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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.
  
  


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