[LM111164], Letter from Arthur Edwin Kennelly to Charles Batchelor, November 7th, 1888


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[LM111164], Letter from Arthur Edwin Kennelly to Charles Batchelor, November 7th, 1888

Editor's Notes

[The ollowin seems to be related to a Kennelly notebook entry titled: On the arrangements necessary to illuminate 15, 60, 120 and 180 lamps on a Brush 30 light arc dynamo intended for 9.6 amperes, at 780 revolutions per minute. NM023 image 23, probably done on either 6 or 7 Nov. 1888] The following scheme will I think meet with all the requirements you have specified.##To light 30 lamps 60 [ditto] 120 [ditto] 180 [ditto] at will from a brush dynamo designed to supply [9.6.?] ampere at 140 volt when making 750 revs per mins##To light 180 lamps 20 series of 60 lamps in parallels taking 9.6 amperes at 1270 vols or 1375 at the brushes.##[drawing]##To light 120 lamps, 3 series of 40 lamps in parallel will be required, the voltage needed being 845, and the current 9.6 ampere.##[drawingt]##To reduce the voltage at the same current from 1376 to the necessary amount, an adjustable short of about 25 ohms will be needed round the magnets making the current traversing them 36 x 9.6 or about 6 ampere the generated EMF thus falling to about 6/9.6 or 860. The current in the shunt will be about 3 amperes##To light 60 lamps, 2 series of 30 lamps in parallel will be needed, the necessary voltage being 635 and current 6.92 ampere. The same shunt on the magnets will reduce the current in them to 6.10 x 20/36 or 10 - 10 ampere and the EMF generated to about 4 x 4 / 9 x 6 = 1270 '' 620 but taking saturation effect into account this estimate will be to low by perhaps 70. The exact regulator will be under control by the shunt.##To light 30 lamps, one series of 30 will be required. The same voltage of 635 being demanded at 3.2 amperes Without any shunt the generated EMF would be over 3.2/9.4 = 1370 that is over 60 volt= Whether it would be as high as 700 cannot be stated without actual trial. If it falls too low then either fewer lamps must be lit, say for example 25 instead of 30, or they must be seen in two series of 15 in parallels the required voltage being 316 and the current 6.4 ampere. The shunt round the magnets would then probably have to be reduced to 11 ohms carrying 3.2 ampere in order to bring down the generated EMF.##The first step then is to find practically what voltage will be supplied by the dynamo at normal speed when the current it is allowed to generate is 3.2 amperes. That is to say some 60 lamps should be joined up with the dynamos in##single series and lamps shortcircuited until the right brilliancy of the remainder is reached, when the ammeter should indicate 3.2. If the number of lamps then left at work is 30 or whatever number is demanded for the ----- smallest load, then the wiring can be commenced with a view to having that number in simple series. If however the number that the machine will support on 3.2 ampere is too small, the required 30 must be arranged in 2 parallel series and the wiring arranged accourdingly with a shunt for the magnets.##For a single series of 30 however the connections will be :--[drawing]##For 180 lamp plug 123##120 [ditto] 456##60 [dittto] 78##30##8##Yours faithfully##A.E. Kennelly





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