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 function and testing of Battery Capacity Ampere Hour Meters and Accumulator Capacity Indicators.
| Identifier | ExFiles\Box 54\2\ Scan231 | |
| Date | 24th May 1928 guessed | |
| X4457. Battery Capacity Ampere Hour Meters and Accumulator Capacity Indicators. Prov. Patent No. 8972 & No. 33061. These Instruments are specially designed on the Volt-meter principle, which enables us to obtain approximately a one inch scale length, between the maximum or fully charged voltage and the safe minimum voltage of a Battery respectively. This is considerably greater than the length of the corresponding part of the scale of an ordinary Voltmeter. The comparatively great area permits of the scale being calibrated so that accurate readings can be taken when a load equivalent to a 10 or 20 hour continuous discharge is put across a Battery. The main characteristic of a Battery is voltage, and as the voltage drops so does the amperage proportionately. Voltage taken on open circuit is unreliable and very misleading, whilst voltage on a closed circuit of a 10 hour rate discharge, indicated over a scale area, between the maximum or fully charged voltage, and the safe minimum voltage of a Battery, is the only reliable way of obtaining an indication of the state of charge. These Instruments will also enable one to obtain the constant voltage control system, which is now fitted to a large number of cars. To prevent the Battery being overcharged, if the Battery is disconnected from the charge circuit or the dynamo switched off when the pointer reaches the Red Line at the extreme end of scale, which is the maximum voltage of the Battery on charge. When a Battery is being charged above the normal rate the pointer would reach this Red Line before it is actually fully charged. The accuracy of the charged condition of Battery will not be effected if the pointer is allowed to pass beyond this position. These Instruments are calibrated to the Battery Makers’ instructions, and the correct charge rate and specific gravity of acid stated on the Battery should be adhered to. For standard equipment we can supply both these Instruments compensated for variation of charge. They can be corrected up to 50% above normal. Blue print showing how this particular type should be connected in the charge circuit will be supplied upon request, as both the Battery Voltage as well as the charge current passes through these Instruments. When testing these Instruments for accuracy, it is necessary that a new Battery, which has been filled with acid of the correct specific gravity, and charged to the Battery Makers' instructions, be used, owing to so many variables to consider, such as the condition of the acid and of the plates. Allow a period of three or more hours after charging has ceased, for the Battery to settle, and the voltage to become constant, then connect the Instrument together with an accurate 10 hour rate load shunt across the Battery, observe the Ampere Hours indicated, and compare with the length of time required to discharge the Battery to the Red Indication mark on low portion of scale, which is the safe minimum discharge voltage indication. When these Instruments are fitted to Motor Cars, the load of the lamps is approximately equivalent to a 10 hour discharge rate, and the indication obtained by switching on the lamps is sufficiently accurate for the owner driver to know how long the Battery will continue to supply the demand made upon it without re-charging. Special 2-volt testers can be supplied with various load shunts, suitable for testing any Capacity Battery. If a Battery has been overcharged and is in a very poor condition, or the plates are not covered by the correct specific gravity of acid stated by the makers, the pointer would not remain stationary after a load equivalent to a 10 hour discharge is connected across it. The pointer would gradually decline to the discharge position, indicating that the Battery requires attention. The Hydrometer is necessary for testing the specific gravity of acid, but will only give a reliable indication of charge when the acid in all the cells is new and | ||