Advice Needed With Kato n Layout Expansion

[freescopesdad]

My current layout (Kato n scale, DCC ECoS 5.1) is an around the wall product of using available garage space (detached, unheated, California central valley location) while also accommodating parking my Miata within the layout. For a number of reasons, both good and bad but mostly good, the Miata has been sold and the entire garage is now my oyster. In building the current layout I probably made every rookie mistake in the book, but in the end I enjoy it as do others I have shared it with. It does NOT lend itself to operations, but that isn't my thing anyway. Planning, building, and running trains are what I enjoy most about this hobby. The layout started out as an L, 10x12 feet, was expanded to 10x17 feet, then 17x17 feet in its current configuration (see current layout picture).

So... The layout as is consists of a long single main line around the perimeter, or, optionally, across a removable duck under which was removed when I parked my car in the garage. A second main line, call it the local, is about half the length. In expanding the current layout into the garage center with a peninsula, my main goal will be to significantly lengthen this second main. I have no elevation changes on the layout and do not plan any, so I will employ a 15 degree crossing for access (see proposed layout picture).

I have gone through at least 25 iterations with Anyrail, so nothing is etched in stone, but is probably close. My main concerns have to do with electronics however. The original bus is 14 gauge, extended 3 times with Wago connectors. Drops are all Kato blue/white 24 gauge, about every 3-4 feet, less than 18" to bus connections. I control about 35 turnouts with DCC Concepts decoders powered separately. I don't have any issues with track power with up to 4 DCC sound locomotives running (plenty for a single operator) and perhaps 2 more idling. The current plan is to extend the bus around the perimeter of the new peninsula with Wago connections once more.

Questions... Is it time to rewire the entire bus with perhaps 12 gauge or should I wire as planned and upgrade if necessary? Or is it time to consider adding a booster to the layout (although I'm not sure what that would even entail)? I don't currently have any track power issues on the layout, and I do not plan to run more trains than I currently do. I do have access under the entire layout so that is not an issue.

I welcome your thoughts and/or suggestions.

[peteski]

Since the accessory decoder get the separate power for the switch machines, they use very little power from the DCC bus.  Will you run many lit passenger trains? How many amps does your current DCC booster supply?   If you are the only operator then there really isnt' any need for separate power districts.

If you don't see any issues now,  I believe 14 AWG wire should be sufficient for a DCC bus for your size layout and the 24AWG feeders should be fine too.  What is the longest leg of your DCC bus from the booster to the end of the bus?  14 AWG wire has a resistance of 0.026 ohms/ft and 12 AWG 0.016 ohms/ft.  Since it is a 2-wire bus, the total resistance will be double (or 0.052 ohms/ft for 14 AWG and 0.032 ohms/ft for 12 AWG). The Wago terminals likely add some slight resistance, but likely not very significant.

Knowing the worst case current consumption will allow for calculating a voltage drop over the bus.  N scale sound equipped locos likely don't consume more than 0.5A each (silent ones a about 0.3A) maximum.  Accessory decoders likely use in more than 0.05A each.  6 sound-equipped locos will in a worst case consume 3A. I don't know how much current the DCC Concepts decoders need.  Assuming that those handle multiple turnouts each, how many total of those decoders you have?

[freescopesdad]

Thanks for the reply. The ECoS supplies 5 amps to the track. No lighted passenger trains. And the DCC Concepts stationary decoders are powered by an external 12V supply, not track power.

[peteski]

Thanks for the reply. The ECoS supplies 5 amps to the track. No lighted passenger trains. And the DCC Concepts stationary decoders are powered by an external 12V supply, not track power.

I understand that the DCC Concepts decoders have external power connected to them (for activating the switch machines), but they still connect to the DCC bus. I suspect that the decoder part of those decoders is using DCC-bus-supplied power. Iit is likely be equivalent to a non-sound mobile decoder in a loco sitting at idle.  That is usually 25-30mA (0.02 or 0.03A).  In either case it's not a significant additional load on the DCC bus.

Can you estimate the length of the longest section of the DCC bus from the booster to the end of the us?  Are we talking about 80, 100, 150 feet?  I'm trying to be scientific about this to figure out the maximum voltage drop using 14 and 12 AWG wires.

[freescopesdad]

30-35 feet. ECoS is centered in the layout.

[peteski]

30-35 feet. ECoS is centered in the layout.

Ok, so to calculate the voltage drop on 35 foot bus, lets pick 3A current draw (which is likely a generous estimate).
The total resistance of 14 AWG wire bus is 2 times 35 times 0.026 =  1.82 ohms.  At 3A the voltage drop at the very end of the bus would be 1.82 times 3 = 5.46V. It will of course be less the closer you are to the power source.

The total resistance of 12 AWG wire bus is 2 times 35 times 0.016 =  1.12 ohms. At 3 A the voltage drop at the very end of the bus would be 1.12 times 3 = 3.36V

Don't let those number scare you. That would be the absolute worst case scenario where all of the 3 Amps would be consumed at the very end of the bus. That is not realistic since in real operations the current will be consumed at various places on the bus, and also just a fraction of the 3A.

Let's pick half way point on the 14 AWG bus. The total resistance at that point will be 0.91 ohms and the load will be couple of sound locos, consuming total of 0.25A each (0.5A total).  The voltage drop in that scenario would be only 0.5 times 0.364 = 0.46V. that is negligible.
With 12 AWG wire it would be 0.5 times 0.56 = 0.28V.  These calculations apply to a single leg of the bus.

I would just stick with the 14 AWG bus unless you notice performance degradation.