Renewable Energy Questions/Discussion > Wind and Hydro

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

(1/3) > >>

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 :D

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.

Navigation

[0] Message Index

[#] Next page