Rotary Switch for Hidden Sidings

[Andrew_ECML]

Has anyone ever used a Rotary switch to operate hidden sidings?

My thinking is that if you get a SP3T Rotary switch, then you can select 0, 1, 2, 3 (where 0 is off).

If you have 3 points and you wire up the output of 1 to Points 1 in the thrown position, output 2 to Points 2 in the thrown position, output 3 to points 3 in the thrown position... Then each of those outputs could also have a "normally closed" relay wired up to the other side of the points such that if the circuit isn't getting juice then the point is switched back to a default position.

Lastly setup a SPST "Normally Off" Momentary Switch to power the whole system (including all the relays). So the user would flick the rotary switch to the siding they want, press the button and change all the points at once.

It's kinda an idea I've had dreamed up for my fiddle yard, but I wondered if it had been tried before? Successfully? What do I need to be aware of?

[Tricky Dicky]

When a number of points need to be thrown at once the most common method used is a Diode Matrix. Brian explains it on his website very well.

https://www.brian-lambert.co.uk/Electrical-Page-3.html

I would echo the advice given regards wire sizes, diode current ability and making sure your switches are up to the total current draw. You could use a rotary switch to select the pattern of point movement and a single switch to trigger them although I would imagine it would be easier to just have a momentary push switch for each pattern. A hefty CDU is essential as some solenoid motors can draw up to 3A each.

Richard

[Brian]

Hi
Two things to remember when using Solenoid point motors;
1) Most commonly obtainable rotary switched have very low current rated switch contacts. Frequently no more than 250 milliamps (1/4 Amp). Solenoid point motors often draw around 3.5 to 4.0Amps while their coil is energised. Plus of course the coil must only be powered for a split second as the coil will burn out if left powered! While a relay(s) operated by the switches position should allow higher currents to flow via the relay contact the relay must only be energised momentarily and its normally closed (de energised) contact cannot be allowed to continually feed the solenoid coil!

2) There are two distinct styles of rotary switch - Break before make or Make before break contacts. That is, in the former turn off the switches contact before moving to the next position (B before M), while the latter allows power to flow momentarily in both switch contact outputs as the switch is turned (M before B).

Route selection has been used by multi pole rotary switches for years, but frequently with a master push button allowing power to only flow when depressed and on multi point routes via a diode matrix.

Where solenoid points are used, the use of a Capacitor Discharge Unit (CDU) wired immediately after the power supply and before any switching is highly recommend, as these store power and release it as a "Beefy" pulse into the solenoid coil(s). Normally, only one CDU is needed for all points.

Rotary switches are frequently used in DC track feeding where Cab Control wiring is used and also they are often used in manual control of multi aspect colour light signals!

Edit Richard posted a couple of minutes ahead of my offering!

[Andrew_ECML]

Thanks for sharing that!! I did some reading up on Diodes and it says they only allow current in one direction. That sounds like it would be very useful and solve a lot of potential problems where you could end up creating short circuits by having complicated points control.

[Brian]

You mean as a diode matrix which has already been explained and an example linked to.
Diodes are indeed one-way valves to the flow of electricity. But there are many types of diode (Including LEDs which are a diode that illuminates when power is allowed to pass the correct way through the LED). They can range from Thermionic valves to semiconductor types. Some diodes can only pass and block reverse milliamps while others can pass and block Amps. Their forward current and their reverse blocking current are the main issues that have to be considered when fitting them. EXAMPLES.... IN4001, 1N4002, 1N4003 etc range are all the same Rectifier diodes but each has a higher reverse blocking voltage than the previous end number. So 001 is 50volts 002 is 100volts while 003 is 200v up to 1N007 which is 1000 volts. However, each diode in the 1Nxxx range can only pass safely 1.0Amp forward. Data chart for the 1N400x range https://www.farnell.com/datasheets/639187.pdf Where more current is needed to flow such as in a diode matrix for multi solenoid point operation then the 1N5400 (50volt) to 1N5408 (1000 volt) range of rectifier diodes is frequently used. Here the reverse blocking current rating is the same as the 1N400x but the forward current is now 3.0Amp Data chart for the 1N54xx range https://www.farnell.com/datasheets/314353.pdf
So all diodes are not equal.