### DC Motor Start Control Should Pay Attention To The Problem

- Oct 09, 2017-

Start-up control is a very important step in the DC motor, the starting control of the DC motor need to pay attention to the following side of the problem.

1. DC motor wiring

Power plant generally take the parallel DC motor, the armature terminals for the H1 and H2 and the windings of the terminals for the B1 and B2, and its connection is H1 and then B1 after the DC power supply positive, H2 and then B2 Connect the negative of the DC power supply.

2. Reduce the starting current of the DC motor.

In general, in addition to less than 4KW DC motor can be directly started, all the DC motor starting should be the starting current down to the rated current of the motor less than 2 times. To reduce the starting current, the general start in the motor, in the armature circuit, the string starting resistor to limit the starting current or motor starting, reduce the motor starting voltage to limit the starting current. As a result of the armature circuit in series into the starting resistance, the use of equipment is simple, economical and reliable, it is widely used.

For 220V, 11KW DC motor: DC motor rated current: Ie = 11000/220 = 50 (A), the estimated internal resistance of the rated internal pressure drop of about 8% of the rated voltage, then

DC motor internal resistance: Rs = 0.08 ⅹ 220/50 = 0.352 (Ω)

Motor starting current: IQ = 220 / Rs = 220 / 0.352 = 625 (A)

The direct starting current is more than twice the rated current of the motor, enough to damage the armature windings.

When the series-level 3Ω resistor is started, the starting current of the motor: IQ1 = 220 / (Rs + 0.352) = 220 / (3 + 0.352) = 65 (A)

The starting current can meet the start requirements, but also to reduce the current purpose.

3. Coil problem of DC contactor

For the use of DC contactor, the contactor coil should be long-term operation. And for the CZ0 series contactor, are short-term operation, so as a long time to run the contactor, the coil must not burn, so after the start of the end, should be run to contact the stringer into a about 150W, 1000Ω Of the resistance to prevent the coil burned accident.

4. Measurement of DC current

For the measurement of DC current, the general use of shunt type, in the main circuit string into 100A, 75mv shunt, shunt positive and negative connected 75mv 0 ∽ 100A ammeter.

5. Circuit diagram of DC motor starting wiring with first - order series resistance to reduce starting current.

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