Saturday, November 14, 2015

"Uh, oh..." he said (Tortoise vs. Micro-Mark switch machines)

You probably realize that I became a quick fan of Micro-Mark's "Switch Tender" switch machine after my friend Pete (who uses them extensively on his layout) loaned me one and I discovered first-hand how incredibly easy they are to install. I hadn't planned on powering any of my turnouts, but as I got more into researching and building Old Saybrook I realized that having turnouts operated remotely by the tower would be as cool as it would be prototypical so I started looking around for machines.

I'd always assumed that I would go with the ever-popular, industry-standard Tortoise machine, but the cost ($18 each) and instruction sheet were both pretty intimidating. So when the Switch Tender went in so quickly and I saw I could get them for under $14 each, I figured I had a winner. I only needed machines to move the points - I wasn't planning on signals or any other fancy stuff, so all those "extra" contacts on the Tortoise machine would just be wasted money and increased complication. Consequently, I now have an even dozen Switch Tenders installed on my layout.

Well, it turns out my analysis may have been woefully short-sighted and based on a false economy.

My rethinking started when I couldn't get the machines to work with my LED indicators. I did eventually get everything to work together, but in the meantime I got a text from my friend Randy about why the Micro-Mark machines might not work as expected:
"Uh oh ..."
The link is to an article comparing the Switch Tender to the Tortoise. Suffice it to say the Switch Tender comes out very poorly. Here are the highlights:

  • The Switch Tender (ST) has a stall current of 65ma (4x greater than the Tortoise) and a throw draw of 26ma (8x greater than the Tortoise), so a 50 ST machine layout would need 3.25 amps of power, compared to less than 1 amp for the Tortoise.
  • "The high current draw of the Switch Tender also eliminates the possiblity of wiring LEDs directly in series with the motor for panel indications..." (emphasis added, since this is what I experienced - and this likely precludes my connecting trackside signals to the motor power supply wires).
  • The ST is supplied with a 150 ohm resistor to protect the motor when it's stalled. Increasing the resistor to 300 ohms results in a motor that won't even move. Apparently, Micro-Mark "selected their resistor to provide the minimum value of protection to a stalled motor, which was not designed to be stalled."
  • The higher current draw makes using DCC stationary decoders impractical.
  • The ST exerts 5.5-6 oz of thrust on the points of the turnout, compared to less than an ounce of torque supplied by the Tortoise. The direct coupling the ST requires between the motor and the points may result in failure of the turnout points over time.
  • The ST provides no switching or other auxiliary contacts for frog powering, signaling, panel indicators, etc.
Now, to be fair, some of these shortcomings are what keeps the price down. If you don't need extra contacts, for example, why pay for them? At least that was the lion's share of my reasoning. I'm pretty confident I have a good workaround that will allow me to use panel light indicators (addressing the 2nd bullet point above), and I have only 12 ST machines - well under the 1-amp-per-16-machines that Micro-Mark recommends (and discloses, to their credit). That takes care of the 1st bullet. And I don't use - nor do I ever plan to use - stationary decoders with the machines. So bullet 4 isn't an issue for me.

But the other issues bother me - especially how stalling is handled and how much stress the machine puts on the turnout points. The stalling issue probably explains the constant, relatively loud hum I hear whenever the machine is on. I don't know what to do about the points. I'm hoping Micro-Engineering turnouts can handle the pressure.

Bottom Line: I'm still apprehensive about how difficult the Tortoise machines may be to install, but - admittedly - I've never actually tried to install one. And the ST install is a little more complicated since you need to add "stop screws" to keep the bracket from twisting over time. So if I had it all to do over again, I'd probably suck it up and use the Tortoises. We're only talking $4 difference per unit. Sure, at dozens of machines, that can make a huge difference.

But at just one dozen? It's just $48 - chump change in the grand scheme of layout costs. And that's not counting (perhaps the inevitable cost in time and money of) eventual/inevitable replacement of turnouts/broken points and burned-out switch machines. And $48 is certainly worth the peace of mind that comes with using the industry standard.

Mea culpa - caveat emptor - YMMV

At least I'll be giving the Micro Mark machines a good beta test over time - and you'll be the lucky beneficiaries of what I discover in actual, day-to-day operation.

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