Accessory Power Wiring

A layout has a number of things that need power other than trains: turnouts, building lighting, control systems, etc. Some of these need to be isolated from each other, but others can share a system, and in general larger supplies are more cost-effective (there are some cases where that’s not true though).

Some related issues are summarized on my Power Wiring page.

I expect to have the following systems, but this is still very much open to change:

- Lighting Power
This is for building and street lights, and similar, and intended to drive LEDs. This will most likely be a set of 1 - 2 Amp “wall wart” type supplies providing regulated 15V DC to a local bus within a scenic region. I might use 12V, which is native for some things like LED Strip lights, but 15V allows chains of four LEDs on one wire, rather than three, and can simplify wiring of larger structures.

- Turnouts
I’m still clarifying how I want to do these, but servos with associated (cheap) microprocessors are one possibility. Those will need dedicated 5V wall-wart type supplies, and separate supplies for the electronics from the servos.

- Signal systems
These will likely operate off of whatever I settle on for a control bus, which will also need some kind of power. Likely a 12V bus, or rather a set of such with one per section of the layout, similar in design to the lighting power system, but separate from it.

- Control bus
I will have some kind of control bus, and the various devices on it may need power. Some of these systems allow powering the bus itself (either centrally or in sections) and having most devices draw power from the bus. Others will need per-device wall-wart supplies (or equivalent). Exactly what I’ll use here depends on selection of a control bus, but in general I want this to be independent of other systems, both for isolation and to allow future replacement as technologies change.

While I could use higher-current supplies, wall-warts are cheap. Their main downside is that they use power even when not in use, but to address that I’d just have a series of outlet strips under the layout on a switched circuit, so I could kill all power to the various systems when shutting down the layout. Some systems with batteries (e.g., throttle-charging stations) would need continued power, but those would be handled separately.

The advantage to wall-warts is that they isolate one system from another, limiting the effect of noise on sensitive circuits, and I can use regulated supplies that give me specific power levels regardless of fluctuations in utility power, which makes capacity planning and system performance more predictable.

Since currents in these various systems are not likely to exceed even one amp, I could use fairly small wire. However using somewhat heavier wire will make it more resistant to damage if snagged by tools when I’m working under the layout, and will also nearly eliminate voltage drop from long runs of wire. I expect to use at least 22 gauge wire (0.644 mm diameter), and might go as large as 18 ga (1.3 mm dia.) depending on the specific connectors I use. I expect to use a lot of this wire, and even bought bulk it’s not cheap, so smaller gauge has an advantage there.