# What resistance should a DC motor have?

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## How many ohms should a DC motor have?

The meter should read a low resistance in the area from 10 to 30 ohms. If the meter reads an infinite ohms reading or an open circuit, rotate the end shaft of the motor. The meter should give various ohm readings as the motor shaft is rotated.

## How can you tell if a DC motor is bad?

Look at the DC motor’s specifications for volt ohms. Compare your reading to the voltmeter reading. If there is a difference of 10 or more ohms, there is a problem with the motor.

## What is the lifespan of a DC motor?

The brush life for medium horsepower DC motors with good commutator film with commutator surface speeds of 2,500 to 4,000 feet per minute is an estimate. The maximum life is 10,000 hours with the minimum being 2,000 to 5000 hours.

## Can you meg a DC motor?

Connect one lead of the DC motor to the megger probe and the other lead from the megger to the frame or metal case of the DC motor. Press the power button on the megger or turn the hand crank. The battery unit will take a few seconds to analyze the voltage travel and soon a reading should appear on the LCD screen.

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## What causes a DC motor to fail?

A winding failure—which is often caused by a breakdown of the winding’s insulation—will cause a short in the motor. Common causes of winding failure include high temperature, too many starts, contamination, too much current, excessive voltage and physical damage.

## How do you test a DC motor field?

The most common method used to check for shorted windings is to perform a drop test. In this test an ac voltage, normally 110 volts, is applied to the field leads. The voltage drop across each field pole is measured with a voltmeter. In a healthy motor, all voltage drops should be equal.

## How do you find the resistance of a motor?

Touch the red (positive) lead of the multimeter to the positive end of the wire windings around the motor. Touch the black (negative) lead of the multimeter to the negative end of the wire windings around the motor. The reading that appears on the multimeter screen is the resistance in ohms.

## How do you tell if an electric motor is burned out?

You should test the windings for a “short to ground” in the circuit and open or shorts in the windings. To test your motor for short to ground, you’ll need to set the multimeter to ohms and disconnect the motor from its power source. Then inspect each wire and look for infinite readings.

## What is a good megohm reading for a motor?

The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.

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## Should a motor have continuity?

The windings (all three in a three-phase motor) should read low but not zero ohms. … It will usually be low enough (under 30 Ω) for the audible continuity indicator to sound. For proper motor operation, all windings must have megohm readings to ground, i.e. to the motor enclosure.