How many Buses?

[basementcalling]

No, not Wheels of Time models or Greyhound, but wiring. I need bus line planning help.

How many different bus lines do you have under your layout? How do you calculate power needs and how can I be sure in running a 12v bus line that it carries enough amps to do the job without unintentionally interfering with loco net or track bus signals for the DCC?

Everything I want to add to my layout seems to require a power supply: LED lights in the paper mill - needs power beyond what a 9 volt battery can long supply. Servos and touch toggles from Berrett Hill Trains - nice product, but each control panel and every 8 servos requires 12 volts. Boosters for DCC and power blocks so the whole layout doesn't short at once. Sure I have wall warts that supply the power, and an old desktop and laptop computer with power supplies in them I suppose I could tear out and learn to repurpose.

I've been banging my head against the wall, probably because I cannot get my mind around how to route wires from all the 12 volt supplies and wall warts I need for things like control panels, LED structure lighting, etc... well enough, to go under the layout to bang my head on the bottom of the benchwork, though I am sure that will come with time.



I have one electrical outlet perfectly positioned for the majority of the layout right under the base of the peninsula where I figure to locate the majority of the DCC doodads (command station, boosters, various boards and reversers and such), and three other sockets that are in the walls the bench work runs around on each other side of the room, though I discovered they are all on the same 15 amp house circuit along with the overhead lights.

My progress impediment is I have no idea how to calculate power needs. I thought about buying an outdoor extension cord and running it along the stud wall my central peninsula surrounds and then adding a UWL labs certified 6 socket extension cord on the end, but I may well wind up with more than 6 low voltage power supplies plugged in. And this is probably overkill and I have no idea if it violates code, though I was told if I use Underwriters Lab approved devices that I would be in the clear.

There has to be a better way. But I cant see how trying to do a bus line of 12v voltage will work and not drop off so much that by the time I run the wires under the benchwork and around the layout, that the end of the feed will have enough energy left to actually power anything.

[peteski]

It is not that complicated (especially with AC household power).  Most wallwarts  have their power rating mentioned on a label.  Your entire layout (not including room lighting)  will consume much less power than a single 1500W hairdryer. 

In DC, power is easily calculated. Just multiply voltage over maximum current. So a 12V 1A wall wart can produce up to 12W of power. On the AC side, there are some power losses so it will consume slightly more (say around 15W of AC power).

Your household circuits are either 15 or 20A.   While not 100% exact, in AC you can also calculate power by multiplying voltage by current.   If you use the power triangle formula a 15A household circuit can supply 15 * 120 = 1800 W. for safety margin you don't use the circuit at 100% load, so a 15A circuit should be able to continuously supply around 1400 W.  That is a lot of wallwarts!

You would probably be better off centralizing your AC supplies. In each of your dual wall outlets plug in a power strip with as many outlets as you can find, then plug in all the wallwarts in those power strips. You can get power strips with long cords, so you can mount the strips under the layout.  Then run your DC wiring to the final destinations.

[bbussey]

I'm currently using two buses, one for the track power and the other for accessories.  The accessory bus is powered by a AC transformer at 9v (or 12v, don't remember at the moment) and 6A.  The accessory bus is powering everything other than the track, such as control panel LEDs, turnout automation, and dwarf signals.  When the capacity of the first accessory bus is reached, I'll add a second bus with a second transformer.

I have amp meters on both buses, but it is easy enough to keep track of the amp load on your accessory bus.  Just check the specs of everything you are adding to the bus for the mA usage and total that against the amp rating of your power source.

[peteski]

Just check the specs of everything you are adding to the bus for the mA usage and total that against the amp rating of your power source.

And don't exceed about 80% of the supply's rated current.  Most inexpensive supplies aren't designed for a constant 100% load.

Voltage drop on the DC bus can also be calculated.  You need to find out the resistance of the bus wire you'll use.   There are many charts and calculators to do the job, like http://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table

So if you have a 12V DC bus 30' long, that is 60' of wire (since the electricity travels from the supply, to the load on the end of the bus, then back to the supply.  If you use 14 AWG wire, the resistance per 10' is 0.025 ohms.  Thus 60 ' will have total resistance of 6 * 0.025 = 0.15 ohms.  If the load on the far end of the bus was 2A (as an example), then the voltage drop over the bus would be 2 * 0.15 = 0.3V  So the device which consumes 2A on the end of the bus would see 11.7V instead of 12V.  That is still well within acceptable voltage range for most 12V devices.

As you can see, all the calculations can be done using elementary grade math. 

As far as crosstalk between the buses goes, with DC you don't have to worry about that.  But if you feel like being cautious, just leave couple of inches between each bus.

[John]

How big is the layout .. thats the first question?

Diagram?

[basementcalling]

How big is the layout .. thats the first question?

Diagram?

John, 19x20. About 1/2 is double decked with 18 inches max width except the one blob which is 48 inches wide. One yard area will be 2x11 feet. I went with high, narrow benchwork to bring the N scale models into closer view. A rough track plan is available in the Idaho Belt layout build thread.

Thanks for the reassurances. An an ignorant electron for sure, though I did build my own wet cell battery in science class. Once.

I am also planning to use LED strips to illuminate most scenes on the layout, specifically those on the lower deck under upper deck areas. With just 12 inch deep scenes most places and  10 inch railhead to deck bottom clearance, they are almost a must.  I'm pushing the envelop  on deck separation  for sure. But with only around 11 inches under the decks to route wires and leave room for lighting and turnout motors, it could get kinda cramped underneath.

[mighalpern]

 you don't need a lot.    I have 2 wall warts that supply 12 volts DC and max rating for 2 amps, that I got from www.allelectronics.com I have one running all my tortoise , about 35 of them including the panel LED's. For tortoise I figured 20 ma. at stall although they say about 16 ma.  so 2000 ma's available is alot .  The other is supplying  lighting power for buildings and my turntable. 1 wall wart for my radio receiver and I have a command station and boosters at 5 amps each all plugged into 1 power strip to a 20 amp plug in the garage.  Never had any issues and I can plug in my vacuum and it still does not trip.  I'm probably at the 80% cap, Each is color coded and breaks out thru terminal strips.
good luck

[jagged ben]

Making some assumptions...

- That your train control is all DCC
- That you may want to control turnouts and other devices with DCC
- That you might want to power scenic lights or other accessories
- That you might want to run everything you might ever need for anything, including detection and signals

Then my advice would be ...

- DCC track power bus
- DCC accessory power bus on a different power district (e.g so you can still throw turnouts if a loco shorts the track)
- 12V DC bus, for whatever else needs it
- 12V AC bus (same)

[railnerd]

Free-moN gets a lot of mileage out of two busses, one for track, one for accessories/lighting.

If I had my druthers, BOTH busses would be DCC. Rectifying and regulating 12V AC 60Hz takes much larger capacitors, by contrast, DCC has a much higher frequency.

-Dave

[peteski]

Free-moN gets a lot of mileage out of two busses, one for track, one for accessories/lighting.

If I had my druthers, BOTH busses would be DCC. Rectifying and regulating 12V AC 60Hz takes much larger capacitors, by contrast, DCC has a much higher frequency.

-Dave

Don't forget thought that DCC signal starts off as a filtered DC which is then fed through high-power switching MOSFETs which make it into the higher frequency signal. So, you still need the humongous capacitors (just in a different location).  Plus the 60 HZ AC is free (it comes out like that right out of the power transformer) where boosters (which generate the DCC signal) are fairly expensive and complex electronic devices.

Plus that higher frequency signal is then subject to all sorts of weird behaviors over a long bus, and often you need to install snubbers on the bus ends. No such problem with the standard sinusoidal 60Hz AC.

Trust me, using DCC signal as a power source for devices which don't need it is not the way to go.

But I also agree with you that 12V DC should be the only other power needed on the layout (besides the DCC bus).  I don't know of any devices which specifically need 12V AC.  Even is some out there are designed to accept AC power that usually means that they have a bridge rectifier and filter caps built-in. But they will happily ruin from DC too (and as a bonus you don't have to worry about polarity).