DCC Systems are selected based on needs of locomotive capacity and operator capacity. The general rule of thumb is two locos per amp in HO scale, and four per amp in N-scale. You only count the number of locos actually running, not parked.
The Power Cab is a complete self contained starter set with 2 amp capacity /13.8v DCC track voltage - suitable for Z, N, HO, S, and On3 scales.
This information was provided by Mark Gurries via his fantastic DCC Website.
FAQ on POWER CAB POWER RATINGS
1)What is the Power Cab's Current Rating?
SIMPLE ANSWER: The maximum continuous current rating is the same as the OUTPUT current rating printed on the NCE supplied power supply.LONG ANSWER: The answer depends on the power supply you connect to it as long as it rated at 3amp or less. See question 4 for more info.
2) How many Engines can I run on my Power Cab? (Motors made in 1985 or newer but excludes brass engines)
First thing you need to know is the Engine only consume power of any consequence when they motor is running. Engines sitting still on the track with only background sound and headlights on do not consume enough current to worry about. So the better question to ask is: How many MOVING Engines can I run on my Power Cab?
Simple Answer: If you make some good assumption about the current rating of the motors, then a worse (most conservative) MINIMUM number of engines possible. Assume Power Cab is rated at 1.5Amps.
N Scale Motor = 0.25A. Maximum engines = 1.5A / 0.25A = 6 Engines.
HO Scale Motor = 0.5A Maximum engines = 1.5A / 0.50A = 3 Engines.
O Scale Motor = 1.0A Maximum engines = 1.5A / 1.00A = 1+ Engines.
Why Minimum? Because the only time you can draw this much current continuously from the motor is when the train has a full load going upgrade at a high rate of speed and just making it up the hill. In practice nobody does that and as a consequence, the actual motor current needed is far less. In other words, you can typically run a lot more engines (1.5x) than the minimum with no problems. NOTE: IGNORING POWER LIMITATION, The maximum running trains the Power Cab can control is 12 engines. The power limitation issue will be reached first.
3) I fear my motors will overload the Power Cab. How can I tell if I need to upgrade the power or not?
Two ways to find out.
METHOD 1: Run and test. Run all the trains you plan on running at the same time on the layout that are realistically Manageable. Realistically Manageable? Anyone can run more trains, the question is can you keep them all under control so they never run into each other or crash somehow. As soon as you get going, you will quickly find out if you have enough power or current. The Power Cab will shutdown and restart with No harm done. If the Power Cab does NOT shutdown, your good to go. Either way, you will find out your answer.
METHOD2: Measure each engine and calculate. The great thing about the PowerCab is that it can measure the motor/locomotive current FOR YOU and let you see for yourself how much actual current is being used. How? Follow these steps.
a) Go to the SET UP THE CAB PARAMETERS menu. Press "ENTER" key.
b) Display will now say: "SHOW TRK CURRENT 1=Y". Press "1" key.
c) Press PROG/ESC key.
The clock display will be temporarily replaced by the current meter display. IF you attempt to do any programming or cycle power, the clock display will be restored.
Now place the engine of concern on the track connected to a train you plan on running with the engine. Run the engine on the worst part of the layout (heavy grade and/or on a sharp curve) but at the speed you plan to run the engine at. It is best to remove all other engines from the track so you can get a good accurate reading of JUST the engine current your running. You will notice the maximum current is a function of the speed and where it is running on the layout. The display will show the current consumed by the engine giving you the actual number. Note the highest current you saw. That is your actual current giving you a better understanding of how much current it will consume. Repeat for all your engines of concern. (Note: The number is much less than the stall current rating of the motor. If you do not know what that means, do not worry about it.)
4) What is the Power Cab's Maximum Current Rating? (Using a non NCE Power Supply) The NCE manual says: Power Input Requirements: 10-15V regulated DC, 3A maximum Power Connector: 5.5mm x 2.5mm center positive
What you need to know:
a) The NCE Power Cab does not regulate the track voltage. The power supply does. Hence the DCC track voltage is about the same as the power supply's DC output voltage rating. So get a power supply that is somewhere between 12VDC and 14VDC. A 13.8VDC is a common voltage the emulates a car battery voltage.
b) The NCE Power Cab does not set the current limit. The power supply does. Hence the Power Cab current rating is the same as the power supply's current rating. However, if the current exceeds 3Amps, the NCE Power Cab will shutdown to protect itself. So one must be vary careful about the selection of the power supply used with the Power Cab.
A) You cannot run 3Amp continuously or the Power Cab will overheat with the Power Cab shell deforming due to the high heat build up. It is strongly recommended you use multiple DCC circuit breaker with each set I < 2amp trip current for the layout. The Power Cab feeds all of these circuit breaker which then feed the various parts of the layout. The DCC circuit breakers will isolated any short circuit and protect the Power Cab from over heating when there is a short circuit.
B) The Power Cab 7 foot long flat cable will lose a lot of voltage and may get warm when running a lot of trains. The cable and associated cab bus RJ 12 jacks and plugs are not really designed to support 3Amps efficiently.
Best Recommendation: See question 5. More power and better operating experience.
5) What do I do if I need more current than offered by the Power Cab?
Upgrade the Power Cab system to use a NCE SB5. These are combination Command Stations PLUS 5 Amp booster in a single box. It is the intended power upgrade path for the Power Cab. It will allow your Power Cab to be unplugged and used like any other cab giving you the MISSING walk around capability you desire. You also keep you Power Cab and it associated PCP panel for the programming test bench where it will do the most good as a Power Cab.