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 chosen 'cut-in' and 'cut-out' tensions for an automatic switch.
| Identifier | ExFiles\Box 48\3\ Scan235 | |
| Date | 16th April 1921 guessed | |
| -2- Contd. "hunting" effect on the automatic switch; on the contrary, if the automatic switch cuts in for a tension of 13v.5, there would not be any back current running through, and the armature will be firmly held on "cut-in" position. Moreover, with an ordinary charged battery, it is useless for the dynamo to cut in before it has reached 13v.3 because no charging current will go through the battery but only a very small one. It is for these reasons we have chosen 13v.5 as "cut-in" tension. For the "cut-out" tension we have chosen 11.5v so that in the case of a run down or very "weak" battery at the very moment of the "cut-in" the current passing through the dynamo armature produces what we call "lost volts" (dueto the armature resistance)these "lost volts"lower the external tension of the generator which tension arrives then at 12 v. {VIENNA} (battery tension) but then we have certainly a charging current because our "cut-in" tension being 13v.5 in these conditions, the charging current going through the series winding locks the armature in the "cut-in" position. On the contrary, if we had taken the said 12v. 2 as "cut-in" tension and say 11v.9 as "cut-out" tension, we should have a "hunting" effect again. These are the reasons why we take 13v.5 as "cut-in" tension and 11v.5 as "cut-out" tension. On the other part regarding the second paragraph of your note we beg to tell you that the "cut-in" tension of our automatic switch when it is warm is 14v.5 and then | ||