Using Tortoise for DC Power Routing

[JohnJ]

I'm still in the DC dark ages, and am in process of building a staging yard for my HO layout. To save on hardware costs and simplify wiring, I'd like to use my Tortoise switch machines to power the tracks in the yard. If a switch is lined for a yard track, I'd like to power that track. Otherwise, the track would be dead. This is easy to do using the internal switches on the Tortoise.

My question is the power rating. I'll be using an MRC 200 power pack, which lists the following output: 15.V DC, 18.5VAC, total output 17VA. I assume the "VA" stands for volt-amp. Now, the Tortoise internal switches are rated for 1 amp. My locos don't have sound, and I usually run 3-4 Genesis/Atlas/Bowser type units on my trains. I'm unfamiliar with the conversion from volt-amp to amp; am I likely to run into trouble with this arrangement?

Thanks in advance for any input.

[edwardsutorik]

"volt-amp" doesn't actually convert to "amp". They aren't the same thing.

But. In this case, you can divide volt-amps by volts, which will then give you amps. 17VA / 15V = 1.13A, which should be the maximum output of your power pack.

Since you say you are already running 3-4 locomotives, and the power pack hasn't gone into overload and cut out, it appears you're below the max.

I doubt that Tortoise actually did any tests for max current through their contacts. Hopefully, they DID run 1A through them, at least.


Anyway, I expect what will be of great use to you is to hear that others have pulled it off successfully. Or not. And I expect there's folks here who have experience.



Ed

[jonklein611]

Seems to be low risk, as Ed's math shows. I'd be concerned if you were drawing 1A+ while the switch machine was in motion, but for your use case this would be unlikely. Wouldn't hurt to pull out the ol multimeter and verify the amps you're pulling, but again unlikely to be at 1+ amps unless you stall something.

[edwardsutorik]

There's two kinds of problems with contacts.

One kind is damage caused when the contacts switch power on and off. You get arcing at the contacts, and this can damage them over time. As Jon Klein noted, the usage described in this case will likely not see this happening very often (it DOES happen to switching relay contacts EVERY time).

The other kind is when the contacts are closed. To the extent that there's resistance on the contacts, heat will be generated that can damage them. Under normal circumstances, there will be very little resistance at the contacts. It doesn't SEEM like there'd be a problem in the described usage, but any arcing damage to the contacts will increase the contact resistance and generate that heat.

The more times you switch power on and off with the contacts, the closer you will get to failure. If you NEVER do it, they'll likely last for years and years.


Again, my "future" predictions are based on theory. Hopefully, people who've DONE it will speak up.



Ed

[JohnJ]

Thanks for the feedback. My main goal is simply not to burn the house down; if I destroy a Tortoise a few years down the road it's not the end of the world. I will experiment and see how this works out, as it will save me some time and effort on this project. This staging yard, while not huge, is a pretty laborious undertaking and is soaking up materials like a sponge. Thanks again!

[cwgreg]

The tortoise internal switches are rated for 1 amp each according to the Circuitron instructions. They should work for you on DC.
Our club uses Fulgurex machines in tandem with the tortoises to switch power into x sections between zones on our DCC layout because there is a brief risk of high amperage (5 amps) from the boosters/circuit breakers in a short situation.

Greg

[JohnJ]

I can't speak for how well this thing is handling power, but overall my plan appears to be a success. Using the Tortoises to route the power seemingly works perfectly.