Decoder installation in an O Gauge SanCheng City loco

Discussion in 'Techniques' started by GrahameH, 12 January 2020.

  1. GrahameH

    GrahameH Western Thunderer

    May I ask if any of the WT members has a SanCheng GWR City Class locomotive which has been converted from Analogue to DCC please ?

    I would like to convert mine and as yet haven't had the "courage" to open it and see what the wiring consists of internally. I don't have an instruction sheet ( assuming it was originally enclosed with the model ? ).

    I have hardwired quite a few locos over the years, either kit built or proprietary models and I am certainly not fazed in that respect, but it would be very useful to known what lies ahead before I take the plunge with this locomotive.

    Any thoughts or advice / photos of an install would be most gratefully received.

  2. BrushType4

    BrushType4 Western Thunderer

    The wiring is really easy. You’ll not have any trouble at all.
  3. GrahameH

    GrahameH Western Thunderer

    Thank you, could i ask if you've done one ?

    Any help would be good before the screws ping across the carpet !!!
  4. paulc

    paulc Western Thunderer

    Be brave .
    Cheers Paul
  5. GrahameH

    GrahameH Western Thunderer

    Thank you, whilst I consider myself to be that I would prefer to do the conversion with the knowledge from someone who is able to advise upon how it is actually done.

    The model is an expensive investment in my eyes and therefore wish to carry out any work in the knowledge that it is being done in the correct manner, and any possible problems highlighted before taking my tools to it.


  6. simond

    simond Western Thunderer


    Rick Williamson. G0G, wrote;

    I don't know if Bachmann Brass and Sang Cheng have the same provenance, but for what it is worth, and from memory a few years ago.
    I bought a Bachmann Hughes Fowler Crab 2nd hand that ran a bit slow, noisy and needed converting to DCC for my railway. After unscrewing the chassis cover plate beneath the loco everything came apart easily along with the coupling rods ect. The motor and gearbox was a hulking great affair that I was very concerned would not take a 1.5amp DCC chip. The motor and gearbox was one unit that appeared to disassemble via destruction. Having enjoyed good performance from cannon motors fitted to ABC gearboxes, I decided that the Crab would get the same. The problem was the rear driving axle that was part of the motor/ gearbox. Using a single slaters axle, bushes and wheel set. The slaters bushes slid vertically into the chassis slot left by the motor/gbox so no problem achieving the fit in terms of fore and aft relation to the other axles. The problem was how to register the bush vertically in the chassis. I assembled the slaters axle, wheels and bushes together, slid them into the chassis slot. I may have had to open out the slot slightly by filing, but only slightly. I then placed it on a piece of level track and tack soldered the bushes. Did a rough assembly and it ran fine. Yes a classic bodge but it worked fine. Also the Slaters coupling rod bushes fitted nicely into the existing rods. Oh yes the pickups fitted the slaters wheels just fine. This conversion required no machining.
    If you intend to just rewire the existing motor gearbox then you are not going to open Pandora's box. The Bachmann was robustly screwed together, made to come apart and go back together. I would however try to ascertain what amperage the motor will draw before putting a chip near it.
    This probably more than you wanted, hope it helps.

    3 LINK likes this.
  7. simond

    simond Western Thunderer

    In case anybody’s wondering, Grahame has a problem with the G0G website so I’m being the go-between/carrier pigeon/owl.

  8. simond

    simond Western Thunderer

    Current draw measurements. Adequate controlled DC supply, multimeter with 10A range, locomotive, bufferstop.

    Connect ammeter in series with supply & loco, drive loco & check running current. Then drive up to bufferstop & stop in contact. Wind up the juice til the wheels spin, whilst watching the ammeter (or set it to capture the max value, some of them do). The peak current should occur just before the wheels spin. You can expect it to be several times the running current.

    Don’t leave the motor stalled for more than a couple of seconds and it’s very unlikely to be damaged. (but I offer no guarantees!)

    Be very, very careful if it’s coreless, indeed, probably don’t do it at all.

    And of course, stalling it for a long time (minutes) is very likely to overheat and damage it.

    Don’t repeat the test until certain that it has thoroughly cooled down again, probably best to cool it down by running light engine at moderate speed for 5-10 minutes, followed by a period of “off”.

    3 LINK likes this.
  9. GrahameH

    GrahameH Western Thunderer

    Hi Simon,

    Thank you very much for the above investigations and to RW for his detailed explanation, would you be so kind as to pass on my thanks.

    There is a large amount to ponder upon not withstanding the electrical testing ( which would be done by me as a matter of course ).

    I naturally didn't expect the proposed conversion to be an "out of the box" type shell off / wire / shell on which can sometimes be the case, that said I think there ought to be some discussions / investigatory chats made on Sunday at Bristol with a couple of people attending who may well give me further guidance.

    Oh ! And to your pigeon / owl too !!

    simond likes this.
  10. simond

    simond Western Thunderer

    Further news!

    David (Jinty) occasionally posts here and on RMWeb, I’d suggest a quick pm or two



    I have quite regularly fitted DCC decoders to San Cheng built locomotives.
    I haven't done a 'City' class but I have done 8F's, Black 5's, 4F's, Hall and numerous tank engines.
    All have been fitted with a Zimo MX645R except one Black 5 which I fitted a MX645P22 decoder and ADAPLU adaptor board. The adaptor board gives two advantages: 1) The decoder can be removed easily. 2) The adaptor board takes the total load of the 645 up to 2.2 amps max, 1.8 amps nominal.
    I used the adaptor board for extra current draw as it was going to work on a garden railway.

    The Black 5 of Ramchester fame is one I did, which pulls 5 x Sidelines brass coaches around regularly, all that, through a Zimo MX645R

    Hope this helps


    David Magill
    GOG: 22806
    GrahameH likes this.
  11. simond

    simond Western Thunderer


    two more:

    Dave Watts

    If it helps, I have fitted a ESU Lokpilot XL V4 to a San Cheng City. There is room down the firebox end. As I recall you need to remove a couple of screws at the cab end and a couple under the bogie. Then remove the four screws on each side below the hornblocks and the body should lift off. Smoke box door on mine opens so you can get a feel for how much room you have before taking it apart. My decoder is held in place with some Black Tack from youchoos. I think some form of stay alive is worth considering.


    John Riley

    An esu 5l will be sufficient it now has a built in stay alive as Dave says you take 2 screws out at the front (the ones ‘that are flush not the countersunk ones ) two at the back outside corners of the cab and the plates holding the cranks body lifts off
    you have hardwire the decoder but there is plenty of room in the boiler and smoke box. The smoke box door opens

    use your from her nails to pull on the dart

  12. GrahameH

    GrahameH Western Thunderer

    Thank you Simon and please extend my thanks to Dave Watts and John Riley please ( still waiting for the Guild to sort out my little problem ! ).

    I've been looking at the loco and made a few assumptions about getting into it, the above replies confirm what I was basically thinking about and with room in the smokebox area too !

  13. simond

    simond Western Thunderer

    Thanks already passed on!

  14. just seen my typo's good old auto correct should read use your fingernails to pull on the dart
  15. GrahameH

    GrahameH Western Thunderer

    Don't worry, so long as it doesn't mess with my nail varnish i'm sure it'll be ok ! :D