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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 Excerpt:...KW =--, where rj is the efficiency, or the ratio between the useful power given out at the terminals and the total power absorbed in abtaining it.J By substitution of the quantity KW, reduced to horsepower in the above equation, we obtain as the normal torque kW Tm = 85,000 inch-pounds... (68) The commercial efficiency of dynamos varies considerably with their type and size, but in the greater number of cases it ranges from 70 in small to 90 per cent. or more in large machines; an average value of rj is therefore about 0-85. Thus the coefficient for the conversion of the horse-power input into kilowatts of output may 1 Cp. Unwin and Mellanby, Elements of Machine Design, Part II, p. 285. See Niethammer, Berechnung und Konstruktion dcr Gleichstrommaschinen unci Gleichstrommoloren, Part II, p. 369 ff., from which the treatment in the latter part of the present section is derived in part, and to which the reader is referred for a fuller discussion of the whole subject. In the case of a separately excited machine, the exciter of which is not driven from the main dynamo shaft, the power absorbed in the field should strictly be taken into account in calculating the commercial efficiency, although in our present connection such loss in the field stands outside the calculation of the strength of shaft. 746 be taken on the average as = qqq X 0-85 = 0-63, and any equation expressed in terms of horse-power must be divided by this coefficient kW to express it in terms of kilowatts, or Tm = 100,000-inch-pounds. If w = the output in watts,.if w where = the watts per rev. per minute--a quantity the importance of which in dynamo designing has already been mentioned. If then ra be the radius of the arm in inches (Fig. 134), or the distance from the centre of the shaft to the...