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Author Topic: Simple generator  (Read 22312 times)

Offline shantaram

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Re: Simple generator
« Reply #30 on: January 23, 2015, 06:11:12 AM »
Hi kEho, instead of building  rotating machine, you can replace p magnets with c shaped electromagnet exited with 50/60 Hz supply.
shantaram

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Re: Simple generator
« Reply #30 on: January 23, 2015, 06:11:12 AM »

Offline broli

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Re: Simple generator
« Reply #31 on: November 24, 2015, 02:44:39 PM »
Progress is still being made on this idea, I decided to pick this concept back up and finish what I started. I had ordered a custom cut toroidal core from China a while back and have most components ready for assembly.

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Offline gotoluc

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Re: Simple generator
« Reply #32 on: November 24, 2015, 09:46:28 PM »
Very cool Broli 8)

Maybe you can use my Bucking Field Reluctance Motor Design to turn your generator: https://www.youtube.com/watch?v=TeO9iM2-29o

It may be a perfect marriage ;)

Thanks for sharing

Luc

 

Offline broli

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Re: Simple generator
« Reply #33 on: November 25, 2015, 04:54:51 PM »
Thanks gotoluc, I'll have to make sure it runs first before I can let it get married :) .

Meanwhile here's an interesting thought experiment. Take a sufficiently long solenoid with a ferromagnetic core inside of it. Get two magnets near it so they attract each other and close their flux path through the core of the solenoid. Now move one of them back and forth as to periodically increase/decrease the total amount of flux the solenoid is seeing in order to induce a voltage. This will give rise to a current if allowed to flow.

Now here's is the interesting bit. How is this induced current of this (arbitrary long) solenoid counteracting the movement of the reciprocating magnet? If you played with long solenoids before you'll know that their effect on anything (even a compass) is negligible near their middle. So where is the back-force, if any, coming from that tries to counteract the movement of the magnet?


Offline gotoluc

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Re: Simple generator
« Reply #34 on: November 25, 2015, 07:15:44 PM »
Thanks gotoluc, I'll have to make sure it runs first before I can let it get married :) .

I understand ;) ... maybe later when she's ready.

Meanwhile here's an interesting thought experiment. Take a sufficiently long solenoid with a ferromagnetic core inside of it. Get two magnets near it so they attract each other and close their flux path through the core of the solenoid. Now move one of them back and forth as to periodically increase/decrease the total amount of flux the solenoid is seeing in order to induce a voltage. This will give rise to a current if allowed to flow.

Now here's is the interesting bit. How is this induced current of this (arbitrary long) solenoid counteracting the movement of the reciprocating magnet? If you played with long solenoids before you'll know that their effect on anything (even a compass) is negligible near their middle. So where is the back-force, if any, coming from that tries to counteract the movement of the magnet?

Yes, interesting things when cores get long. To bad eddy currents increase and PM flux spreads all over the core.
If you would be willing to make a video demo of it I would definitely like to see it.

Thanks for sharing

Luc

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Re: Simple generator
« Reply #34 on: November 25, 2015, 07:15:44 PM »
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Offline broli

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Re: Simple generator
« Reply #35 on: June 20, 2016, 02:39:35 PM »
The generator has been built for a while but sadly it didn't run very smooth to say the least. One of the lessons learned was that magnets can be too strong and using Neo's can be overkill in a lot of cases. I used waaay to little steel for the flux to be fully captured so the setup was leaking flux all over the place, it looked liked I was using a non ferro metal at times, the magnets were that overpowering, and causing massive eddy current on the bearings. Concerning the bearings I also learned that when the load is mainly axially you are better off using thrust bearings to avoid massive friction. Regular bearings are designed for radial loads not axial loads.

Anyway after this setback I decided to return to the fight. I settled on a relatively "cheaper" design to built. A toroidal core that is only wound for 180°. It's funny how I discovered how similar it looks to this concept:

http://overunity.com/1463/toroid-magnet-generator/#.V2fjRTVBHBw

Yet noone wondered what would happen if you only used one coil instead of both fighting each other's flux and forcing it out of the core causing it to interact with the rotating magnet. Using a single coil there should be no reason for the generated flux to escape the low reluctance core. But reason is not enough when it comes to violating established laws there we experiment.
I won't go into detail to as to why it is designed that way but it doesn't take a genius to figure it out.

In fact it's currently being built.

Offline broli

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Re: Simple generator
« Reply #36 on: June 20, 2016, 09:15:31 PM »
Here's a small update, I haven't made the whole assembly yet but out of curiosity I did a quick and dirty run just spinning it by hand.

https://www.youtube.com/watch?v=vgl0-wF2t8M

It's surprising to see the signal, it almost looks like a square wave, you don't expect that from an electric generator.

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Re: Simple generator
« Reply #36 on: June 20, 2016, 09:15:31 PM »
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Offline gyulasun

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Re: Simple generator
« Reply #37 on: June 21, 2016, 12:19:05 AM »
Hi Broli,

Thanks for the update. Do you have permeability data for the toroidal core used? Just curious, trying to understand the squarewave-like waveform. If you have an L meter, would you check coil inductance without and with the magnet in place at some position?
Does this induced waveform change when you have some kOhm resistive load across the output coil?

Gyula

Offline broli

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Re: Simple generator
« Reply #38 on: June 21, 2016, 12:54:54 AM »
The core is standard silicon steel with a strip thickness of 0.23mm. I have an L meter but atm the magnets I used are not the final ones, also the gap distance of the stator core and rotor magnets is too big now as I can't get them too close before they jump to each other. I'll be doing that when I have stator and rotor rigid.

Also I had an assumption and it looks like FEMM confirmed it, the simulation shows almost a triangle like waveform for the flux through the coil over time. This thus should give a square wave like shape for the induced voltage as the below graph shows.

This is quite interesting if you think about it because the interaction between the coil and magnet seems to be only taking place at the edges of the coil, meaning if the magnet is small enough and the disc sufficiently large the coil and magnets interact for only a few degrees and the rest of the way it keeps on changing the flux but the magnets are then so far away from the edges that they no longer interact with it.
« Last Edit: June 21, 2016, 11:47:15 AM by broli »

Offline gyulasun

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Re: Simple generator
« Reply #39 on: June 21, 2016, 05:32:00 PM »
Thanks for the details. Though I thought that saturation could not be a ruling factor in the induced waveform
but I did not think the flux changes like a triangle wave and this results in a square wave-like induced voltage waveform.

I wonder What may cause the coil interact with the magnets only at its edges. Common sense suggests
the coil cannot have definite poles at its two edges when wound onto a closed ring core. Can you explain that?

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Re: Simple generator
« Reply #39 on: June 21, 2016, 05:32:00 PM »
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Offline broli

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Re: Simple generator
« Reply #40 on: June 21, 2016, 09:18:31 PM »
Well here's a video of connecting a dc source to the coil and inspecting the rotor interaction.

https://www.youtube.com/watch?v=nPTEpe6wRNA

I also did a simulation by applying a DC current and calculating the torque all the way around. Strangely enough it seems the torque is almost constant untill the magnets cross the coil edges and then the torque flips and remains constant again. Again this is not what conventional generator does, usually you see a nice sinusoidal torque graph.

Offline gyulasun

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Re: Simple generator
« Reply #41 on: June 22, 2016, 12:48:18 AM »
Thanks for this test. It suggests thinking of some core saturation from the input 6.3 A current
which surely biases the core and probably makes the ring core magnetically asymmetric.
This is the only explanation I can think of why the rotor magnet poles align with the coil ends:
those are the places where the electromagnet poles are created.
It comes from this that at lower input current levels, say under 1 Amper or even less, the interaction
gradually disappears I think because the core cannot become magnetically asymmetric and the
magnetic poles are able to close into each other within the ring core as in any 'normal' closed
magnetic circuits without an air gap.

My observation from the video is that the 'rotor' would always want to align with the coil edges in attraction.
Should you have a ball bearing with even less friction, I think the torque would 'behave' in a more 'sinusoidal' way.
When the rotor is turned to the 12 o'clock and the 6 o'clock direction, it is magnetically the farthest position
from the coil edges and the attraction forces at the coil edges are simply not enough to influence rotation.
Have you thought of replacing the rotor with a compass and see the effect when input current is say 0.1 Amper only?
At such lower level core excitations the saturation should get to a minimum hence the asymmetry
cannot yet develop as much. With the compass 'needle' the sensitivity of your "rotor" may get increased.
Then you could increase input current too and see the behaviour.
Sorry that I dare to assume the bearing is what mainly causes the bitty rotor movement,
especially in the first half of the video,  though it works more readily in the second half of the video.



Offline lumen

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Re: Simple generator
« Reply #42 on: June 22, 2016, 03:06:52 AM »
I wonder how it would respond with the DC current and only a single magnet on the bar.
Suspecting that the magnets could be acting on the field outside the winding and not the field in the core.



Offline broli

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Re: Simple generator
« Reply #43 on: June 22, 2016, 08:26:33 AM »
gyulasun, very good point. I haven't considered saturation. I did a quick check in FEMM with sillicon steel and indeed it seems 5A is saturating the core. It's only when I go below 1A the magnetic field strength in the core goes below saturation. Attached graph shows the field strength in the core at different currents in FEMM.

Here's a repeat of the experiment with 0.5A of current instead of 5A:
https://www.youtube.com/watch?v=lnU54W_ikkY

And repeating the experiment at this low currents indeed reduces the torque considerably as you can see, but the question is whether this just a linear relation ie. 10x less current = 10x less torque?


However it might be my imagination but now the torque also seems to be only concentrated near the edges of the coil whereas previously it seemed to be uniformly around the core.

I'm currently doing a torque simulation with much higher elements count to get rid of the jitter I have been getting in the data. The current torque data indicates a non zero AVERAGE torque all the way around... ???
So I upped the accuracy by decreasing the element size in FEMM and I'm collecting data per degree instead of 5 degrees. The initial few data points show a much cleaner data distribution, there's hardly any jitter now, but it will take many hours before the complete run finishes.
« Last Edit: June 22, 2016, 11:42:52 AM by broli »

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Offline broli

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Re: Simple generator
« Reply #44 on: June 22, 2016, 02:03:53 PM »
Well the more accurate simulation is complete and as I thought the anomaly all but disappeared, the average is near zero now and the graph is almost jitter free.

However this brings us to the next subject, the torque is almost CONSTANT until it reaches the edges and then it does an instant flip....it's the exact opposite of what I thought would happen. A single pole motor/generator usually has a sinusoidal curve for it's torque vs angle graph. I added the counter torque graph based on the current torque graph and previous induced current graph.

Now let's go a step further and do some power calculation, the average counter torque seems to be 0,00165Nm at 1A output. If we want to keep the rotor spinning at 10000 RPM and extract 1A from the coil it will cost us 1.727W of mechanical power. This seems rather low :).

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Re: Simple generator
« Reply #44 on: June 22, 2016, 02:03:53 PM »

 

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