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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).
Suggesting the best method for moisture-proofing ignition coil primaries by baking and varnishing.

Identifier  ExFiles\Box 69\1\  scan0134
Date  27th August 1928
  
To BY.{R.W. Bailey - Chief Engineer} from EFC.
c. BY/RD.
c. Mr. Brock.

X.8710

EFC3/T27.8.28.

IGNITION COIL PRIMARIES

We suggest that the best method of ensuring moisture-proof coil primaries is to bake the coil, after winding with primary only, for a fairly long period of time to ensure the drying out th of the inner layers, and then thoroughly to varnish the whole of the exposed portion of this primary whilst still hot, a non-synthetic spirit-base varnish being used. Subsequently a further shorter period of baking should take place.

We do not think wound primaries should stand as at present unvarnished and unwound (secondary) after baking, for any appreciable time, i.e. more than an hour or so, or there is sure to be some amount of moisture in the cotton covering.

EFC.
  
  


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