Energy harvesting using a brushless generator

MaxHeadRoom

Joined Jul 18, 2013
24,999
No magnets required on the stator, normally the stator would be laminated, but at that frequency I don't see it necessary.
And again the required demands seem trivial as already mentioned.
Max.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
No magnets required on the stator, normally the stator would be laminated, but at that frequency I don't see it necessary.
And again the required demands seem trivial as already mentioned.
Max.
I don't see a necessity for laminating the stator either, eddy currents at that frequency/power are most likely negligible. So you're saying that it's better to have a p.m. rotor? Because on the other hand, it's easier to wrap coils around individual magnets and assemble them into a circle than wrapping the coils around individual stator teeth, I think.
 

MaxHeadRoom

Joined Jul 18, 2013
24,999
I am just going by some of the construction of simple motors out there, they generate when back fed, from the Fisher-Paykel to the RC type motors, whether out runner or in runner, they are the same principle.
I figure it is easier to wind on soft iron than using magnets which I believe are not going to be as effective.
motors, but the same principle in reverse.
Max.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
I am just going by some of the construction of simple motors out there, they generate when back fed, from the Fisher-Paykel to the RC type motors, whether out runner or in runner, they are the same principle.
I figure it is easier to wind on soft iron than using magnets which I believe are not going to be as effective.
motors, but the same principle in reverse.
Max.
Which brings me to my next constraint... the generator must be what the guy in the video (who gave a very clear explanation, btw) is an inrunner. That's because the outside of the assembly that I have in mind cannot be allowed to rotate.

On the other hand, by design an assembly done by wrapping coils around magnets cannot be used as a motor. Maybe that's why I've never seen that configuration out there? Other than maybe a single p.m. magnet used as the rotor would be cheaper?
 

MaxHeadRoom

Joined Jul 18, 2013
24,999
Which brings me to my next constraint... the generator must be what the guy in the video (who gave a very clear explanation, btw) is an inrunner. That's because the outside of the assembly that I have in mind cannot be allowed to rotate.

On the other hand, by design an assembly done by wrapping coils around magnets cannot be used as a motor. Maybe that's why I've never seen that configuration out there? Other than maybe a single p.m. magnet used as the rotor would be cheaper?
You have to go back to M. Faraday's original principle, a magnet moving over a coil. Also Fleming's right hand rule.
The outrunner or inrunner is exactly the same principle when used as a generator.
Max.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
Oh, I see. This is one of those threads. One with unknown goals with ever changing parameters that needs to be guessed at? Et tu Caesar?:p:D:eek::rolleyes::)
It's me alright ... but it's actually one of those other threads :p ... in which I cannot fully disclose what I'm doing because it's work related ... :oops::(

Anyway ... my goal is actually quite simple and clear: Maximize the energy output of a compact (let's say 2" o.d by 1/2" long) brushless generator assembly working at 100 rpm, while maintaining simplicity and minimizing the number of components.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
Maybe I've been worring about the chicken and the egg all along:


“…...the magnetic field comes up to the stings there and magnetizes the strings. That’s one of the things that most people don’t understand. They figure that string is waving there and cutting the magnetic lines of force. Nuts. That isn’t it. The magnet, all it does is magnetize the string. Now you’ve got a waving magnetic field. And we have a fixed coil with a waving magnetic field to induce voltage. If you want to, take the magnet out. One you’ve magnetized your strings, it will play until the string loses it. Players think the string, the magnetic field from the magnet comes up to the string and by twisting the magnetic flux back and forth that’s what induces the voltage. That’s not what happens."
 

shortbus

Joined Sep 30, 2009
9,326
I understood this. But will not try to force anyone to use my ideas, and will only argue to a certain point. It is just like you saying the output of a reluctance sensor is AC, a quick Google will tell you it's not. Like you saying that the reluctor will get magnetized and stop working, when the same thing is happening in a BLDC or stepper or your single magnet rotor or anything using a permanent magnet and a coil of wire. Any magnetic material within the PM field will get magnetized, but they still work, because the residual magnetism is less than the PM field.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
It is just like you saying the output of a reluctance sensor is AC, a quick Google will tell you it's not.
Well, right or wrong, I'm about to find out ... and if it turns out that the thing produces dc, then it means that reality is wrong and that it will have to adjust its facts to match my views ... just kidding :D:p

Anyway, it was your idea to consider guitar pickups for my application, and I liked it. Mainly because it's easier for me to implement.

If it doesn't work as expected, then I'll definitely go back and reconsider the other proposed scenarios.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
Except #36 does not represent a BLDC/AC motor or typical Alternator.;)
Max.
No, it doesn't ... it resembles rather a circular guitar pickup ... I'm not sure exactly why, but I have a feeling that that configuration will be able to extract more power from the rotor's motion than the BLDC type ... I'm guessing that guitar pickups must obtain the largest amount of power from the vibrating string so it can later be amplified with the least amount of distortion possible.

On the other hand, I can always abandon the pickup idea and go for the BLDC. It's just that the pickup config is easier and faster for me to implement.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
I would have thought the #42 would have been easier to fabricate.
What makes you say that? o_O

Wrapping and adhering coils around individual magnets is straightforward enough. And arranging them in a circle inside a plastic casing is simple for me because I own a cnc router that can cut said casing. :cool:

On the other hand, #42's circle and teeth would have to be made from iron (which I can't route) and each coil would've to be formed separately and then installed, adjusted and adhered on each tooth.

As I said, I cannot improvise by hacking a step or brushless motor, and have to build the assembly myself from scratch.
 

shortbus

Joined Sep 30, 2009
9,326
Well, right or wrong, I'm about to find out ... and if it turns out that the thing produces dc, then it means that reality is wrong and that it will have to adjust its facts to match my views ... just kidding
It is a sine wave just not AC, because it doesn't change polarity, just goes between a peak and zero volts.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
It is a sine wave just not AC, because it doesn't change polarity, just goes between a peak and zero volts.
Ah! ... so you're saying it's an offset DC sinewave? ... very interesting ... since the device will have three pairs of coils (I intend to connect each pair in series, to boost voltage output) I'll test only one pair at a time, with one end as ground reference ... then we will know ... and if it turns out I'm right and the sinewave indeed changes polarity, you'll owe me a beer. And if I'm wrong you'll still owe me a beer for all the fun you've been having in this thread ... :D
 

MaxHeadRoom

Joined Jul 18, 2013
24,999
Ah! ... so you're saying it's an offset DC sinewave? ... very interesting ...
That is why some get confused when looking at the output of a back driven BLDC, the reason is the stator whether it is Star or delta there is no 'neutral' to reference to.
For example, when aligning the hall sensors to each winding using a 'scope, a virtual neutral is established by three resistors from each of the three windings and each of the other ends are connected together. this is the 'scope common or virtual neutral reference.
The pdf shows the output and relationship and the virtual neutral 'zero'.
Max.
 

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Thread Starter

cmartinez

Joined Jan 17, 2007
7,632
That is why some get confused when looking at the output of a back driven BLDC, the reason is the stator whether it is Star or delta there is no 'neutral' to reference to.
For example, when aligning the hall sensors to each winding using a 'scope, a virtual neutral is established by three resistors from each of the three windings and each of the other ends are connected together. this is the 'scope common or virtual neutral reference.
The pdf shows the output and relationship and the virtual neutral 'zero'.
Max.
Wait a minute ... this is what I'm beginning to think:
  • My favored setup with permanent magnets (let's call it the guitar pickup setup) will produce an offset DC sinewave because the magnetic field acting on the coils never changes direction (although it changes intensity)
  • A BLDC-like setup will produce a real AC sinewave because the magnetic field acting on each pair of coils does change direction every 180°

Am I right?
 
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