The ring contacts are arranged in a line in such a manner that a
circular contact-piece, made of thin sheets of copper, can be forced
through them in turn by means of a central screw spindle. The mains for
charge and discharge are attached to the fixed disc contacts on the
central screws, and the regulating cells of the battery are coupled to
their respective contact rings by sockets at the back of the board.
The difficulty with the battery transformer system is the introduction
of 400 to 500 volts into the houses, which would be necessary
without the batteries are always fixed in sub-stations from which
a low-pressure current, say of 100 volts E. M. F., could only be
distributed.
A method has been devised by Mr. Henry Edmunds to obviate this
disadvantage. He also uses the high-tension current to charge the
batteries, but by means of a distributor, which is automatically
worked by the current, each group of cells is charged in turn, when it
is entirely cut off from the supply main to the house, through which
current is perhaps being taken for lighting purposes. The system is now
being adopted by the Cadogan Electricity Supply Company, Chelsea.