Operating Principles

Initially all sections are live and the relay coils are not energised. This is to permit “normal” operation of non magnet fitted trains by simply switching the system off.

Electrical section track breaks are all in one rail only (the same one!)

Ideally all electrical sections are a minimum length of 12” (300mm) plus the length of the longest train.

As a train enters a section it protects itself to the rear by isolating the section it has just traversed. Shortly afterwards it also re-energises the section behind that one ready for the next train.

Example.

A train enters section X, once the rear of the train is about one loco length beyond the isolating gap between sections W and X its magnet passes over reed switch iW (code for isolate W) which cuts the power to section W. The distance between iW and the isolating gap between sections W and X is to prevent any effect of the gap being momentarily closed by any metal wheels in the train. If a train in the rear had already caught up and coupled onto the rear, the extra loco length over the train length would prevent the second loco stalling and putting an unacceptable load on the first train.

A short distance after passing over iW it passes over reed switch eV (energise V) which re-energises section V that had been isolated earlier when the train passed over iV in section W.

The position of iV varies from the others if V is the first isolated section. A train may be held at the start of W by a preceding train. In this case iV needs to be operated by the train stopped in W to protect it in the rear, so iV is situated close to the start of W.

Typical Relay wiring diagram.

All contacts are shown in the non- energised state.

When a magnet closes reed iX the relay coil is powered and the relay contacts change over. The power to the track is cut, and the relay coil continues to be powered after reed iX opens again via reed eX and the now closed right hand relay contacts. When a magnet momentarily opens reed eX the relay coil looses power and the contacts revert to the original state, restoring power to the track until the sequence repeats.

The current price from my favoured supplier for a relay and two reeds suitable for the above circuit is £2.60 inc. vat. P&P is free on orders over £25.00 ex vat and £3.45 + vat on orders less than £25.00

If a relay with additional contacts were used they could control a simple red/green signal. I suppose further contacts could be used for amber and double amber aspects, but I’d need to think hard about that one.

Neil Robinson 2006.