CHAPTER VII. 



THE PRACTICAL OPERATION OF DYNAMOS. STATION 

 EQUIPMENT. 



80. General instructions for managing generators and motors. * 

 Dynamos are usually provided with an eye-bolt to which ropes 

 or chains for lifting may be attached. In handling a dynamo, or 

 in removing an armature for repairs, great care must be exercised 

 to avoid abrasion of the windings. An armature should never be 

 laid upon a hard floor but should always rest upon a soft bed of 

 sacking. 



The bearings should be kept thoroughly lubricated with a fine 

 grade of oil. Carbon brushes do not need much oil lubrication, 

 and in any case oil must be used very sparingly on the commu- 

 tator, since the sparking tends to char it, and furthermore, the 

 oil collects dust and retains the worn-off particles of carbon and 

 copper producing a gummy coating which leads to poor electrical 

 contact between the brushes and the commutator. 



The commutator should be cleaned occasionally with a tightly 

 woven cloth (free from lint), and, after this operation, a mere trace 

 of oil, or preferably vaseline, may be applied to the cloth and 

 thence to the commutator. 



The tension of the brush springs should be ordinarily adjusted 

 to give a pressure of about 1.5 pounds per square inch of contact 

 surface between the brushes and the commutator. Too little 

 pressure leads to chattering of the brushes and consequent spark- 

 ing and roughening of the commutator. Excessive brush pres- 

 sure gives rise to excessive brush friction and undue heating of 

 the commutator and brushes. 



*This discussion, and the discussion of dynamo diseases or faults, is adapted from 

 the excellent little book " Practical Management of Dynamos and Motors," by F. B. 

 Crocker and S. S. Wheeler. 



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