snubbers

[Ken Z]

I have seen people talk of adding snubbers to their NCE layouts.  I have a friend who added "capacitors" to his Digitrax layout and then removed them because they didn't work.  (whatever that meant) I have a large layout with Digitrax and my power is split into 4 districts with 70 foot runs.  I have had no issues however I would always want to error on the side of making things as bullet proof as possible.  I don't want to add something not necessary, that seems snobish but if it is prudent to snub, I am glad to do that.   

Ken Zieska

[G8B4Life]

Snubbers help suppress high voltage spikes which can do serious damage to DCC decoders. The longer the bus wire run the more the issue becomes something to become concerned about. If your runs are 70ft long I'd certainly suggest adding them. For their cost compared to a blown decoder (like a LokSound or SoundTraxx) it can only be worth it.

A snubber is actually just a single capacitor and resistor connected across the bus at the end, forming a terminator. You could by the components for less than a dollar per snubber or even buy them ready made.

Alan Gartner's site goes into it a bit at http://www.wiringfordcc.com/track_2.htm in the section "Considerations for Layouts with Long Bus Wires". It's worth the read.

- Tim

[TwinStar]

Does the same concept apply to a fixed DC layout?

[Alan]

Yes, although a DCC buss is somewhat more sensitive for one additional reason. In addition to the electrical noise on the buss caused by running electric locos, both DC and DCC can suffer from power-on and short circuit spikes that cause voltage 'ringing' on the bus - voltage overshoot and undershoot as the system stabilizes after a transient event. DCC, unlike DC, suffers control signal integrity from ringing on the buss. Too much ringing equals signal loss. Snubbers can help dampen spikes and suppress ringing in both cases however, are not generally needed on a DC layout unless the bus is especially heavy and long. If power supply capacity is of no concern you can also dampen a DC bus (RailPro DC bus) with a simple resistive load.

http://www.lkorailroad.com/powering-the-lko-part-iii/
and
http://www.lkorailroad.com/big-honkin-resistors/

[Alan]

Someone over at MRH has encountered bus wiring ringing https://model-railroad-hobbyist.com/node/36978

[G8B4Life]

The OP actually encountered it just shy of  2 years ago and updated the progress a few days ago. Verily a long time between updates.

Does go to show how big the spikes with ringing can get; surprised they didn't actually blow any decoders.

- Tim

[atsfguy]

Since the use of snubbers work on DC layouts, are they necessary or useful on Railpro layouts?

[G8B4Life]

I don't think the usual DCC snubber (resistor and capacitor) works for DC but I'm no electronics expert. Alan gives a very good writeup of the problem in his blog posts linked to in one of his posts above. Now Alan has some very long buses but found he did not actually need the negate the ringing. I forget why now and it's probably due to what else he connected to the buses that others may not do so it's a your mileage may vary situation but I'm pretty sure that unless your buses are super long you shouldn't need any dampening.

- Tim