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Peter's Model Railroading | Articles | Rolling Stock | PRR N5c
S-CAB: Battery-powered Lights


Brian Walsh (a Canadian S-scale modeler) and I contacted Neil Stanton about a solution for lighting the interiors of cabooses and passenger cars when the objective is to have a completely dead-rail layout (i.e. no electricity on the rails at all times). One of the features we really like about the S-CAB solution is that it provides for safe from-the-track charging of the battery. The beauty of that approach is that you neither need to open up the car (or engine), nor have an ugly dangling plug hanging out of the car (or engine) to be able to recharge the battery inside. Just have a piece of track on your layout to which you can apply anywhere from 6 to 18 volts (DC or DCC), park the car (or engine) there for a few hours, and the battery is fully charged again. Neil came out with a product he calls the "BPS-Lite". This small circuit board handles the charging of the battery, provides the power for interior LEDs, and allows for easy turning on and off of the lights and battery. On this page I document the components I received from Neil, and my installation experience. Note that a 3-page document is included with the package, identifying the parts, the wires, and how to install the parts. My commentary on this page is to be considered as supplemental; always go by what the product's documentation says, because there may be future enhancements that I have not documented here.
(external link: S-CAB)

The BPS-Lite is a small circuit board which measures 1-1/3" (34mm) by 2/3" (17mm). One side of this board holds all the circuitry components, with the tallest part being the white battery plug. This makes the height of the board with its components to be 1/3" (8mm).

The back of the board has two reed switches. Get a magnet to within 1/2" of either of them, and you will turn the power to the battery (and thus the LEDs) on or off. So, this board needs to be mounted such that these reed switches are within a 1/2" distance from a surface on the model that can be reached with a magnet (a side wall, an end wall, the roof, or even the bottom). If the car is made of plastic or non-ferrous metal, placing the board inside the model is fine. If the model is made of brass, a creative solution may be required. One option is to mount it under the car's bottom hidden between the underbody details. The reed switches can be reached if a magnet gets close to them; they don't have to be touched.

The BPS-Lite does not come with a battery. Neil offers a number of batteries. The one you get depends on your application. For my caboose installation, I chose the smallest one he sells, the BPS-420 (delivering up to 420mAh). The larger the battery, the longer the charge lasts, or the more LEDs one can power from that battery. In the case of a caboose, there are usually only a couple of LEDs to power. These might be two marker lamps, and perhaps some interior LEDs. However, the BPS-Lite's maximum continuous output is rated at 1 amp. Larger currents can be supported temporarily, but may significantly heat the components, and thus potentially shorten their life-span. You can hook up quite a few LEDs before you reach 1 amp, though. So, one could hook up a string of passenger cars with interior lighting, all being powered by one BPS-Lite. In that scenario, a larger battery may be recommended, especially if your model has the space.

My BPS-Lite came with two standard 5mm LEDs already attached to the two LED outputs. Plugging the battery into the battery socket was all that was required to test the board. Using the magnet attached to a pencil (sold separately, but one comes with the S-CAB starter set; any magnet will do, though), I was able to turn those two LEDs on and off. A white LED lights up on the board to indicate that the power is on. The two LED outputs shown with the LEDs, are hard-wired with a 470-ohm current-limiting resistor, so no extra resistor is needed, unless you want to dim the LEDs further. There is another pair of outputs available on the board. These are the white and black wires, shown on the right-hand side in the photo. These provide the battery's power directly (so they are also controlled by the battery's on/off state), but they have no current-limiting resistor installed. So these could be used for additional LEDs, such as interior LEDs in a caboose, or for extra LEDs within the passenger car, or to be routed to additional passenger cars. Just remember that the total maximum output of all the outputs combined cannot exceed 1 amp.

So, let's sum up the connections of the BPS-Lite (represented by the color of wire connected to the board; see photo above for reference): yellow/green pair (2x): LED output, protected with a 470ohm current-limiting resistor. white/black pair: extra battery output (not protected with a current-limiting resistor). gray pair: polarity-independent power pick-up from the wheel wipers for charging battery (18v max). red/black socket: for battery plug. There are two connections available on the board for which no wires are provided. They are used for providing for an alternative method of turning on or off the battery power. The ON one is above the LED connections. The OFF one is between the battery socket and the black wire for the extra battery output. These are to be used as normally-open, momentary-on switches (i.e. a quick power application to the ON connection turns the battery power on; a quick momentary power application to the OFF connection turns the battery power off). If you have an application where you need to remote-control the on/off state of the battery, then that is where these are used. In most cases, these can be completely ignored.

The BPS-Lite has a few features, some of which are optional just in case you have some special scenario. Overload protection is provided so that the output is limited to continuous use of 1 amp (up to 3 amps is possible, but this yields undesirable heating of the components). If the battery is empty, the BPS-Lite will re-direct the electricity from the wheel wipers (if present) to the output directly, but it is limited to a maximum of 0.5 amps total. This is handy for when you are running on a club layout and your caboose or passenger car's battery runs empty; if the layout has DC or DCC power on the rails, the LEDs you have connected to the BPS-Lite will continue to be powered. Note, however, that the buffer of the battery is no longer applied, so you will be back to depending on how clean the rails, wheels, and wheel wipers are (in other words, you might see the lights flicker if there is no good contact). The battery fuse will protect the battery from a short-circuit in the system, but the battery may need to be replaced if the fuse is tripped. A 3.5 amp fuse will protect the amount of damage if there is a short-circuit detected during charging. Wheel wiper voltage is normally limited to 35 volts, but that is not provided for in this board, because the DCC standard does not allow such high voltages to be used on layouts. However, adding a component to the board can enable this voltage limit, if that is possible in your special scenario. By default the BPS-Lite will NOT automatically cause the battery to be turned on when power is applied to the wheel wipers. This is so that the LEDs are not turned on if the car is parked on a piece of track that has power (otherwise you would never be able to turn them off if there is power to the track). If this feature is desired, though, the instruction manual shows which component needs to be removed from the board to have it automatically turn on when power is detected. If you are planning to use the BPS-Lite in that manner, I would recommend that you let Neil know about that when you order it, since the component is an SMD (Surface Mount Device), so they are very tiny parts.

Charging the battery is done by connecting anywhere between 6 and 18 volts to the two gray wires. When you do, a small yellow/green LED on the board will light up, indicating that it is receiving a charge. The amount of time to fully charge the battery depends on the size of the battery. The small LED turns off when the charging is complete. If knowing this status is important to you, you may want to position the board in such a manner that it is visible through one of the car's windows.

For those of you curious about how much weight these components add to the car, the above configuration comes in at 0.5oz (14g).

I will now cover the actual installation of the BPS-Lite and the LEDs into my specific model. After removing all previous wiring, and the trucks, I drilled two extra holes to get the wires connected to the wheel wipers to go through the floor. I decided to put them close to the bolsters, so that the amount of "pull" of the wire on the truck was reduced from where the wires were before (you will see two holes about a 1/2" further toward the center of the car). Make sure to drill the holes large enough to allow the wire you are going to use some free movement.

The wheel wipers I am going to use do not allow for soldering to them, so I formed this small piece of sheet brass into an "L" shape, drilled a hole into it for the truck mounting screw to go through, and applied solder to the other side. This piece will rub against the wheel wiper, thereby transferring the electricity to the wire that will be soldered to the brass sheet.

I then soldered a length of wire to the brass sheet. Be sure to position the wire as shown, because it will go directly from the bolster into the nearby holes drilled into the floor.

This is one wheel wiper clipped from its sprue. I had ordered an extra set of wheel wipers from Richmond Controls (see other article on this car). These are meant for HO-scale, but they are plenty long to fit S-scale axle spacing. I had to trim them once installed.

Getting all the parts installed on the truck before installing the truck mounting screw is a bit of a challenge. So, I used Aleene's Tacky glue, to glue the brass sheet to the bottom of the truck. The toothpick is there to make sure the screw-mounting hole is aligned. I am mounting the wheel wiper to the bottom of the truck rather than in between the truck and car's bolster, because the wiper offers less resistance in that position rather than it being further away from the axles. Rolling resistance of the wheels will be increased dramatically by the wheel wiper, so I wanted to keep it as low as possible. Is rolling resistance in a caboose a bad thing? Not necessarily. I have operated on layouts where a section of the train had to be parked on a piece of track that was on a grade, which caused the free-rolling cars to run loose. A caboose with some resistance might just be the solution. The trucks, by the way, are American Models caboose trucks.

I then assembled the wheel wipers to the caboose truck. Note that this truck has wheels that electrically connect one side of the wheel to the axle, while the other wheel is insulated from the axle. Make sure that both wheels are in the truck in the same direction. As you can see, the wheel wipers still need to be trimmed. Even though the wipers are mounted to the bottom of the truck, I could not see them when viewing them from the side when the truck was on the layout. Note that the second truck is done in a similar manner, but pay attention to which side the brass sheet with the wire is attached to the truck with respect to the non-insulated wheels of the truck. The second truck needs to pick up the power from the other rail, of course.

Here is a close-up of the truck installed on the car. You might just be able to see the brass sheet. Any of the shiny parts can be painted flat black in the future, if they are visible (except for the section of the wiper that rubs against the axles.

To verify that it all worked, I soldered a regular LED and a 1K ohm resistor in between the two wires that came into the body from the trucks. Make sure that you determine which truck picks up the positive and which picks up the negative from a standard power supply or 9-volt battery, else you risk burning out the LED. It is hard to see in the photo, but the reflection on my hand shows the green LED burning when I applied a 13-volt power supply to the track on my layout.

With the charging solution implemented, we can now start to work on placing the interior components. This is probably the hardest part of the project. You want the parts and wires placed such that they are not directly visible if someone looks through the windows of the car. The easiest of the parts to place is the battery. It just fit between the two lockers in the car. A battery can only be charged so many times, so there is the future potential of it needing to be replaced. However, I don't want it bouncing around in the car, so I attached it to the bottom of the car with some Aleene's Tacky Glue. This holds it in place, but if the need arises, I can rip it out. I put it in the center of the car for weight distribution, and for the wires to still reach the BPS-Lite circuit board, which I plan to install near the roof of the cupola. The red and black wires will likely be visible through the windows, so I may paint them a flat black later on.

I experimented with how to mount the BPS-Lite board. I tried different ideas, but the only one that fit well and still would allow for access from an external magnet was at the roof of the cupola. I built a platform to hold the board near the roof, but in the end it just didn't work out. So, I actually implemented my original idea, which was to glue the board to the under side of the roof. I used a 5-minute epoxy, because I needed it to stay in place. If I need to remove the board (for example when the battery needs to be replaced, because the plug is right up against the cupola's window), I'll have to use some force, and probably some of the paint on the roof will come loose. However, that is relatively easy to fix. The BPS-Lite board is actually wrapped in a clear film, so that is what is being glued, not the board's components. I glued the tops of the reed switches to the roof, so there are only two spots where the glue is actually making contact. I let that cure overnight to be safe, and so now it is a matter of routing the wires so that they are not visible, and yet be long enough to allow me some wiggling room with the roof.

After quite a bit of careful routing, here is the final result. Five SMD LEDs lit up, exactly as I had originally envisioned; two marker lamps and three interior ones.

The two pair of green/yellow wires coming off of the BPS-Lite board are routed to the exterior marker lamps. Since those outputs already have a 470-ohm resistor installed on the board, they can be routed directly to the LEDs. They were previously installed with magnet wire, so I simply cut the magnet wire to length and then soldered them to the green/yellow wires (after figuring out which wire was the positive and which was the negative for each of the marker lamps).

The interior lights I soldered each to a section of PC tie board (with the appropriate gaps filed into it), added a 100-ohm current-limiting resistor, and then wired them in parallel to the black and white output wires of the BPS-Lite. The two gray wires were soldered to the pick-up wires coming in from the trucks (for charging the battery). Although it may look easy, and because I only have a couple of photos to show for it, it took me three weeks of calendar time (too much work; too little play) to get all these wires routed, glued, and connected. The roof has to stay very close to the body, otherwise there would be very long wires hanging in the car, which would be visible. This made working in the space even more confined.

The final touches include trying to hide the wires inside the car as much as possible. I made a small "bridge" out of three pieces of strip styrene and glued that to the floor with Aleene's Tacky glue to force one of the gray wires down, while still allowing it to move left and right. The other gray wire (which was soldered to the blue wire coming in from the truck pick-up on the right) was glued to the gap between the battery and the locker. The glue is still drying at the time when I took this photo.

In the upper corner of the car where the two gray wires start to come down from the roof where they are connected to the board, I put a strip of styrene angle to control their movement. They can move up and down, but at least they will not swing into the open area of the car.

With the installation complete, I wanted to test the system. I left the five SMD LEDs on. They stayed lit for 9 hours and 15 minutes. Doing some quick math, with a 420mAh battery, that means they used (420 / 9.25 = ) 45mA per hour. That averages out to 9mA per SMD LED. Next, I charged the battery, which took 53 minutes before the green LED on the board went out (see the photo for the green light being barely visible under the roof). I shared the numbers with Neil, and he said that that was about what he expected from my set-up, so all looks good.

The whole car has taken a bit of a beating over the years. It is the last car of every train I ran at our club layout for the 4 to 5 shows we do per year. I have lost count as to how many times it has been rear-ended by another train following mine when I had to stop my train due to some emergency or another on the layout. Also, packing and unpacking for shows takes its toll on the car. So, part of this project will be to touch up the exterior before I call this project done. However, the interior needed some paint here and there to hide the new parts and wires. The floor was painted with the same PolyScale paint (still have 2/3rds of a bottle left!). I painted the top of the battery, because I noticed that I could see it if I looked through the porthole windows.

The many components and wires on the underside of the roof have been painted black with an acrylic flat black. I did not paint the BPS-Lite board, and, of course, stayed clear of the two SMD LEDs mounted on the left and right side of the roof. I did, however, paint the area around the white battery plug, as that was plainly visible through the cupola windows. Now it is much less noticeable.

And, this is what it is all about. A substantial amount of effort, but I can now run my caboose with all of its lights on, on my dead-rail layout.

This is what it looks like with the room's lights turned off.

The S-CAB BPS-Lite board is nearly trivial to use. You plug in the battery of your choice, and wave a magnet over the reed switches. That's all there is to it. It gives us the ability to have the lights on while operating on a dead-rail layout. Even if your layout has power to the rails, the battery provides the buffer so that it will eliminate the annoying flickering of the lights. With its 1-amp rating, you can use it to power a good number of SMD LEDs (and maybe a small animation). Charging via the wheel pick-ups is an easy-to-use feature that eliminates the need to constantly handle the car. As this article showed, the use and operation of the BPS-Lite is nearly trivial; it is the installation of it that will take some planning, and will require a bit of time and creativity to install without its main components being visible through the windows of the caboose or passenger car. I think this is a great addition to the S-CAB line-up of products. Thank you, Neil.