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).
Fault investigation into the reversal of dynamo polarity causing cutout points to stick.
| Identifier | WestWitteringFiles\T\November1928\ Scan098 | |
| Date | 19th December 1928 | |
| To R.{Sir Henry Royce} from EFC. c. BJ. E.{Mr Elliott - Chief Engineer} c. EW. Wor.{Arthur Wormald - General Works Manager} EFC2/T19.12.28. XN40 X440 S.S. DISTRIBUTION BOARD GREEN LAMP SWITCH. Further to our EFC4/T3.12.28, EFC3/T12.12.28 EFC4/T12.12.28 and your R/M11.12.28; another complication has now arisen in this connection. It had not been noticed previously on 18-EX, though it may have happened, but we have run up against it on chassis 19-EX, viz. the fact that the battery current running, with the charging switch in the first or M & B. position, from the B terminal of the distribution box backwards through the dynamo armature and field to the C terminal and thence through the green lamp switch coils, is of just sufficient magnitude to reverse the residual polarity of the dynamo sometimes. The fault was first brought to our notice by the fact that the cutout points (19-EX) became stuck together. Investigation showed that it was possible for the dynamo when switched on to excite in a reverse direction, with the result that on the first contact of the cutout contacts, a heavy battery current would flow to correct the excitation. In some cases this correction is automatically effected and all goes along normally, but it is dangerous in that the cutout contacts may be welded together in the process and will not subsequently break when they normally should do so. It will be agreed that we must get away from this condition. At the same time we want to satisfy the condition that the green lamp shall not remain on in the M & B. position. If the green lamp coil were connected to B, magnetic reversal of the dynamo would not occur, whether B -contd- | ||