How to Make a Pole Changing Switch or Current Reverses How to Reverse a
Small Motor.
The switch shown in Figure 76 is a very simple device which will be found very handy for many purposes. It consists of two brass levers mounted alongside of each other and connected together with an insulating strip or yoke bearing a handle so that they can both be moved together. The levers are pivoted at their back ends and provided with binding posts marked B. P. and B. P. in the illustration. The front ends of the levers swing over three switch contact points properly spaced so that the levers touch the adjoining contacts at the same time. The contacts are marked 1, 2, and 3.
[Illustration: FIG. 76.—A Pole changing Switch for reversing Small
Motors or the direction of an Electric Current.]
We will suppose that the experimenter has some device operated by a battery and desires to arrange the apparatus so that he can quickly reverse the terminals of the battery so as to send the current through the device in either direction quickly and at will. The apparatus to be operated should be connected to the two binding posts mounted on the switch levers and marked B. P. and B. P. Connect the negative pole of the battery to the contact marked 2 (the center one), and the positive pole to both 1 and 3 (the outside ones). When the switch is thrown to the right so that the levers rest on the contacts 2 and 3, the right hand lever will be positive and the left hand one negative. When the switch is thrown to the left so that the levers rest on 1 and 2, the left hand lever will be positive and the right hand one negative. The current has been reversed.
[Illustration: FIG. 77.—Top view of a small Battery Rheostat]
A switch such as this makes it possible to quickly reverse the running direction of small motors. In order to accomplish this, connect the two brushes on the motor to the two switch levers. Connect the contracts 1 and 3 (the two outside ones) together and lead the wire to one terminal of the battery used for operating the motor. In case the motor is operated by a generator or from the 110 volt current, connect the wire to one terminal of the power source. The middle contact on the switch (marked 2) should be connected to one end of the field winding on the motor. The other end of the field winding should be connected to the remaining battery terminal or power source.
Moving the switch back and forth will send the current through the commutator in opposite directions and cause the motor to run in either direction as desired.
How to Make a Small Battery Rheostat for Regulating the Speed of Small
Motors, Etc.
*A Rheostat* is a variable resistance for regulating the amount of current flowing in a circuit. It is a very useful device about the experimental laboratory. It may be used, for regulating the speed of small motors, the amount of current flowing into a storage battery when recharging, the brilliancy of a lamp, etc.
[Illustration: FIG. 78.—Details of the Rheostat Base. The lower part of the illustration is a cross section.]