Programming track

[Crosland]

I remain skeptical of the NCE programming mode. The problem seems to be the different ways the NMRA recommendations are being interperated. Yes there is nothing wrong with have full voltage track power, the issue being to my mind that while this is delivered at a lower amperage it is not momentary as per the NMRA specs of 100ms, but continuous. 250ma at any continuous voltage between 7-22v is more than enough to run many motors at quite a speed, and to my mind capable of frying electronic circuits when flowing the wrong way due to a short etc.

 

With typical NMRA language, the service mode programming environment is only a recommendation, albeit within a standard, and is open to interpretation. The exact wording is "it is recommended that ... an environment with limited energy ... limited energy is defined as 250 mA, sustained for more than 100 ms" https://www.nmra.org/sites/default/files/s-9.2.3_2012_07.pdf

 

There's a problem with that last part, as 250mA sustained for more than 100 ms would be excessive.

 

This "limited energy" was fine until users found they could not program their sound decoders or anything fitted with a stay alive due to increased current consumption and especially the initial inrush current when the track power is first turned on. This led to one manufacturer to design a "programming boosters", to provide the extra power, which kind of goes against the grain of the spec.

 

Let's look at the wording again "250 mA, sustained for more than 100 ms". What about 500 mA sustained for only 50 ms? Or 1000 mA sustained for 25 ms? Or 5000 mA for less than 5 ms. Basic physics tells us they all represent the same "limited" energy, and are within the letter, if not the spirit, of the Standard. The problem is we do not really know what was in the mind of whoever wrote the standard this way.

 

The SPROG allows for the very high inrush currents seen with sound decoders and stay alives, and checks that the current has decayed below 250mA within 100 ms each time power is applied during programming cycles. After that, it applies the same current limit during programming as it does during running, which is why you can test run a loco on the programming track. The SPROG also has a very fast cutout (around 5 ms) which protects the loco/decoder/motor, the downside of which is that it doesn't play well with some bock cut out modules. 

 

Andrew

[RAF96]

Andrew

Re NMRA limited energy. I was convinced the blurb said '...more than 250mA for more than 100mS constituted an overload...', which makes more sense, but as usual I can't find it again in my printout.

Rob

[Razzmataz]

Re Post #47, I looked up www.dccinterface.com but there is very limited information on the "Arduino Model Railway DCC interface". Just some pictures showing a two connector DCC interface (Track Bus?) and a three way connector marked +, - & Ard. I presume that the interface comes with full instructions. Could Ian Jeffery or some one else who has one, confirm this.

Edited September 15, 2017 by Razzmataz

[Pannier Tank]

How about a raspberry pi and a sprog - you can even get a sprog shield ( http://www.sprog-dcc.co.uk/pisprog.shtml ) . 

 

Pi-Sprog One added to my Christmas List!