Tortoise Powered Turnout Shorts

Many layouts the use PowerRouting turnout (non DCC friendly turnouts) with a Tortoise motor will use a set of tortoise contacts to power the live frog so the power routing does NOT depend on the point rails for electrical contact.    When doing the installation, sometime the installers will encounter random shorts when throwing the turnout.  It comes and goes as the point rails move.  The problem is one of relative timing between two sets of electrical contacts wired in parallel that are moving at the same time.  The point rail contacts vs the Tortoise contacts.  If one contact completes it's throw before the other starts to throw, then there is a momentary solid short circuit until the second contact catches up with the first.  

There are two solutions to this problem:

1) Convert the turnout to a "DCC friendly Turnouts" and solve ALL the known electrical issues beyond this article alone.  
For more information, go here: DCC Friendly Switches/Turnouts

2) Leave the turnout alone and modify the Tortoise itself.  That is what this page is going to discuss.

This section is copied from Don Crano's website.  Don Crano, a DCC expert, passed away in October 2011.  He will be missed.   Unfortunately it is unclear about the future of his DCC website which has lots of valuable DCC information.   With that in mind, I decided to reproduce this valuable topic of his below with minor edits.

Modifying a Tortoise!

Or you might ask WHY?

First let me state, the Tortoise is not only my favorite slow motion stall motor, it is the only one I currently use on my layout. And the only one I recommend with today's electronics in DCC, and with low current stationary decoders it is a natural fit. It is one of the smoothest operating, highest quality switch motors out there. So this is by no means meant to say the Tortoise has a design flaw or any problems as they are. Only to show a way to modify the contacts so they can be used in a more common arrangement of only making contact at the end of travel more similar to that used by most other switch motors, such as Scale Shops, GB, added contacts on Switchmasters, even the twin coils types.

So now you ask so why this article?

Well lets look at it this way, if the contacts are going to be used to power point/frogs the fact they switch at the center of travel means there is a good chance of a short.  When a switch motor starts to move, the points may or may not start to move at the same time, there is more then likely some play in the linkage, if the points are a little stiff, the linkage may have to bend a little, etc.  If the switch motor switches contacts before the points, this is a short circuit.  By having the contacts only make contact at the end of it's travel you have a little more room for error on the linkage and timing.  But with the contacts changing in the middle of travel, you lost half the tolerance you could have, and linkage and timing are much more critical.

Also there are other methods that can be used. Such as using a stiffer wire to move the points. This will help insure the points move in a closer relation with the Tortoise. But there is a draw back. A stiffer wire means more pressure on the points against the stock rails. If this pressure is to great, it is always working to move your turnout out of proper gauge. Another is to make sure your points move free as possible and be very careful with the alignment of the Tortoise. The draw back here is one it is very time consuming, and two things do not always stay that way, and if the points start to stick just a little, you are back where you started.

It should be noted that if a Tortoise is properly installed and one makes sure their turnouts are free, there should be no need to make any modifications at all. But we all know things do not work out as planned all the time.

There is also another advantage to having the contacts make at the end of travel, especially on the slow motion machines and DCC. If you use a computer and software such as WinLok, you can actually watch the switch make it's transition with positive feedback and using the aux. contacts for this. Here there is no other way to get this nice ability to be able to watch the motor make it's transition on the CRT, other then possibly adding external contacts.

Now one may ask why did Circuitron, Inc the makers of the Tortoise make their contacts so they Make-Break-Make across the center of travel, instead of only Make at the ends of travel. They make the contacts switch at the middle of travel for a reason. By their surveys, the large proportion of their customers (approximately 70%) never use the contacts to for route or frog switching. And this is not surprising when you consider the number of layouts that use non switching points and insulated frog turnouts, such as Atlas and Peco. Circuitron also has specific applications notes covering the install with Shinohara and Peco brands of turnouts, as well as frog and signal wiring. Then consider the large number who would use the contacts for signal and panel lamps. Combine the slow speed of the Tortoise, with the large middle Break (Dead-Band area). During this time, the signals or panel lamps would be dead. So they do have their reasons for making the contact as they do.

But then there are us, the DCC crowd. We would like the advantages of having the larger Break area, to take advantage of system/computer feedback and other reasons as above. And we also know with LED's we can take advantage of the 15mA stall current, and use it to limit current for LED's in series with the Tortoise. So the contacts do not come into play when used this way for signals and panel lamps.

Does any of this mean you need to make any of these or any other modifications to the Tortoise for it to work correctly absolutely not. If you are not having any problems with your Tortoise, do not understand any of the above, it should be clear that you do not have to worry about any of this. If you are concerned about the contact rating of the Tortoise contacts, please see the notes at the bottom of this page.

But if any of the above applies to you. Then in this case, what I have to offer here is in my opinion a good way to accomplish this. And the reason I chose to do this is simply because Modifying the contacts works great, is easy to do, and gives you a wide latitude of timing and installation is nowhere as critical. And we can take advantage of using the internal contacts for positive position and actual traverse indication with computer and software. But there are a couple of draw backs. One is you have to open the Tortoise up to do this, and this leads to number two.

Doing this modification will void your Warranty!

This does not bother me, but if it bothers you, then you might as well stop reading now!


If you are still here
, then I will show you what you need to do, it a simple and easy fix. First thing you need to know is how to open the Tortoise up. There are 5 Phillips head screws on the front. There are one in each corner, the label will cover part of each of these 4 screws. Then there is one under the middle of the label. This one you will have to feel for it, then punch through the label to get to it. Look at the picture and you will see all five, including the one under the label. I even circled them for you. 

Once you remove the screws, carefully separate the two halves of the cases. Take a second and look things over. You will find the PCB with the motor attached to it, the pivot arm and several gears. Do not worry it all goes back together in a logical fashion. All the stepped gears are the same, and the small gear on the step goes to the outside of the case. Just be careful of the wiper contacts on the pivot arm, both when you remove it and put the PCB back in.

Again notice the WARNING on the lower portion of the label. Still game to do this, then read on and I will show you the next step or two.




Here is what a stock Tortoise PCB looks like, on the left, when you get it out of the case. Notice the contact area that I have circled, you can see how close the contacts actually come to each other. Keep in mind, the wipers on the pivot arm will take almost half the gap up as it wipes across the PCB. You can also modify the lower contacts if you like. But I usually only do the one set. Keep in mind that the pivot arm pivots at a point close to the center hub on the back of the motor, and the linkage point is just below the hole in the upper portion of the PCB, so any thing that opens up the contact area is multiplied by the distance from the contacts to the linkage point.













Here is what it looks like after the modification, on the right. Notice how much more space there is between contact make points. This allows the Tortoise to move almost it entire travel before the contacts will make. You will notice that here I actually removed trace material from the PCB. Normally I do not do this, but thought I should here for example purposes. I usually only cut though the traces at the outside points. It is easier to do, and just makes the rest of the inner traces left dead. You can do it either way, there is no problem as long as you are careful not to cut to much away. A good way to find out how much you can cut from the center of travel is once you have it apart, put the PCB and pivot arm back in and hold the case together by hand. Then move the pivot arm back and forth it's full travel, this will mark the traces on the PCB and show you how far they travel. If you look real close on the picture on the left, you can see the marks. Just make sure you do not cut beyond those travel lines, or you will not have a contact to make.

Please note in the pictures how the traces are cut, they follow the arc of the contact fingers. Make sure you cut the traces of foil following up from this arc. The foil cuts must follow this arc as shown in both the non modified and modified pictures. The contact clearance is minimal, and a straight cut would likely cause a short.

That's it, place a drop of oil such as Labelle 102 on the contacts, this will help keep them from wearing noticeably. Then just put it back together replace the five screws, and you are all set.




NOTES:

1) As per Steve Worack President of Circuitron, Inc.
"As to the contact rating, we rate the contacts for 1 amp SWITCHING. They will safely carry 4-5 amps, and the short circuit protection of DCC systems makes contact or circuit board "frying" a fairly remote possibility. In truth, with over 3/4 million TORTOISEs in the field, I have never gotten one back with burned up contacts. And MANY of these are being used for Hi-rail and G scale."

2) So it appears there is no problems with DCC at 4 to 5 Amps. But I will still recommend using either an 1156 [12V 30W] automotive tail lamp, or some form of fast acting circuit breaker, such as the PM-4 or otherwise. Since a short here is still going to shut down the entire booster district unless there is either some form of current limiting or sub-district fault protection.

3) Please do not contact Circuitron about any of these modifications, they are my idea, and my way of handling this. Circuitron has more important things to do, such as keeping up production of the Tortoise to meet demand. If you have questions or problems with your stock or non-modified Tortoise I am sure that they will want to hear from you. But any questions to do with these modifications of the Tortoise, then please contact me.

4) Remember doing these modifications will also void your Warranty and I do not assume any liability either so you are on your own. But if you follow directions, you should not have any problems either.

5) I would like to thank Steve Worack President of Circuitron, Inc. for the helpful facts and tips he has supplied.