Solenoids

 Today's West of Scotland talk was on Solenoids. Soenoids are still extensively on some model railway layouts.

H&M, Peco and SEEP are common manufactures. Some early controllers have a 15v ac supply which can be used to operate the solenoid. Push buttons or passing contact switches are normally used to operate solenoids due to the large  operating currents involved.

These passing switches are expensive at around £9 to £16 for every single point.

With the voltage drop across the solenoid a higher voltage is sometimes used supplied by a Capacitor Discharge Unit (CDU)

The circuit of  a typical Gaugemaster CDU was discussed costing around £15.  Davy then showed us an equivalent Veroboard version for around 71p that would work with a centre off SPDT switch. 

The MERG dual CDU version using a simple on/off switch uses a circuit that operates the solenoid and charges the opposite direction capacitor at the same time. If this unit is placed near the point only a single wire is required to operate  the control relay. This kit is available from the Kitlocker in two versions, PD3-1000 at £7.73 or PD3-2200 at £8.15.

A single circuit version was demonstrated that can be built for around £1.34 on veroboard.

Another version currently under development was shown which used high power MOSFETs  to replace the transistor relay combination. Hopefully this will be the subject of a later talk in the New Year.

The circuit diagrams for these units are available from Davy Dick.

Over the next couple of weeks the video for this talk will be available on the West of Scotland web site

Keith Shovelin then demonstrated a programmable flasher that uses existing PMP kit 21 Dual Flasher and PMP 20 Versatile timer. 

The versatile timer utilises a 5V supply for the controlling PIC. The NE555 of the Dual flasher uses a 12V supply and the two are not compatible. A non inverting  Optocoupler ( see Chapter 18 of Davy's book available on the MERG website) is used to interface the two circuits.

The circuit for this again will be made available on the WOSAG site. An alternative would be to redesign the Dual flasher to work on a shared 5 volt supply.

As usual, a well attended and interesting talk.