Page:Popular Science Monthly Volume 88.djvu/812

 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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