Pre-Wiring Tortoises

There are a number of ways to wire your Tortoise switch machines. For many years I simply soldered the wires to the metal pads on the circuit board as shown above. However this approach can have its downside as the metal pads can come loose under stress from the wires and heat from the soldering iron, and replacing a Tortoise can be a real headache.

Another approach is to use these card edge connectors that slip onto the circuit boards. The great thing about these is it makes it so easy to swap out a defective Tortoise–just pop off the connector, replace the Tortoise, and snap the connector back on. Of course the downside to these connectors is the added cost and tedium of soldering wires to the metal contacts, and the ones with screw terminals like those below are even more expensive.

So when I was installing a couple dozen Tortoises under Monroe Yard last month I also spent some time thinking of a way to make it cheaper and easier–here’s what I came up with.

First, since I use 20 ga wire for my Tortoise connections, I got out a 1/16″ drill bit. I used it to increase the size of the holes pre-drilled in the circuit board. Next I cut a bunch of black, white, red, green, and yellow 20 ga wires and added a male crimp on connector like those shown above to one end of the red and green wires and a male bullet connector like the one below to the yellow wires. These wires will be used to connect one of the SPDT switches to track power and turnout frogs.

I then soldered the red, green, and yellow wires metal pads numbered 2, 3, and 4, in that order. That leaves the yellow wire to feed the frog and matched the yellow wires I had already soldered to the underside of each turnout. I also added a white and black wire to the metal tabs labelled 1 and 8–these will be attached to the wires that power the Tortoise coming either from a control panel or an accessory decoder.  The white and black wires will be connected to their feeds with standard wire nuts. At this point all of this soldering was done on my workbench instead of under the layout and was easier than attaching wires to those little clip on connectors.

OK, with all the wires attached I started installing the Tortoise switch machines. Using a template I pre-drilled the mounting holes and popped them in place. The hardest part was feeding those actuator wires up through the holes in the turnout throwrods–I still haven’t found an easy way to do that.

The final step is making the connections. The red and green wires
need to be connected to the track power bus so I installed a T-tap suitcase connector on each bus wire and inserted the male crimp-on connector into it as shown above. If I need to swap out a Tortoise it is an easy matter to just pull the connectors apart which also makes it easy to correct the polarity at the frog. I connected the yellow wire on the Tortoise to the yellow wire from the frog by sliding the male bullet connector into a female one that I had added to the yellow frog wires. Again, these can be quickly separated if the Tortoise needs to be swapped out. Finally I made the wire nut connections with the white and black wires.

The end result is that all the wires are installed on the Tortoise before getting under the layout, and they can each be quickly separated if the Tortoise needs to be replaced or to correct polarity to the switch machine or the frog. Yes, this will likely mean that in order to get the polarity correct some red and green wires will end up attached to green and red wires but I can live with that. The crimp on connectors I used are dirt cheap when bought in lots of 100 and are easy to install. If you are concerned that over time corrosion may become a factor you can apply a little No-Ox-Id, a petrolatum based conductive grease with oxidation inhibitors and metal wetting agents designed for this type of use.

11 comments

  • I make a harness with a blue edge connector on one end and an eight pole terminal strip on the other. Once the Tortoise is installed and working properly I remove the installation assembly and replace it with the harness. The terminal strip is screwed to a vertical board under the layout to make it easily accessible. I am doing a process similar to Nelson Moyer on the RCW site http://blog.resincarworks.com/layout-design-with-nelson-moyer-part-4/ but I make my bench assembly for the accessory bus items to be installed on a vertical board on my L-girder layout with most of the terminal strip connections on the bottom edge. Working inverted is not a preference only a necessity for the Tortoise installation.

  • Larry, In answer to your actuating wire problem. I have found, when I use that method, the easiest way to make that wire go through the hole in the throwbar is measure it to fit your situation and to start at the top of the layout, drop it down through the hole, Then make the bend and fasten it to the tortoise . I have found this much easier than looking up from under poorly lit benchwork. I rarely use that method now. I use a mechanism Dick McEvoy published in RMC many years ago. The Tortoise is mounted horizontally and a square brass rod , bent at 90 degrees becomes a fulcrum . A piece of piano wire goes from the Tortoise to a small hole drilled in the horizontal part of the rod. The linear motion becomes rotary motion and the rod is just above ground level anywhere you want it to be. A small hole drilled through the rod is where the piano wire is slipped through and it goes to the throwbar . You no longer need to be worried about putting the massive hole between the ties at exactly the right place. I’ve also used this to throw a pair of points with one motor in a crossover.

  • After I drill out the holes, I run the wires in from the back side and solder. (At the workbench) This takes the strain off the foil tabs. The wires are left long enough to connect to a European connector that mounts on the benchwork.

  • I also use 24 AWG stranded wire which goes thru the holes. The short length of wire hasn’t made a difference in the operation. After the terminal block I use 22 AWG or 18AWG wire

  • I installed most of my turnouts more than ten years ago, and not much was said then about what we are discussing now. By the way, what color are frogs? You guessed it! That’s why I use a green wire to the frog. Who would have guessed!.

  • I wire all at the bench and leave enought wire that I can gentle loop and tape to the side of the motor. Then I make my connection to a terminal block. This take all the stress off the solder joint. I have never had one go bad.

    • Robert–that really is the most important thing, get the stress off those metal traces on the Tortoise circuit board. Unfortunately the little holes they pre-drill are too small for the wires sizes most use and it becomes easier to just solder the wires to the board instead of running them through the holes. Once they are attached through the holes it doesn’t matter whether you use some kind of quick disconnect connector or a terminal strip–Larry

  • Larry,

    A great approach that can be used on other components that may need swapping out.

    Thank you again.

    George

  • You can also use a silicone based di-electric grease used in autos.

  • I use cheap European style plastic blocks which can be cut to size.
    These are the white or clear plastic items seem on layouts with
    the small screws. They work the same as the blue item, but the
    wires are easy to change should that be need. They screw directly into
    the layout or a pre-wired separate module board.

    • Joel–I have those and use them in place of the old fashioned black plastic terminal strips. They are great for connecting wires to a power bus.