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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).
Bench tests for the Bensport and 40/50 dynamo, detailing output loss at high speeds.

Identifier  ExFiles\Box 60\3\  Scan243
Date  14th September 1933
  
x6044.

Wor.{Arthur Wormald - General Works Manager} From Ha/Wst.
c. to C.
c. to E.{Mr Elliott - Chief Engineer} By.{R.W. Bailey - Chief Engineer}
c. to PH. Da.{Bernard Day - Chassis Design}

Ha/Wst.3/HA.14.9.33.

BENSPORT AND 40/50 DYNAMO FOR USE WITH C.A.V. VIBRATOR REGULATOR.

Further to our report ref. Ha/Wst.7/KT. 28.8.33 we have now completed our bench tests on the Bensport dynamo with armatures made up with stamped slotted iron plates instead of milled slotted plates.

The difficulty with our present dynamos as preliminarily referred to in our previous report, is that owing to the heavy iron losses in the armature at high speeds, the available output for a safe temperature rise is very much reduced at high speeds than at low speeds. For instance on the Bensport dynamo although an output of 16.5 amperes at 13 volts can be obtained for a given temperature rise at 2000 R.P.M. an output of only 12.0 amperes can be attained when the dynamo is running at 5,000 R.P.M.

We attribute this loss in output to :-

(a) Commutator heating due to increased sparking at high speeds.

(b) Heavy iron loss causing excessive heating of the armature iron core.

On previous tests we have been able to show that even with much improved commutation there still existed a large increase in heating with increase of speed suggesting that the iron loss was the most important factor.
  
  


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