Stalling kitbuilt loco after chip fitting, help please

[OliverSR]

I recently aquired a kitbuilt finecast SECR D Class. It ran smoothly on analogue with no binding or shorts with pickup from wire wipers on one side with insulated wheels and through the chassis on the other side. I then proceeded to fit a gaugemaster Small OPTI decoder DCC26 so I could run it on my main layout. The appeal of this decoder to me was the price, fact it was pre insulated and had a detachable harness so I can fit the harness then plug in the decoder after and not break the wires like I have done on Hornby decoders before. I fitted the chip ensuring it was the correct polarity and all wire joints were insulated with heat shrink. Upon testing the loco it runs well for a second before stalling and then starting again but due to the locos sweet running before I don’t believe it’s a pickup or mechanism issue. I have tried a couple of other the same decoders in the harness with the same results. Are there any CVs that I could try adjusting to improve the running or did I pick a poor choice for decoder for this loco and is there an alternative that would fit into the same harness to save rewiring again?

I would be greatful for any advice/ideas as the loco is a really nice train and I’d love to have it running smoothly on dcc.

I’ve tried to include enough info but if I have missed anything out please let me know.

OliverSR

Edited June 17, 2018 by OliverSR

[smokebox]

Put the loco on dc and check the stall current. Then check that you decoder can handle that current. It sounds like the loco is taking more current than the decoder can handle.

[34theletterbetweenB&D]

You are not going to like this. It's an unfortunate fact that DCC is intolerant of momentary short circuits, where DC is very tolerant. So a 'perfect runner' on DC can be a beast on DCC.

 

The model's live chassis construction is one I would never recommend for DCC, the fact that all the connected metal components of chassis and body are live to one rail is a hostage to fortune. A momentary contact between any part of a wheel tyre on the insulated side rail with any part of the loco structure causes a short.

 

Run the loco in the dark, you may then be able to see the sparks indicating where the shorts are occurring. If you are lucky it may be a few vulnerable spots which can be insulated with electrical tape. But the contact may be occuring well out of sight inside splashers or other structure and then you have to proceed by informed guesswork.

 

A better course is to fit insulated wheels all around, and arrange wiper pick ups on what is currently the live to rail side, thus fully isolating the chassis.

 

A work around on DCC. Some decoders allow reduction of the time out after track supply is lost with immediate resumption at previous speed, check your decoder manual for what is available. That reduces the effect, but will probably still detract from smooth running.