a decoder with a stay-alive unit. The decoder is the Zen Z8ND, this comes with the decoder built onto the 8-pin header plug and a separate stay-alive module.


To get access to the DCC socket, lift off the cast "ballast load".




Pull off the blanking plug and cut off the two capacitors. Removing the capacitors is important to persuade the motor to run properly with the decoder. The capacitor across the motor terminals is easy to cut off and preserve for future use, but to remove the capacitor on the pcb, I simply destroyed the device with the cutters. You need a steady hand and some fairly small cutters to take out the pcb capacitor without touching the inductors nearby. I undid the screws on the pcb and lifted out the pcb to remove this capacitor.


With the blanking plug removed you can see the markings for pins 1 and 8 on the pcb, but the Zen decoder has no markings to see. So I plugged in the decoder so the crane travels cab first when the controller is set to 'forward' (the decoder has its factory default direction setting). There are no lamps in this model and I haven't worked out a reason to plug in the decoder the other way round.




There are a few possible places in the model to put the stay alive unit. Under the cab roof is an obvious choice, or even underneath the chassis, but I settled on one of the spaces beside motor, below the ballast load. Doing this means the ballast load will not sit quite as low as it did before I started, but this approach does keep the wiring short. It is also easy to do, but I had to make the stay-alive unit smaller to fit it in.


I cut a slit through the heat shrink cover on the stay-alive unit and removed the cover. Both the decoder and the stay-alive unit come with generous lengths of wire, far too much to tuck away inside the model, so I unsoldered both wires from the stay-alive unit. Then I cut about 20 mm off the wires from the decoder, and soldered the remaining wires onto the stay-alive unit.


The wires for the pick-ups have some slack in them. I lifted these out of the space beside the motor, tucked the stay-alive unit into the space, and rearranged the wires on top. This decoder has a wire connection for a control function, so I coiled this up and tucked it in as well. It seems worthwhile to keep this wire at its full length in case I put the decoder into another model. The ballast load then drops back into place.


Decoder configuration:

  • Initially, the crane gave short uncontrolled spurts of speed on two locations on the layout. The locations were consistent, and the model jumped fowards at high speed for a short distance, 150 mm or so. I resolved this by disabling analogue mode, i.e. switch off bit2 in CV#29. Many thanks to Chris of DCC Concepts for helping out with this so promptly and effectively.
  • On the track, the maximum speed of the crane was far too high, so I set CV #5 to a value of 150 instead of the factory default 255. This brings finer control, and the crane starts to creep along with the throttle set to step 1 of 28.


Lilliput Plasser and Theurer ballast tamper .. 23 October 2018


My Plasser and Theurer ballast tamper was supplied with factory-fitted DCC, but did not run at all well. I had a spare 'Zen' decoder and stay-alive module left over from an earlier conversion, and it seemed sensible to try this as an upgrade in the ballast tamper. There is very little space to hide the DCC parts and their wiring in this model, so I chose a hard-wired installation. There is room to install an 8-pin socket in one of the cabs, but this will be rather conspicuous on the finished model.


I did my first test run with temporary wiring and the stay-alive unit tied onto the top of the model:


I made a lot of alterations to the model and they will invalidate the guarantee. The approach probably invalidates the guarantee of the new decoder too:


1. Unclip the body shell from the powered chassis.
2. There are two long bare wires from the powered chassis to the trailing bogie ... pull out the powered chassis, taking these two wires with it.
3. Remove and discard the factory decoder, the filter and wiring distribution board, the capacitor on the motor terminals, and all of the original wiring except for the two wires attached to the powered bogie.


4. On the chassis, temporarily detach the powered bogie and then remove and discard the entire close-coupling mechanism.
5. File or grind down the underside of the chassis at its outer end to make a flat surface to install the stay-alive unit. If desired, reduce the depth of the metal tabs on the edges of the chassis too. This makes future dismantling easier.
6. Return the powered bogie to the chassis ... this is a bit of a fiddle. I suspect the factory installs the bogie before the motor, but I managed it eventually.


7. Prepare and install the new decoder (these notes are specific to the Zen decoder):

  • Cut off the shrink-wrapped sleeve and the eight-pin plug.
  • Note the black and blue wires for the stay alive unit, and the usual red, black, orange and grey wires - keep these six wires and remove all of the other wires
  • Wrap the decoder in insulating tape and secure to the side of the motor with a small cable tie.
  • Trim and solder the orange and grey wires to the motor terminals.


8. On the stay-alive module:

  • Cut off the shrink-wrapped sleeve and make a note of the locations of the blue and black wires.
  • Unsolder and discard the blue and black wires.
  • Fix the stay-alive module to the space created on the underside of the chassis.
  • Trim and solder the blue and black wires from the decoder onto the stay-alive module.



9. Cut two short lengths of copper-clad strip and secure onto the metal chassis to create solder pads for connecting the wires from the pick-ups.

  • Solder the red and black wires from the decoder onto the pads.
  • Solder the red and black wires from the powered bogie onto the pads.
  • Cut two new wires for the pick-ups on the trailing bogie, and solder these onto the pads. I used blue and green because I had run out of red and black.



10. Solder the two new wires onto the pick-ups on the trailing bogie:




11. Install the chassis into the body shell and test.


I had already used my decoder in three earlier models, including a hard-wired install, and its harness was getting a bit tatty. For me, it seemed best to remove the unwanted wires completely. If I had bought a brand-new decoder I would try to coil up the unused wires, in case I ever wanted to add some lighting to the model.


The space above the motor is cramped, and I had to flatten off the lugs of the exhaust moulding to make space to let the chassis fit back into the body shell.


The model runs really well with the DCC Concepts decoder, and the stay-alive unit is mostly hidden, even looking upwards like this:


I like this decoder - it works well with modern motors like the Bachmann ones in the tamper and the self-powered crane here, but it does not work at all well with the pancake motors used in old Fleischmann and Lima models. Because of this, I have restricted my use of it to modern models which need a small decoder and can benefit from its stay-alive module.

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