4. Solar powered vs mains powered circuits

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As we've mentioned earlier, modern track circuits are often either solar powered or mains powered.

Solar power is used in locations where the average power requirement is low and easy access to AC mains is not available. The power supply is generated through an array of solar cells raised onto an elevated mount, a regulator or charge controller, and a specially designed secondary battery with a storage capacity of 10 days' normal loading.

Mains electricity is what you usually use at home. It sits at around 240 volts, which is a much higher voltage than what is produced by batteries. 'AC' refers to alternating current.

The main failure characteristics of solar and mains-powered DC track circuits are very similar.

Some common scenarios that you might encounter include:

  1. A flat battery on the approach track
  2. An open circuit in one of the track circuits
  3. A short circuit in one of the track circuits
  4. A broken rail in one of the track circuits


Option 1: Flat battery

With a flat battery, the issue mainly appears after sunset as the track circuit will run off solar power during the daytime. This could happen due to a fault in the solar charger, high resistance in the battery charge circuit  or poor battery condition. Conversely, it could be as a result of solar panel theft and the battery fails due to lack of charge. The track relay will be de-energised and the crossing will be operating continually.


Option 2: An open circuit in a track circuit

This could be due to broken track leads, blown fuses in the feed or wiring issues at the relay. The track relay will de-energise and the crossing will be operating continually.


Option 3: A short circuit in the track circuit.

There is an obstruction on the track to create a short circuit resulting in the relay being de-energise and the crossing operating continually.


Option 4: A broken rail.

This is similar to option 2, but the track feed has not failed. Typically during this type of failure, the feed supply will rise higher than normal and the relay will be de-energised. The crossing will be operating continually as well.

Next, watch the video below from your mentor, Daniel, as he talks through how you would approach each of these issues. Take notes on solutions for each scenario, and save them for next week!

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