Changeing Inrunner Motor laminations only on rotor ?

[jk1]

i was thinking about changeing the lamination thickness on a motor from 0.5mm to the smallest commonly available lamination thickness, is that 0.2mm ? but i was wondering is it possible to change this only on the rotor of an inrunner and not on the windings ?

Reason being is that i can see it easily possible to do on the rotor , but very hard or impossible on the windeings.

My question is would you still get the full reduction in eddy current losses or just half or less ?

where could i get custom made 0.2mm motor laminations made ?

 

[parabellum]

Most if not all BLDC type motors have no lamination on the rotor. Those are most popular.
Brushed motors have windings on rotor, sometimes on the stator as well , so fail again. If you want to change lamination, winding must go.

 

[jk1]

Most if not all BLDC type motors have no lamination on the rotor

My rotor looks like this,

http://endless-sphere.com/forums/viewtopic.php?f=30&t=50066

you can see a few photos down the rotor, and you can see the many thin laminations that its made off.

 

[amberwolf]

major could tell you better, but i think unless you do the windings/stator you're not gonna get much out of it.

i think the rotor lams on that tm motor are simply there to help minimize eddycurrent losses in the magnet backing/rotor.

perhaps changng those would get you a bit of improvement but i doubt it would be worth the work and cost.

it may not be worth doing for the stator/windings etiher unless you are using hte motor in conditions that cause high eddy current losses.

 

[parabellum]

Most if not all BLDC type motors have no lamination on the rotor

My rotor looks like this,

http://endless-sphere.com/forums/viewtopic.php?f=30&t=50066

you can see a few photos down the rotor, and you can see the many thin laminations that its made off.

I actually thought , this is just the simplest/cheapest way to make iron rotor without casting and magnet segmentation is the way to reduce eddy current on the rotor. Miles has the answer for sure.

 

[cycborg]

Laminations are there to reduce eddy currents, and eddy currents occur when there is a changing magnetic field. The field in the stator is due to the windings, so it changes at the commutation frequency. The field in the rotor is due to the magnets, so it is essentially constant. Therefore eddy currents are zero and there is no need for laminations. I suspect the rotor is laminated for manufacturability, as parabellum says.

That's the first-order analysis. In reality, if the winding field doesn't match the BEMF waveform, then the windings will induce time-varying fields in the rotor that will appear as ripple on top of the rotor's DC field. But the entire field in the stator is time-varying, so laminating the stator has a much greater effect on eddy-current losses than laminating the rotor.

Better start unwinding.

 

[major]

The rotor is the field for the motor. The magnets produce essentially a constant field and constant flux thru the rotor. Eddy currents are induced in conductive material by changing flux. Since the flux in the rotor never changes, there will be no eddy currents in the rotor steel and therefore no eddy current loss. Changing to thinner rotor lamination will make no difference except to increase the stacking factor which means a little less active material due to imperfect layering.

The laminations were likely used for the rotor construction for cost reasons. That material was already bought and paid for as drop from the stator punchings. Some eddy currents may be induced on the face of the magnets if they or the coating are conductive. This is due to the changing flux as seen on the magnet face by the armature teeth sweeping past as it rotates. This flux typically does not penetrate deeply and is not seen in the rotor steel.

The above is concerned with surface mounted magnets. Interior mounted magnet (IPM) rotors may have legitimate reasons to use laminations.

 

[cycborg]

Interior mounted magnet (IPM) rotors may have legitimate reasons to use laminations.

I've been waiting for an excuse to post this because it's cool, and this is as good a place as any. This is from a series of videos showing the manufacturing of the BMW i3. I've cued it up where they show the rotor fabrication, which is a laminated IPM. If you rewind a few minutes you can see the winding of the stator. Amazing automation.

http://youtu.be/1u7XiBnwPCw?t=8m10s

 

[Miles]

As has already been said, the laminations are just for ease of manufacture on this motor. In some cases, when the poles are not segmented, having a laminated rotor yoke can actually increase rotor losses.... Anyway, for sure, it's not worth altering the rotor on this one.

 

[Gab]

The above is concerned with surface mounted magnets. Interior mounted magnet (IPM) rotors may have legitimate reasons to use laminations.

Is the cyclone rotor an IPM design ?
photo of it here:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=51346

 

[Miles]

The above is concerned with surface mounted magnets. Interior mounted magnet (IPM) rotors may have legitimate reasons to use laminations.

Is the cyclone rotor an IPM design ?

Yes, it is.

Even with surface mounted magnets, there are some cases where a laminated yoke can help to reduce rotor losses.

 

[Gab]

Yes, it is.

Even with surface mounted magnets, there are some cases where a laminated yoke can help to reduce rotor losses.

What is the ratio of rotor losses vs stator losses on a Brushless IPM motor? like say you just made the rotor laminations half as thick then the stator laminations would you reduce the eddie current losses by half or 1/4 ? compared to if you changed both the rotor and stator to have the same half as thick laminations ?

 

[Miles]

There's no simple answer. If you want to do this out of curiosity, go ahead but, not with the expectation of any discernible benefit.....

edit: I looked up the cyclone motor you're referring to. It's an 8 pole, 12 teeth, double layer winding. All the air gap harmonics are in sync with the rotor so, there's nothing much to be gained by changing the rotor laminations AFAIK.

 

[larsb]

I don't agree about the general statements "there are no eddy losses in the rotor"

The changing magnetic field in the rotor is from the stator - since there is an air gap then the eddy losses are small but still there. For rotors with magnets on the outside of the rotor the losses should be mainly in the magnets, for internal magnet or countersunk magnets there will be more eddy losses also in the steel.

It could be worth changing laminations if the rotor gets heated quickly at full throttle / no load.