DCC Loco Conversions - 16 - Dublo & Wrenn Diesel Shunter

Discussion in 'DCC Control' started by Jim Freight, May 1, 2022.

  1. Jim Freight

    Jim Freight Full Member

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    I have three of these, Hornby Dublo and Wrenn, two green Dublo bodied (D3302 & D3763) and one Wrenn with the red NCB 72 body.

    D3302 has an original re-magnetised magnet, but D3763 has a NEO magnet to reduce motor power consumption as despite having a higher than usual winding resistance its current consumption was high at 0.5A at 6V (0.25A more normal), using a NEO magnet reduced the current to 0.38 to 0.4A. Which is more in keeping with the small decoders I use.

    An intermittent fault with the NCB 72 has prevented completion at this time, it needs reversion to DC to fix, may be an armature fault. (Fixed 18/10/22 and 19/10/22, see my replies on this thread).

    Three attempts were required to find the most appropriate decoder family to use.

    Very Important - the Ringfield motor was modified as in article 12, failure to do so can destroy a decoder.

    https://platform1mrc.com/p1mrc/index.php?threads/dcc-loco-conversions-12-dublo-ringfield-motor.5993/


    1 - Digitrax DZ126

    A very good and compact decoder, my first choice, easy to site due to it's small size, shrink wrapped and some output protection.

    This was easily installed as the basic DZ126 has flying leads which only needed trimming to length.

    1 DSCF0137.JPG

    Ran well on the rolling road and test track but ran with cyclic speed variations on the layout, not a pickup issue as that would cause significant stop starts, this was more likely a motor feedback issue.

    Turning off BEMF and torque compensation feature made no difference to the cyclic speed variations when running on the layout, so could it be dirty layout track, extra cleaning made no difference.

    Okay, so taking the rolling road and test track out to the shed and connecting them to the layout track resulted in same poor running again. So not the layout track condition.

    Track power voltage fine according to the RRamp meter.

    I have had issues with vintage loco motors being unhappy with a particular decoder family, but decoder versus layout power, that's a new one on me.

    Try another decoder family.

    2 - Hattons Mini-Harness MD4

    A good all rounder but does not readily tolerate power pickups of vintage locos, I just tacked it into place and tried again, ran fine on the rolling road and test track connected to layout track, but as expected not happy on points and odd unevenness of sidings track. Not good for a shunter.

    So initial running problem looks like a vintage motor - decoder intolerance, worsened by long power supply runs.

    Try yet another ...

    3 - Rails oF Sheffield RoS-6D

    These have what they call advanced brown out protection which is said to be equivalent to having stay alive, certainly much cheaper and more compact than a large decoder with an attached stay alive package.

    Whereas a stay alive module will power the loco as well as the decoder it appears to me that the brown out protection keeps only the decoder micro-chip active, but so far in 3 other locos and certainly these shunters it works very well.

    The shunters ran smoothly without issue on the layout, admittedly the vertical alignment of some yard track needs improving, and the deeper flanges of these locos easily find particles of ballast stuck to the rail side causing the tread to lift off of the rail.

    So what was the cause of the original on layout poor running?

    No idea, however when an issue like this occurs whether RF issues on radio control cars or software incompatibilities on PCs, if a solid satisfactory work around achieves my needs I just go with it and move on.

    The final installation looks as below, the RoS-6D is a 6 pin decoder to which I solder wires to the track power input and output to motor pins. The two extra I crop off, as I will never use them. Heat shrink sleeving, un-shrunk, acts as a strain relief and stop shorts between pins or to the loco chassis.

    The decoder is fixed in place with a double sided sticky pad, but as it is taller than the DZ126 which has wires only, no pins, it would only fit at the front of the chassis. Depending on the thickness of the wires and manufacturing variations it may be necessary to trim back reinforcing ribs on the inside of the loco body as I had to do on one of the shunters.

    In the images below the wire from the pickup plate was yet to have the heat shrink sleeve shrunk, after which it was pushed down the hole in the chassis leading to the pickup plate.

    So the final installation is as below.

    2 DSCF0140.JPG

    3 DSCF0141.JPG

    4 DSCF0142.JPG

    Discussion always :welcome:

    Jim

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    Last edited: Feb 24, 2024
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  2. Jim Freight

    Jim Freight Full Member

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    Wrenn NCB (Class 08) Shunter

    On reverting this loco to DC and testing over a few days there has been no issues with this loco.

    However the driving wheels are well worn, the plating is totally worn through to the alloy underneath next to the flanges, so it would appear that the issue is one of pickup from the track being unreliable due to that wear and the ragged edge of the plating towards the outer edge of the tread.

    Anyway, I fitted a RoS-6D and it runs much better, not perfect but certainly acceptable, it was reluctant to run at all with a Digitrax decoder.

    So it would appear to me that the Rails decoder with 'advanced brown out protection' is pretty effective, it's also much cheaper than decoders with added stay alive modules.

    However, it cannot power a loco like a stay alive, but fills the gap to prevent a decoder resetting on short power pickup failures, i.e. brown outs, in a cost effective manner.

    If I find there was a red herring I will update this information :hammer:

    Jim

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    Last edited: Feb 24, 2024
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  3. Jim Freight

    Jim Freight Full Member

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    Wrenn NCB (Class 08) Shunter - The Fix

    Problem


    This loco proved problematic as it would randomly short circuit the track power, initially I thought it may have been armature related but the decoder was not harmed, but on reversion to DC running without the decoder it ran fine.

    Investigating this further I found it was due to excessive end float of the undriven axles, the centre one in particular.

    This loco has suffered significant wear to the wheel plating and to the chassis, although the loco is heavy enough to not have power pickup problems the chassis wear was a problem.

    The strong collector wires have forced the cast centres of the uninsulated drivers so firmly against the chassis that it has been worn away such that the axles float too far towards the collector wire side.

    Normally this would not be a problem, however this model has cosmetic outside frames modelled as per prototype appearance, so when the axles float too far the insulated wheels could momentarily touch the live outside frames, DC running would just produce a few sparks, but DCC reacts fast and shuts down the track power.

    Tweaking the side frame to increase the gap between the wheels and the side frame works up to a point, but with this loco the endfloat was so great that when the axles get pushed sideways against the collector wires the outside cranks then short against the sideframe.

    Solution

    The approach I have taken is to insert washers between the uninsulated wheels and the chassis to reduce the endfloat and bring the axles back to where they should be. Not wanting to remove wheels from axles (particularly difficult due to the method used to attach the outside cranks) or disturb old wheel bushes I have used a technique that I have used previously on other locos, some wagons and even a tea towel holder over the kitchen sink.

    I modify the washer, be it fibre, nylon, brass, steel or in this case beryllium copper to be more of a horseshoe shape that I spring onto the axle, this can be quite fiddly depending on access but works well.

    The image below shows the washers I used for this loco, these 'crinkle' washers are for light locking of 3mm metric nuts, and so fit a 1/8th inch axle just right, also shown is a sketch of how I modify the washers in this case with tin snips.

    The crucial features are that the throat is just smaller in width than the axle diameter so it will stay put but can still be sprung on, it's size depends on the washer flexibility and washer dimensions relative to the axle diameter. The cuts are angled to aid the positioning and springing into place of the washer.

    DSCF0986.JPG

    In the second image I show where the washers were fitted, it was impossible to fit one between the uninsulated driven wheel and chassis but possible between the gear and the chassis. This also properly aligned the worm gear with the worm which is a plus.

    DSCF0988.JPG

    I then added a touch of oil to these washers and straightened up the outside frames and now it runs well on DCC.

    Jim

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    Last edited: Feb 24, 2024
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  4. Jim Freight

    Jim Freight Full Member

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    Wrenn NCB (Class 08) Shunter - Return of Tripping Track Power

    Problem

    This loco is going for the prize of most irritating conversion.

    No sooner as all was well, it then started tripping the track power, but only when the plastic body was fitted.

    Solution

    The metal handrails for the drivers door are a chunky wire and the bottom ends scrape the loco chassis.

    When the body was refitted after all being well with the axles the upper end of the left hand handrail was just making contact with a spring pivot post.

    On the programming track no problem, on the running track it would intermittently trip the track power again, so it would seem there was a resistive connection not detected when programming, but low enough to trip track power, but luckily not low enough to allow enough current to burn the decoder.

    The image below shows the problem, flattening the handrail internally at that point has created enough clearance to stop this short.

    DSCF1003.JPG

    Summary

    Was this a problem in parallel with the endfloat issues, or one that developed when removing and refitting the body numerous times, who knows, hopefully I can just use it now!

    Jim

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    Last edited: Feb 24, 2024
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