DCC Loco Conversions - 5 - Worth the Effort? – Part 3 of 5

9) Pickups

9.1) Wipers

Pickups must be in good order, clean, sound, with good contact force and wipers aligned correctly. It is amazing how many new locos can be deficient in this way straight out of the box which is probably due to poor quality control at manufacture and subsequent assembly.

We are advised not to over lubricate and then two Hornby Ruston diesels that I bought new recently had gear grease all over the wipers, other locos of other brands have had wipers the wrong side of the wheels or misaligned.

When dealing with pre-DCC and particularly vintage locos wear, grime and misalignment is expected and must be attended to.

Some chassis notably Tri-ang may have spring wires of an omega shape pressing against the wheels and clipped without solder to brass bushes. Some work fine, some are nothing but trouble, typically found on old 0-4-0, 4-4-0 locos and power bogies. The wire is difficult to solder and probably needs a special solder, I think it is just better to replace the wire with thin phosphor bronze strip soldered to the brass bush.

9.2) Wiring

Poor soldered joints may at first glance look ok but if they look rather dull or have a rough looking surface appearance may be very weak, some may even come apart with a gentle touch. It is important that all soldered joints are checked for strength and continuity, suspect joints need to be reflowed, or if they are already a large 'blob' remove it, cleanup and re-solder.

Old wiring can often be unplated, i.e. plain copper and can corrode, also it blackens, so if you need to re-solder, the use of non-corrosive liquid flux will be necessary, and if that does not work replace the wires.

9.3) Stay Alive

The stay alive facility offered with some decoders will not help if the pickups are poor all the time, they only offer assistance to ignore momentary interruptions in power to the decoder to prevent it shutting down and rebooting, which translates to the loco hesitating.

Stay alive is offered by some decoder manufacturers and can be very expensive, particularly Lenz, however Lenz is a superior brand.

I have tried the DCC Concepts Zen decoders (in 2016) with Stay Alive which did not work for me, two issues, loco run away above step 10 out of 28, and wires breaking away from the PCB. Duff batch?

However the old DCC Concepts DP4SA have proved very good for my Lima and Tri-ang power bogie conversions. I was lucky enough to buy a batch at clearout prices from Hattons due to its large bulk compared with current direct 8pin direct plug in decoders.

Recently Rails of Sheffield have brought out their new range of decoders in conjunction with DCC Concepts with what is described as “Brown-out protection for silky-smooth motor operation (like having a built-in stay-alive!)”

So far I have tried these on a couple of conversions with mixed results, certainly improved a Tri-ang Britannia with steel wheel treads. This loco was initially fitted with a Hattons decoder but would lose pickup at speed over long radius Peco Electrofrog points (set straight) but would pass over them okay at a crawl. Quite the reverse of what normally happens with poor power pickup.

However an old British Trix Warship diesel would hunt badly with BEMF enabled. The term 'hunting' refers to when an engine or motor surges in speed and then settles back to a lower speed in a cyclic fashion. Likely cause here was too much backlash in the worn gear train causing instability in the feedback required by the BEMF system. A second Warship hunted mildly. However after fitting a Gaugemaster DCC93 to both they run well with BEMF, which just goes to show that one decoder family does not suit all locos. But I digress.

By far the best approach is to add extra pickups, have at least two per rail (some can have just one), preferably more and increase the weight especially of 1970s mainly plastic with traction tyre designs of loco. However this will depend on available space and your skill set.

Update May 2022. The new Rails decoders are proving quite effective in the Dublo locos I am converting to DCC operation including a layout running issue, Ref 5.1.

9.4) Staggered Pickups

A further point to consider on a large layout when feeding it power from multiple power units, e.g. Lenz Command unit and Booster units are staggered loco pickups. I define staggered pickups as picking up power from one rail only per axle, e.g. on a diesel with two bogies, left rail pickup by one bogie and right rail by the other bogie. Same can apply to steam outline locos where loco pickup is from one rail and tender pickup from the other rail.

When a loco with staggered pick-ups bridges two sections fed from different power sources (command unit or booster(s)) it does not see a complete electrical circuit and so stops.

This problem first manifested itself when the main fiddle yard and the mainlines were originally fed from different sources, one from the command unit and one from a booster.

As this problem only affected some mainline locos which in reality would not enter the industrial branches the straightforward solution was to modify power distribution so that the FY and mainlines were both fed from one unit.

The marshalling yard arrival and departure roads are fed from the same power source as the mainline so problem solved. Shunters and branch locos are short and do not have staggered pickups so they can traverse easily between separately powered areas, e.g. yard sidings, arrival/departure roads and the industrial branches.

10) Wheel Arrangement

Without doubt some of the worst are 0-4-2, 0-4-4 and 4-4-0 chassis, DCC ready or not. Unless the pony or bogie truck has pickups fitted they are generally unstable in motion and need careful balancing to achieve reliable enough continuity of power pickup. I avoid any more of them of any age.

11) Plastic Chassis

These can be found in the smaller cheap locos by Hornby and in old-timers from Airfix GMR, e.g. the 4F, okay if they are true but if distorted not much can be done. My 4F had been assembled badly and over the years caused the chassis to bow such that it would rock on the centre axle. Luckily I was able to slot the centre axle holes in the chassis so all 6 wheels would sit on the track.

12) Metal Chassis

The main thing to look for is cracking, swelling and disintegration of die-cast chassis made of Mazak, this is not repairable and can affect any locos, used or not. It is caused by too high a percentage of impurities in the Mazak alloy. Internal crystals form and expand causing swelling and breakdown of the structure of the metal, the object just self destructs to dust, colloquially called Mazak Rot.

I have found a front bogie from an elderly British Trix A3 with this problem and also where used as ballast weights in tenders of Lima Crab locos. Plastic parts are easily ripped apart by the expanding metal.

Hornby tender drives are not immune and will cause motor seizures due to jammed axles.

Lead ballast can with time acquire an oxide coating to jam a close fitting body shell in place, e.g. a British Trix A3, lead is probably not allowed in our toys now over health hazard concerns.

13) Weight

Notice how much heavier DCC ready locos are now compared with the pre-DCC locos of the 1970s onwards, even more exotic materials are used on tiny locos like the Sentinels. Weight plays a significant factor in how your loco will perform with DCC, and bearing in mind very few have any form of suspension, weight and chassis accuracy to keep all the wheels on the track is crucial. So is flat and even track, but that is up to us!

Typically the small cheapies with the plastic chassis are also very light, I have had very little success with these even though they are easy to fit decoders into ready or not.

Next, assessing motors

Jim

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References

5.1 Rails Decoders in Dublo Locos

An example of a layout issue resolved with a Rails decoder with brown out protection.

https://platform1mrc.com/p1mrc/index.php?threads/dcc-loco-conversions-16-dublo-diesel-shunter.6005/


Image: A Bachmann 57xx fitted with a Digitrax DZ126 6 wire decoder.

 

Update to (9.3) relating to Rails of Sheffield decoders.