60x30x5mm 110KG or N45 D50-H3mm 120KG ? What is the maximum expected power?

[adrian]

I'm planning to build an alternator and i'm trying to decide between 2 magnet types:
N52 60x30x5mm 110KG and N45 D50-H3mm 120KG
The N45 D50-H3mm 120KG Disc magnet seems stronger but is about 2 times cheaper than rectangular. And i know that rectangular is better for this type of projets. So my question is, is it worth paying two times more for rectangular? I understand that stator built with Disk magnet will have a significantly bigger Diameter, this is not a problem, i can have all the parts machined pretty cheap comparing to magnets price.

To give a little more information.
I'm planning to build an alternator that has 2 rotors with 24 magnets per rotor and a 3 phase 18 coil stator for 200-300 volts.
And i have several more questions about the design and the most reasonable magnet from efficiency/price point of view
1. Does it matter if the magnet is only 3 mm thick? if it is as strong as other 10-15mm magnets?
2. What is the optimal air gap between the rotors? Optimal coil thickness? If a 3mm magnet is as strong as a 10mm magnet does it mean that air gap is the same?
3. Approximate maximum alternator power at 150-200RPM?

[electrondady1]

welcome to the forum
3mm seems  thin
the thickness of the stater is generally the same thickness as  the magnet.
the thickness of the magnets effects the flux density in the air gap.

[adrian]

welcome to the forum
3mm seems  thin
the thickness of the stater is generally the same thickness as  the magnet.
the thickness of the magnets effects the flux density in the air gap.

So i should be looking for thicker magnets. And if there are magnets from both sides (2 rotors), should stator still be as thick as one magnet or as thick as 2?

[Mary B]

As thick as one magnet typically.

[electrondady1]

adrian, you want to build an alternator but what is the alternator for.?

are you building a wind mill?  or is this  an experiment to learn how one works?
 if your building a windmill you need to decide on what size and copy the design others have built closely.
 i think there are still archives of what others have built over the last 15 years. hundreds of people have built alternators and windmills here.
 

[electrondady1]

in the 12 years since i joined, i don't recall any one using mags that are less than 1/4" thick.
thinner mags will have good flux density close to the surface but as you move away flux density declines swiftly.
the other aspect is the physical strength of the stator . when under power the coils are changing polarity constantly and there are real forces involved trying to pull the thing apart .
a stator 1/2" thick is typical.
please come back with what you have in mind
 



 

[adrian]

in the 12 years since i joined, i don't recall any one using mags that are less than 1/4" thick.
thinner mags will have good flux density close to the surface but as you move away flux density declines swiftly.
the other aspect is the physical strength of the stator . when under power the coils are changing polarity constantly and there are real forces involved trying to pull the thing apart .
a stator 1/2" thick is typical.
please come back with what you have in mind
 

I would like to build a 1-15KW vertical wind generator. Magnets will cost me most likely 75% of the price of the alternator. So i'm trying to find the most suitable magnets for this project at most reasonable price and lowest price / watt. Exact output power is not critical as long as it is in that range. I know that arc magnets are the best, then rectangular then square then probably disk if talking about he magnet form. Though, If i can get disk magnets as strong as rectangulars but 2 times cheaper, am i correct if i say that i should go for disk magnets?
Output voltage 200-600V, i might go with 3 phase 18 coils (24 magnets on each stator). I'm planning to use and MPP to maximize efficiency.
Found this calculator
https://www.kjmagnetics.com/calculator.asp
I'm deducting that let's say a 100 pounds pull force magnet 1/2 magnet thick, at 1/2 distance from magnet has almost the same pull force as and 250 pound pull force magnet that is only 1/4 thick.
I can have coils built of any size with any wire thickness and any form. I still don't know approximately how strong and what size should be the magnets for 1kw and for 10kw. I know there are many moving parts here, but approximate sizes will help me a lot to estimate the total price.

[electrondady1]

gee, that is huge .
here is a link to a 15kw vertical https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwid5LG6i6zKAhVKHR4KHaX5CsIQFgg0MAU&url=http%3A%2F%2Fwww.xindaenergy.com%2FVertical-Axis-Wind-Turbine-Generator-15kw-p91.html&usg=AFQjCNHZR1W7JoK4VU4lXcKp-nxcJQjljg&sig2=3IevUz3Y3cj-Maxj8zotdA
cost between $20,000-$40,000

i build little vertical mills as a hobby. maybe 100 watts.

[DanG]

Just like racing cars on a quarter-mile track, it is hard to beat large raw cubic inches of displacement (engine/magnet)...

Google found a european source matching your examples...

Disc volume ~6cm³ @ ₠4,34 w/ bulk purchase.
Quader volume ~9cm³ @ ₠9,90 w/ bulk purchase.

3mm Disc is 1/8" thick, 5mm Quader is 1/5" thick. Both are too thin in my opinion, to use efficiently magnets that thin the stator/rotor air-gaps would have to be near a millimeter and for a home-built the chances of stator/rotor rubbing/crashing are just too great... bearing slop, coil expansion from overheating, coil or magnet adhesive failing, foreign object (ice, magnet chips, iron filings,etc.) damage...

Consider...

Quader 60x30x10mm... volume ~18cm³ @ ₠13 w/ bulk purchase.
Disc D50 H10mm... volume ~20cm³ @ ₠13,6 w/ bulk purchase.

The time tested DanB-built low speed 3-phase alternators tried to always use 1/2" (12.7mm) or greater for many reasons...

[electrondady1]

at one point Dan was offering to build alternators for vertical mills . i have trouble accessing archives now but i think they are good for 3000 watts.

[adrian]

3mm Disc is 1/8" thick, 5mm Quader is 1/5" thick. Both are too thin in my opinion, to use efficiently magnets that thin the stator/rotor air-gaps would have to be near a millimeter and for a home-built the chances of stator/rotor rubbing/crashing are just too great... bearing slop, coil expansion from overheating, coil or magnet adhesive failing, foreign object (ice, magnet chips, iron filings,etc.) damage...

I'm pretty sure the strength of the magnet should also influence the thickness of the air gap. For example if i have 1 magnet that is N35 and another one is N52 and the're both same size, and the pull force of the N52 is 2-3 higher, then N52 should add a few extra mm to the thikness of the air gap comparing to the design that uses N35 magnets


https://www.kjmagnetics.com/calculator.asp

Using this calculator if i set the size of a Disk magnet to 2 in diamter and 1/2 thick then it's pull force at 1/2 distance is 9.28 lb for an N35 magnet. If i change magnet type to N52, then same Pull force is achieved at distance 0.63 in versus 0.5.

[adrian]

Just made the calculation and it seems that an N52 , 1in diamter 1/2 thik magnet at 1/2in distance has the same pull force as the magnet above that is 2in diameter and only 1/8 thick. From the design point of view i would have to use more wire, which means higher resistance and bigger stator diameter.
Is higher resistance in this particular case bad?

[DanG]

Don't get all fixated on pull force...  induction coils will not be a flat plane that traps/shorts free standing flux lines into the shortest path back to the magnet, what is needed is the gnarliest strength of standing lines of flux extended past the FAR side of the coils so any motion has the full depth of coils 'cutting' those flux lines and inducing voltage/current almost equally on the near and far side coil windings.

Remember you are likely needing larger wire diameter and that means thicker coils...

The latest & greatest N-values are not needed, pull or lifting force does not translate to alternator output.

How about reading some of the archived posts here in this worldbook of DIY windpower forums?

https://www.google.com/search?q=n35+vs+n42+site%3Afieldlines.com

Use the search add-on " site:fieldlines.com " then add your terms.

[adrian]

Don't get all fixated on pull force...  induction coils will not be a flat plane that traps/shorts free standing flux lines into the shortest path back to the magnet, what is needed is the gnarliest strength of standing lines of flux extended past the FAR side of the coils so any motion has the full depth of coils 'cutting' those flux lines and inducing voltage/current almost equally on the near and far side coil windings.

Remember you are likely needing larger wire diameter and that means thicker coils...

The latest & greatest N-values are not needed, pull or lifting force does not translate to alternator output.

How about reading some of the archived posts here in this worldbook of DIY windpower forums?

https://www.google.com/search?q=n35+vs+n42+site%3Afieldlines.com

Use the search add-on " site:fieldlines.com " then add your terms.

Yes, you're right, i should care more about  gnarliest strength. Thank you