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).
The investigation and testing of a new dynamo battery automatic cut-out switch.
| Identifier | ExFiles\Box 168a\3\ img234 | |
| Date | 7th October 1935 | |
| He/Mt.19/MA.7.10.35. NEW DYNAMO BATTERY AUTOMATIC CUT-OUT SWITCH TO R.R.SCH.845. It has been observed that with our new voltage regulated system the operation of the existing cut-out is very uncertain when the battery is fully charged and only a small charging current flowing from the dynamo to the battery. Upon investigation we found that this was largely due to the magnetic circuit being too saturated and not delivering the magnetic tractive pull necessary to hold the contacts firmly together under all conditions of running. Further with the larger currents now in demand it was found that the single contact caused too much volt drop when carrying a heavy current. A new cutout has therefore been designed to RR.Sch.845 with a much improved magnetic circuit and with two pairs of contacts in parallel to share the current when carrying the charging current. The size of wire on the series winding has also been increased. This switch has now been fully tested in the Laboratory and our test results are as follows :- (1) Investigation of Tractive force. To confirm that the modified magnetic circuit was better, a test was made comparing it with a standard cutout. In each case the spring and contacts were removed, and the armature allowed to rest on the stop. The tractive force, at this point, was then measured; first with the shunt winding, excited at 12.0 volts, alone, and then with the assistance of the series winding, excited with various currents from 5.0 to 20.0 amperes. Excitation. Tractive Force. Std. Expl. Shunt winding only at 12.0 volts 8.0 ozs. 1 lb. 2.75 ozs. with additional series current of 5.0 amperes. 11.25 " 1 lb.13.75 ozs. 10.0 " 13.0 " 2 lb. 4.0 ozs. 15.0 " 13.75 " 2 lb. 9.0 ozs. 20.0 " 14.5 " 2 lb. 12.0 ozs. | ||