# Generator/Alternator efficiency



## WCRiot (Nov 25, 2007)

I have some questions about how to make a generator/alternator more efficient.

Please keep this in mind when answering my questions. I do not care about the fuel consumption of the Fuel powered motor turning the "generator".
I am asking this question to try and understand alternator design.

Is the drag "rotational resistance" of the alternator related to its efficiency? If I need a more efficient alternator what would I change to increase its efficiency? (again, not worried about the drag it puts on the motor turning it).

What I am trying to figure out is. How can I make the best charging system for a car battery if I didn't care about the parasitic drag from the alternator?


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## Amberwolf (May 29, 2009)

Since efficiency is essentially defined as power out/power in, then you would want to have the least drag possible, with the most power output. It's impossible to get zero drag and still have power output, but if you could, that would be 100% efficient. 

As to the steps needed to get higher efficiency, I don't know all of them.

One of them would be to ensure as close to zero physical friction of the alternator/generator shaft bearings.

Another might be to use permanent magnets instead of coils for the rotor, and then have the stator be the pickup coils that generate the power you will then use for battery charging, etc.

Ensuring a constant speed of the generator at a particular load would also help, by taking away the necessity for power-wasting voltage regulation circuitry, because you could spin it faster the higher the load, so that the voltage always stays the same. However, the complexity to do this probably wastes as much or more energy as just having the voltage regulation on it in the first place. 

Fatter windings for less resistance would probably help, too, up to a point. 

I'm not even much of an amateur at this stuff, much less an expert, so I am sure my thinking is incomplete or even incorrect in some parts, but that's my off-the-cuff thoughts. 
________
Leather Cam


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## WCRiot (Nov 25, 2007)

I mentioned alternators rather than generators because generators are much more dependent on speed to generate their power. Being that at low speed a generator is not generating any power at all (this is one reason why you don’t see generators in cars anymore.)
So if we were looking at an alternator would the issue of maintaining a constant speed matter?

Maybe using the word efficiency was my mistake. If i wanted to design a new type of alternator that would produce more power output than today's alternator's. Would my limiting design factor be the drag the alternator produces? Because I want to develop an alternator that places more drag on the engine because it is producing more voltage.

But the drag of the alternator might yield an inefficient alternator itself? correct?


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## Amberwolf (May 29, 2009)

WCRiot said:


> So if we were looking at an alternator would the issue of maintaining a constant speed matter?


Don't know.
 


> Maybe using the word efficiency was my mistake. If i wanted to design a new type of alternator that would produce more power output than today's alternator's. Would my limiting design factor be the drag the alternator produces?


No, your limiting design factor, since you said you don't care how much drag it puts on the source of it's energy, is the size of the alternator vs the size of the vehicle it is in. You will need a larger alternator to house the larger windings/etc to generate more power, especially if you are talking about massively more power than the few hundred watts that existing ones can produce.




> Because I want to develop an alternator that places more drag on the engine because it is producing more voltage.



I think you mean "capable of producing more current", if you are trying to make something that will charge batteries faster. If you just mean to charge your entire EV's high voltage pack with it, then yes, more voltage would be correct. 
 


> But the drag of the alternator might yield an inefficient alternator itself? correct?


"Inefficient", yes, by definition. However you will be, by definition, increasing that drag to get more power out of the alternator. You have no choice.
________
MakeMeCumNow live


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