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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Design and shipment of an auto charge control switch for a 6-volt system.

Identifier  ExFiles\Box 59\1\  Scan319
Date  30th April 1928
  
To OY. from EFC. 14008

EFC4/T30.4.28.

AUTO CHARGE CONTROL SWITCH.

We have now handed to Mr. Pope for shipment to you an auto charge control switch, arranged to the best of our ability to suit your 6-volt system. This switch contains all out up-to-date developments with the exception that :-

(1) The resistance winding in series with the main winding is of Eureka instead of Manganin. There is not much in this, but Manganin has a slightly lower resistivity without having a much higher temperature coefficient.

(2) This same resistance winding is arranged with two Eureka wires in parallel simply for convenience and to avoid further delay. There also is very little in this.

The two items to-gether mean that the temperature compensation is not quite so perfect as it would otherwise be, but the ratio of Eureka resistance to copper resistance is approximately 3 to 1, so you will see that the change of operating voltage from cold to hot is not very serious.

We attach a diagram of connections of the auto charge control switch which gives the directions of current through the instrument, and the directions of windings of the coils. You will see that the switch is arranged with four terminals, so that there is no electrical connection between the switch exciting windings and terminals on the one hand, and the dynamo field resistance winding, contact points and terminals on the other.

The more exact numerical test details are as follows :-

Contd.
  
  


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