PRR FA-2/FB-2 - S-CAB
09/30/2013
The factory-original motor that comes in the American Models FA-2, which is a Mabuchi RS-385SH, has been removed and replaced with a NWSL motor (see my other article). The old motor was rated at 6 to 24 volts, normal drain of 0.89 amps, with a stall current of 4 amps. Jameco sells these for $1.95, so that should give you some idea of the quality of this motor. After I did my first install of the S-CAB system, no matter what I did, beyond anything like speed step 1 or 2, the engine was traveling at light-speed. After consulting with Neil Stanton (the inventor of the S-CAB system), and Dave (owner of NWSL), remotoring this engine was the only solution. So, this article is a complete re-write documenting my second install of the S-CAB system into this engine. I simply followed the steps I had done in "version 1" of this article. Before, the install took me four days of modeling sessions, but this time around it only took me two days (I didn't have to figure out where everything could fit).

By the way, if you are not familiar with S-CAB, I have a separate article about the S-CAB system and the optional battery power supply.

The first photo shows the Battery Power Supply (BPS) board on the left, and the receiver/decoder combo-boards on the right. Neil was kind enough to pre-program the NCE decoder for me to the engine's address of "24", hence the label.
S-CAB
The other part needed for the installation is the battery itself. This was a custom-order from Neil Stanton. It is essentially two normal NWSL batteries (I used one of those standard batteries in the NW2 installation) bound together to provide a total of 2000mAh of storage. Under the green electrical tape is the circuit that protects the batteries from over-/under-charge.
S-CAB
I started the installation by removing all electronics, leaving only the wires from the wheel wipers and the frame. One side of the wheels pick up power from the wheel wipers, while the other side picks up power from the wheels through the trucks/gear tower and to the wire screwed to the top of the rear tower. Important note: the entire metal frame of the engine and the towers are connected to that rail. What this means is that all electrical contacts must be fully insulated, or else you can cause a short that may shorten the life of the electronic components. Note that this photo shows the original motor in the frame.
S-CAB
I replaced the spliced-up wire that was in there from previous work with this red wire, which connects the two sets of wheel wipers together. The power pick-up from the wheels is only going to be used to charge the battery in the engine.
S-CAB
Still showing the original motor in the frame, this photo shows the final conclusion I came to as to where to install the battery. Although the interior of this engine is quite cavernous, the huge battery could only be fitted in this spot. This turned out to be a good experiment, because when I later sent the frame to NWSL to have it re-motored, I specified that I could not have the second flywheel on the motor, because I needed that space for the battery pack. Although the available inside height in the engine is 1-5/8", I thought about putting the battery upright, but it is just a hair taller than that.
S-CAB
And finally a photo with the new motor installed. It is an HO-scale motor, so that opened up a lot more space in the frame. However, I proceeded to install the three parts into the engine just like I had done before. This photo shows the parts that make up the frame upon which the battery will be installed. I cut the parts out of 0.040" styrene sheet.
S-CAB
Using five-minute epoxy, I attached the two side pieces to the rear truck mount. A simple plastic clamp is used to hold the pieces in place while the glue sets.
S-CAB
During my first install I discovered that the red wheel-pick-up wire would sometimes get in the way of the shell as I tried to install it, so I had made a styrene guide to keep it in place. I did that again with this install, by simply gluing three scrap pieces of styrene to form this channel. The wire is attached to both wheels, so it needs to be moveable.
S-CAB
I then glued the battery support shelf to the two styrene side pieces.
S-CAB
The battery was attached using Aleene's Tacky Glue. From the first install, where I had used the same glue, I found that it was relatively easy to snap the battery off, while not damaging anything. This will come in handy when it is time to replace the battery.
S-CAB
The next step is to install the BPS board. I made this styrene stand so that the board doesn't touch the metal frame of the engine. A little bit of custom cutting and shaping was required.
S-CAB
This is the other side of the stand, with the board slipped into its position.
S-CAB
I added two vertical strips of styrene to hold the board upright. I then glued it onto the frame using five-minute epoxy. The board is a bit of a tight fit here, because it cannot go past the metal frame edge on the back of the engine, otherwise the shell won't fit. To the left of the styrene stand you will notice a hole. That is where the screw goes in to attach the frame to the shell. The shell has a female mounting hole on the inside, so the board has to clear that as well.
S-CAB
The BPS board simply fits in its mounting bracket. I could then solder one of its gray wires to the truck pick-up on the top of the tower, and the other gray wire to the red wheel pick-up wire on the other side. Note that the black rectangular part on the BPS, the ON reed switch (just to the right of the vertical styrene strip) faces out of the engine, so that a magnet can be used to turn the BPS on.
S-CAB
External Reference:
The BPS board that comes from Neil includes an OFF switch (a push button) that must be mounted on the engine to be able to turn off the power from the battery (to avoid it from draining when not in use). Neil posted an HO-scale installation example on his web site where he mentioned that he used a reed switch to turn OFF the power. A reed switch is built into the BPS board to turn ON the power from the battery. I thought it was a brilliant idea, so I asked him which ones he used. He said he used the same one that goes on the BPS board, which is a Digi-Key HE549CT-ND. So I ordered a set of ten of them (shown in the photo below), and this is the first engine where I am trying one out.
S-CAB
Just like the reed switch on the BPS board, this one has to face out and be able to be within a half an inch of a magnet. I removed the push button switch from the two orange wires, and soldered the reed switch in its place. I then made a styrene mount. Both the mount and the reed switch were attached with five-minute epoxy.
S-CAB
The last board to install is the receiver/decoder combo. I, again, built a simple styrene stand to hold this board in position. Here, too, the issue is to keep the board clear of the edges of the metal frame (so that the shell fits), and clear of the mounting hole to its right. Note that the blue rectangle, the antenna, is facing out of the engine.
S-CAB
The board is loose in its mounting stand, and I was afraid that as wires move around in the engine that the board might interfere with the mounting hole of the shell. I had a spare shell mounting bracket, so I put it over the mounting hole, and used another piece of scrap styrene to make sure the board stays clear of that mounting hole.
S-CAB
I could then solder the wires between the BPS board, the motor, and the decoder. I used a styrene angle piece to keep all of the wires neatly together and away from the shell and all the moving parts.
S-CAB
External Reference:
For this installation I am only using the engine's headlight. I am going to be doing a lot of super-detailing to this engine later on, so I wanted to be able to remove the shell from the frame when I do that. I, therefore, decided to use a two-pin connector (GRS part #GRS906). These are handy things; get a couple of packages of them!
S-CAB
Here it is installed between the decoder's white and blue wires and the LED mounted in the shell. A resistor was soldered in series to limit the LED's current.
S-CAB
The connector works great. I did a quick test of the frame on the work bench, and it worked great. I love the ability of using the reed switch to turn the engine's power on and then off. Very easy to do, and non-intrusive. I will report my performance results when I have them compiled.
S-CAB
I found that when I installed the shell, the headlight wires came very close to the motor and the rotating drive shaft. So, I built this contraption out of two strips of styrene angles and some strips of flat styrene across them. I then glued it to the frame using five-minute epoxy.
S-CAB
After testing I found that the front truck derailed. Upon close inspection I noticed that the headlight wires hit the side of the front truck, and so the truck wasn't free to move left and right. This triggered the derailment. I superglued the wires to the side of the shell, and tried to do it such that the wires are not visible when looking through the cab windows. I also painted the back of the headlight LED with black acrylic paint so that the interior of the shell doesn't light up like a Christmas tree when it is on.
S-CAB
Test Results
I have tested the engine running light on my layout with no track power on the rail. I did a full ten-hour charge. Over the course of the next two days I ran the engine light on my layout (no power on the track) back and forth on the 20-foot mainline. It has momentum set up, so it completely stopped, and then started up again in the opposite direction. After SIX HOURS and fifteen minutes of running, I grew seriously tired of having to flip the direction switch on the throttle every minute! It showed no sign of slowing down, so this configuration is more than capable of being used for an operating session.

I took a spur-of-the-moment video of the A-B-A units running on my layout.