Milestones:First Studies on Ring Armature for Direct-Current Dynamos, 1860-1863


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Pisa, Italy
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First Studies on Ring Armature for Direct-Current Dynamos, 1860-1863


A dynamo with a slotted ring armature, described and built at the University of Pisa by Antonio Pacinotti, was a significant step leading to practical electrical machines for direct current. Groups of turns of the closed winding were connected to the bars of a commutator. The machine worked as a motor also.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

School of Engineering, University of Pisa, L-go Lucio Lazzarino 1, 56123, Pisa, Italy Latitude 43.7209875 Longitude 10.389789899999982, 43.7209875, 10.389789899999982

Details of the physical location of the plaque

The plaque could be mounted on the wall near the entrance of the main lecture hall, placed inside the main building of the School of Engineering. How is the intended plaque site protected/secured, and in what ways is it accessible to the public? If visitors to the plaque site will need to go through security, or make an appointment, please give details as well as the contact information visitors will need in order to arrange to visit the plaque.

How the plaque site is protected/secured

The School of Engineering has a porter’s lodge. Because since the building also contains classrooms for university students, the site is usually open to the public for six days/week (Monday to Friday from 8:00 am to 8:00 pm, Saturday from 8:00 am to 1:00 pm). During this time visitors are free to visit the plaque.

Historical significance of the work

Antonio Pacinotti (1841-1912) learned the principles of electromagnetism in his youth and under the direction of his father, Luigi Pacinotti, Professor of Technological Physics at University of Pisa. Then, early in 1859, he began to develop and build an electromagnetic machine with transverse electromagnet which was the basis of the invention of the Direct Current generator or dynamo. Later he stopped the project because on May of the same year he volunteered, in the ongoing war as a sergeant of the 2nd Company of the Tuscany Division Military Engineers. In 1860, he returned to Pisa and after passing university exams, with the help of Giuseppe Poggiali, a technician in the Phisics Laboratory, he built and tested his machine, the first practical dc generator. The results of his experiments and a detailed description of his dynamo were published in the Italian scientific journal Nuovo Cimento in 1864. About the invention, Pacinotti wrote: "The electro-magnetic machine of which the first ideas are here recorded, was built by me in a small model; [...] This machine has only one fixed electro magnet. It works very well as a magneto-electric machine, since always gives a very intense current in one direction". In another note, dated 22 and 23 June 1860, Antonio Pacinotti wrote that the machine works well both as a motor and as a dynamo. In September, 1860, he declared that his machine with respect to other similar devices, such as the Clarke machine, has the advantage of producing direct current, with a constant rotation speed. Although other scientist attempted to build similar devices some years earlier, Pacinotti's machine was the first practical direct current dynamo because it did not produce severely isolated pulses of electric current. At the Vienna Exhibition in 1873 he presented his invention of the 1860s, and for the first time received wide credit. A medal of progress was granted Professor Pacinotti in Vienna, and other medals of honor were given him in 1881 at Paris. The Pacinotti's invention radically contributed to change electricity from a curiosity into a profitable, reliable technology. In fact, until the mid-1800s, the unique source of electric power was the Volta's battery. Unfortunately this kind of electric source was not reliable or cost effective for any regular electrical use. The combination between the dynamo and the invention of the electric light bulbs, available by 1879, allowed the “electricity revolution” both in social and industrial environments. DC generators were installed at the Pearl Street station facilities in New York City, the earliest commercial power generating plant, mainly used for electric lighting. In the same years, DC motors were introduced in some manufacturing industries to substitute the single huge steam engine, so far used to drive all the belts machines running at the same speed. This fact contributed to barely increase the productivity of the factories and most importantly to improve working conditions and safety for the workers. Antonio Pacinotti died in Pisa, on March 24, 1912. At the time of his death he was professor of technological physics at the University of Pisa, succeeding his father since 1881; he was also a senator of the kingdom of Italy.

Features that set this work apart from similar achievements

With the idea of using a simple device called “commutator” and the ring and toothed types of armature, Antonio Pacinotti contributed to develop the first practical direct current dynamo. The devices previously investigated by other scientists were not able to be used as commercial generators since they produced severely isolated pulses of electric current or they were characterized by low efficient design. Although Pacinotti tested his invention by using a permanent magnet as the source of the magnetic field, he described the operation of the machine with reference to an electro-magnet. This was a further improvement, since the use of an electromagnet as a field source allows to increase and to control the electric output.

Significant references

References [1] Il Nuovo Cimento, vol. XIX, 1864, pagg. 378-384 (see the attached english translation of the paper) [2] M. Guarnieri, "When Cars Went Electric, Part One [Historical]," in IEEE Industrial Electronics Magazine, vol. 5, no. 1, pp. 61-62, March 2011. [3] J. L. Sprague, "Frank J. Sprague Invents: The Constant-Speed dc Electric Motor [History]," in IEEE Power and Energy Magazine, vol. 14, no. 2, pp. 80-96, March-April 2016. [4] Andrews, J.D.F., "Dynamo-electric machine or motor", 1892, USA Patent n. US474624 [5] E. Ambrose, "The distribution of electricity", Journal of the Royal Society of Arts, Vol. 90, No. 4625 (OCTOBER 30th, 1942), pp. 727-749 [6] C. Mackechnie Jarvis, "The History of Electrical Engineering. 4. Machinery for the new light: part 2", Journal I.E.E. September 1955, pp. 566 - 574

Supporting materials

Media:Pacinotti macchinetta elettromagnetica english.pdf Media:2 when cars went electric.pdf Media:3 frank j sprague.pdf Media:4 dynamo electric machine.pdf Media:5 THE DISTRIBUTION OF ELECTRICITY.pdf Media:6 The History of Electrical Engineering.pdf


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