IEEE Power & Energy Magazine - January/February 2021 - 88

this takeover will be presented in the
" Competition " section.

Brush Dynamos
Before 1877, manufacturers of arc
lighting dynamos tested their machines
mainly to ascertain that the devices
would make arc lamps produce satisfactory light. Testing for efficiency
was not a high priority, and little was
known about the relative efficiencies of
the different makes of dynamos. In the
fall of 1877, the Franklin Institute, in
Philadelphia, began systematic tests of
Brush, Gramme, and Wallace-Farmer
dynamos. Siemens dynamos were
not tested because a machine was not
made available. The Brush and Wallace-Farmer machines included arc
lamps provided by those companies,
but, as noted in Journal of the Franklin Institute, the Franklin Institute
" quickly established the suitability of
the Brush lamp as the source of light
for all the machines. " At the end of the
trials, in the spring of 1878, a committee evaluated the results and concluded
that " the small Brush machine, though
somewhat less economical than the
Gramme machine, or the large Brush
machine, for the general production of
light and of electrical currents is, of the

various machines experimented with,
the best adapted for the purposes of the
Institute for the following reasons: It is
admirably adapted to the production of
currents of widely varying electromotive force and produces a good light....
It possesses great ease of repair. "
Zénobe Theophile Gramme (1826-
1901), born in Belgium, invented a dynamo more suitable for industrial uses
than earlier ones. In partnership with
French electrical engineer Hippolyte
Fontaine (1833-1910), he founded Société des Machines Magnéto-Électriques
Gramme, in France, in 1871, which
began manufacturing the dynamos in
1872. Brush decided to design a dynamo more suitable for commercial arc
lighting than the Gramme machine. He
built his first dynamo in 1876 at his father's farm, with components made at
Telegraph Supply and with other parts.
In the absence of a steam engine, he
attached the device to a horse-drawn
treadmill used for sawing wood. It
worked. He filed a -patent -application on
11 November 1876. P
- atent No. 189,997
was issued 24 April 1877.
Brush designed his dynamos (Figure 4) for optimally feeding a constant
current to multiple arc lamps in series.
The armature, commutator, and ar-

figure 4. The Brush 40-light No. 8 dynamo of 1880. It was 89 in long × 28 in
wide × 36 in high, weighed 4,800 lb, and used with 2,000-candlepower lamps
in series. (Source: The Brush Electric Light. Cleveland, Ohio: Brush Electric
Company, 1881.)
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rangement of the field magnets (Figure 5) all differed from Gramme's
design. Gramme's circular armature
rotated on a spindle between field
magnet poles above and below, exerting a strong inducing action upon only
the outer edge of the armature. Brush
used two U-shaped field magnets facing each other across a gap in which a
circular armature rotated, so both sides
of the armature were exposed to the inductive influence of the field magnets.
Brush's " open-coil " armature was
unprecedented. His bobbins of wire
were not connected in a single circuit
(closed coil). Instead, only each pair
of diametrically opposite bobbins was
connected, with the two free ends of
the conductor thus formed attached
to diametrically opposite segments of
the commutator. Each pair of bobbins
was independent of the other pairs.
The popular No. 7 dynamo had four
pairs of bobbins and a commutator
with four separate rings of metal to
accommodate them; each ring consisted of two nearly semicircular segments separated by gaps designed to
enable the proper functioning of the
current-collecting brushes (Figure 5).
All dynamos prior to Brush's used
closed-coil arrangements.
The sophistication of Brush's invention, when he was 27 years old and
with a degree in mining engineering,
was made apparent at a meeting of the
American Institute of Electrical Engineers on 22 May 1891, at which the
lecture " A Study of an Open-Coil Arc
Dynamo " was presented. The resulting
14-page article, which contained many
experimental data, failed to explain exactly why the open-coil dynamo was so
successful for powering arc lights. The
following is an excerpt:
Of all the dynamo machines in
use at the present day, perhaps
the internal action of none is so
little understood as that of the
arc lighting machines of the open
coil armature class. Much concerning the regulation and general behavior of these machines
seems utterly at variance with
what one would naturally expect
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