Following on a thread from Andy Lock
https://www.009society.com/forum/index.php?topic=4581.0 (https://www.009society.com/forum/index.php?topic=4581.0)
I was asked to show how I provide back-up power to the live frogs on my layout.
The method will probably appear like overkill to some - but it works - and I shall show an updated method that I am going to use on my forthcoming "test track"
(https://i.imgur.com/hDSNZdb.png)
This is how it is done.
Instead of a single momentary action changeover switch providing the CDU pulses to the point motor, I use a double-pole switch. The second pole is used to change over a rely that is wired as a latching relay.
the 1.5k ohm resistor provide enough current to hold the relay "on" but not enough to make it turn "on" by itself - that is done by the switch providing a 12V pulse. similarly, the relay unlatches when the switch takes to coil to ground.
One set of contacts in the relay are connected to the point frog and stock rails; the other set is used in the control box to light the mimic panel.
OK - the new method:
(https://i.imgur.com/HaChw59.png)
This makes use of the "two diodes and a capacitor" method of switching a point motor. It uses a "normal" changeover switch (i.e. it is not centre-biased) When the switch is at 12V the capacitor charges up through the upper diode and solenoid (in the diagram) operating the point motor. No continuous current flows after that.
When the switch is at ground, the capacitor discharges through the lower diode and solenoid, operating the motor in the other direction.
By using a double pole switch, the second set of contacts are taken to the frog and stock rails.
Simples (to quote an annoying toy meerkat!)
fuller details on my web site at
http://www.hnorwood.co.uk/files/points2.htm (http://www.hnorwood.co.uk/files/points2.htm)
What happens if a point switch is inadvertently switched when the power to the layout has been off for some time, long enough for the capacitors to loose charge? Do you get a short in the track when the power is turned on again?
Also, when the power has been off to the layout for a long time, long enough for the capacitors to discharge, do all the capacitors charge up again at the same time, pulling a lot of power from the 12v supply when you power it up? (I guess an aditional capacitor on the +12v supply would sort this out?)
I suppose the big disadvantage over using a microswitch local to the point is having run at least one wire from the frog back to the panel? Ok on a small layout but not so good on a large layout where points are is some way from the panel.
I'm still trying to work out why you'd bother. I use a point motor microswitch and haven't experienced any issues so that belt and braces method seems a bit OTT.
Quote from: Hobby on February 26, 2021, 16:01
I'm still trying to work out why you'd bother. I use a point motor microswitch and haven't experienced any issues so that belt and braces method seems a bit OTT.
I suppose if your points motor doesn't have easy mounting for a microswitch it would be a pretty good way to go. Mind you that means the frog wire then had to go back to the control panel and with your solution they only have to go to the point motor which is normally pretty close.
Quote from: B.Meldon on February 26, 2021, 15:20
What happens if a point switch is inadvertently switched when the power to the layout has been off for some time, long enough for the capacitors to loose charge? Do you get a short in the track when the power is turned on again?
Also, when the power has been off to the layout for a long time, long enough for the capacitors to discharge, do all the capacitors charge up again at the same time, pulling a lot of power from the 12v supply when you power it up? (I guess an additional capacitor on the +12v supply would sort this out?)
I suppose the big disadvantage over using a microswitch local to the point is having run at least one wire from the frog back to the panel? Ok on a small layout but not so good on a large layout where points are is some way from the panel.
Yes - some valid points (no pun) there.
On switch on, the points should go to the positions set by the switches.
There could be surge at switch on if several switch over - I have decided to put tell-tales on the control panel that show the state of each point, and make sure all the switches are set to ground at the end of a running session (or at least before any running session)
A low value resistor in the dc supply should limit any over current - and of course you don' t know what is supplying the "12V" anyway! :)
Quote from: Hobby on February 26, 2021, 16:01
I'm still trying to work out why you'd bother. I use a point motor microswitch and haven't experienced any issues so that belt and braces method seems a bit OTT.
Your point is? (no pun)
I do not use accessory switches on my layout. I have had no problems with running Angst-Lesspork. And yes, all the wires go back to the control box - in fact each half of the layout can be operated "stand alone" if I wish to run only one side at a time (being careful not to drive anything off the edge!
I was asked to show how I did it - and I have.... You don't have to like it... :)
And being the one that asked - I'm grateful to Hugh for taking the time to present his thoughts and methods.
Having had to mess (and no longer will) with the set up of the Seep motors, got fed up of the Peco method, and fiddled with many a micro switch I have searched for better methods I have moved toward a system that eliminates physical set up with mechanical switching.
so, Hugh, Thank you.
Quote from: hughn on February 26, 2021, 20:10
I was asked to show how I did it - and I have.... You don't have to like it... :)
And the thread has developed into a discussion on the subject, that's what happens. Hugh, please don't take offence, my question was genuine, why would you bother? It seems like an awful lot of extra wiring for no logical reason when frog polarity switching can be done at the point motor itself using a microswitch.
You say you don't have any issues, fine, but neither do I using the micro switches, but that doesn't actually prove anything other than our experiences differ. It seems you have a convert in Andy but you still haven't told us actually why you chose to do such complicated wiring instead of just using the simple solution, which was the question I asked!
Quote from: Hobby on February 27, 2021, 08:54
You say you don't have any issues, fine, but neither do I using the micro switches, but that doesn't actually prove anything other than our experiences differ. It seems you have a convert in Andy but you still haven't told us actually why you chose to do such complicated wiring instead of just using the simple solution, which was the question I asked!
How do you mount your microswitches Blair? I have seen several good methods, but always willing to learn more.
I use servos in 3D printed brackets for points, they have mounting points for microswitches which works well but you have to adjust the servo horn carefully or you can get a short. (Which in my case stops the servos too)
(https://live.staticflickr.com/65535/50985145481_4d95b4afd2_z.jpg)
If I have to use a point motor I have always used the Peco or H+M ones. I use the Peco accessory switch which the sell for the PL10 motor, the other has a built in one from what I remember. Nothing fancy, just the commercial ones.