Monday, 24 August 2020

The Grey Boxes

 Just noticed a couple of entries about the contents of the trackside cabinets and the batteries inside the new grey boxes which NC is installing at the moment.

 The grey boxes have been tumbling off the production line in my garage for some time. They are based on a proven, reliable system which I developed a decade ago for the new signal box at Gotherington.  Here is a brief description of how it works.

 The box contains two Cyclon 2V 25AH batteries which are the heart of the track-circuit system. They are extremely rugged and compact. When  properly looked after they have a minimum, 10 year maintenance-free life. NC's recent tests on some of the oldest batteries we have, show that they are still in excellent condition after years of trouble-free service.

The batteries are kept at a steady 2.25V per cell by a simple electronic regulator which is also in the grey box. The normal feed to the track circuit is therefore 4.5V. The regulator's input normally is 48V, fed down a pair of wires from the signal box. In the event of a supply failure the batteries are capable of maintaining the feed to the track circuits for several days. When the supply is restored the regulator recharges the battery.

 NC's plan is that the grey boxes eventually will replace the variety of  track circuit supplies currenly installed along the length of our railway. 

 The production line is still open!

Kevern 24/08/20



  1. Thankyou Kevern, nicely explained, still don't quite understand how this all works but your system seems to be able to help keep the trains running. A back office to the line nobody realises until things don't work! Great work by you and your team, well done all and thanks.
    Paul & Marion

  2. Very interesting blog gradually getting my head round it. Great job you are doing.

  3. Sorry to correct you Kevern but actually most of the track circuit boxes are fed with 13.8V from a floating signal box PSU. Some of the furthest, where the cable loop resistance is too high, are fed with a 24V PSU. I did experiment with 48V for the very furthest, crowbarred with a 30V Zener diode to protect your charging circuit (34V max input I believe), but when I open circuited the battery the current was too high for the Zener. Now fed from 24V too, just enough current to keep the cells charged. NC.


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