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Author Topic: Under the table switch machines.  (Read 4144 times)
WoundedBear
A Derailed Drag Racer


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« on: August 17, 2009, 12:12:25 PM »

Does anyone have any experience using stall motor switch machines? I am looking specifically at the "Switch Tenders" from Micro-Mark.

http://www.micromark.com/SWITCH-TENDER-SWITCH-MACHINE,8394.html

If I read this correctly, an old trainset power pack should be able to handle 10 of these without a problem....correct?

I'm sick of the "snap" type machines, and I like the idea of these stall motors holding tension on the points.

Any opinions?

Sid
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pdlethbridge
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« Reply #1 on: August 17, 2009, 12:54:48 PM »

My brother and I installed switch master switch machines on his layout over 20 years ago and they are still going strong. We have not had to replace any of them yet.
http://www.builders-in-scale.com/bis/sm-home.html
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jward


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« Reply #2 on: August 17, 2009, 05:56:06 PM »

tortoise is the one everybody i know swears by.
i had several on a previous layout, and had no problems with them after i replaced the throw rod with a thicker piece of piano wire.

contrary to popular belief, the tortoise machines have enough torque to them to hold the points over without power. if you are using a small power pack to power them, you may want to consider this fact and use the old pushbottons that you used for your twin coil motors. you'll need to add a pair of diodes in between your pushbuttons and the tortiose, as they throw one way ofr the other depending upon the polarity of the current passing through them. this is easy, and any diode rated at 1 amp or better should work.

to wire the motors in this manner, take your two diodes, solder the naode of one to the cathode of the other. run a wire from this solder joint to the tortoise, and connect each of the two loose ends to a pushbutton terminal. run another wire from your tortoise to the common return to your power supply, as per the tortoise's instruction sheet.

to operate, simply hold the pushbutton down until the motor stalls, then release. if you have the throwrod adjusted correctly ( at full throw, the points should just snug up against the stock rail, too much pressure and the points will bounce back when the button is released) the points will hold their position until thrown back. the advantage of this method is that your power consumption, and therefore the size of your power supply, is much less. this method will not work with capacitor discharge units, it will only work with straight ac power.
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Jeffery S Ward Sr
Pittsburgh, PA
Jim Banner

Enjoying electric model railroading since 1950.


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« Reply #3 on: August 17, 2009, 11:03:14 PM »

Ten of these motors just might put an old power pack into overload, depending on its rating.    Some (many?) old packs were rated at 16 volts, 8 VA.  That means 16 volts at 1/2 amp output.

The motors are rated at 60 mA stalled at 12 volts dc.  Applying 16 volts dc will increase that stall current by 1/3 to about 80 mA.  Ten motors all stalled (their normal state) would draw 800 mA which is a 60% overload.  A 1/2 amp power pack would not be happy.

The solution is to use the ac output of the power pack.  Use two diodes to rectify the output into two dc, 1/2 wave power supplies, one positive, the other negative.  The two supplies will produce about 8 volts each (measured with a conventional dc voltmeter) but their peak voltage will be the same as before.  This means the motor will turn with about the same strength as before but will draw only about  40 mA at stall.  Ten of these motors will then be within the capabilities of the power pack.

If you need a diagram of this, including how to hook it up using single pole double throw (SPDT) switches, let me know.  If you need extra contacts for switching the frog, such as with Atlas Custom Line turnouts, or for signals, just substitute a DPDT switch.

Jim
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WoundedBear
A Derailed Drag Racer


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« Reply #4 on: August 18, 2009, 10:53:00 AM »

Thanks for the replies guys.

Jim....I'm going to have to dig out my power supplies and check their specs.

As for diagrams....you bet I'd like to see them....the more knowledge the better. Since I haven't started on any of the wiring, I was thinking of using 3PDT switches and the Micro-Mark machines.

I doubt there will ever be signals on my railroad, but I'm pretty sure I'm going to need to power some frogs. Is there anything that needs to be modified on an Atlas turnout to power the frog, or do you just buff the frog clean and solder the wires to their proper holes?

Sid
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pdlethbridge
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« Reply #5 on: August 18, 2009, 01:12:38 PM »

tortoise have the contacts to power the frog built in. switchmaster recommends a snap action switch be added on.
Get them here cheap
http://www.allelectronics.com/make-a-store/item/SMS-196/SPDT-SNAP-ACTION-SWITCH-W/LEVER/-/1.html
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jward


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« Reply #6 on: August 18, 2009, 01:18:53 PM »

atlas has a solid brass power bus bar included with their snap relay. it works very well, much better than trying to solder to the frog. i believe the atlas frogs are cast in pot metal or something very similar, and they don't take solder easily. one of the switch ties isn't as thick as the others, and this is where the bus bar hides, the frog has little "eyes" on the side where the screws go.

it would be a very simple matter to make your own bus bar out of brass strip, and drill and tap it for the screw.
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Jeffery S Ward Sr
Pittsburgh, PA
SteamGene

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« Reply #7 on: August 20, 2009, 01:48:50 PM »

Whatever you do, don't get the Atlas under table switch machines.  Even the Atlas tech doesn't like them!
Gene
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Chief Brass Hat
Virginia Tidewater and Piedmont Railroad
"Only coal fired steam locomotives"
WoundedBear
A Derailed Drag Racer


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« Reply #8 on: August 20, 2009, 02:17:14 PM »

 Grin No worries, Gene.

I tried a couple of the Atlas ones on my old layout....never again.

I ordered 10 of the Switch Tenders from Micro-Mark this morning. I spoke to Jim Banner yesterday on the phone, and he has offered to send me some basic wiring diagrams to get me started. (Thanks Jim!)

I'll admit that wiring is my weak link, so to speak......but with some help and probably three thousand more questions, I think I'll get it....lol.

Sid
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WoundedBear
A Derailed Drag Racer


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« Reply #9 on: August 20, 2009, 02:21:45 PM »

Almost forgot.....

To JWard....

Thanks Jeffery.....I had a look at what Atlas supplies in their kit and it is indeed a small brass strip and a couple self tapping screws.....I have screws in stock and can cut the strips out of brass shim stock that I use in the garage.

Sid
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Jim Banner

Enjoying electric model railroading since 1950.


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« Reply #10 on: August 22, 2009, 10:15:40 PM »

The diagram I sent to Sid was really quite simple, but I thought others might find it useful too.  It should work as well with the Switch Tender Switch Machine as it does with the Tortoise (which it is labelled for.)  The Switch Tender comes with a 150 ohm resistor which is normally wired in series with the motor and I would use it with this circuit as well.  However, if the points needed a bit more push, then I would not hesitate to reduce its size or even eliminate it.  This circuit applies only half the power to the motor at stall as the circuit suggested by Micro-Mark, but still applies full torque.

The advantage of this circuit over the Micro-Mark circuit is the use of double pole double throw switches to achieve the same results that otherwise require triple pole double throw switches.  DPDT switches are as cheap as $.50 each including shipping on eBay while 3PDT switches are 8 to 10 times as much.  The other advantage is lower power consumption, allowing you to use more Switch Tenders for a given transformer or power pack.  Note that this circuit uses the ac terminals of a power pack or an ac wall wart.  It will not work on dc.

The bicolour LEDs and their resistors are optional but add a nice touch to a control panel or they may be installed in signals masts so that you can tell at a glance which way a turnout is set.

Jim

     
« Last Edit: August 22, 2009, 10:39:47 PM by Jim Banner » Logged

Growing older is mandatory but growing up is optional.
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