[PT032AAE1], Technical Note, Thomas Alva Edison, May 18th, 1887


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"Important & Immediate [drawings fig. 1, fig. 5, fig. 8, fig 7, fig 6, fig 8 fig 7, fig 2, fig 3, fig 4] Dyer-- This is the specification of the Dynamo I spoke to you about. The current being derived electrically from the heat through the action on magnetism-- The proper name for the motor would probably b Magnocaloric Engine or Magnothermic Engine-- I prefer the latter name-- The name of the current generator which I now describe I call a Magnothermic battery The object of the invention is to Translate heat energy into electric energy by the action of heat upon magnetized iron. The invention consists in acting upon magnetized iron by an increase & diminution of heat at intervals to diminish & increase the magnetism of the iron. The action of which serve to induce electric currents in wire wound around such magnetized iron-- The intermittent currents being properly comutated into a continouous one-- Two iron rings AA' fig 1 2 &3 form the north & south poles. Electro magnets or steel magnets m m m m fig 1 & 5 magnetize the rings-- There may be several such magnets Between these two polar rings are bundles of thin iron tubes B fig 1 fig 5 fig 7-- These tubes are 1/8 diameter and are composed of iron .006 thick drawn through a die into a tube with ends abutting. The object of using such thin iron is that it shall gain and lose its heat rapidly The powe of the generator being proportionate to this property The several bundles of tubes pass through hole X fig. 3 of the 2 pole pieces and project at both ends. They are packed tightly in these holes by asbestos or other infusible material. The whole of the iron of the tubes are powerfully magnetized by the rings & serve as armatures across the poles-- Around each bundle is a bobbin of wire pyroninsulated insulated so that it is enabled to stand a rather high temperature without changing the insulation. These bobbins are shewn as C in fig 2 fig 1 as c fig 7 fig 6. The whole of the bobbins are connected together electrically after the manner of the Gramme Ring armature. In fig 6 are shewn the communtating devices-- as the coils do not rotate it is essential that the equivalent of the usual dynamo brushes must be rotated. There is a disk N on the rotatin shaft k This disk has 2 metallic pieces see fig 8-- marked No 1 & 2 Electrical contact with each block is continuously maintained during rotation by the springs 5 & 6 resting on the disks 4 & 3 which are insulated from the shaft but both are in contact with the block one to one block & one to the other. There are 8 fixed springs see fig 6 the ends of which bear on the periphery of N. The blocks are coming into contact as they pass around-- Each spring is connected to a wire between the coils by air extra wire h as in the gramme ring armature. Now if the apparatus be arranged as in fig 1 over a furnace R with grate bars Q heat in the form of flame & hot gases would pass upwards and as the only outlet is through the several bundles of tubes B they would be instantly heated, & soon reach a temperature where they would cease to be magnetic; This demagnetization of the iron causes a powerful induc[t]ive current to be thrown into the coils of wire surrounding the tubes. Now to properly collect these current sinto a continuous form it is essential that while one half of all the tubes are acquiring heat & losing magnetism the other half should be losing heat & acquiring magnetism to do this I use a rotating guard o fire clay material which serves to close the outlet of 1/2 of all the bundles of tubes so the flame or hot gases cannot enter them while the other 1/2 are open to the flame-- This rotating guard is best shewn in figs 7 8 & in fig 2 the whole apparatus is upside down The guard being shewn more plainly as it is also shewn in fig. 3. The shaft being extended down to bring out the character clearly to the eye This guard is rotated by any suitable power & the speed should be such that with any given fire The maximum electromotive force is obtained-- It is obvious that it might be run by an electromotor receiving current from the machine itself in this case it would be self regulating any lessing of the electromotiv force due to too great a speed would slow the motor down & thus increase the E.M.F. The action of the apparatus is very simple-- heat enters 1/2 of all the bundles of tubes. This lessens the magnetism & an inductive current in one direction is send round the coils. The other 1/2 of the coils are cooling hence are increasing in magnetism. This sends an inductive current in the opposite direction-- Now both currents meet at one common point ie the commutator springs & the result is a multiple arc the 2 currents coming togeter as one as in a gramme ring-- As the guard S is constantly advancing-- That coil wich has reached the highest temperature is suddenly covered by S instantly it commences to lose heat & acquire magnetism, while a moment before it was gaining heat & loosing magnetism-- at this instant of increasing & falling of temperature The bobbin of wire is by the action of the commutator thrown in among the opposite 1/2 of bobbins-- while at the same time a coil from this 1/2 I uncovered & instantly the current changes sign in its bobbin as it now rises in termperature. Thus by the direction action of heat on iron powerful electric currents are generated without the use of engine & boilers-- The field of force magnets may be permanent steel weights or electro magnets and be energized by the apparatus itself or by an extraneous source of electrcitiy, a slight initial magnetism must be given the field magnets to permit them to build up-- As the generative capacity of the appratus depends upon the differences of temperature & the rapidity with which the bundles of iron tubes lose their heat it is obvious that the inlet air for the furnace may be made to pass through those bundles which are guarded by the guard S for the time being & thus rapidly cooled & this heated air will material assist in raising the temperature of the furnace gases & thus ensure the rapidity & at the same time waste heat is utilized. Claim. The electric generator sub as described & other as you may suggest patent England France & Germany"







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[PT032AAE1], Technical Note, Thomas Alva Edison, May 18th, 1887

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


May 18, 1887