Electric motors. The inclusion of DC motors in a network of 110 or 220 volts. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electric motors. The inclusion of DC motors in a network of 110 or 220 volts. Encyclopedia of radio electronics and electrical engineering

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In a home workshop equipped with machines with electric motors, it may be necessary to connect and connect to the mains DC motors. There are several schemes for this.

The most widespread is the switching circuit using a starting rheostat that lowers the starting current, since when the engine is turned on, a starting current occurs that exceeds the nominal value by 10-20 times. The winding of the electric motor may simply not withstand, and this will lead to failure of both the motor itself and other circuit elements.

Connect the starting rheostat in series with the armature circuit (Fig. 100).

Electric motors. Inclusion of DC motors in a network of 110 or 220 volts
Rice. 100. Scheme for connecting a DC motor to the network: L - a clamp connected to the network; M - clamp connected to the excitation circuit; I am a clamp connected to an anchor; 1 - arc; 2 - lever; 3 - working contact.

Such a scheme is most suitable for engines with a power of more than 0,5 kW. The value of the starting resistance of the rheostat is calculated by the formula:

Electric motors. Inclusion of DC motors in a network of 110 or 220 volts

where Yap is the starting resistance of the rheostat (Ohm); U - mains voltage (110 or 220 V); 1nom - rated motor current (A); Yaya - armature winding resistance (Ohm).

The procedure for connecting a DC motor to the network is as follows:

- the lever on the rheostat is set to idle contact - 0;

- turn on the mains switch and move the rheostat lever to the first intermediate contact.

In this case, the engine will be excited, and the starting current will flow in the armature circuit, the value of which will depend on the large resistance that is formed from all four sections of the starting rheostat;

- with an increase in the armature speed, the starting current should decrease, which will reduce the starting resistance; to do this, move the rheostat lever to the second, then to the third contact, etc., until it is on the working contact (the rheostat lever cannot be kept on intermediate contacts for a long time, since starting rheostats are designed for a short operating time and delay them in this mode leads to overheating and failure).

There is also a procedure for disconnecting DC motors from the network, since they do not turn off immediately: first, the rheostat handle is moved to the extreme left position (of course, the engine will turn off, but the excitation winding will still remain closed to the resistance of the rheostat) and only then turn off the power to the engine. If you neglect this shutdown procedure and turn off the electric motor immediately, then at the moment of opening the circuit, such a large voltage may arise in it that the motor will fail.

Author: Korshevr N.G.

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