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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).
Dynamo tests for a 3-charge scheme when fitting a 40/50 dynamo to a 20/25 HP chassis.

Identifier  ExFiles\Box 163\6\  img174
Date  22th June 1932
  
X6016

To FN.
from Hs{Lord Ernest Hives - Chair}/Wst.
c. E.{Mr Elliott - Chief Engineer} HY.{Tom Haldenby - Plant Engineer} Wor.{Arthur Wormald - General Works Manager}

Hs{Lord Ernest Hives - Chair}/Wst. S/KT. 22.6.32.

X600

40/50 DYNAMO FITTED TO 20/25 HP. CHASSIS
WITH 3 CHARGE SCHEME.

We have been carrying out some dynamo tests with the 40/50 dynamo with various grades of resistance, with the idea of arranging the 3 charge system on the 20/25, with this larger size of dynamo. This is necessary for two reasons -

(a) To safeguard the battery during summer running owing to the fact that the battery on the 20/25 is of smaller capacity and weight than the 40/50.

(b) To avoid over-running the headlamps.

The results we have obtained are as follows -

With the dynamo in the full charge position arranged to operate only when the headlamps are on, the dynamo will cut-in at 9 m.p.h., and will reach a peak of 13 amps.

With the dynamo arranged with one stage of resistance incorporated in the field circuit, i.e. for winter charge running, without headlamps, the dynamo will cut-in at 12 m.p.h. and will reach a peak of 9 amps.

With the dynamo arranged with two stages of resistance, i.e. for summer charge conditions, the dynamo will cut-in at 16 m.p.h. and reach a peak of 6 1/2 amps.

We think these resistances are about right, and should suit the dynamo battery requirements on the 20/25 chassis. At the same time the side-lamps will not tend to be overloaded as regards voltage owing to the fact that with the first stage of resistance incorporated, the maximum charge will be 2 amps. less than the present standard 20/25 HP, in the side and tail position.

We wish to point out that we do not recommend with this scheme, putting the full charge on the
  
  


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