Electric motors

[Sandro Baptista]

Guys,

Please someone answer me for sure the following:

For very small motors the power indicated on the plate is the nominal electric power consumption of the motor or is the nominal mechanical power delivered by the motor shaft?

[mad fridgie]

Hi the power indicated is the "output shaft power" , Input power is normally indicated, indirectly by the amps

[Sandro Baptista]

Thank you.

Does that also happens with domestic electric equipment motor like vacuum cleaners, mixers, etc.?

[taz24]

Hi the power indicated is the "output shaft power" , Input power is normally indicated, indirectly by the amps


Well i did not know that :o :o

Just shows every day is a learning day :D

Thanks taz.

[goshen]

Guys,

Please someone answer me for sure the following:

For very small motors the power indicated on the plate is the nominal electric power consumption of the motor or is the nominal mechanical power delivered by the motor shaft?

Hi i disagree with mad the ratings on the motor plate are the nominal current and or watts drawn by the motor .:)will be happy to hear why u think otherwise!!

[Yuri B.]

Hello. Power rating (the rated power) of a motor - of all motors not just the common to us induction motors - is the mechanical power. But it is expected only at the rated voltage, the rated frequency, some factors also such as ambient temp should also be abided to.

[US Iceman]

The ratings indicate the maximum motor output in mechanical energy equivalent units (HP or kW). The current listed is what the motor will draw when the motor is operating at its maximum output, which is normally based on a service factor of 1.

If the connected load (to the motor) requires less energy than what the motor is capable of providing, then the current decreases, because the load is less.

[monkey spanners]

I think this is why those little shadded pole motors have two wattage ratings on them e.g. 10/38W. It does 10 watts work but takes 38W to do it.

[mad fridgie]

Hi i disagree with mad the ratings on the motor plate are the nominal current and or watts drawn by the motor .:)will be happy to hear why u think otherwise!!
You are incorrect amps are not nominal but maximum (at rated conditions)
Kw rating is maximum shaft power, if you do not need maximum power, then amps will reduce, this may not be lineal, as efficiency and PF may change.
for this reason when selectin cables,swithing gear and protection tou should always use current.

[nike123]

In case of motors, the output power (mechanical at shaft) is rated in kW while the input power (electrical, drawn from the electric grid and that includes magnetization component) has to be rated in kVA.

[Quality]

, if you do not need maximum power, then amps will reduce, this may not be lineal, as efficiency and PF may change.
.

now ya talking;)

[Sandro Baptista]

Thank you again.

So you also confirm that does that also happens with domestic electric equipment motor like vacuum cleaners, mixers, etc.?

[mad fridgie]

Thank you again.

So you also confirm that does that also happens with domestic electric equipment motor like vacuum cleaners, mixers, etc.?
I would not be so bold to say that domestic equipment for the purpose of "selling" that these rules apply (internal parts yes)
I see vacuum cleaners stating unblieverably high wattage, the moter would have to be 100% efficient, I think there is a bit of marketting spin?

[Quality]

Because domestic equipment is not normaly continuosly rated thier claimed power rating may a bit ambitous but for how long:eek:

[US Iceman]

I think part of the difference in smaller electrical devices is due to something called duty cycle. Motors can run slightly overloaded or at a full load condition for only short durations and certain intervals. These intervals give the motor or device time to cool down. It's similar to the number of allowable hot starts per hour on bigger motors.

It has something to do with motor insulation and cooling.

[goshen]

You are incorrect amps are not nominal but maximum (at rated conditions)
Kw rating is maximum shaft power, if you do not need maximum power, then amps will reduce, this may not be lineal, as efficiency and PF may change.
for this reason when selectin cables,swithing gear and protection tou should always use current.
HI i stand corrected i miss understood look at this link it explaines all;)
http://ecmweb.com/mag/electric_understanding_induction_motor/

[Frikkie]

I think part of the difference in smaller electrical devices is due to something called duty cycle. Motors can run slightly overloaded or at a full load condition for only short durations and certain intervals. These intervals give the motor or device time to cool down. It's similar to the number of allowable hot starts per hour on bigger motors.

It has something to do with motor insulation and cooling.

This would be especially true of vacuum cleaners where very large airflow through the appliance can give very efficient motor cooling.

[Sandro Baptista]

This would be especially true of vacuum cleaners where very large airflow through the appliance can give very efficient motor cooling.

So, in that case the current (A) absorbed will be higher than the nominal, indicated in the vacuum cleaner because the electric power input it will always higher than the mechanical power.