NCE DCC anomaly with largescale polarity

[Tim Brien]

I received my new NCE 10 amp DCC system yesterday. Today, I ran it using four LGB locomotives. All ran perfectly until time came to power down the system and later repower it. Now I am aware that historically LGB chosen polarity is different to the NMRA protocol. This disparity it seems is the cause of my dilemma.

When the system is repowered and a loco chosen from the recall list, the initial loco selected seems to be 'asleep'. The issue seems to be that when a loco is selected from the recall list, 'reverse' polarity is automatically chosen by the system, although 'FWD' is illuminated on the display. If headlight selected to the 'on' position with 'FWD' displayed on the screen, the rear light actually is on. Cycling the 'Dir' button to 'Rev' and then 'Fwd' direction 'wakes' up the loco and all is well. Sometimes simply selecting forward throttle will also sort out the issue. I put this down to track polarity disparity between a stock wired LGB loco and the NMRA protocol. Apart from dismantling and changing track polarity contacts, is there a workaround, or is this a quirk when trying to combine NMRA and the long accepted garden scale 'reversed' polarity practice?

 

[ntpntpntp]

That's an odd one Tim. Can't say I've ever noticed this happening with my stuff. I agree that locos tend to be "asleep" until you sent the first command down the track to the decoder. This is noticable with my QSI sound-equipped locos which fire up when I cycle the direction or light button after entering the loco address.

Given that the dcc signal is an alternating waveform I don't see how any polarity issue could be involved, so it's a bit of a mystery?

I must admit the first thing I tend to do is switch on the light and cycle the direction of a loco before moving off, just to make sure it's going to go where I expect! Especially with double-ended locos like my little Hartland Mack which has no visible indication of which way round it is on the track except for the headlight! I've read this is one reason why some folk like having directional lights on locos even if the real thing doesn't.

 

[Tim Brien]

Ross,
link provides good general info, thankyou.

Nick,
your actions by cycling the fwd/rev direction is what I found 'wakes' up the system, so it seems you may have the same issue as me, but by cycling your direction commands, prior operation, you bypassed the 'sleep' step. Also, simply ignoring the recall list and directly inputting the loco cab number after 'Loco Select' action will sort things out. I certainly did not expectr this situation. It only occurs after powering up the system and using the recall function.

 

[ntpntpntp]

Next time I fire up the layout I'll try it and see if I get the same phenomenon. It's a nice day out today but I'm at home off sick so shouldn't really go outside and play!

 

[Tim Brien]

Nick,
a friend of mine with the same NCE system has a similar issue with one of his locomotives. He runs non-LGB U.S. prototypes to which he fitted NCE decoders following their wiring instructions. One loco he mixed up the track input to the decoder, with the result when he 'recalls' the loco on powering up, the rear light comes on automatically, even with 'FWD' direction displayed. After FWD driving input commanded, the rear light extinguishes and the front light illuminates.