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).
Comparison report between a 21000 turn secondary coil and a standard 18000 turn secondary coil.
| Identifier | ExFiles\Box 164\5\ img120 | |
| Date | 18th January 1932 | |
| X6058. 18. 1. 32. 21000 TURN SECONDARY COIL D.72503 44 SWG VERSUS 18000 TURN SECONDARY COIL 42 SWG. (STD) Comparing these coils side by side we have :- (a) Turns per layer. With the 21000 turn coil the max length of layer is 1.600" which with 44S.W.G. (.0032") wire means 500 turns per layer. With the standard coil the max length of layer is 1.475" which gives us 370 turns per layer. (b) Voltage between layers. As the voltage is directly proportional to the number of turns assuming 100% interlinkage and minimum leakage the increase in volts per layer of the 21000 turn coil over standard will be 35%. The voltage stress per layer is thus considerably larger. We should thus certainly require an extra turn of paper insulation per layer to avoid breakdown and as the coil with 21000 turns has only 42 layers as compared with 51 standard there would appear to be sufficient room to do this without increasing the present overall diameter of the winding. (c) Total secondary voltage. With the distributor running at 700 r.p.m. with .55 mr at 12 volts and standard Ballast the maximum regular sparking voltage given by the 21000 turn coil was 10,750 volts and by the standard 18000 turn coil was 7.500 volts. (d) Minimum voltage to spark over 5.5 mm gap. 21000 turn coil 5.5 volts. Standard coil 6.5 volts. These 21000 turn coils gave good results on test no misfiring being registered on "picking up" on top gear with the coil hot and with .030" plug gaps. HS{Lord Ernest Hives - Chair}/GWH{George W. Hancock - Head Chateauroux} definitely confirmed the superiority of this coil on 18.G.4. in France. HS{Lord Ernest Hives - Chair}/Wst. | ||