CapacitorDischarge switch machine power

Discussion in 'FAQs' started by Hunkiedoo, Jan 10, 2003.

  1. Hunkiedoo

    Hunkiedoo Member

    My #2 sad story :( I built a CD switch machine power supply per Peter Thorne's book "Practical Electronic Projects for Model Railroaders", chapter 5. It worked fine until I fried it one day when I shorted something while wiring up an other switch machine. I bought a 2nd home-made one,(someone said it was actually made by P. Thorne), but I fried it too - same cause!

    Right now you're probably thinking "the best I can do for this fellow is to suggest he take up slot car racing & leave MR to competent people". Please bear with me. This is the first time i've been abletovent&Ihaveallthesequestions&people actuallyanswer!Sorry, lost it there: OK now.

    1. How do I test capacitors, transistors & diodes to see if they are still functioning? All I have is a multi-meter & limited electrical knowledge. Duuuh, there's a surprise!

    2. Are these switch machine power supplies available commercially?

    3. If I get/make another one, is there some way to protect it against electrical mistakes, maybe by adding more diodes?

    4. Is there any alternative? (I don't think I have any alternative; I feed all my sw machines with bell telephone wire. "Regular" current from the power pack doesn't work. I presume it's because of the tiny wire & long runs).

    PS thanx to all for the answers to my earlier post. Much appreciated.
  2. kettlestack

    kettlestack Member

    Hi Hunkiedoo,
    There are three CD circuits in that book chapter, which one did you make?

    The circuit in fig 4 is virtually bullet proof as fas as short circuits are concerned.

    When you said yours "fried", what exactly happened? .. destroyed by heat? .. simply stopped working or what?

  3. Hunkiedoo

    Hunkiedoo Member

    CD power

  4. kettlestack

    kettlestack Member

    It sounds as if you have connected the CD -ve terminal to your track "common" terminal. The CD input supply should be ac or dc separate from any other power sources. I believe you will find that your transistorised CD circuit is still OK.

    What confuses me is that a turnout motor operating pin/lever/whatever should be insulated as part of it's design by the manufacturer.

    For the benefit of those who might not know how to wire turnoutout machines I've included this diagram.


    Attached Files:

  5. Vic

    Vic Active Member

    Yep I'm might "cornfused" here too.....

    First of all like Errol said that circuit is "bullet proof" and diode protected.

    Second, unless Shinahora has changed something that I'm not aware of I don't know of any connection thru the turnout's throwbar. They, to the best of my knowledge, are power routed and the point rails pick up their power from the stock rails depending on which way the points are thrown. There should not be any connection between the switch machine coils and the rails.

    The only thing that I can think of that would have caused this catastrophe is that the the output of CD unit was connected to the output of the power supply or most likely due to a wiring error the was some connection to the rails of the track as evidenced by the loco trying to move when the whole thing failed.

    On the Shinahora turnouts the area between the the point rails where the rivet is located is electrically "hot". The use of a metal throw rod thru the rivet hole will cause an eletrical short to the track but unless there was some connection between the machines coils and that rivet the turnout would have thrown but the track would have been shorted.

    Solution.....mount the switch machine to the outside (longest side of the throwbar) where it is not in contact with the metal piece between the point rails.

    Sorry to have written so much...trying to work thru this as I typed.
  6. 60103

    60103 Pooh Bah

    What sort of switch machines are you using? I know that some of them have the ground connected through to the mechanism; we spent a lot of time on one layout making sure that there was some plastic between the switch machine and the switch.
    Does anything give problems when you turn the machines by hand?
  7. Vic

    Vic Active Member

    Hi David, Thanks for reminding me....I once ran into that exact situation with some N J International switch machines....after 20 + of them had been installed!:eek: Due to a mfg. mistake one of the contact tabs was bent the wrong way. Had to remove the machines to bend the tab back....but even with a short on the coils it did not effect the CD unit. I'm still sorta "stumped" on this one.
  8. Woodie

    Woodie Active Member

    I'm stumped on this one too. How a turnout switch could/should be in contact wil any rail or both rails, for that matter, to make a loco move.
    What power source are you using for the CD unit?

    BTW... I'm not familiar with shinohara turnouts, but I would imagine the hole for the turnout motor pin would be completely insulated from the tracks.

  9. Vic

    Vic Active Member

    Hi Woodie, Here's a pic of a Shinahora turnout...this one's hon3 but no matter...they're all built the same.

    Note the metal piece between the point rails...when in contact with the stock rail(s) this piece is energized. Many modelers mount a twin coil machine under the table and use the hole in the rivet for the swithch machine's throw rod....if that rod is metal it will short the rails thru the metal pieces of the switch machine.

    I mount mine under the table but off to the side so that the metal throw rod comes thru the plastic throw bar and no short results. I then wire thru the aux contacts on the switch machine and the metal piece between the points to the frog to ensure positive contact all the way thru the turnout.

    This one's a real "booger" aint it!!!:D

    Attached Files:

  10. Woodie

    Woodie Active Member


    I use Peco turnouts and switches. I just tested a new/spare I have, and the pin is not electrically connected to the coils/wiring/mountings/lugs in anyway. Completely insulated. (used a multimeter).

    I see what you mean about the Shinohara turnouts, but even if the pin was put through the metal hole of the draw bar, it still should not short anything. (uinsg a Peco motor, anyway).

    I use the 17 V AC output of my controller to power the turnouts. I ain't put a CD unit on it yet (but I should). Just careful, using momentary switches.
  11. Vic

    Vic Active Member

    An oldie

    Built this old CDU maybe 25 years ago:eek: "Rude and Crude":eek: but it works:) Ain't never burned out a machine using it:) 24 Volt transformer from an old copy machine. Don't know how many volts it puts out but if you short the output it will jump a spark almost an inch long:eek: :D

    Woodie...take a look at the switch machine in the pic....since its made on a metal frame that's how the metal throw rod can short the point rails.

    Attached Files:

  12. Woodie

    Woodie Active Member

    Can't say I'm familiar with those switch machines, Vic. They look a reasonable size too. I'm sorta having trouble, from that pic anyway, as to how they work. What is that big loop of thick wire for?? They the same ones as hunkiedoo is using?
  13. Vic

    Vic Active Member

    Hi Woodie, Here's a better pic. We call these "twin coil" machines here in the States. They are very powerful...although rated at 12 VDC you most always have to use a CDU to throw them but they will throw the stiffest turnout. The thing is really a push pull solenoid with a latching spring, bellcrank and aux. contacts.

    The plastic gizmo that its mounted on is call a Rix Rax...It allows you to mount the machine vertically under the table for easy adjustment and without having to make complicated linkage to throw the turnout....the next pic shows one mounted "under the table"

    Attached Files:

  14. Vic

    Vic Active Member

    Here's the machine on a Rix Rax mounted under the layout.

    Attached Files:

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