Author Topic: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio  (Read 1968 times)

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brandnewb

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It has been brought up to my attention that it would help if one would use some kind of magnet to coil ratio. As to the why I am still very much in the dark but that is been ok up until now.

Now as to the loads on said alternator (BTW this is all related to a direct connection to alternator and battery as an MPPT controller should do away with all this complexities if I understood things correctly)

It is said that there is something as asynchronous loads and synchronous loads. But I fail to grasp my head around it ;(

Can one please elaborate a bit in layman's terms what will happen to an alternator / turbine if the load is not "matched" and most importantly (as that seems to be the information missing in all the sources I can find) why is that while still keeping things beginner level?

EDIT: because if there are no real objections to going for a 1 to 1 ratio, what ever the load will be for that matter, I will just go and try something near to it. I mean if things will keep charging and spining without fail then I would consider that a nice to know.

EDIT2: in other words. What would be the problem with having a nice consistent 3 phase sine wave converted to dc going into a battery?
« Last Edit: December 02, 2023, 08:24:58 AM by brandnewb »

Mary B

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #1 on: December 02, 2023, 11:57:59 AM »
You need something to divert that DC when the batteries are fully charged. Without it you cook them. Hence the MPPT charge controller or a PWM charge controller. You need a dump load fr excess power, many use a water heater with heating coils that can handle the raw DC voltage and get hot water as a side benefit.

joestue

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #2 on: December 02, 2023, 07:37:39 PM »
There are like 4 different questions here. Each has many threads already on them
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #3 on: December 03, 2023, 09:13:19 AM »
There are like 4 different questions here. Each has many threads already on them

I tried and found a lot of information excluding the why in laymans terms.
So please allow me to politly but bluntly ask you to  please humor me with a few of those examples you refer to. I for one could not find them.

Adriaan Kragten

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #4 on: December 04, 2023, 07:50:50 AM »
The first question is the ratio in between the number of poles and the number of coils. First you have to understand this for a 1-phase winding and then for a 3-phase winding.
Assume that the armature has 8 poles and that you have a 1-phase winding. Then you need four coils. Each coil has two radial legs. The two radial legs are connected to each other by an inner and an outer coil head. The coil must have such a shape that, if the left leg is opposite to a north pole, the right leg is opposite to a south pole. The voltage generated in the left leg is then in phase to the voltage generated in the right leg and both voltages are strengthening each other maximally. An 8-pole armature has the same magnetic position if it has rotated 90°. So a rotational angle of 90° corresponds to a phase angle of the generated voltage of 360°.

Next assume that you want a 3-phase winding. This means that there must be a phase angle of 120° in between the phases. This angle corresponds to a rotational angle of 30°. Assume that the three phases are called U, V and W. So the coil pattern of the coils of phase V has to be rotated 30° with respect to the coil pattern of the coils of phase U. The coil pattern of the coils of phase W has to be rotated 60° in the same direction with respect to the coil pattern of the coils of phase U. This rule is right if all coils have the same winding direction. Changing the winding direction from left hand to right hand results in a shift of the phase angle of 180°.

So you have totally 12 coils for an 8-pole generator. If you lay the four coils of phase U first, then the four coils of phase V and then the four coils of phase W, you get a 3-layers winding with a lot of crossing coil heads. Mostly the 12 coils are not laid this way. Normally one uses a 2-layers winding in which first six coils are laid in the sequence U1, V1, W1, U2, V2, W2. There are no crossing coil heads of the six coils in this first layer. Then a second layer is laid with the coils U3, V3, W3, U4, V4, W4. There are also no crossing coil heads for the six coils in this second layer

The disadvantage of a 2-layers winding is that you get crossing coil heads for the coils in the first and the second layer. So for most axial flux generators, the second layer is cancelled. So you have only one layer with the coils U1, V1, W1, U2, V2, W2. But this means that twelve possible positions for radial wires are not used. The coil figuration for a 1-layer, 3-phase winding is given in figure 9 of my report KD 341 for an 8-pole axial flux generator with rectangular magnets. The upper picture gives the ideal coil shape. The lower picture gives a shape with a larger thickness of the coil bundle. So if you have understood this explanation you can use a similar theory if the armature has more than eight poles. A 1-layer of 2-layers 3-phase winding is only possible if the number of armature poles is dividable by four, so if the number of poles is 8, 12, 16, 20 and so on.

Your question about matching can't be explained on a simple level because you must understand the rotor formulas first. Matching is explained in chapter 8 of my report KD 35 (available in English and in Dutch). Perfect matching means the the generator is loaded such that the rotor runs at its design tip speed ratio and so at the point of the Cp-lambda curve for which the Cp is maximal.

« Last Edit: December 04, 2023, 08:19:51 AM by Adriaan Kragten »

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #5 on: December 04, 2023, 11:19:32 AM »
Yes Sir!!, It is always great to hear/see you elaborate. Thank you Adriaan!

If I were to do something completely foolhardy. Like a party trick we used to do in our younger years.
And hook up a near 1 to 1 ratio'ed magnet to coil alternator with a rather large torque behind it directly to a LifePO4 (16S (48V))battery bank.

Will this merely degrade the battery life span or will things become dangerous?

EDIT: assuming there is a charge controller in between otherwise things will get dangerous even when the alternator is "matched" ;) So never directly . That is just a completely insane party trick.

EDIT2: The reason I am hammering on this is because if there is no real clear documentation on what can go wrong them I am willing to just deep dive and see. I mean what can go wrong right? ;)

MattM

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #6 on: December 05, 2023, 12:40:18 AM »
You need a controller that can dump excess loads somewhere or you may have much more excitement than intended.
« Last Edit: December 05, 2023, 06:49:37 AM by MattM »

Adriaan Kragten

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #7 on: December 05, 2023, 04:14:37 AM »
Yes Sir!!, It is always great to hear/see you elaborate. Thank you Adriaan!

If I were to do something completely foolhardy. Like a party trick we used to do in our younger years.
And hook up a near 1 to 1 ratio'ed magnet to coil alternator with a rather large torque behind it directly to a LifePO4 (16S (48V))battery bank.

Will this merely degrade the battery life span or will things become dangerous?
;)

This question isn't clear to me. What do you mean with a 1 to 1 ratio magnet to coil?

As I explained earlier, if you have a 1-phase winding, the number of coils must be half the number of armature poles for an axial flux generator with no iron in the coils. The pitch in between the right and the left leg of a coil must be the same as the pitch in between a north and a south pole. But if you have a 1-phase winding for a generator with iron cores in the coil, the number of stator poles and so the number of coils must be the same as the number of armature poles otherwise the magnetic flux won't make loops through the cores. So now you have a 1 to 1 ratio. However, such a generator will have very strong preference positions when an armature pole is just opposite to a stator pole. But as you are making an axial flux generator with no iron cores, this situation isn't relevant.

The disadvantage of a 1-phase winding is that there is a very strong pulsation of the rectified DC-current. If a battery is charged by the wind turbine and if the battery is loaded simultaniously by a constant load, it means that there is charging and discharging of the battery with a high frequency and this isn't good for the lifetime of the battery. This is one of the reasons why 3-phase generators are more common. Another reason is that you can get much more copper in the winding for a 3-phase winding than for a 1-phase winding.

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #8 on: December 05, 2023, 08:45:19 AM »
I am not done yet with MK II :( . the temperature makes it so that I need far more breaks than I would have needed with less cold weather.

Anyway. I will already give a hint of what is about to come so that one can rest assured that I am also making physical progress.

15727-0

This turbine will have guy wires of no less than 10mm diameter. The only way I saw possible to do that whilst keeping the structure freestanding was to eliminate the bottom arms.

More to follow

ADDITION:
15728-1

My fingers hurt. too cold outside

ADDITION2: And as per usual I am open to constructive criticisms. In fact the success of this whole endeavor depends on it.


« Last Edit: December 05, 2023, 09:56:38 AM by brandnewb »

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #9 on: December 05, 2023, 10:09:34 AM »
I deliberately chosen to make a new post rather than an EDIT or ADDITION.

Because otherwise this important question might go unnoticed.

So I have quite a bit of components making up the guy wire structure.

I already have a gut feeling what the weakest link is. Most likely the screws used to keep the outer most rings in place.

But since I no longer have a house to design and build that also means I no longer have a structural engineer ;(

Are there any quick guides/ online calculators that can help pin point the weakest link?

 


Mary B

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #10 on: December 05, 2023, 12:39:03 PM »
I deliberately chosen to make a new post rather than an EDIT or ADDITION.

Because otherwise this important question might go unnoticed.

So I have quite a bit of components making up the guy wire structure.

I already have a gut feeling what the weakest link is. Most likely the screws used to keep the outer most rings in place.

But since I no longer have a house to design and build that also means I no longer have a structural engineer ;(

Are there any quick guides/ online calculators that can help pin point the weakest link?

If you don't stake that base down with LONG stakes(like 3-4 feet!) it is going to flip over.

MattM

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #11 on: December 05, 2023, 09:27:50 PM »
MaryB-

He's doing top braces.  It's not flipping over.

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #12 on: December 06, 2023, 12:35:29 AM »
I am not sure what top braces are but if that means having guy wires connected to the structure at the top above the top arms then I would like to prevent having to do that because otherwise technically it would not longer be a freestanding structure.

Same goes for staking it to the ground.

I left some space on the ends of the wooden feet to stack heavy stones as counter weights. Then it will be still be a freestanding structure and it would be far easier for me to fend off jealous municipality pencil pushers should they want to have a say

But last storm of 19.1 m/s winds did make me nervous so I might end up having to abandon keeping the structure freestanding.

Adriaan Kragten

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #13 on: December 06, 2023, 03:11:00 AM »
The maximum wind speed which may occur in The Netherlands is about 35 m/s near the coast. I have measured a maximum wind speed of 25 m/s some years ago but I live inlands where the average wind speed at open terrain and at 10 m high is only about 4 m/s. The rotor thrust increases with the square of the wind speed. So if the situation is critical at about 20 m/s, it will be disastrous at 35 m/s. One of the disadvantages of VAWT's is that the thrust can't be reduced by turning the rotor out of the wind.

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #14 on: December 06, 2023, 07:35:27 AM »
Yes thank you Adriaan, You triggered in me that I should be measuring wind speed at the turbine location and not above my roof where the weather station is currently installed.

I will move it down to where the action will be so I can make proper correlations between wind speed and blade velocity.

I do have some sad news though ;(

While I am playing with my new 4 channel oscope (that is leaps and bounds more reliable than this toy I tried before) I get more reliable readings. Not at all +13V ;( only 2V so far at similar frequencies. I might come back and ask some questions about it but before I do I want to have read the whole manual.

One could argue though that this is good news, not sad.

EDIT: good news because now at least I am not lead on a wild goose chase eventually leading no where.

Also this makes me more determined to try any and all magnet configuration to make sure one can get 52V at 3m/s (I have changed from the earlier suggested 5m/s to 3m/s based on what is more likely to be the prevailing wind speed.)

Now with challenging conditions like these I must do some more deep dives. Please all rest assured it all leads to the best VAWT a simpleton can make. I hope it will be awesome.
« Last Edit: December 06, 2023, 08:45:03 AM by brandnewb »

Mary B

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #15 on: December 06, 2023, 12:13:52 PM »
The maximum wind speed which may occur in The Netherlands is about 35 m/s near the coast. I have measured a maximum wind speed of 25 m/s some years ago but I live inlands where the average wind speed at open terrain and at 10 m high is only about 4 m/s. The rotor thrust increases with the square of the wind speed. So if the situation is critical at about 20 m/s, it will be disastrous at 35 m/s. One of the disadvantages of VAWT's is that the thrust can't be reduced by turning the rotor out of the wind.

Typical winter storm I see 35 m/s... for 3-4 days, summer I can see 45+ m/s but that is a short burst of 15-30 minutes usually. There is a reason I way over build towers...

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #16 on: December 07, 2023, 02:03:34 AM »
wow. those are harsh conditions.

I am really interested to learn what wind speed readings I will get from the weather station if I attach it to the turbine. I will do that soon.

Also I will probably anchor the MK II to the ground for the time being as long as I have cups as blades. Going free standing might become an option when the air wheels are ready for service. If ever.

MattM

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #17 on: December 07, 2023, 07:11:46 AM »
And here I thought your C-channels were going to be mounted above as a cross brace.  Now I'm starting to think your buckets are going on them.  Even 18 gauge will probably twist if those are used for the arms.  They will be lighter but also not have as much strength as wood of comparable size.  And they will crack from fatigue.  The cracks will form near where they mount near the rotor.  On the other hand, if you can keep them under a constant tension then they can do well.  That is if its what I think you mean to do.

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #18 on: December 07, 2023, 07:19:23 AM »
yes sir!! constant tension. there will be no where to twist or turn to once I am done hooking all up ;)

brandnewb

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Re: 3 phase alternator: loads: manifestations of suboptimal magnet coil ratio
« Reply #19 on: December 31, 2023, 03:46:42 PM »
but to narrow it down to the question at hand.

how can we signal the title of this thread when a system is operating?

{1}cogging is one thing I know about. But I am sure there must be many more I am not aware of yet{1}

JW

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