How many Tortoises off a 12.8V, 1.2A AC power source?

[Cajonpassfan]

I am using an AC transformer with "steering diodes" to power a handful of Tortoise-operated turnouts. I'm also using the same power source to light red and green LED's to show position of these turnouts (normal or reverse) on the panel. Now I'd like to add more Tortoises to the circuit. How many Tortoises can I reasonably expect to drive off this 12.8V , 1.2 A AC power source? Is 15 too many?
Otto K.

[jdcolombo]

Hi Otto.

A Tortoise pulls about 15ma at stall (they actually pull less in operation - about 4ma).  Red and green LEDs vary a bit and the current draw will depend on what value you use as a dropping resistor, but 20ma is a fairly common "typical" draw for an LED.  Put these two together, and you have 35ma per Tortoise, including the indicator LED.  That means you should be able to power 30 of them from a 1.2 amp source (30 x 35 = 1050, or a bit over 1 amp).  I'd say you will be fine with 15.

John C.

[jagged ben]

If you use pushbuttons instead of toggle switches to throw the turnouts, then you can do a whole lot more because you really only need enough power for the LEDs, plus the max number of turnouts you'd throw with one pushbutton.  It is not a problem for the tortoise to only get power when being switched, we have a couple hundred on the club layout done this way.  The one disadvantage is you have to hold down the pushbutton until the turnouts finish throwing, which can be 3-5 seconds.

[Cajonpassfan]

Thank you guys.
John, that's kind of what I figured, just wasn't sure whether the steering diodes come to play thus reducing available power. I'll just wire it that way and if there's an issue, I can always split it off and add another power source. Just trying to keep it simple....
Jagged, I prefer to use the stall feature of the Tortoise with my mostly Atlas turnouts; that way there is always positive pressure against the points and less opportunity for mischief like wheels picking the points....
Otto K.

[jagged ben]

Jagged, I prefer to use the stall feature of the Tortoise with my mostly Atlas turnouts; that way there is always positive pressure against the points and less opportunity for mischief like wheels picking the points....
Otto K.

If you've never tried it the other way then you may be surprised that it pretty much makes zero difference.  The stall motor stays in place when not powered. 

Then again, there's no need to try if you have plenty of power available for the stall method.

[Cajonpassfan]

If you've never tried it the other way then you may be surprised that it pretty much makes zero difference.  The stall motor stays in place when not powered. 

Then again, there's no need to try if you have plenty of power available for the stall method.

Lol, that's true. But I do "try it" every time I shut the power off, and guess what, you're right, the Tortoises stay put.  Plenty of  positive pressure on the points; who knew
Well, I'm sticking to toggles for the handful of additional locally controlled turnouts anyway; (the bulk of my switches are DCC accessory/macro controlled). But, good to know...Thank you!
Otto

[mighalpern]

Hi Otto:
I am using a 12 volt DC.  walwart with 2 amp capacity
I am driving close to 40 tortoise with this only  I also have the LEDs in line with the tortoise which is my dropping resistor
just an FYI
Miguel

[peteski]

Otto,
could you give a bit more detail as to the actual circuit?  A diagram would be really helpful in understanding it. Even if you sketch it by hand , take a photo of it and post it here.

For example, by steering diodes do you mean that the diodes are used as a rectifier to produce pulsating dual-polarity  DC voltage needed for the switch machines (as the motors will not work from straight DC). Or are using the diodes as a matrix to throw multiple turnouts at once?

Then the LEDs:  are they on a separate circuit controlled by the machine's auxiliary contacts or are the LEDs wired in series with the motor?

[jagged ben]

Otto,
could you give a bit more detail as to the actual circuit?  A diagram would be really helpful in understanding it. Even if you sketch it by hand , take a photo of it and post it here.

For example, by steering diodes do you mean that the diodes are used as a rectifier to produce pulsating dual-polarity  DC voltage needed for the switch machines (as the motors will not work from straight DC). Or are using the diodes as a matrix to throw multiple turnouts at once?

Then the LEDs:  are they on a separate circuit controlled by the machine's auxiliary contacts or are the LEDs wired in series with the motor?

I don't think it makes much difference to the original question.

Since he mentioned an AC power source I'm assuming he is using toggle switches and two diodes per turnout to produce half-wave DC.  This method is simple and easy, but doesn't allow for one pushbutton (or a rotaryswitch) to throw routes.   You can do that with a diode matrix but you need DC power, and it's quite a bit more work to put together, albeit a more elegant result in my opinion.

[peteski]

I don't think it makes much difference to the original question.

The original answer was counting the LED current draw separate from the motors.  If LEDs and motors are in-series, then the LEDs do not consume any extra current. Plus, I'm simply curious.

For example, if the transformer was a center-tap type then using the center tap and a bridge rectifier you could have dual-polarity pulsating DC power supply.  Again, I'm curious as to what the circuit looks like.

[Cajonpassfan]

Oh, Jagged is right, but I do like curious minds Peteski. Here's the diagrams. The things I like with the toggles is I don't have to wait several seconds to make sure the (perhaps hard to see) turnout is thrown all the way, and also the fact the LED's don't fully light up until the Tortoise movement is maxed out.
Otto K.

[Cajonpassfan]

Hi Otto:
I am using a 12 volt DC.  walwart with 2 amp capacity
I am driving close to 40 tortoise with this only  I also have the LEDs in line with the tortoise which is my dropping resistor
just an FYI
Miguel

Thanks Miguel, good to know. Theory is great, but it's always good to get confirmation in practice!
Best, Otto

[peteski]

Thanks Otto!  So you are using the circuit described by jagged ben.  The diodes act as positive and negative half-wave rectifiers.  The LEDs are in-series with the motor, so the same current goes through the LED and the motor (the LEDs do not consume any extra current). If you use a single pair of LEDs then the voltage across the motor is reduced by about 2 volts (or if you use 2 pairs as shown in the diagram, the motor sees 4 volts less).  That results in even less current being consumed by each circuit.

Looking at the Circuitron's web page about Tortoises, confirms what has been stated here earlier: Lowest Current Drain Switch  Machine Available (4 ma. during operation, 15—16 ma. at stall).   (At 12V).  That is 0.016 A per machine.  If you have LEDs in series with the motor then the current for each circuit will be even slightly less.   But the important thing to remember that the machines consume most current at rest (which seems very non-intuitive).

On the same page I quoted above Circutron also sells a "wall-wart" type of power supply: 110 volt AC wall plug adapter outputs filtered 12 volts DC at up to 500 milliamps of current.  Sufficient to power up to 30 TORTOISE™ Switch Machines.  500 milliapms is 0.5 A

To check if things add up, divide the power supply current by the highest (stall) current consumed by each machine. That is 0.5 / 0.016 = 31.25. So 30 machines is realistic.

In your specific situation, to determine number of machines which could theoretically be powered up by a 1.2A supply divide 1.2 by 0.016. That is 75.

But I would not recommend using a wall-wart power suppliy at its 100% capacity. They aren't designed for that.  We found that out on friend's layout. We used a 12VDC 1A large wall-wart to power the Tortoises.   We had enough machines hooked up to use about 900 mA (0.9A) or 90% of the supplies capability.  I had to service something under the layout after a 2 hour operating session. I touched the wall-wart and it was quite hot to the touch.  Way hotter than I would expect it to be.

Our solution was to get another of those supplies and split the switch machines with half of them going to each supply. That made them run much cooler (where they barely got warm after few hours of operating).  We did that for safety reasons. Since those supplies do not have any thermal protection circuit, we were afraid that if the layout was accidentally left powered on for a day or 2, the supplies could overhead and cause a fire. In your case I would say that attaching up to 60 machines should be safe.

I also don't know how good is your hearing and how quiet it gets in your layout room, but on my friend's layour we noticed that when the room was quiet there was a distinct hum coming from all the machines. With just a few is it not really noticeable, but with dozens of them the hum becomes quite noticeable.

The power supplies we used were filtered DC (that means they had a filter capacitor installed inside). Bud again because they were inexpensive supplies, the capacitor was quite small for the job and at load it was not capable to properly smooth out the pulsating DC voltage coming from the rectifier. My solution was to add a much larger capacity capacitor to each circuit. That totally eliminated the hum.

You are using unfiltered pulsating DC. I would expect the hum to be much louder than what we heard on my friend's layout.  Maybe you don't hear it, or maybe it just doesn't bother you.  But either way, it is harmless to the machines and LEDs.

Oh, and I agree with you that the way you have the LEDs hooked up is really good. Not only that simplifies the wiring, it gives a clear visual indication of the machine being fully thrown (the LED stays dim while the machine is in the process of throwing).

[Cajonpassfan]

Thanks for the thorough writeup Peteski.
Maybe its my hearing, but I never noticed any buzzing from the four Torroises I have wired this way so far. Of course that maybe because their transformer is located just under them and generates a little buzz.

For clarification, I have over 100 Tortoises on the layout, but only need 15 turnouts wired this way; the rest are DCC powered and controlled via NCE Switchits and Switch8's which allow me to "Macro" up to ten turnouts per command...a very slick arrangement for assigning routes in and out of staging and complex trackwork in large yards. Select Macro#, or TRK #, hit Enter, done! I don't even bother with schematic panels anymore, just place small track identification plaques in strategic locations (see pics). The DCC powered Tortoises are silent.

However, as much as I like DCC turnout control, I find there are certain circumstances where the engineer is physically right there and it's simpler to just flip a switch (as in lining a crossover to allow a helper engine to escape). Hence this arrangement at Summit.
Thanks again, Otto

[jdcolombo]

I've got about 80 Tortoises; for all but a couple of them, I use the stall-motor switch machine boards that used to be sold by Rob Paisley in Canada: http://home.cogeco.ca/~rpaisley4/556Stall08.html

These boards provide a lot of different control options, but lately I've been thinking about going to DCC control for my main yards and staging.  My yard is about 20' long; it is separated into an EB classification yard and an WB classification yard, per the NKP prototype in Bellevue, OH.  But because of the length, it means that my yard operators have to rely on each other to align switches at the other end of their respective yards (or else constantly run into each other doing it themselves), and the DCC option would seem to make this all much simpler, as well as providing for simple route control for each of the six yard tracks.

Otto, what do you use for DCC control of your Tortoise machines?

John C.