Split, How magnets and volumes affect output --- Induction Motors for Wind

[m12ax7]

--Mod edit--
This deserves its own thread, as it can and does include some very beneficial information on the subject


I'd like to bring this thread back to subject (just for a little bit).
I see the thread title as having two separate issues (with their own sub-groups)

Using an induction motor, unmodified as a alternator or machining the rotor down and adding magnets to the rotor. Sub-groups, rewiring stator and or skewing the stators lamination's.

Zubbly of course went all out and wrote the book (wish I had a copy).
I recall that he had discussed both magnetic area and volume (cubic inches) VS. theoretical power out.

I had e-mailed Zubbly a question about the "estimated" magnetic volume on one of my servo motors and it's "name plate" KW rating.  Sad to say that Zubbly never had a chance to follow up on my inquiry.

Getting to the crux of my post here,  my servo motor is rated at 8.5KW (46NM) and I've estimated the total magnetic surface area at 94.5sq in. and it's total mass is (also estimated) 8.86 cubic inches.

This servo, when compared to some of the motor conversions I've seen posted has "much MORE" magnetic surface area and "much LESS" magnetic mass (cubic inches).   Although I haven't measured I believe that this servo has much less "air gap".

I believe that this is accomplished by using "many smaller" magnets that fit around the rotors circumference and conform to it's arc.  Which also allows the rotor to have about a 95% magnetic (coverage) surface area.

There is a question here and I'm NOT sure how to ask,  So I'm looking for more of a "general" discussion  about magnetic area vs. volume vs. air gap in a motor conversion and possible power out.  And,  how might it compare to a Servo motor (which in my mind is a manufactured induction motor conversion).

ax7

Mark

[oztules]

Mark,
There are too many variables... magnet strength to name the first..... plus the volume is irrelevant for your questions of what will it make.

This is simple and complex.... If you measure the rpm/volt, you will get the idea of what sized prop MAY suit.... because the next question will also dictate that.

If you know the resistance of the stator windings, and the rpm/volt you can get a very good idea on output, and even draw a therotical power curve


Now the IF..... theres always an IF isn't there.

For an axial thats all we need.... for a conversion/ stepper/ servo we will be current limited by the armature reactance.... and that will dictate the upper limit of current... not power.

The upper power limit will be the current limit amount x the max operating volts. Remember, if you get lots of volts at too low rpm, you can use a buck mppt, or a transformer, to get the voltage you want at higher current than the servo can deliver. It is regulated by the AMP TURNS.... not by the rpm or volts.

Also, the sparse population of the rotor of conversions verses the total coverage of a commercial servo will skew the figures Zubbly worked with.... he also said they were very rubbery as too many variables come into it.. but I believe he had a very rough rule of thumb... but can't recall the number, mostly because I felt it was near useless except to get a slightly less than wild estimation... and that did not take into account the armature reaction, which is the single biggest blocker to more power with them at any max rpm your prop will do.

So get the Voc at a particular rpm ( any) and you can draw the voltage graph, and then short the windings and see what the max current is. Then you have everything you need.



....................oztules

[m12ax7]

Thanks Oztules for the reply.

My location pretty much rules out any type of wind turbine, I'm in a river valley (remember the river?).   

If any thing,  I (CURRENTLY) envision something like whats shown here,  lower right hand image.

http://www.gcktechnology.com/GCK/pg2.html

Of course,  such an installation eliminates many obstacles.  No worries about cogging,  no worries about tower height, no worries about furling and I'm sure you could come up with a few others.

I'm also thinking of "trying" to drive this servo with my Kubota compact tractor (18 hp diesel) off it's PTO.   But I'll wait for warmer weather.

[oztules]

In that case (water) you can transform up as well

On the Kobota, I cam see transformers in the mix too. You have loads of torque, and rpm. If current limit kicks in too soon, just push up rpm, and transform to lower voltages.



................oztules

[m12ax7]

I see that the link I posted doesn't take you to the right page.

Click on the link and then click on articles and then select "Edison Patents Awards Articles"   then look at the lower right hand corner.

[oztules]

we talked of this 2006.... it's 2012.


I ...Wont be really impressed until you actually do something with this.... (and I wouldn't know where to start I might add in all honesty)


...................oztules

[bvan1941]

oztoules, m12ax7

Gents this is a graph of a Fanuc Servo plotting: RPM'S - VOLTS - AMPS - WATTS (3X) - WATTS (SINGLE PHASE)

Official Specs:     3.1KW -  2000RPM'S - 146V -21A

I computed that the (single phase) resistance /impedance to be: 7.1 Ohms  (146V (divided by) 21A

Using that information I plotted the graph. I suspect that the discussion above does apply here! When I'm able to use actual data I will plot that against the computed graph I've attached.

I was wondering if you all could look at my figures and give your inputs as to the validity for these numbers. I don't have very
"thin skin,"  I'm more interested in finding knowledge and building a truth table for these Servos I have.
Thanks,
Bill

PS: Am trying to learn how to post pixs here.
If this doesn't work----tell me
 

[bvan1941]

PS: I just checked my computation for the single phase resistance again and came up with 6.95 Ohms &%$#@ !! Have no idea how I came up with 7.1 Ohms at this point !!
Bill

[oztules]

I don't have a motor like that to compare Bill..... but looking at the structure, your resistance is not your impedance with this kind of motor. For an axial, it is good enough, but with tight airgaps, that will no longer be the case. You have in fact got synchronous impedance to worry about... not resistance.

...and the synchronous impedance will involve the resistance in the stator, and the frequency reactance of the stator at x rpm, and the amp turns in the stator trying to mess up the rotor field....

That makes a power graph very hard to guess at, unless you have a history with a certain type of motor, and thats called experience.

From the theoretical standpoint, it is just too hard to guess at the flux, ampturns,stauration..etc...... in short, it's all up in the air. I would not attempt to guess. It needs a simple bench test, and plot the figures. You may end up with a simple rule of thumb.... but I'm not that smart from here.




.........oztules

[bvan1941]

oztules,
Thanks for the reply. I'm putting this forth as a "trial horse," so that we might learn from the supposed theory against actual experience.  As I progress, I'll try posting some actual figures. I do want to learn what you were explaining to m112ax7, especially
about frequency reactance and stator impedance as it affects the max current available and ultimately power.
Bill

[ghurd]

Zubbly estimated the max power output at 150W per cubic inch of neo in his style of conversion.

He thought it could go up to about 175W per cubic inch with much more effort, but the gain would not be worth the effort and possible problems.  Not worth chasing that last bit of power because of the extra work.

Keep in mind, he knew the realistic air gap, the surface area of each of the neos he would use, reductions due to a flat neo in a cylinder, how tight they could be reasonably packed in, etc.  So he knew how thick the neo should be.
That, plus he was Zubbly, let him estimate power per cubic inch.

I often wondered if the impedance in a Zubbly style conversion would be less than a servo motor because of the coil shape.
Zubbly's were basically square-ish coils.
Servo motor coils are very long and very narrow (at least the ones I had appart were), and Mr. Flux says thats bad on several levels.

Transformer coils are square.
I never saw a transformer coil 1/4" wide by 5" long... if you know what I mean.
G-