[D8855ABK], Letter from Arthur Edwin Kennelly to Thomas Alva Edison, August 6th, 1888


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[D8855ABK], Letter from Arthur Edwin Kennelly to Thomas Alva Edison, August 6th, 1888

Editor's Notes

"I have investigated the effect of doubling the present "entrefer"[ie, air gap bet. armature & magnets] of the No. 20 Dynamo on its output. More than double the present amount of wire could be put on the armature--about 2-40 times. If the present output of the machine at full load (400 amperes) is the heat limit of the armature, then the same limit would be reached with 2-4 times as much copper at 55% increased output, owing to the greater depth of winding probably at 50% increase. At the same time, the voltage would fall neglecting magnetic leekage 45%. The great increase which would naturally take place in the leakage might incrase the fall as much as 60%. To redeem this lost voltage, the ampere turns would have to be increased proportionately if the iron core are left unaltered, this is to say from 440 lbs copper to say 900 lbs copper, and taking into account increased diameter and heating probably 1000 lbs. The loss of energy in the magnetic field would incrased from 400 to perhaps 1000 watts, so that to take the present machine and bore it out to double the entrefer would mean increasing the copper on the magnets to the value of $200 and [unclear] energy at an increased rate of 2 cents per hour in the fields, which the output would be incrased from 400 to 600 amperes. If such a change were contemplated it would probably pay to increase the diameter of the iron cores in order to save heat and wire." Yours very faithfully, A.E. Kennelly [Marginalia: "File"]




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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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