Battery Power MU Plug - USA Trains SD70 MAC

by Paul Norton

INTRODUCTION

Aristo-Craft, Plug and Play diesels are sold with MU plugs on each end. This project shows how to add the same plug to a USA Trains SD70 so you can use a power car to run it. While this project deals with a specific locomotive, the principles should be the same for other USA Trains six axle diesels

NOTE: Nothing in this project prevents this locomotive from being restored to track power for re-sale at a later date. As the locomotive’s track power wiring will be unplugged during this project however, it will require a power car to run it. A power car is simply a battery car with a receiver added for on-board, radio control. To view an article on how to build a power car, just click on the following link.
Power Car

Up to four, 2-pin plug sets are required for this project.

They are available from All Electronics under part number CON-240 for $1.35 each.

REMOVING THE TRACK SLIDERS

Remove the railings from the sides and ends of the locomotive to prevent possible damage and set them aside for now.

Place the locomotive upside down in a soft cradle, taking special car to protect the three chime horns. Remove the small screws outlined in yellow from each track slider bracket with a magnetic tipped screwdriver. Using needle nosed pliers, pull the track sliders towards the outside of the motor blocks, so that the slot in the sliders clears the tabs on the bottom cover, and pull up.

If this fails, or you lose the screw or slider spring in the motor block, remove the bottom covers. Before removing the covers, stuff cardboard or foam between the top of the block and the frame to keep the motor blocks from dropping and dislodging the axles and their bushings. Unlike the axle bushings [O] in two axle motor blocks, the main axle bushings < O > in these blocks are rotated 90 degrees, tits up if you’ll pardon the expression. The smaller bushings [O] on the secondary shafts are not.

NOTE: The track sliders are the only components removed during this project. They should be sealed in a baggy and taped in a pocket of the locomotive’s Styrofoam packaging.

Fasten the track slider brackets back in place.

OPENING THE CAB AND LONG HOOD

Remove the four screws from the base of the fuel tank. Remove the fuel tank and set aside for now. Install the fuel tank screws back in the frame so they don’t get lost.

Under the cab there are two very small screws, highlighted in blue, in the side of the frame by the cab. A very small (2 or 2.4 mm) Phillips screwdriver will be required to remove them.

NOTE: A six piece set of precision screwdrivers from The Source in Canada (stock number 640-1962) is $8, and from Radio Shack in the USA (stock number 64-2969) is $6. The 3.8 mm screwdriver is my most used tool for large scale train work.

There are ten more screws, highlighted with yellow, holding the cab and hood to the frame. These are hidden in deep burrows in the frame and will require a long Phillips #1 screwdriver to remove them.

CAUTION Do not remove the side frames or the motor blocks to access any of the screws, as the U-joint between the pivoting and main motor blocks may come undone. The U-joints can only be accessed by removing the top cover on the main motor block.

The first two screws are directly behind the front pilot.
The next two are hidden under the front truck. These are the hardest to remove. The truck will have to be turned and the screwdriver inserted between the side frames and the motor block between the center and rear wheels. The wheels may have to be pushed against the motor block for clearance.
Two are in the middle of the empty area left by the fuel tank.
Two are behind the fuel tank, in front of the rear truck.
The last two are under the rear, pivoting motor block.

CAUTION: Do not lift the shell too far up or the front headlight wiring may unplug.

Turn the locomotive over. Carefully lift the shell from the rear. The long hood and cab will lift off as one piece.

INSTALLING THE MU PLUG(S)

CAUTION: The two pin plugs sold by All Electronics are not always colour coded the same as the plugs in USA Trains or Aristo-Craft diesels. If the plugs are not the same, just click on the following link to see how to change the wires so that proper polarity is maintained.
MU Plug Wiring

There should be two plugs from the front motor block, but only the plug indicated with the yellow arrow has two red wires and two black wires attached to one side of it. This plug is for the front truck, track power pick-ups, the other is for the front motor.

Undo the track power plug. This isolates the front truck, track power pick-ups and prevents battery power from being feed back into the tracks.

There should be two plugs for the rear motor block, but only one plug has two red wires and two black wires attached to one side of it. This plug is for the rear truck, track power pick-ups, the other is for the rear motor.

Undo the track power plug to isolate the rear truck, track power pick-ups.

Drill a 1/8 inch hole, indicated by the yellow arrow, in the center of the rear pilot above the cut bar and right under the anti-climber. Place a couple of pieces of masking tape on the anti-climber to protect it from the drill bit.

The hole should pass through the pilot and through the front wall of the box on the frame behind the pilot.

Drill a 1/8 inch hole, indicated by the yellow arrow, through the frame in the center of the box behind the pilot.

As only the male halves (indicated with red arrows) of the All Electronics, two-pin plug sets are needed for this project, unplug the females halves and set them aside. They can be used later for power cars and other projects. Hereafter the male halves of the sets will be referred to as an AE plug.

Slide a 3/4 inch length of shrink wrap over the wires of an AE plug until it reaches the back of the plug. With the tab of the plug facing up, feed the wires through the hole in the pilot over the coupler cut bar and through the hole in the wall of the box behind the pilot. Gently pull the wires until the shrink wrap is snug against the pilot. The plug should be able to move sideways without rubbing on the anti-climber. Now thread the wires through the hole in the center of the box on the frame.

Insert another AE plug into the open plug that is attached to the power distribution board. This open plug used to carry track power from the rear motor block, but will now carry battery power from the rear MU plug.

Gather the ends of the wires of the two AE plugs. Trim the wires to a useable length and strip 1/4 inch of insulation off all four wires. Slip a 3/4 inch length of shrink wrap over one of the red wires, and over one of the black wires. Solder the red wires together. Slip the shrink wrap down over the joint and warm it until it seals. Repeat for the black wire. Tape the wires to the rear weight.

The MU plug on the rear pilot will be used to connect a trailing power car. If you wish to MU this locomotive with others, a second plug will required on the front pilot. Repeat the process above, except the second AE plug will connected to the open plug on the power distribution board, indicated with the yellow arrow, that used to carry track power from the front truck.

THAT’S IT! You have completed the installation of an MU plug or plugs on your USA Trains SD70. All that’s left to do is test to ensure the unit is wired correctly before re-installing the shell.

TESTING THE MU PLUG(S)

Plug a power car into the MU plug on the rear pilot. If a power car is not available, connect the female portion of an All Electronics plug set to a small power pack for testing. Test to ensure the headlights and motors are both operating in the proper direction.

If a second plug was added to the front pilot, repeat the test for it.

If the headlights and motors are not in synch, check the colour coding of the wires of the AE plugs to ensure they line up with the USA Trains plugs.

ASSEMBLING THE LOCOMOTIVE

Once the MU plug(s) have been tested; the shell, fuel tank and railings can be replaced. When installing the shell to the frame, all wires should be inside the mounting posts so they do not get pinched between shell and the lip of the frame.

CONGRATULATIONS! The MU plug(s) will allow you to run your SD70 locomotive with a power car and enjoy all the benefits of battery power and radio control.

Double click on the arrow in the center of the screen to view a short video.

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Last Modified 8/25/08 3:24 PM