Dcc Bus resister

[Newby]

I am just starting to build a layout and started to add a DCC bus around the inner edge of the boards for the track. A friend who used to have a layout told me some time ago that I need to a track bus and another separate one for for the points or accessories. But from memory he also said I need a resister or something on the end, that is all I have in my notes.

Can someone help please, what is the resister, where does it go, do I need one on the track bus or on both?

Sorry so many questions, subject to what I need where can I buy it/them?

[Steve M]

Your friend's suggestion is similar to my setup - a DCC bus, 12vDC bus for lights etc and a 16v bus fed from a CDU for points. Basically a separate supply bus for each different voltage.
The resistor you refer to is a DCC snubber - you will want one at each end of the DCC bus.
A good source of more detailed explanations for each can be found on Brian Lambert's website.

https://www.brian-lambert.co.uk/index.html

[Brian]

Hi
As Steve has said, what you're referring to is a DCC filter or 'snubber' by another name. It consists of a 120 to 150 Ohm 2 watt or 3 watt resistor and a 0.1uF ceramic capacitor wired together in series then across the end of the DCC bus pair. Note: a Bus filter isn't a necessity, but can help remove voltage spikes appearing of the DCC bus pair, which can cause decoders inside locos to do things that are not expected or even cause them to fail completely if the spike voltage become very high. Usually two filters are used, one at each end of the bus pair. They can be obtained ready-made from DCC Concepts or make your own for a few pence each. See https://www.brian-lambert.co.uk/DCC-Pag ... #busfilter

Ready made https://railsofsheffield.com/products/d ... 48QAvD_BwE

If you're planning on having DCC operated point motors and other lineside DCC operated accessories, then using two DCC Bus pairs is the way to go IMO. However, the Track bus pair should be fed via a separate DCC all electronic circuit breaker. The Accessory bus bypasses this breaker and is directly fed from the DCC system. Then if a loco causes a short circuit (often by being driven into a set of points that are set to the other direction) the trip will remove the short to the loco but the accessory bus should still operate, allowing the point motor to be moved over and then the power will be restored automatically to the loco as the short circuit has been removed. All-electronic circuit breakers are available from several suppliers and one such is Coastal DCC https://www.coastaldcc.co.uk/search.php ... it+breaker


The alternative and where live frog (Electrofrog) points are used is to swap the frog polarity with a Frog Juicer on every point!

[Newby]

Ready made https://railsofsheffield.com/products/d ... 48QAvD_BwE

Thank you Steve and Brian

So if I am understanding correctly, I add one of these on the end of the track bus and on the of the accessories bus.

I am sure many will say why spend so much when you can do it for much less, but at this stage I need things simple

Thank you

[Steve M]

One on each end of the DCC bus. If the accessory bus is a simple 12v DC supply for lights then no snubber needed.
If however the accessory bus is for DCC control of accessories (possibly not in your case) then I guess snubbers could be used as a protection for accessory decoders but personally I've not heard of it.

[Newby]

I will use Cobalt Digital so yes DCC

Thank you

[Brian]

No need for DCC filters to be installed on a bus pair that is used to operate and power accessories via decoders, such as Cobalt digital point motors etc

[Steve M]

No need for DCC filters to be installed on a bus pair that is used to operate and power accessories via decoders, such as Cobalt digital point motors etc

I'd not heard if them being used on an accessory bus - that explains why.