View Full Version : Can anyone help me design an axial flux alternator ?

Perry Holbrook
05-12-2018, 4:06 PM
On my list of projects is to dabble with producing some electricity with a wind turbine and a water wheel. Not wanting to generate much power, just want to power several strings of led landscaping lights.

The heart of these projects is the design and build of an alternator. I'm thinking maybe something in the 6" to 8" diameter size. I have searched a good bit and have found several videos and articles on the subject. However, I have yet to find anything that explains how the math works for an efficient design. The variables are numerous, magnet size and strength, coil wire size, number of windings per coil, anticipated rpm, clearance between magnets and coils,etc. I am hoping to find maybe a chart or a list of formulas with explanations on how the math works.

Anybody done this before or care to educate this mechanical engineer who struggles at times with electrical theory.


Pat Barry
05-12-2018, 6:22 PM
I'd look at using a car or motorcycle alternator for this. Get one from a junkyard. Just a thought

Arthur Fleming
05-12-2018, 6:29 PM
I am passing on hearsay, here, but a person that I have talked to was trying to generate some power, and said a treadmill motor was great for these applications. How accurate that is, I have no idea, just thought I would put it out there (here LOL)

Perry Holbrook
05-12-2018, 7:04 PM
Yeah, I do understand that if you spin a DC motor it will generate voltage and current. From what I have read so far, when you spin these slowly, they are marginal in producing much usable energy. If you speed it up with pulleys and belts, you lose even more efficiency, plus increasing the amount of wind speed needed to start the turbine spinning. The fun in this project is to learn something new in my old age plus I tend to add an element of art to these kind of projects. I'd like to have the alternator be part of the design, probably hidden as the hub or bearing block.


Bill Dufour
05-13-2018, 12:32 PM
I wonder if a computer case fan might be a good starting point. I think you really want a ac generator with no brushes use a rotating magnet instead of a powered armature.
Bill D.

Rod Sheridan
05-14-2018, 7:50 AM
I would want a permanent magnet alternator for low power applications, it would remove brush frictional losses.

Many motorcycles use a PM alternator, perhaps a trip to the scrap yard would be in order...............Regards, Rod.

Steve Rozmiarek
05-14-2018, 8:43 AM
I've never heard an alternator called and "axial flux", what does that term mean?

Perry Holbrook
05-14-2018, 6:28 PM
I used axial flux alternator in the title, hoping it would catch the attention of someone who knows what they are. Looks like I'm not the only one that has never heard of these. Basically you wind coils using magnet wire of a determined gauge with a calculated number of windings. You make a calculated number of these coils and embed them in resin in the form of a doughnut of calculated size. On the outside of the doughnut you make another doughnut shape of permanent magnets, again the number of magnets and their strength must be calculated. The outside ring of magnets rotate around the stationary coil windings, generating a voltage and current that is determined by the selections of wire, magnets, coil size and number, etc.

Apparently it's really the only way to build small generators using wind or water if you want any kind of efficiency. It also allows a way to use the energy generator as part of the artist design of the project.

If you want to see some of these that others have built, you can find them on U tube. I just can't find anything on how to make all the above mentioned calculations, to get a design put together. Still hoping someone on here has already figured this out.


Steve Rozmiarek
05-15-2018, 8:55 AM
I googled it after reading your response Perry, and it does look like an interesting project! I bet there are a few folks on here who have the electrical engineering background to help you out. My ham fisted approach would involve trial and error, many different configurations, possible shock, and probably a fire...

Frank Pratt
05-15-2018, 9:21 AM
If you want to see some of these that others have built, you can find them on U tube.


Great! I can see half my day being wasted now.

Perry Holbrook
05-15-2018, 12:10 PM
Due to the cost of the magnets, trial and error is my plan C.