I want to use Tortoise switches with the Atlas non-derailing board. I made a mock up on a small piece of plywood with an Atlas switch, the non-derail board, a Tortoise switch motor, and the provided Atlas switch push button. I've wired up everything according to this schematic from Atlas,  http://download.atlasrr.com/pdfs/TORTOISEREV1.pdf , using a 16 VAC transformer to power everything including the non derail board. The Tortoise switch motor throws both directions, both with the push button switch and running a box car over the insulated rails. The issue I have is an audible hum from the Tortoise that I would like to see if I can get rid of, as I imagine 20 plus of these would be annoying.  A search came up with a possible solution of using a capacitor after the diode but I am unsure how to apply that. Link to that discussion also provided with a diagram near the bottom. Does anyone have any ideas with a possible simple solution to this?


Also, I want to use  J2 on the non derail board to power the closure rails since I'm using J5 for the Tortoise. Is there anything that needs to be done or is that relay already active and activated from J1?



Original Post

The capacitor suggestion in the link would look like this:

tortoise option 3 with capacitors

The idea is the 25-cent capacitors smooth the pulsing DC voltage that follow the diodes.  I did not get from the discussion if someone actually tried this.  But from a technical perspective, I'd think this method has some details to work out.  With your existing diode method and 16V AC supply, the switch motors receive a voltage of about 12V DC.  By adding capacitors of a size that would effect meaningful smoothing, the voltage the Tortoises would see would jump up to 16V DC or more.  The voltage would depend on how many of your 20+ switch motors were "straight" vs. "diverge".  I think I read somewhere you don't want to apply more than 12V DC to these motors(?).  If you pursue this option, I'd install 12V DC regulator electronics after the capacitors to generate solid/smooth +12V DC and -12V DC.  There are eBay voltage regulator modules where you could do this for less than $5.

The last post in the link thread suggests 2 DC supplies connected in series.  This is the method 2 from the Tortoise instructions. 


For example, this could be 2 12V DC wall-warts.  Suitable wall-warts that can power dozens of Tortoises are about $2 on eBay (free shipping from Asia).  I'd suggest a pair of 50-cent screw-terminal adapters to simplify wiring so you don't have to splice into the coaxial barrel plugs. 

12v dc wall-wart and screw-terminal - december 2017 ebay

Obviously you need access to a pair of wall-outlets.  If this is a show-stopper and you want to use your existing 16V AC source then the diode method augmented by capacitors and the like can be further detailed. 

I'm ignorant as to your 2nd question.


Images (3)

Circuitron recommends a max of 14VAC for this purpose because the Tortoise is designed for a max of 12V DC. When half-wave rectified, 14VAC gives an effective 12V DC because of RMS (AC voltage is actually RMS because not constant but rather sine wave). You are actually overloading the Tortoise motors by suppling 16VAC half-wave rectified, hence the annoyingly loud 60Hz hum. I use 14VAC and the hum is subdued and not annoying.

Aha.  Someone who actually knows something has stepped forward!

tortoise option 3 with diodes

So if your transformer output cannot be lowered from 16V AC to 14V AC, try additional diodes as shown.  3 additional diodes on each side as shown lowers the effective AC voltage from 16 to about 14.  You can add more diodes if the hum is still objectionable.  Presumably you bought/have more than 2 diodes since you usually have to buy a pack of 10 or whatever!   Or 2 cents a piece - free shipping from Asia.

1n4003 diodes 2 cents each


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Thanks for the input guys. I can't utilize the capacitors because the 2 reversed diodes are joined together to feed the Tortoise per the Atlas pdf. instruction. So there would always be 2 diodes per tortoise switch coming from the atlas non derail board. Well, I guess I could if I keep throwing the switch every few seconds to keep one of the capacitors from exploding.  I already have a bunch of diodes I can use so I'll add in the extra ones to see if it reduces the humming enough to make it palatable. While testing whether the J2 relay was active and could be used for closure rail switching, it was switching between the 2 rails when the switch was thrown so all good there, my meter actually showed 17.8 vac not the 16 vac on the label. I wasn't planning on using this transformer, I just had it handy to try a mock-up of 1 switch, so I'll probably buy a lower voltage one and check the voltage first. 

I also used a DPDT relay with a 12 vdc transformer with success as well. It looks like you can build 20 or so dpdt relay boards with screw terminals and nylon standoffs for about $25. That route adds a ton more soldering and wiring than just a coupe of simple diodes, but does not have the hum from the half wave DC. 

Thanks again,


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