Alternator phase angle (importance of...)

May 11, 2026 Last reply: 2 months ago 4 Replies

Hello all. I have been reading a book again, things cannot go well...



I have no idea if the words I use are correct nomenclature, so if it seems I'm over explaining my question, it's rooted in a known ignorance.



A car alternator has three phases positioned at 120 degrees to each other. The negative "sweep" are also obviously at 120 degrees but 180 degrees out of phase. This I understand.



In the graph of this, the peaks and troughs are regularly spaced along the time time axis. When rectified, the peaks are all positive and seperated by 60 degrees. This I understand.



My question is: Do the stator widings have to be configured at 120 degrees?



Without changing the physical position of the stator windings, it seems that they could be wired up so each peak, when graphed, can be at 0, 60, and 120 degrees, with thhe troughs at 180, 240, and 300 degrees.



This graph leaves regular gaps between the groups of peaks and troughs, but when the generated electricity is rectified, the peaks are - like the 120 degrees-phased layout - all seperated by 60 degrees.



Is there a reason one method is used and the other isn't?



Thank you all in advance for putting up with my trivial questions!



No. Peak voltage will be at 0 degrees where the other two phases at 120 and 240 degrees.

With respect to each other, yes. In practice there are multiple pole pairs where the polarity changes multiple times each revolution.

They are usually connected in a star formation. That means the peak between windings voltage is root(3) x single (star to phase)

If the phases output in a non symmetrical way the output will not conform to 3-phase and be more akin to single phase. The efficiency would be awful.

My explanation here is nothing like the quality found in Wikipedia and other articles on 3-phase alternators. You might also be better off referring to sketches that you can upload to photo sharing sites and link here.

Thanks.

The article on wikipedia was too much for me to understand. I very much needed a simple explanation.

We seem to have overlooked something here ...

the purpose of an alternator in a car is to provide a DC supply, NOT a 3 phase supply - "efficient" or otherwise

also ... theres nothing limiting the number of stator windings to 3

No. The alternartor is a 3 or more phase AC generator. The 6 diodes and the electronics that turn it into a regulated DC supply are nor strictly part of an 'alternator'

Well obviously there is. It boils down to cost and complexity with no concomitant performance gains

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