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 method for testing magneto volt-ampere capacity and calculating the figure of merit.
| Identifier | ExFiles\Box 4\5\ 05-page335 | |
| Date | 21th April 1925 | |
| X.430 X2791 MAGNETO TESTS - VOLT AMPERE CAPACITY AND FIGURE OF MERIT. The volt ampere capacity figure can be obtained by observing the open circuit volts and closed circuit amperes of the primary winding of the magneto at a speed of 2000 r.p.m. (lever central on sleeve magnetos) and multiplying them together. Then, dividing this by the weight of the magneto, we obtain the figure of merit. The observed results are given in the attached table. An average volt ampere capacity figure by which to judge magnetos is about 39, and an average figure of merit for the same purpose is about 3.0. A magneto with this figure of merit and of weight 13 lbs. might give at 2000 r.p.m. open circuit volts approx, 12.25 short circuit amperes approx. 3.15. The latest Watford is one of the magnetos which comes nearest to these figures. One particular magneto of this type (No.72972) weighs 12.5 lbs. and at 2000 r.p.m. the open circuit volts and short circuit amperes are 10.25 and 3.22 respectively, giving a volt ampere figure of 33.0 and a figure of merit of 2.64 volt-amperes per lb. weight. EPC. | ||