!!

Not Registered?

Welcome!  Please register to view all of the new posts and forum boards - some of which are hidden to guests.  After registering and gaining 10 posts you will be able to sell and buy items on our N'porium.

If you have any problems registering, then please check your spam filter before emailing us.  Hotmail users seem to find their emails in the Junk folder.


Thanks for reading,
The NGF Staff.

Author Topic: Wiring a tactile switch to power a point motor  (Read 293 times)

0 Members and 1 Guest are viewing this topic.

Offline bob lawrence

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 111
  • Country: gb
    • Awards
Wiring a tactile switch to power a point motor
« on: December 30, 2018, 11:41:45 PM »
Hi, would like to know how to wire a momentary tactile switch, like the one below, to operate a point motor. I have done it before but for the life of me can’t remember how I did it.



Offline sprogman

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: 17786
  • 2mm Association Number: 4557
  • Posts: 367
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #1 on: December 31, 2018, 10:14:49 AM »
What sort of point motor?

How is the point motor powered?

What is the current rating of the switch?

Offline bob lawrence

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 111
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #2 on: December 31, 2018, 03:16:26 PM »
Thanks for replying sprogman, all relevant questions which I failed to think about, having only used Peco point motors and powering from Hornby Select didn’t even think there may be any others, not a clue regarding current ratings.
However have finally figured it out and for anyone interested this is how it’s wired to power two points switching a loco from one track to another.


Offline ntpntpntp

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 2900
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #3 on: December 31, 2018, 04:03:38 PM »
Any reason why you've gone for those particular switches? I'd be concerned about the current rating, as the examples I've looked up are only rated for about 50mA?

I use micro-miniature push-button switches on my control panel, but my points are run via individual locally mounted CDUs so the switch and the wiring from control panel to the point only has to pass a small trigger pulse not the actual current to the point motor.  The switches I use are only rated at 0.5A (still 10x more than your tactile switches?), usually you need to allow for more than that for direct firing of a typical point motor. 


https://www.rapidonline.com/sci-r13-81-red-micro-push-button-switch-78-0090

Mine's definitely a more expensive approach, but it has worked well since the mid 90s when the layout was built.
« Last Edit: December 31, 2018, 04:11:10 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Nigel Cliffe

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 623
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #4 on: December 31, 2018, 04:53:44 PM »
I'll also add to the concerns - what is the output on the side of the Select ?  Is it AC or DC ? 

If its DC, then the back-emf from the point motor coils will burn out switch contacts in short order, even ones rated at 0.5A or more.   To stop that, a diode has to be added over each coil to kill the back-emf pulse.

I'd be fitting something in-between the switches and the turnout motors.  A CDU system is one option, there are several others.   Those allow the use of lower power rated switches, which will then be reliable in operation. 


- Nigel

Offline bob lawrence

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 111
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #5 on: January 01, 2019, 02:33:31 PM »

Thanks for the replies.
I have used these switches since I saw them used on a n gauge layout at a show some time ago and liked the idea. I have used them on another, dismantled, layout. My current layout has manually operated points because there aren’t that many and are all at the operating position.
I have a small, 5’ x 2’ double oval in the process of being built and intend using these on that hence this post.
The Select is 15v DC output. I have no idea what back emf means could this be explained please so I can consider it in future.
I haven’t fitted one in this test rig but would always fit a CDU, if needed, on any layouts anyway, this is without any knowledge of current, ratings, back-emf’s and so on.
As an aside, having brought up the questions regarding current, ratings, back-emf, and I’m sure there must be plenty of other such terms, how important are they and under what circumstances should I take them into account?


Offline ntpntpntp

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 2900
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #6 on: January 01, 2019, 03:09:14 PM »
I have used these switches since I saw them used on a n gauge layout at a show some time ago and liked the idea. I have used them on another, dismantled, layout. My current layout has manually operated points because there aren’t that many and are all at the operating position.
Bottom line is they're only for low power electronics which use a fraction of the current a typical model railway application will put through them. They're not suitable for what you're doing, and will fail!

Quote
I have no idea what back emf means could this be explained please so I can consider it in future.
"Back Electro-Motive Force".  You can find explanations via google etc, though some will get a bit technical/theoretical!
When you send a current through an eletromagnetic device such as a motor or solenoid point motor it generates a magnetic field which moves the iron core.   When you disconnect the power, the magnetic field collapses and generates a current back through the wiring.   Nigel mentions this in the context of point motors and switches because the rapid field collapse can generate quite a high voltage and current (even though only very briefly) which could cause an arc in the switch contacts and burn them out.

Quote
I... would always fit a CDU, if needed, on any layouts anyway.

Very sensible, it fires a brief high DC current burst through the point motor which gives good "thump", then limits any further current flow to prevent burn-out.   Again, way more current than those tactile switches are designed for I'm afraid.

Quote
I’m sure there must be plenty of other such terms, how important are they and under what circumstances should I take them into account?
I would argue a working knowledge of how electric circuits flow and the meaning of voltage, current, resistance etc. are necessary if you're going to use components other than those sold specifically for your particular model railway application, otherwise you can end up choosing the wrong components for the job, wiring them together incorrectly, and end up with either stuff not working, or creating damage through arcing, overheating etc.  Even at the low voltages we use on our layouts you need to take some care, for example shorting out a CDU capacitor creates a quite impressive spark!
Definitely don't go anywhere near the mains side of the transformer etc. as that could be fatal!
« Last Edit: January 01, 2019, 03:13:51 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline sprogman

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: 17786
  • 2mm Association Number: 4557
  • Posts: 367
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #7 on: January 01, 2019, 03:12:58 PM »
Perhaps time to mention https://www.merg.org.uk/ebook.php free to non-members courtesy of the author and MERG

Offline Nigel Cliffe

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 623
  • Country: gb
    • Awards
Re: Wiring a tactile switch to power a point motor
« Reply #8 on: January 01, 2019, 03:45:39 PM »

Quote
I’m sure there must be plenty of other such terms, how important are they and under what circumstances should I take them into account?
I would argue a working knowledge of how electric circuits flow and the meaning of voltage, current, resistance etc. are necessary if you're going to use components other than those sold specifically for your particular model railway application, otherwise you can end up choosing the wrong components for the job, wiring them together incorrectly, and end up with either stuff not working, or creating damage through arcing, overheating etc. ....

I'd also add that there are some traders who appear at model railway shows, and have model railway oriented websites, who sell switches and the like for operating turnout motors.  Those switches are not up to the job of operating a typical Hornby, Peco or Seep turnout motor and will probably fail due to arcing at the contacts quite quickly.   So that basic working knowledge is, unfortunately, needed to separate guff from suitable products used appropriately.

 

 

Please Support Us!
May Goal: £55.00
Due Date: May 31
Total Receipts: £55.00
Below Goal: £0.00
Site Currency: GBP
100% 
May Donations


Advertise Here
anything