The connectors (Fig. 76) are clamped firmly to the side of the bar and soldered, and then the clamp is removed, the surfaces soldered being much larger than the sectional area of the bars.
Mica insulation is used between and at the side of the bars. The slot is in. deeper than the bars, so that it leaves a space below the same to insulate them from the iron. There are 74 bars in the commutator, each connector on one end of the armature leading to a bar.
The brushes may he placed 60° or 180° apart. On the ma chine shown, they have been placed 60° apart, but, all things considered. 180° is preferable.
The iron of the armature runs in such close proximity to the field-magnets (the clearance necessary for rotation being the only gap in the magnetic circuit) that the expenditure of energy on the field-magnets is very small, being less than per cent of the total when the machine is fully loaded.
This must be conceded to be a remarkably good result when the slow speed of the machine is taken into consideration.
The following table gives the results of a test of the ma chine illustrated, made by Dr. W. E. Geyer and D. G. Jacobus, 31 E., at the Stevens Institute of Technology: The Denro2ier Multipolar-Disk Dynamo is illustrated in Pig. 79. The winding, which char aeterizes the Desrozier machine, is shown in Figs. 77 and 78, and is arranged for an armature divided into 5`?.. sections. By this arrange ment the space between the poles is fully utilized : each section has a well-defined position, and an armature so constructed affords every facility for repairs and for inspection while at work. By a modifica tion of the collector and its connections, M. Desrozier has avoided an increase in the number of coils, lie connects each triple coil not to a single bar but to three, 120° apart in the case of a 6-pole machine. The brushes, in lieu of uniting the ends of a triple coil, only unite the ends of a single coil, and each single coil is short circuited several times under each brush at every revolution. This method of con necting up will be understood on examin ing Figs. 77 and 78. The connections would be inextricable if the inventor had not made use of the properties of the in volute. The wires are therefore all with a special piece of apparatus. called the analyzer, and which is placed beween the disk and the collector. three wires of each coil come from the center of the armature to an insu lated disk : wire 1 passes on straight to the collector-bar ; wire 1 is wound in involute on one side of the disk, and runs thus to bar 1'; wire 1" passes through the disk, is backward through 120 , and terminates at bar V% In this way all the wires are arranged side by side on either face of the analyzer, and no mistakes are to be feared. It
is not necessary to enlarge further upon the practical ad vantages of these arrange ments, allowing as they do very satisfactory working of the collector. It would be impossible otherwise to stop sparking without increasing the number of coils, or in creasing the distance between the successive poles. Several Desrozier machines have been built by the firm of Br6guet, and placed on board the French ironclad Formidable. These machines weigh 2,640 lbs. each. run at 350 revolu tions. and have an output of 175 amperes at 70 volts ; their electrical efficiency is 82 per cent, and their commercial effi ciency is 79 per cent. It varies very little with the work. According to the inventor, it is very probable that the efficiency of the Desrozier dynamo would be considerably higher if constructed to meet ordinary commercial requirements.
The Fritsche and Pischon Dynamo is illustrated in Fig. 80, and is known as the " wheel " dynamo, owing to the peculiar shape of the armature.
The armature-bars consist of specially shaped pnnchings of sheet-iron and sheet-copper, which are riveted together. They are long and thin, and are illustrated in Fig. 80A. The punchings are soldered and riveted at the top and bottom to the specially shaped brass castings A and B. Copper bars are screwed on to the castings A, which are then turned off on the circumference and serve as commutator blocks. As the armature-loops are connected in series, two sets of brushes only are required. The lower castings B are mortised on both sides, and by this means the whole armature is clamped to gether with strong cast-iron hubs, (1, which have brass end-rings, D. in order to magnetically insu late the hub from the armature-bars. Pressed board insulation, E, is used between the ring D and the armature-spokes. The largest machine that is being built at present is designed for 180 K. W., and the following data regarding it will be interesting : Output 150 volts 1,200 amperes.
Speed 100 revolutions per minute.
Weight of armature 8,800 lbs.
Weight of copper on fields 1,080 lbs.
Total weight of machine complete 20,240 lbs.
Loss in magnet and armature con ductors ........ 365 per cent.
The following is a table of sizes and general data of the standard Fritsche machines: