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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).
Experiments to reduce excessive iron loss in armature cores using pre-slotted plates and Stalloy material.

Identifier  ExFiles\Box 60\3\  Scan244
Date  14th September 1933
  
-2- Hs{Lord Ernest Hives - Chair}/Est.3/NA.{Mr Nadin}14.9.33. Cont'd.{John DeLooze - Company Secretary}

Our opinion has all along been that this excessive iron loss is due to our practice of milling the winding slots in the armature after assembling the core of round stamped plates. The idea of building the core of a number of plates scale insulated or painted with varnish is to prevent the formation of eddy currents which are induced by the rapid magnetic flux changes in the armature when running fast, but our milling process must effectively short circuit all the plates thus causing heavy eddy current loss in the core.

As previously explained the present experiment was to build the armature core with plates already slotted before assembly thus obviating the milling process. By this means we should reduce costs and improve the ampere output of the dynamo at high speeds by reducing the eddy current loss.

For the purposes of this experiment each armature was wound with 12 conductors per slot of 17 SWG. wire.

The first armature tried had "Stalloy" plates. This material is noted for its low iron loss when subjected to high frequency magnetic flux changes.

The result was most encouraging. Although we were using 17 SWG. instead of the 16 SWG, which is difficult to handle on production, we obtained an output at slow speeds of 15.6 amperes at 13 volts and at 5000 R.P.M. this output was only reduced by .6 ampere as against 4.5 amperes on the standard machine.

As expected however due to the fact that "Stalloy" has a lesser permeability than the "Lohys" iron used on production and also that only 12 conductors per slot were used instead of the standard 16, the "cutting in" point was higher, i.e. 20 M.P.H. instead of 18.5 M.P.H. on the Bensport chassis.
  
  


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