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 testing of two battery capacity ampere-hour meters from C.G. Vokes & Co.
| Identifier | ExFiles\Box 54\2\ Scan237 | |
| Date | 12th July 1928 | |
| To B.Y. from EFC. {E. Fowler Clarke - Electrical Engineer} c. Roy. {Sir Henry Royce} X4457 EFCL/T12.7.28. BATTERY CAPACITY AMPERE-HOUR METERS FROM C.G. Vokes & Co. We have had two of these instruments for test, one with a nickle finish and one with a black finish, but otherwise purporting to be identical. We find, however, that they do not compare very well as the voltages for corresponding readings on the black instrument are systematically 5% higher than those on the nickel instrument. The black instrument is the more nearly right of the two, and the voltage readings for various points on the scale are as follows :- Reading. Voltage. Zero 10.4 Red to yellow 12.0 10 12.1 30 12.4 60 12.9 Yellow to blue 13.0 77 13.2 Half way blue 14.2 Full scale. 15.5 for P.R. Phantom When this instrument, connected to a battery charging at normal rate, is reading full scale, the battery is only approximately 85% charged, and in our estimation would never get fully charged if the charge were switched off when the instrument reached this point. In time it would gradually lose ground. Having completely charged the battery and allowed it to stand overnight, the battery being known to be in a condition in which it would give 77 ampere-hours on the 10 hour rate, the reading of the instrument was only 60. During the first portion of charging at normal rate, the needle is reading on the figural scale but naturally reads somewhat higher than the capacity already put in the battery. It looks as though a compromise is intended on this scale between the charging and discharging circumstances, though it is stated in their notes that it is intended to be reading correctly when the battery is discharging the 10hr. rate.† Indications of the instrument during charging would be more wrong when the instrument is connected to the distribution board on the car owing to the volt drop in the leads. Thus, as arranged, it would scarcely be considered suitable for such indications. † as stated, however, it reads low on discharge. Contd. | ||