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).
Performance of car batteries, comparing different types and proposing changes to charging specifications.
| Identifier | ExFiles\Box 54\1\ Scan043 | |
| Date | 21th November 1925 guessed | |
| Contd. -4- It may be a good thing to get a big proportion of acid volume to plate volume in some ways, as I believe you have, at any rate greater than the Exide, but if this big volume of acid is not available for active circulation during charging (or discharging) its value is more imaginary than real. That is my view of what happens - namely, that the electrolyte can circulate among the plates and separators better in the Exide battery than in the P & R, and help to keep the battery internal resistance down. At any rate the fact remains that on the sandwich battery on the car, with the same current passing through the cells, the voltages were 3.0 with P & R's, and 2.5 for Exide's, and the effect has been noticed previously, though not paid so much attention to. But as I say, we are making further observations on both the 40/50 and 20 HP. systems, working on both batteries, with, in each case, a set of correct chassis wires and distribution board and cutout, and I shall be pleased to let you know the result of these tests as soon as available. In the meanwhile you might put it up to your experts for consideration that the effective true battery resistance during charging at 12 amperes is perhaps 20 times as great as the resistance during discharge at 100 amperes. If a charging rate of 12 amperes absorbs half a volt per cell, a discharge rate of 100 amperes at the same resistance should absorb nearly 4.2 volts, which is more than twice the E.M.F. of the cell. I want the battery resistance on charge to be no more than the battery resistance on discharge. I am going to add a clause to the general specification under the heading "Charging Rate" that when the battery is charging at the rate of 12 amperes, the potential difference on the terminals of each cell must not exceed a certain figure. Should you have an opportunity, you might like to try the effect on the output of putting an Exide battery on your own car. Contd. | ||