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).
Technical letter comparing starter motor and generator performance, discussing electrical loads and cold weather starting issues.
| Identifier | ExFiles\Box 23\2\ Scan079 | |
| Date | 11th August 1920 | |
| -2- Contd. Reverting again to the enclosed chart, you will see that at 10 ft. pounds torque, which represents approximately cold weather conditions, the R-R motor will consume 200 amps and will turn the engine at 26 R.P.M., whereas the new Bijur motor will take 220 amps and will turn the engine at 41 R.P.M., which means all the difference between starting and not starting. Replying to your second paragraph, we certainly consider that the starter should start the motor under all conditions - even the worst winter conditions. The R-R motor does not do so because it does not turn the engine fast enough in cold weather. Replying to your third paragraph, 4-EX is being packed ready for shipment equipped with the original Bijur starter motor and generator, which have now run 10,000 miles. The disassembled regulator, which ran 9,000 miles, is packed with the car. With regard to the generator, the difficulty in this country with the 3rd brush machine is the very great difference in the use to which individual cars may be put. One car may be used principally for touring and another car largely for town work. The same car at different times of the year also may be used for town work and for touring. The Bosch people have built us a generator which is an approximation to our ideal Smith curve, although it falls short of the peak. This generator has been on 24-PE but has not been sent with 4-EX because it is noisy and does not supply enough current. I have already written you (Oy6-C28421) suggesting that the specified R-R generator output curve is not high enough. We find that on 24-PE with 2 body lights, 2 dashboard lights, and 2 head lights (30 candlepower) 2 side lights (4 candlepower) and 1 tail light and battery ignition, we are taking between 7 and 9 amps. Under these conditions, the R-R specified output curve will not balance the lamp load. With a constant voltage system no such trouble arises. The amps. may be as low as 4 to a fully charged battery and will rise to 18 or 20 to a rundown battery and will always balance the lamp load at all speeds and will never overcharge the battery sufficient to damage the plates or produce excessive gassing. We have actually found this to be so. Contd. R.R.235A. 100(T) (S.H 159 11-8-20) G.2800 | ||