POWER PLANTS FOR TELEPHONE OFFICES 715 



Reduction of Maintenance 



It will be evident that many of the foregoing developments will 

 reduce maintenance of power plant equipment as well as its first cost. 

 The automatic regulating devices substantially reduce or eliminate 

 the attention which would otherwise be required to readjust machines 

 to compensate for load conditions. When this regulation is applied to 

 generators which are floating batteries, it may also result in substan- 

 tially increasing the life of the batteries, thus deferring replacements. 

 The commercial generators are designed for and equipped with carbon 

 brushes, and will require a minimum of attention. 



The introduction of the enclosed type of small battery and the im- 

 provements in operating methods of large batteries are decreasing 

 evaporation and spraying, thus reducing additions of water and the 

 repainting of exposed equipment in battery rooms. The new methods 

 also reduce the number of periodic overcharges or eliminate them 

 entirely. 



Combining Objectives in Signaling Machine Development 



In designing new equipment it is, of course, desirable to accomplish 

 as many objectives as possible. In this connection, mention might be 

 made of a combination machine which may properly lay claim to 

 attaining four important objectives, namely: improved service, 

 reduced cost, simplified installation and reduced maintenance. 



Several years ago it was the practice to secure ringing current for 

 subscribers' bells and also for various tones and signals from a small 

 motor-generator set, subject to generator voltage variations amounting 

 to 35 volts as the load on the machine changed and the supply line 

 voltage varied within stated limits. Each large central office unit 

 required these motor-generators, one driven by a line motor and a 

 reserve set driven by a battery motor. Direct current at + 110 and 

 — 110 volts for controlling coin box telephones was furnished by two 

 sets of dry cells or storage cells. In either case a third or spare battery 

 was provided. 



To replace the ringing sets and coin control batteries a combined 

 ringing and coin-control motor-generator set has been developed and 

 is being used except in the smallest offices, eliminating the cost and 

 the maintenance of the separate batteries, giving closer voltage and 

 frequency regulation for ringing, and automatically continuing service 

 in spite of outside power failures. A description of the features of this 

 equipment showing what it will do may be of interest as this represents 

 a typical development. 



Associated with the generator is a transformer, the primary winding 



