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 use and interpretation of a Cadmium Electrode for checking accumulator cell condition.
| Identifier | WestWitteringFiles\N\July1925-September1925\ Scan263 | |
| Date | 15th September 1925 guessed | |
| -3- Contd. Cadmium Electrode. The Cadmium Electrode is a useful laboratory device for showing up the electrical condition of the positive and negative elements. It is hardly suitable for the use of the average accumulator user because for one thing it necessitates the possession of a very sensitive voltmeter. Voltmeter readings are taken between the cadmium electrode, which is dipped into the electrolyte of the cell, and the two elements in turn. The contact resistance of the cadmium and the electrolyte would be very considerable so that a voltmeter taking only a few milliamperes is essential. On a secondary cell discharged down to 1.80 volts and discharging, but otherwise in good condition, the positive plates should be 2.05 volts positive to the cadmium electrode, and the negative plates should be .25 volts positive to this electrode. The cadmium electrode is the negative datum for the instrument and both plates are (in this condition) positive to it. As a rule for the interpretation of the instrument used with the cadmium electrode, it should be remembered that the positives should be as positive as possible to the cadmium electrode and the extent by which the reading falls short of 2.05 is a measure of the weakness of the positive element. The negative should be as little positive as possible to the cadmium electrode and the extent to which this reading exceeds .25 is a measure of the weakness of the negative element. In the case of cell weakness it is generally the negative element which is wrong. It has been so in nearly all cases in our experience. When a cell shows a terminal P.D. greater than 1.80 volts, due to being in a higher state of charge and/or not discharging, the reading of the positive element should be more than 2.05, and that of the negative element less than .25. If, in this condition it is judged that one of these readings shows too little difference from the limit, even though it be within it, it still may be that one of the elements is in wrong condition. Therefore the final decision as to the condition of the elements must be arrived at by allowing the battery to discharge to a terminal P.D. of 1.80 volts, when, if one element shows itself to be Contd. | ||