Rotating Magnetic Field's and Inductors.

[hoptoad]

With all this talk of efficiency, I think many will appreciate the level of innovation and efficiency involved in the making of this product.


https://www.youtube.com/watch?v=9mzV7Y9B0tk

[picowatt]

That is in regards to the universal motor mods.
It must be true that the stator windings are doing 50% of the work, and the rotor is also doing 50% of the work -equal and opposites. So by removing the stator windings and replacing them with PMs, then we can say an efficiency increase of 50% has been made-if we take the motors starting efficiency as the 100% starting point, in that that was the maximum efficiency of that motor before the PMs were installed.

Tinman,

A quick read of searches related to motor efficiency indicates that this is an overly simplistic view.  Besides I²R losses, there are also iron losses, eddy current losses, brush resistance losses, cooling (fan)/windage losses and bearing/brush friction losses.

Although cheap consumer universal motors can have very poor efficiency ratings, a properly sized industrial universal motor is typically around 70% efficient.

Ignoring for now the additional sources of loss mentioned above, what are you stating the efficiency improvement would be for a 70% efficient universal motor if the stator EM's were replaced with PM's? Are you saying that the efficiency would improve by 15%?

(Also of possible interest was a paper I glanced thru that discussed additional eddy current losses produced when NdFeB magnets are used instead of ferrites.)

PW

[tinman]

Tinman,



PW

A quick read of searches related to motor efficiency indicates that this is an overly simplistic view.  Besides I²R losses, there are also iron losses, eddy current losses, brush resistance losses, cooling (fan)/windage losses and bearing/brush friction losses.

I agree with all this,but if you have a look at the losses you posted,some are removed when the stator electromagnets are replaced with ferrite or ceramic permanent magnets. Resistive losses that existed in the stator windings are now gone-iron losses that existed in the stator cores are now gone-eddy current losses from the stator cores are now gone-cooling needs are now reduced to accommodate the cooling of the rotor only. Brush friction can also be eliminated with a small redesign of the motor,but this has nothing to do with what effects the permanent magnets have had on the motor.

Although cheap consumer universal motors can have very poor efficiency ratings, a properly sized industrial universal motor is typically around 70% efficient.

And i have a 2HP permanent magnet motor that is 76% efficient--off the shelf. This is just a universal motor that has had it's stator windings replaced with permanent magnets.

Ignoring for now the additional sources of loss mentioned above, what are you stating the efficiency improvement would be for a 70% efficient universal motor if the stator EM's were replaced with PM's? Are you saying that the efficiency would improve by 15%?

Yes,and 15% would be on the low side. PM DC motors these days are reaching efficiencies of 92%+,and if one takes care with how everything is arranged,then efficiencies much higher that 92% can be reached.

(Also of possible interest was a paper I glanced thru that discussed additional eddy current losses produced when NdFeB magnets are used instead of ferrites.)

That is correct,as NdFeB magnets are made from conductive materials,and ferrite(ceramic) dose not conduct,and so no eddy currents-->or reduced to near 0. Eddy currents can also be reduced within an inductor if an external magnetic field aligns the magnetic domains prior to a current flowing through that inductor-->hence my theory on some of the input energy reduction in my spinning rotor test.

So i ask you these questions PW
1--has useful work been done,or has work been done when heat is converted into electrical or mechanical power?
2--do we or do we not convert heat into mechanical power that is added to the output of the motor,or into electrical power that is added back into the supply power when the stator electromagnets are replaced with permanent magnets?.
3--is there any other way you know of to convert the waste heat from the stator coils into either electrical or mechanical energy other than permanent magnets.
And 4--are the stator coils doing work in a universal motor?.


Brad

[picowatt]

Eddy currents can also be reduced within an inductor if an external magnetic field aligns the magnetic domains prior to a current flowing through that inductor-->hence my theory on some of the input energy reduction in my spinning rotor test.

Tinman,

I am not sure I follow what you are saying above, or can agree with it.

If an inductor has a conductive core within which eddy currents can flow, any dynamic magnetic field applied to that conductive core will produce eddy currents irregardless of its source.

That is to say, an approaching PM will also induce eddy currents in that core.

As for the rest of your post, I'll have to have a bit more coffee...

I do think you will need to consider a high resolution method for observing the acceleration, deceleration, and timing of your rotor in your "spinning rotor tests" if you intend to study this further.  I have a few ideas regarding that if you are interested.   

PW

[tinman]

Tinman,

I am not sure I follow what you are saying above, or can agree with it.

If an inductor has a conductive core within which Eddy currents can flow, any dynamic magnetic field applied to that conductive core will produce Eddy currents irregardless of its source.

That is to say, an approaching PM will also induce Eddy currents in that core.


I do think you will need to consider a high resolution method for observing the acceleration, deceleration, and timing of your rotor (as per the videos) if you intend to study this further.  I have a few ideas regarding that if you are interested.   

PW

Eddy currents--Quote: In a transformer, the magnetic flux created by the primary coil induces a current in the core. This occurs in order to oppose the change that produced the magnetic flux (Lenz's Law). The currents flowing in the core are called eddy currents. These currents produce heat, using up energy and so causing inefficiency.

So,we know that it is the magnetic flux that creates these eddy currents,so if an approaching permanent magnet of the right field orientation induces eddy currents into the core before the current starts to flow through the winding's,then once the current dose start to flow through the windings,the eddy currents have already been produced within the core from the approaching magnet--and so no electrical power is wasted in producing these eddy current's,as they already exist. I believe eddy currents are the result of the magnetic domain alignment,and our PM has already aligned these domains.

As for the rest of your post, I'll have to have a bit more coffee...

Sure,have all the coffee you like,but answer with your own thoughts,and not those biased toward an untruth that agree's with the good old book's of yesty year. They are not hard question's,and deserve a straight forward answer.

Here are the questions again,so as there is no mix up.


1--has useful work been done,or has work been done when heat is converted into electrical or mechanical power?
2--do we or do we not convert heat into mechanical power that is added to the output of the motor,or into electrical power that is added back into the supply power when the stator electromagnets are replaced with permanent magnets?.
3--is there any other way you know of to convert the waste heat from the stator coils into either electrical or mechanical energy other than permanent magnets (added to make clearer)-->where there is no loss incurred,or no work being done.
And 4--are the stator coils doing work in a universal motor?.


Brad