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).
Battery discharge and charge rates, with a proposed testing cycle procedure.
| Identifier | ExFiles\Box 164\3\ img191 | |
| Date | 26th March 1938 guessed | |
| -2- plates of different thickness, as a battery with fairly thin plates and well designed to give good performance and life under normal working conditions, may not give such a long life under the artificial conditions of an intensive test as a battery with thicker plates, which may not be so well designed in other respects. As far as the discharges are concerned it will be appreciated that as the capacity at the one-hour rate is only one-half that at the 10-hour rate it follows that if all the discharges are taken at the one hour rate the battery is only being superficially worked in this respect, and it is not possible to compensate for this by making the overcharges excessive. For this reason, in our own testing laboratory we prefer to take the dis-charges at a rate which will give the plates plenty of work to do, and we generally use the 10-hour rate. As far as charging is concerned we endeavour to keep it reasonably in line with working conditions, and having regard to present day conditions in car equipments we should regard 10% - 15% overcharge as suitable for the purpose. With regard to the rate of charge, the normal rate is quite suitable, and is approximately 10% higher than the 10-hour discharge rate. If objection is raised that such a test would take a long time to carry out, we can only reply that it would have a much closer relationship to normal working conditions than any accelerated test, and would in fact approximate as closely to service conditions as any bench test could be expected to do. As a reasonable concession to the need for speeding up the tests, we should be prepared to take the tests at the 5-hour rate instead of the 10-hour, as the capacity at the 5-hour rate is about 83% of the 10-hour capacity, and this does not represent a serious reduction of the output on each cycle. In this connection, as the battery is required to give starting performance as well as lighting capacity we should prefer to interrupt the series of 10-hour or 5-hour discharges at intervals throughout the life and to take a number of high rate discharges, at for instance the 5-minute rate, and some of these tests might with advantage be taken in the cold chamber. For the 6-HZD11-S and 6-HZD11-G batteries our proposals would be as follows:- Cycles 1 - 20 Discharge at 10.1 amperes (5 hour rate) to 10.8 final volts. Charge at 7 amperes (normal rate), calculating the ampere-hour input at 10% greater than the previous discharge output. Cycles 21-25 Discharge at 210 amperes (5 minute rate) to 8.0 final volts. Charge at 7 amperes. Cycles 26-45 As cycles 1 - 20. Cycles 46-50 As cycles 21-25. and so on. | ||