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Why are brushless alternator main rotor coils much bigger than stator coils? Answered


Not my problem. You're the one who doesn't know the answer, not me.

Mate, I DESIGN brushless alternators for part of my JOB.

Then be so kind and answer are the stator coils smaller than rotor coils to minimize losses or is there some other reason?

I humbly suggest you blew your chance of a response with your rather rude attitude.

Lol, i wasn't rude. As you wish, i'll assume it's to reduce losses.

Ah a matter of opinion.

As I said thicker wire greater currant.

We all know thicker wire carries greater current but that is not an answer to my question. I asked why are there more stator coils than rotor coils, unlike the classical alternator. The asnwer is that the one in the picture is a three-phase brushless alternator.


Alternators are made with three phase stators to prevent load pulse. If they were made single phase the armature would go from no load to full load to no load as it spins. With three phase there is very little change in load.

However magnets come in two poles North and South, they use two coils instead of one to balance the armature and to keep it from vibrating. This also enables the armature to come in 2, 4, 6, and more poles.

The stator's winding's are in 3 phase construction for constant load.

So the coils will be 2 on the armature 3 on the stator.

North and South.

Or the coils will be 4 on the armature 6 on the stator.

North, South, North, and South.

Or the coils will be 6 on the armature 9 on the stator and so on.

North, South, North, South, North, and South.

Josehp, one additional question, why does it seem to be more than 6 stator coils in the photo above?

It has about 18 coils in 6 stars.

It is called a delta star configuration. This is a single star configuration, that alternator would have 6 of these in parallel giving it a smooth load and greater current.

Axial Generator c.png

Josehf, thank you for the answer. I know that 3 phase alternators are up to 50% more effiecient than single phase.

LOL, are you analfabetic or something? Read the question.

"Why are brushless alternator main rotor coils much bigger than stator coil" !

Lol, if rotor coils are bigger (4 in the pic), it necessarily implies there is more stator coils (20+ in the pic).

You said "it is impossible for the stator COILS to be smaller", which is wrong, as they are much smaller than the main rotor coils. Here is a picture. From the number of outgoing wires, you can tell multiple stator coils must be connected in parallel to act as one, otherwise regular AC current could not be delivered.


Your image translated from Turkish is called

"Image of the rotor and stator of the synchronous alternator."

and immediately followed by a block diagram again translated from Turkish

"Electrical technical demonstration of the synchronous alternator."

Look it up yourself.


What I can tell is the size of the coils is the result of the number of turns per coil and the desired current (determined by wire size resistance) that the Turkish engineers needed to make a certain strength of magnetic flux for their machine to perform as desired..

Magnetic strength like the Tesla, Weber per area or flux is a product of ampere turns in a coil. Engineers have to balance the turns, wire size, fill factor and the turn-to-turn voltage insulation to make a coil of desired magnetic strength...

This looks to be an inversion of the old "Ward-Leonard control system" picture #3 converted to a hydroelectric AC power delivery machine..

And to answer questions about why Turkish engineers needed certain coil amp turns in different portions of a dual and complex machine would probably need involvement in the design process that built it...


Firstly, that is a photo of a brushless alternator which is a synchronous machine and there was absolutely no need in pointing that out. Magnetic field "strength" of the coils or flux density measured in Teslas (kg/As²) equals amper x turns x core permeability x core area / m².

Why they use more stator coils than rotor coils remains unanswered, but i assume it is to minimize the core losses and maximize efficiency.

How does one minimize core loses in a DC coil !

I'm sad to have wasted my time..

I was clearly refering to losses in stator coils. DC powered rotor also has inductive losses, that's why it's laminated. Your problem you "lost time".

You repeat basic things like "thicker wire means more current" and "coils are multiple turns of wire" without answering my question. We all know what coil is and what an alternators is. This has nothing to do with wire gauge, which is the same for rotor and stator coils. I refer to physical dimensions of 4 rotor coils compared to 20+ stator coils in the picture above. We are talking regular brushless alternator, not some unusual machine or configuration.

Thicker wire = greater current carrying capacity.

iceng, what are you talking about, have you ever seen inside of an brushless alternator? If no then google it, it usually has 2 or 4 huge main rotor coils and 20+ small stator coils.

Maybe this will help?
Wikipedia is always good and they can use some donations too ;)