Battery Power - RFI Noise Suppression

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INTRODUCTION

Over the past fifteen years, our club has successfully run various forms radio control and battery power. The receiver and battery packs were always contained in a trailing power car, tender or B unit. The trailing power car always provided a reliable radio range of thirty to forty feet which was adequate for our busy club railway.

With the introduction of the 75 MHz receiver, several of our members began installing the receiver and batteries in various diesel locomotives. Unfortunately radio range was not always dependable and sometimes not adequate. The most noticeable problem was poor response to the slow button. As running trains without brakes on a busy club railway was not acceptable, the problem was discussed with members of the Aristo-Craft and My Large Scale Forums.

The problem was identified as Radio Frequency Interference (RFI) generated by the electric motors. The solution was to install “noise” suppression components. Following the advice I received from many forum members, I cobbled together this rather clunky V-4 circuit board.

The board was placed in the fuel tank of my NW-2 and the wires from the motor blocks and receiver were attached to it. The results were amazing. My NW-2 went from zero range to a reliable range of one hundred feet when using a new 75 MHz transmitter with the telescoping antenna. Following that success, a simpler board was designed and tested and found to be just as effective.

NOISE SUPPRESSION COMPONENTS

The perf board, chokes and capacitors were ordered from All Electronics
http://www.allelectronics.com

The perf board is part number ECS-4.

The 22uH, 4 amp chokes are part number CR-224.

The 0.01uf capacitors are part number 103D50.

The four position, terminals strips, part number 1725672, are manufactured by Phoenix Contact.
http://www.phoenixcontact.com/worldwide.htm
Most electronic shops can order them in for you.

The twelve position terminal strip is shown, but four position strips are available.

ADDING NOISE SUPPRESSION TO THE MOTORS

My Aristo-Craft, Plug and Play, FA-1 already had noise suppression components soldered across the motor terminals. If your locomotive does, skip this step.

Solder a capacitor across the terminals of each motor to help suppress RFI.

If you are installing capacitors in the motor blocks of a USA Trains diesel, I suggest removing the brass rods and slip on connectors and replacing them with wires soldered directly to the motor terminals. Every mechanical connection has the capacity to radiate noise.

ASSEMBLY OF THE CIRCUIT BOARD

The following diagram is a top view of the completed circuit board showing the placement of the components.

This diagram is the bottom view showing the points at which the components are soldered (marked X).

Score and snap a small board, 17 columns across and 10 rows deep, out of the larger perf board. Sand the edges smooth.

Drill a 1/2 inch hole in the middle of the board with a Forstner or spade bit.

Superglue (CA) the four position terminal strips to the top of the board with the pins in the holes at:

column 2, rows 4, 5, 6 and 7;
column 16, rows 4, 5, 6 and 7.

Make sure the adjustable openings for the motor wires face out.

Push the leads of the four chokes through the holes in the board at:

column 6, rows 1 and 4;
column 6, rows 7 and 10;
column 12, rows 1 and 4;
column 12, rows 7 and 10.

Turn the board over and solder the two outside pins of the terminal strips to the board. The two outside positions of the terminal strip will be used to attach the motor block wires to the circuit board. The center positions are not used but provide the proper spacing for the outside ones.

Solder the eight leads of the chokes to the board and trim them flush.

Cut a piece of red and a piece of black wire long enough to reach from the noise suppression board to the receiver. Trim a small piece of the insulation off one end of each wire.

Place one end of the red wire through the hole in the board at column 9, row 1 and solder it in place.

Place one end of the black wire through the hole in the board at column 9, row 10 and solder it in place.

When mounting the board, these wires should pass through the hole in the center of the board to keep them away from the motor block wires.

I hot glued this noise suppression board to the bottom of the frame, in the fuel tank of my NW-2. The hole in the board was aligned with the hole in the center of the frame. The wires passed through the holes to the receiver mounted on top of the frame under the hood.

The black wire is attached to grey wire of the Aristo-Craft connector or pin 3 of the receiver.

The red wire is attached to orange wire of the Aristo-Craft connector or pin 10 of the receiver.

I filed a slot in the flange on both ends of the fuel tank of my NW-2 to allow the motor wires to pass through without binding. The wires should be kept as short as possible, but allow free movement of the trucks.

The wires from the motor block are attached to the outside positions of the terminal strips. The wires may be a different colour than those shown.

Placing the noise suppression circuit board in the fuel tank:

minimizes the length of the motor block wires and amount of noise radiated,
keep the motor wires away from the receiver, minimizing RFI, and
allows the motor blocks to be removed by removing the fuel tank instead of the diesel hood.

This is a diagram of the current path.

Note the opposing colour of the motor wires attached to the terminal strips. This allows two motors mounted in opposite directions, to operate in the same direction.

Congratulations! You have made your first noise suppression circuit board. You should be able to obtain about 100 feet of range if you are using a new 75 MHz transmitter with the telescoping antenna.

PROBLEM SOLVING

If you do not obtain the expected range, check the following:

Are the batteries in your transmitter fairly new? Aristo-Craft recommends using Coppertops or similar batteries. Rechargeable batteries do not have the same voltage and decay when left sitting.
Are the batteries for your locomotive fully charged to at least 18 volts? According to rumor, the receiver responds better at higher voltages.
Are you holding the transmitter antenna straight up?
Is the receiver antenna unwrapped and properly placed as high in the locomotive as possible? The antenna should not cross over itself.

Have you tried a Black Kat antenna? I have used one in this project. It is mounted just above the receiver in my NW-2. The manufacturer recommends that the receiver antenna be trimmed to about 1 inch in length and soldered to the Black Kat.

The Black Kat antenna is available from E Cubed R/C
http://www.ecubedrc.com

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Last Modified 7/24/07 12:47 AM