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).
Continued page of a technical document explaining the effects of circuit resistance and bad magnetic circuits on motor speed during testing.
| Identifier | ExFiles\Box 35\4\ scan 128 | |
| Date | 19th August 1922 guessed | |
| -4- Contd. resistance of the circuit is subtracted from the available E.M.F., it being noted that the current remains very nearly the same for a given torque independently of volts and speed. On the load test a bad magnetic circuit will reduce the speed by increasing the amperes for a given torque, and thus absorbing more volts on ohmic resistance, but on the light test, where the ohmic drop is comparatively small, the reverse is the case; a bad magnetic circuit would increase the speed because, owing to the smaller flux, the armature must revolve faster to generate the same back E.M.F. It is for this reason that on the light test we do not specify that the speed must exceed a certain amount, whereas on the load test we do. If the speed is not up to scratch on the load test, it may be due to the brush contact being bad, or in a lesser degree, to the electrical connections of the motor being bad and absorbing some portion of the voltage. Contd. | ||