Model Railway Forum

Hello all,

I was interested in the stud and probe mentioned previously. I didn’t want to intrude or high jack the other post but I was interested in the how to wire up this device for the want of a better word. I am assuming the stud is the positive point and the probe negative.

Dirk

Solenoid point motors consist of two electro-magnets that share a loose magnetic core.There are three connections a common negative and two positive connections one for each coil. The electro-magnets are wired in opposite directions so when each is energised they create opposite magnetic fields to each other. Thus the magnetic fields cause the loose core to move each way depending on which coil is energised.

To wire up a stud and probe first you need a CDU, that has been explained in the other points thread. The common negative is wired to the negative connection of the CDU the other two connections on the solenoids are connected to two seperate studs which can be as simple as a couple of small nuts and bolts. The probe is connected to the positive connection on the CDU. Touching the probe to one of the studs completes the circuit for one of the coils pulling/pushing ( I cannot off the top of my head remember which, not that it matters) the core one way, then touching the other stud energises the opposite coil moving the core the other way.

Richard

Use the Quick Search for "Stud and Probe" or Scroll down this page until you reach the Stud & Probe section. https://www.brian-lambert.co.uk/Electri ... _and_Probe

Many many thanks Brian and Tricky you have certainly made it a hell of a lot clearer than I was believing it to be. The diagrams are easy to follow and now make sense. Now to put it all i to practice.

Dirk

When wiring up solenoids a method called common negative is often used in other words all the negatives are connected together with one wire going back to the CDU.

With Stud and Probe this is not really an issue as only one point is being activated at a time, however if you at some point decide to employ a system where several points are activated at the same time (I outlined one method in the other points thread) Then the common return needs to be a substantial wire. The reason for this is that solenoids can momentarily sink as much as 3A with several switching at once that is quite a bit of current passing down a single wire. I am pointing this out as it might be advisable to future proof the wiring.

Richard

Thanks again Tricky for the tip. I have a couple of spare circuits I pre wired just in case I was going to add lighting and maybe other bits and pieces later so I can seperate the various sections if needed. Very interesting project this wiring really enjoying it making the old grey matter work.

Dirk