Suppressors for Track Bus and Cab Bus.

In NCE-DCC@yahoogroups.com on Sep 15 2005, Mark Gurries <gurriesm@c...> wrote:

3) Add a terminator to the end of the cab bus.  Typically it is a 120 Ohm resistor in series with 0.01uF Ceramic capacitor. (Voltage not critical.)  Adding shrink tubing to insulate the leads, I crimp my terminator into a RJ12 jack so it can move it around when I expand

My jack system.  I plug it into the last jack at the end of the line farthest from the command station.  I add another terminator to the cab bus going the other direction.

Best Regards, Mark Gurries

Larry asked

Is this the same or similar bus terminator I use on the power bus?

Larry

Yes and no

Yes in concept of how one works and how to wiring it up.  No in that the values are bit different. The normal one is the one discussed on the WiringForDCC http://www.wiringfordcc.com/track_2.htm#c2

The section talks about long track bus runs.  Scroll down till you see the topic about unterminated bus ends.  The one show there is:

Track Bus; 0.1uF 50V and 100 Ohms 1/2W

Mark Gurries said on 14 Jan 06 about Cab Bus suppressors.

Cab bus.  In most cases, none is needed.

Cab bus termination would only be recommended on large layouts when:

a) there are lots of control issues with the cabs or throttles (read unreliable) but you know for SURE your cab bus connections are solid and there is no Cab bus power overload.

b) the cab bus picks up a lot of noise from the track bus.  In this case it is best to simply better to reroute the cab bus as far away from any wire related to track power.  Avoid bundling the cab bus with any other wires as much as possible.

There are three buses in a DCC system.

1) Cab Bus: Connects the command station to ALL the wall around or wireless Cab or Throttles.

2) Control Bus:  Connects the command station to ALL the boosters/power Stations used on the layout.

3) Track Bus: Connect a given the boosters/Power station to ALL the sections or blocks of tracks it is powering.

Of the 3 busses, it is the track bus that is most in need of termination for the track bus contains the most power and noise which can couple into other busses on the layout.

Note: Digitrax combines busses 1 & 2 together in a single cable and generically calls the whole cable Loconet.

Best Regards,

Mark Gurries

To convert this one for the Cab bus, we like to get the solution physically smaller if possible.  Unlike the track bus, the cab bus does not have lots of power, high voltage nor does it need a strong termination.

We can do this by changing the capacitor to a 0.01uF and reduce the capacitor voltage rating along with a watt rating reduction on the resistor.  This give us:

Cab Bus; 0.01uF 10V to 25V and 100 Ohms 1/4W

When I say 10V to 25V for the capacitor, actually any voltage you can get will work.  Simply put, get the smallest 0.01uF ceramic cap you can find with wire leads.

Best Regards,

Mark Gurries

Linear Technology

Power Supply & Battery Charger Applications Engineer/Manager

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