# Thread: Motor question for test

1. Senior Member
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## Motor question for test

Having some issues with these

what happens when slip rings short out on motor..

50:1 480/277 transformer with a 0-1 volt meter what is the reading on secondary

What is equivalent to an overcurrent relay

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Continous and non continous equpiment is based upon?

What's the current of 10ohm on 12v battery with 90%vd ad battery

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What type of motor are they talking about using this formula. Ac or DC I say ac because DC motors do not have an efficiency

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4. ac and dc motors have eff
a dc does not have a power factor

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So DC would be the answer

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6. Originally Posted by nickelec
Continous and non continous equpiment is based upon?

What's the current of 10ohm on 12v battery with 90%vd ad battery

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the first is defined in the nec

90% voltage drop at battery?
first how much voltage is left?
R = 10
V = I R or I = V / R

7. Originally Posted by nickelec
Having some issues with these

what happens when slip rings short out on motor..

50:1 480/277 transformer with a 0-1 volt meter what is the reading on secondary

What is equivalent to an overcurrent relay

Sent from my SM-G950U using Tapatalk
Non of these make sense without context. The context may have been in previous questions, or you have left out info, but there are no simple answers to them as you have posted.

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Going off memory

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9. Originally Posted by nickelec
What type of motor are they talking about using this formula. Ac or DC I say ac because DC motors do not have an efficiency

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No motor is 100% efficient. If there was such a beast it would not produce any heat when in use. You always draw more energy from the source then what you get from the output shaft, the inefficiencies is typically friction and the wasted energy is given up as heat.

As mentioned DC motors do not have power factor, which may be your confusion here. Power factor is not so much a direct inefficiency in AC motors, but does contribute to their overall inefficiency as it does result in more losses in the supply circuit to the motor.

Most of your questions are lacking details to give good answers for them.

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Originally Posted by kwired
No motor is 100% efficient. If there was such a beast it would not produce any heat when in use. You always draw more energy from the source then what you get from the output shaft, the inefficiencies is typically friction and the wasted energy is given up as heat.

As mentioned DC motors do not have power factor, which may be your confusion here. Power factor is not so much a direct inefficiency in AC motors, but does contribute to their overall inefficiency as it does result in more losses in the supply circuit to the motor.

Most of your questions are lacking details to give good answers for them.

Plainly and simply, power factor is the actual power in watts, the integral over one cycle of the VA product, divided by the apparent power, which is the product of RMS voltage and RMS current. When voltage and current are constant the PF cannot be anything but 1.
Efficiency, on the other hand, is the mechanical output power divided by the electrical input power. (For motors anyway. For other devices, such as pumps, the definition of efficiency will be the useful work output divided by the mechanical work input. )

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