An Electromagnetic Rectifier and 

 a Polarized Relay 



By R. E. Ryberg 



The Rectifier 



THE storage battery has become a 

 necessity in the laboratory of the 

 experimenter and wireless amateur. 

 The problem then becomes one of sup- 

 plying an efficient means of rectifying 

 the alternating current in the house- 

 lighting mains in order to charge these 

 batteries. They could easily be charged 



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Fig. 1. Wiring diagram for large condenser 



by a small direct-current generator, but 

 not every experimenter has one at his 

 disposal. Almost everyone has an elec- 

 trolytic rectifier for this purpose, but 

 this rectifier, besides wasting current, is 

 a source of constant trouble and requires 

 frequent cleaning. Therefore, the ex- 

 perimenter will welcome any device the 

 operation of which will scarcely afifect 

 the meter. 



Many experimenters have a polarized 

 ringer about their shops, and this will 

 answer very well. If the keeper or per- 

 manent magnet is weak it may require 

 re-magnetizing. 



Fig. 2. Mounting of the polarized relay 



The resistance of the coils is from 

 i,ooo to 1, 600 ohms, so it is readily seen 

 that they will consume very little cur- 

 rent, — about .06 ampere to .11 ampere on 

 th2 no volt supply. 



The clapper rod should be cut as 

 short as possible, and bent outward to 

 engage the permanent contact and 

 stopper. The coils must now be mounted 

 on a suitable hardwood base together 

 with the stationary members, of which 

 there are two, one being used as a con- 

 tact and the other as a stopper. Plat- 

 inum or silver contacts should be sol- 

 dered to the permanent contact and the 

 corresponding side of the clapper rod. 



A condenser K, of large capacity, say 

 ^2 mfd. to 2 mfds. should be shunted 

 across the contacts to reduce sparking. 

 By adjusting the contact C, and the 

 stopper S, Fig. i, this device will work 

 nicely. The wiring diagram is shown. 

 In making the connection with the mov- 

 ing element, it should be soldered up on 

 the clapper rod or the armature. Care 

 must be taken to permit the clapper rod 

 to swing freely. The connection should 

 not be made on the armature support 

 as the current should not pass through 

 the bearing R. This arrangement uses 

 one alternation of the cycle only ; but 

 the experimenter, by placing additional 

 contacts, may take advantage of the 

 complete cycle. 



The Polarized Relay 



The same instrument can be used as 

 a polarized relay with only a few 

 changes. 



A polarized relay is a most useful in- 

 strument for the experimenter. It is the 

 only relay that can be used in multiplex 

 telegraphy and the best relay to use in 

 conjunction with selenium cells and co- 

 herers. The reader will realize a few 

 of its many uses. The instrument shown 

 in the illustration, when used as a re- 

 lay, will operate successfully on .5 milli- 

 ampere. 



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