Unless you are running open frame motors, (really old engines) You should use about .5 amps per train max. With your 3 amp NCE PowerCab you should be able to run 6 trains.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Now that the current requirements are established need to take a look at the running requirements. Specifically how many operators will be running those 7-8 trains. There are limits on the number of throttles that can be used on each system level. While a 5 amp SB3a will meet the current requirements, a PH Pro 5amp system may be needed if more then 4 operators will be active at the same time. Just something else to think about when upgrading.
Martin Myers
cacole How many trains are you going to be running at the same time? How many have sound? That determines how many Amps of power you need on the track. In my experience, one 5 Amp booster is more than enough even for our large HO scale club layout, where we use the NCE PowerHouse Pro 5 Amp system with 5 and 6 locomotive lashups with sound and 100 car trains being pulled up a long, 2 percent grade. The SB3a alone will probably be more than enough power for your layout. Once the layout is operational, you'll know if you need more power when the system keeps shutting down from an overload, provided that overload is not being caused by continual derailments or a wiring error.
How many trains are you going to be running at the same time? How many have sound? That determines how many Amps of power you need on the track.
In my experience, one 5 Amp booster is more than enough even for our large HO scale club layout, where we use the NCE PowerHouse Pro 5 Amp system with 5 and 6 locomotive lashups with sound and 100 car trains being pulled up a long, 2 percent grade.
The SB3a alone will probably be more than enough power for your layout. Once the layout is operational, you'll know if you need more power when the system keeps shutting down from an overload, provided that overload is not being caused by continual derailments or a wiring error.
Our club has the same size layout and the NCE 5 amp handles everything just fine. I would install a DCC amp meter also.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Lighted passenger cars or cabeese that draw track power will also affect your power requirements, particularly if you are using incandescents. Unless you have a lot of passenger cars, though, it's unlikely to be a big contributer.
I've got a decent-sized layout. My Lenz system with 5 amps is more than adequate.
It takes an iron man to play with a toy iron horse.
You will want the Smartbooster anyway regardless of power requirements. With that many ft of track you will need the ability to unplug the Power Cab throttle and move around. The Smartbooster lets you do that.
Simon Modelling CB&Q and Wabash See my slowly evolving layout on my picturetrail site http://www.picturetrail.com/simontrains and our videos at http://www.youtube.com/user/MrCrispybake?feature=mhum
I am planning on perhaps 2 double-head trains (lead loco with sound) running around the double main. Would like to be able to do some switching (couple of locos with sound) while having the other trains run the around the main. I doubt I would have more than 7-8 running at any given time.
The current that you need does not depend on how large your layout is. It depends on how many locomotives you will have actively running at the same time. Each sound locomotive can use about ½ amp. So if your Power Cab can put out 2 amps, you can run four sound locomotives at the same time, and maybe 5, but 6 would be pushing it. (I'm not sure about the number of non-sound locomotives you could run, but it would be at least twice as many.)
Now, to get the 2 amps from the Power Cab to all of your track on a larger layout, you should use AWG 12 wire for your main bus. (Also known as 12 gauge.) The reason for the large wire is to prevent power losses at long distances. (Larger wire has less resistance.) If you were to use small wire for the bus, you would not be able to get the full 2 amps to all of your track. The feeders from the bus to the track should be kept short and they can be 20 to 22 gauge.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
I currently have the NCE Power Cab running my small layout and I am planning on expanding to a large layout with a total of about 500ft of track. Can anyone tell me how much current I would likely need to run this size layout. It is my understanding that I would need the SB3a 5 amp smart booster first and can then add DB3a 5 amp boosters to further increase the amount of current.