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Automotive alternator rotor modification help needed...

Thread starter #1
Hello everyone. I am attempting to design a replacement rotor for an existing alternator unit. The present rotor has a total of 12 pole shoes. I would like to increase the number of poles shoes in this new design, but I'm not sure of the relationship between the number of stator slots and number of poles shoes on rotor. I don't know what determines the number of rotor pole shoes as it relates to the number of stator slots. The total number of stator slots is 72. Looking forward to this discussion. Thank you in advance.
Thread starter #3
It's not a question whether or not it is needed..... I am exploring several different techniques in an attempt to improve performance. This is merely one of them.
Thread starter #5
Thanks for your reply. Yes, this is an automotive lundell claw pole type alternator. I'm well aware of the many different ways to increase voltage output and other performance values of automotive alternators. Even though I'm not an engineer I do have a solid background in high output alternators and have been developing my own units for over 25 years. Please, if you can help me with the area I'm asking about, your help will be greatly appreciated. I'm not interested in any other methods at this time. Thank you for your help and consideration.


Well-Known Member
I'm not trying to be mean or to put you down. But if it was that simple don't you think one of the companies would be doing it? The cost of changing the 'claws' verses adding more copper would/should be very much a less expensive thing. But yet they seem to just add copper(wire gauge), and to do that they also need to modify the stator core stampings to accept the copper.

So I'm not sure where your going with this idea, what are your thoughts on doing what you propose? I'm pretty sure there is some sort of formula they use to figure out the size and number of claws/poles on the rotor verses the winding pattern of the stator. But don't know where it would be found.
Thread starter #7
Thank you for your kind words. Just to let you know, the newest alternators are doing what I am trying to accomplish. They have the engineers and the budget to figure it out..... I don't. Thank you for trying to help me but I understand everyone does not have the knowledge needed to assist me in this endeavor.


Well-Known Member
i haven't taken one of the newer ones apart, so don't know what they are like now. The last one I took apart was from a GM truck, a 2009, and it still had the same 12 claw rotor. After doing some thinking on this if they are changing the rotor pole number they have to be doing something with the stator winding pattern too. A less distributed coil pattern would be needed to work with a higher rotor pole count, and it has to still be three phases. Unless they also changed the rectifier circuit too.
Thread starter #9
I'm not going to get into the details of exactly what I'm doing and why I'm doing it on a public forum...... if you give me your email address I will give you my phone number and speak with you about this matter to see if we can move any further. Thank you. Is their private messaging in this forum?
If you are familiar with Mathworks, there is webpage which discusses a model which you can simulate it and evaluate the performance with different parameters:


Also, something that I do know is that automotive alternators are three-phase devices, and as such everything is a multiple of three. I trust you were familiar with this fact.


Well-Known Member
I also found this paper. That should cover your requirements.
That paper agrees pretty much with what I said earlier, the copper is the way to improved output, not the rotor pole count. When still working (Delphi automotive) they were play/experimenting with the different regulating- rectifying schemes the paper talks about, but their biggest push was the change to 42V for better efficiency. But you couldn't get the engineers to talk much about any of it.

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