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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).
Specification sheet detailing the electrical characteristics of a ballast and primary coil system.

Identifier  ExFiles\Box 69\1\  scan0002
Date  14th February 1924
  
-2- contd

BALLAST.

Approx. resistance (ohms) (cold). .84

Approx. resistance (ohms). 1.35
(when carrying current of same
heating value as working current
at normal speed of timer and with
primary gaps set as below under
Contact Breaker).

Approx. R.M.S. working current of coil I 1.34
at normal speed (amperes).

Approx. average working current C .870
(D.C. value) (amperes).

Ratio R.M.S/average current. I/C 1.54

PRIMARY & BALLAST.

Approx. resistance (ohms) 1.74
(ballast cold).

Ditto, (ballast and primary warm). R 2.53

Approx. time constant under working t = L/R.{Sir Henry Royce} .003795
conditions (sec.) (ballast warm).

Final current at 6 volts, assuming Co 3.16
working conditions (amperes)

Short circuit current (amperes) 1.84

Ratio ballast resistance / primary coil resistance. 1.14

Damping co-efficient. R/2L 132

14.2.24.
  
  


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