page_title: Dynamo
section_title: Practical designs
hierarchical_section_title: Dynamo / History / Practical designs
caption_attribution_description: English: Text from public domain illustration: Figure 328: A large current low voltage bipolar dynamo built for electrolytic work and here shown to illustrate the large size commutator and brushes necessary to collect the large current. The machine here illustrated gives 310 amperes at 7 volts when running at a speed of 1400 RPM, corresponding to an output of 2.17 kilowatts. Carbon brushes would not be suitable for this class of machine because even with copper brushes, whose conductivity is much higher than carbon, the commutator must be of considerable size to give the required brush contact area. The contrast between the axial lengths of the armature and the commutator is very marked. The rocker construction is of the ordinary type, and heavy flexible cables conduct the current from the brush holders to the fixed terminals. My Notes While the size of this device is not listed in the book, the brushes alone are likely to have been 1.5 to 2 inches wide, meaning the commutator is probably a foot wide. The overall machine was probably about three feet tall and about four feet wide, weighing in at several hundred pounds. The short rod on the left side of the copper brushes is most likely a handle, to allow the operator to rotate the position of the brushes. As the speed of the rotor varies, the ideal position of the brushes changes due to the spinning rotor dragging the field lines around with it. Yes indeed, carbon brushes were not good enough for high-current applications. This needs to be mentioned in an article somewhere. Each brush sits in a separate spring-tension carrier, so that as the brush wears away it is pushed down into the commutator to maintain contact. The screws at the base of the unit were used to adjust the flat-belt tension, by moving the entire frame towards or away from the driving engine. Public Domain source: Hawkins Electrical Guide, Volume 1 Chapter 20: Commutation and the Commutator, Page 301. Copyright 1917 by Theo. Audel &amp; Co. Printed in the United States Scanned by Dale Mahalko, Gilman, WI, USA DMahalko (talk) 08:07, 14 January 2008 (UTC)
context_page_description: A dynamo is an electrical generator that creates direct current using a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter.
  Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using rectifiers is effective and usually economical.
context_section_description: The dynamo was the first electrical generator capable of delivering power for industry. The modern dynamo, fit for use in industrial applications, was invented independently by Sir Charles Wheatstone, Werner von Siemens and Samuel Alfred Varley. Varley took out a patent on 24 December 1866, while Siemens and Wheatstone both announced their discoveries on 17 January 1867, the latter delivering a paper on his discovery to the Royal Society.
  The "dynamo-electric machine" employed self-powering electromagnetic field coils rather than permanent magnets to create the stator field. Wheatstone's design was similar to Siemens', with the difference that in the Siemens design the stator electromagnets were in series with the rotor, but in Wheatstone's design they were in parallel. The use of electromagnets rather than permanent magnets greatly increased the power output of a dynamo and enabled high power generation for the first time. This invention led directly to the first major industrial uses of electricity. For example, in the 1870s Siemens used electromagnetic dynamos to power electric arc furnaces for the production of metals and other materials.
  The dynamo machine that was developed consisted of a stationary structure, which provides the magnetic field, and a set of rotating windings which turn within that field. On larger machines the constant magnetic field is provided by one or more electromagnets, which are usually called field coils.
  Zénobe Gramme reinvented Pacinotti's design in 1871 when designing the first commercial power plants operated in Paris. An advantage of Gramme's design was a better path for the magnetic flux, by filling the space occupied by the magnetic field with heavy iron cores and minimizing the air gaps between the stationary and rotating parts. The Gramme dynamo was one of the first machines to generate commercial quantities of power for industry. Further improvements were made on the Gramme ring, but the basic concept of a spinning endless loop of wire remains at the heart of all modern dynamos.
  Charles F. Brush assembled his first dynamo in the summer of 1876 using a horse-drawn treadmill to power it. Brush's design modified the Gramme dynamo by shaping the ring armature like a disc rather than a cylinder shape. The field electromagnets were also positioned on the sides of the armature disc rather than around the circumference.
caption: This large belt-driven high-current dynamo from around 1917 produced 310 amperes at 7 volts DC.  The huge complicated commutator (left) was needed to handle the large current.  Dynamos are no longer used due to the size and complexity of commutators needed for high power applications.
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