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 table of specifications for 20 HP and Phantom 56 coil dynamos.
| Identifier | ExFiles\Box 165\6\ img214 | |
| Date | 29th October 1929 | |
| X.5661 29.10.29. X8660 COMPARISON OF 20 HP. & EAC. DYNAMOS. 20 HP (56 coil) Phantom (56 coil) Weight (lbs) (total) 20.8 29.25 " (arm.) 7.5 11.0 Arm. length (active) 2.75 3.25 Arm. dia. 3.1 3.5 Air gap (radial) .015" .022" Field resis. (ohms). 2.6 4.1 Ar. resis. (ohms) .37 .275 Field wire. 19 SWG. 19 SWG. Field turns/coil. 120 170 Comm. diameter. 2.1 2.2 Comm. length (useful) .925 1.15 Brush contact area. .225 sq.in. .28 sq.in. Brush widths (main) .3"=16.4º=2.6 segs. .280=14.6º=2.3 segs Brush " (control) .2"=10.9º=1.725 " .187=9.75º=1.5 " Armature wire. 19 SWG. 16 SWG. Carcase dia. 5.0 5.5 " length. 5.0 5.85 " thickness. .275" .312" Driving end overhand. .850 .950 Commutator end overhang. 1.675" 1.425" Arm. stamping thickness. .026" .015" EFC. | ||