New Small High speed
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Dynamos
THE present tendency in the design of electric generators for buses, is to provide for higher-speed operation. which means that smaller instruments can be used, whilst the requisite output of electrical energy is maintained. A new range of 'instruments conforming with these principles has recently been introduced by Simms Motor Units, Ltd., Oak Lane, East Finchley, London. N.2.
These generators are of 7-in, diameter, and although of the non-ventilated type, have outputs equal to, and in some cases greater than, those ssocia,ted with ventilated machines. A non-ventilated instrument possesses obvious advantages in that the same regard has not to be paid to the position it occupies on the power unit.
in place of the usual type of commutator cover band, detachable cover plates, seating on oil-resisting gaskets. are introduced. Removal of these plates gives easy access to the brushes for inspection, adjustment or renewal.
The shape of the pole pieces has been improved, and a uniformly graded air gap reduces flux distortion, and improves commutation at high speeds. Maintenance is simplified, as, by reason of improvements in the magnetic circuit, and the increase in active core length, both 12-volt and 24-volt machines in the new 7D range operate with single regulators.
Supplies can he made of generators of the new series which are mechanic ally in with existing machines so far as concerns overall
length. diameter, shafts, cable entry. and so on. Taking two examples of performance data, the type 724 Db. 24-volt machine cuts in at 600 r.p,m., and gives a maximum output of 35 amps., 840 watts, at 725 r.p.m.: the maximum permissible speed is 3,000 r.p.m. The 712 00 12-volt dynamo cuts in at 360 r.p.rn, and has a maximum output of 40 amps., 980 watts, at 510 r.p.m.; maximum speed is 2,500 r.p.m.
The 7D range of Simms dynamos has been designed for operation with the company's new FR series-control units. A37