alternators: does power potential need to be designed to match the intended load

[brandnewb]

I am building an DIY low rpm 3 phase alternator for a DIY VAWT.

Already it shows that the open circuit voltage can reach 150V at 60 rpm.
Once some more upgrades have been realized that voltage will most likely be far higher, maybe even doubled. But wheter that is the case or not is not really relevant to my conundrum.

Now comes the tricky bit.
I have a wind charge controller that starts relaying power to the load (in this case a 48V LifePo4 battery array consisting of 16 cells in series) at 54V and hits the brakes by shorting all 3 phases at 60V

I have a comment earlier on one of my other threads that the battery array will keep the voltage rather constant and that it is the amperage that will increase once wind speed is picking up.
I am hoping soooooo much for that to be correct.

Or is it as other sources suggest that the supplied voltage to the load will be what ever the alternator is putting out?
Increasing design complexity of the alternator and also decreasing the overall usefulness of wind power related setups in general.

[bigrockcandymountain]

It depends on the relative size of the battery and the turbine. 

If the battery is oversized compared to the turbine, it will win and the voltage will stay at the battery voltage until it is fully charged.

If the generator is way oversized, it can cause the voltage to rise fairly quickly even when the batteries are not close to full. 

You also need to make sure your generator windings are good for the amount of amps you will be making.  If the wire is too small, you'll likely burn up the generator. 

[brandnewb]

The battery array has a size of about let say 1 8th of a cubic meter. The turbine is rather large. 4m, diam 5m height.

[bigrockcandymountain]

Ok, so the thing to do some research on is the "C" rate of batteries. 

Lead acid likes about a maximum C5 rate for charging.  That means dead to full in 5 hours. 

So my 428ah 48v bank can be charged at 85.6a or 4108 watts maximum. 

Lithium might handle higher than that or it might not.  Probably not without active cooling. 

If you know the amp hour rating or kwh storage capacity of your battery, you can calculate the max charge rate pretty easy.  I'm not familiar enough with lithium to guess based on physical size. 

[SparWeb]

Already it shows that the open circuit voltage can reach 150V at 60 rpm.

Good so far.  Simple math:  with 150V open circuit at 60 rpm, then it will "cut-in" to a 54V battery at about 20 rpm.  This is suitable for a big VAWT.

I have a comment earlier on one of my other threads that the battery array will keep the voltage rather constant and that it is the amperage that will increase once wind speed is picking up.

Also good.  It will work that way as long as the battery isn't undersized, as BRCM pointed out. 
Read the stickers / stencils on the LiPO batteries and find the amp-hour capacity.  Since they're in series the amp-hours for the string is the same for each cell.

[brandnewb]

I have 16 x 3.2V 280Ah Lifepo4 cells that I intend to configure in series.

The charge rating of the cells is 0.5C and the discharge rating of the cells is 1C.

I also have a wind charge controller that starts relaying power at 54 volts and hits the brakes (shorts the 3 phases) when the voltage reaches 60 volts.

Currently I am using a 0.4mm diam wire in the alternator knowing full well that this wire is too thin. I just wanted to showboat amazing open circuit voltages at 60 rpm a bit on another forum. I am aiming to replace the wires with 1mm diam wires and calculate how many winds i'll need if the target voltage should be a bit under 60 at average wind speeds we have here on this location.

But in general I am rather happy with what you guys have told me here already. It could mean that the brakes aren't constantly being hit on rather windy days, only that the battery array will get charged faster yes?

[Adriaan Kragten]

Correct matching in between a certain generator, a certain wind turbine and a battery with a certain nominal voltage is the biggest problem in wind turbine design. You only can find the optimum number of turns per coil of the generator if you measure the generator on an accurate test rig for a large range of loaded voltages and if you know the optimum cubic line of the rotor of your wind turbine. The optimum cubic line is given by formula 8.1 of my public report KD 35. You have to use that voltage for which the Pmech-n curve of the generator is lying close to the optimum cubic line of the rotor. If this voltage isn't the same as the loaded battery voltage, you have to change the number of turns per coil. Another point is that the generator must have a certain maximum torque level which matches with the torque level of the rotor at high wind speeds. So if the generator is too small, it can be matched well with the rotor at low wind speeds but not at high wind speeds. I have tried to explain this procedure in an earlier post called "Design of a PM-generator for a wind turbine" of november 2021.

If you design a generator with a random number of turns per coil, it will have a certain open DC voltage after rectification at a certain number of turns per coil. This can easily been measured but the open voltage can't be used to determine the matching. The generator efficiency depends very much on the ratio in between the loaded voltage and the open voltage (see measurements given in my public report KD 78). You only get a high efficiency if this ratio isn't very small. If you use the generator to charge a battery, the loaded voltage is almost constant. This means that the ratio in between the loaded voltage and the open voltage is only high at rather low rotational speeds. So only at rather low rotational speeds, the generator will have a high efficiency. The efficiency will always be low at high rotational speeds even if the matching is optimal. For high efficiencies at high rotational speeds you need increase of the loaded voltage but that isn't possible for a battery load. If the wind turbine is connected to the grid by an inverter, this inverter accepts a large variation of the input voltage and so the voltage can be high at high rotational speeds resulting in a much higher effciency at high rotational speeds. 

[brandnewb]

I am happy to admit that I am not in this game to seek for maximum efficiency.

All I care about is to make a turbine that produces usable power and that is easy for everyone to copy paste.

So Adriaan, I am still not advanced enough to fully grasp your in depth comment, to which I am always grateful for of course!

Would you mind boiling it down a bit? I am looking for asnwer more along the lines of
*) no, the alternator needs to be perfectly fine tuned to your battery array. (opening up a whole world of hurt)
*) you can get away with some mismatch as the amps will do some of the finetuning while in operation.

[Adriaan Kragten]

The point is that if you don't know the optimum cubic line of your wind turbine and if you don't know the characteristics of your generator, combining both for a certain battery voltage is purley a gamble. The best thing you then can do is measuring at which wind speed the generator supplies the open battery voltage (so when the rotor is running unloaded). If this happens at a wind speed of about 3.5 m/s, it might work if the generator isn't very small with respect to the geometry of the wind turbine rotor.

It surprises me how much time, work and money people spend in building wind turbines and generators and how little time one wants to spend in aquiring the knowledge to make the proper choices. Without the knowledge given in at least my public report KD 35, it is all try and error. If you have designed something which is far away from the optimum, it always means that you have a high investment per kWh of generated energy. A poor overal efficiency makes that much more material is used and some wrong choices even make that the whole thing isn't working at all. The world has limited recources and people should not use these resources for something which ends at the rubbish dump.

[brandnewb]

Dear Adriaan, I have the utmost of respect for you and all you have done for the field.
If only I could ever be as knowledgeable as you are.

But please understand that I am on a mission, and that mission does not involve complex aspects.

It should be simple. Big turbine, Big alternator output some usefull power.

I am more than willing to debat the fine points once I have my post apocalyptic turbines spinning and producing power.

And in answer to your question why there are still people that invest blindly into a path that seems a dead end.
Well I speak for my self and in my scenario it is rather simple. Money and time is what I have in abundance. Knowledge and skills to learn more I am rather limited at. SO here is me going all in with a simple goal;

Big turbine, Big alternator => output some usefull power.

I my self find it extremely hard if not impossible to wade through the more advanced research papers and for me trying any longer does more harm than good. As in it will grind me to a halt while if I just plow through stupidly then at least I am able to get some results.

[DamonHD]

I suspect one point that is worth taking on is that *matching* the behaviour of various parts is hard to do well on the fly, and if they don't match (too big OR too little, unexpected curve shape, etc) the outcome may be relatively poor.

Rgds

Damon

[brandnewb]

Thank you all thus far for the contributions.

Luckily I am able to calculate how to wind the alternator once I have the results in on how much this upgrade I briefly mentioned earlier.
So I think I should be able to end up with an alternator that outputs a specific target open voltage at a specific rpm.

For me the only thing really important is addressing the question at hand of this thread.
*) no, the alternator needs to be perfectly fine tuned to your battery array. (opening up a whole world of hurt)
*) you can get away with some mismatch as the amps will do some of the finetuning while in operation.

[SparWeb]

Hi Brandnewb
I have some sympathy for what you say as some things are frustrating to me, too.  But I've overcome them and I am the better for it.

My take FWIW: Unless something is really wrong with someone, then they will be able to learn anything they want to.
Why, then, would they be frustrated, blocked, or had trouble in the past?
Many reasons: Bad teachers, lack of role models, bad influences, punitive experiences, and a host of other negativity that poisons intelligent thought.  I can't just wish it away, but there are a lot of people, pressures, and cultural forces that divide people between can and cannot - on no grounds that are inside the people themselves.  I just have to live with it and grit my teeth.

So it's hard to hear when you say you "can't" when everything you're building and experimenting with could be the basis for "you can", once you allow it to.  I have no idea what the barriers are that stop you - that's your personal journey.  If I can be a signpost on that path I hope it's an arrow "This Way" for you.

[Adriaan Kragten]

I have different books about the design of wind turbines in my library which can be understood only if you have a masters degree in technology. When I worked at the Wind Energy Group of the University of Technology Eindhoven from 1975 up to 1990, we gave many wind energy courses to people from developing countries. Most of those people only had a low level of technical knowledge, so all information given to those people had to be given on that level. The basics of wind energy is rather complicated but we had to explain it in the most simple way but without making elementary mistakes. This resulted in the report "Rotor design for horizontal axis wind turbines" and many of those reports were spread all over the world. The Wind Energy Group was a part of CWD, Consultancy Services Wind Energy Developing Countries which ended in 1990 because the gouvernment stopped financing it. But there was still a need for the rotor design report. So In 1999 I have spend about four months in writing everything again but now on a computer to make the report digital. I have also added a chapter about the influence of yawing and a chapter about matching. This resulted in my report KD 35: "Rotor design and matching for horizontal axis wind turbines" which is now available for free for anyone. It should be studied in combination with report KD 196 with questions and answers about KD 35. The information given in KD 35 is given on the lowest level possible to explain the aerodynamics of wind turbines. There are no differential equations so you only need some basic knowledge of algebra and energy. Basic knowledge of energy is given in my report KD 378. I have given many wind energy courses using KD 35 to people of different level and everyone finally understood the given material. It takes only one hour to read the report but if you want to understand everything, you have to answers the questions given in KD 196. This may take you some days but then you know the basics of rotor design and you can check much better if something which you find on the Internet or on You Tube is true or false. So if you find KD 35 too difficult, you simply have not spent enough time with it.

Another very importent aspect of wind turbines is safety. A safety system should limit the rotational speed and thrust at high wind speeds. Different safety systems for wind turbines are explained in my public report KD 485. Many wind turbines are designed by amateurs without any safety system and they will all be blown apart in pieces in a heavy storm. But also many commercial wind turbines have no safety system or it is claimed that the rotational speed is limited by the generator load which is certainly not fail safe. About 35 years ago I was a member of a group of about twenty people in my neighbourhood who have built their own wind turbine. None of those wind turbines except mine had an automatic working safety system. After three years almost all of them were blown into pieces. So working with wind energy and having not enough knowledge is very dangerous especially if people are living close to the wind turbine.

[brandnewb]

yes thank you all, I am really sincere with gratitude thus far.

@Sparweb, I should have found other words to state in the most polite way I know how to ask for contributors not to make things more complex then they seemingly need to be.

I can learn and do so every day. I think I remember replying to you once in where you suggested that I should not ask for hand holding and that I was proud to state that I have learned to do modeling, printing and what have we.
The nuance I am trying to apply is that I have soo much on my plate that I have to pick my battles. Or rather subjects into which dive deeper.

So It would be of sooo much help if one of you people far more versed in the field than I am to confirm if my next idea is sound or not;

I will design the alternator to output around 58 volts when spinning at an rpm that the wind at my location has on average.
The wind charge controller and the battery array it self will deal with some om the varying nature yes?
I won't be heading into a clear disaster this way?

[brandnewb]

And Stephen, You are one cool dude in my books!, Once again I really mean that. I do not do sarcasm all that much. Taking the time to log your journey publicly on your website.
Maximum respect. I will follow your signpost to that way.
Although the design choices I make will differ as the scenario regarding the intended environment are different.

Hi Brandnewb
I have some sympathy for what you say as some things are frustrating to me, too.  But I've overcome them and I am the better for it.

My take FWIW: Unless something is really wrong with someone, then they will be able to learn anything they want to.
Why, then, would they be frustrated, blocked, or had trouble in the past?
Many reasons: Bad teachers, lack of role models, bad influences, punitive experiences, and a host of other negativity that poisons intelligent thought.  I can't just wish it away, but there are a lot of people, pressures, and cultural forces that divide people between can and cannot - on no grounds that are inside the people themselves.  I just have to live with it and grit my teeth.

So it's hard to hear when you say you "can't" when everything you're building and experimenting with could be the basis for "you can", once you allow it to.  I have no idea what the barriers are that stop you - that's your personal journey.  If I can be a signpost on that path I hope it's an arrow "This Way" for you.

[SparWeb]

I will design the alternator to output around 58 volts when spinning at an rpm that the wind at my location has on average.
The wind charge controller and the battery array it self will deal with some om the varying nature yes?
I won't be heading into a clear disaster this way?

No disasters in that.  Try aiming for a bit more open-circuit voltage than 58V at your average wind speed.  You'll prefer cut-in to happen a bit sooner than that.  If the average is 10mph, then maybe aim for about 6 mph.  But when doing the windings of alternator, you aren't working directly with wind speed, yet.  You are working with RPM when winding and testing an alternator.

[brandnewb]

thank you sir!!

[brandnewb]

here is another example in where my brain capacity just fails

using the right hand rule, as common for generators, why do some designs out there go for attracting fields with a conductor running through it?



My, presumeably flawed, logic leads me to believe that this should lead to a theoretical 0 flow of electrons.

[SparWeb]

The diagram doesn't look entirely meaningful to me.  I assume the cylinder is a wire and the other blocks are magnets.  For this to make sense, the wire has to be a loop.  A segment like that doesn't do anything because it can't carry a closed-circuit current.
But if the loop just isn't shown because this is just a "section view" then OK, I get your drawing.  If that's true, then "right hand rule" only matters if you have a current in the wire, and that puts a force on the wire sideways.  The reverse works, too, so if you push the wire, you would make a current flow.

[joestue]

here is another example in where my brain capacity just fails

using the right hand rule, as common for generators, why do some designs out there go for attracting fields with a conductor running through it?

(Attachment Link)

My, presumeably flawed, logic leads me to believe that this should lead to a theoretical 0 flow of electrons.

The whole point is to get a mostly uniform field of as high a strength as possible for a given volume of space (for which the rotor spins in).

Also the field should be uniform so that the rotor core doesn't saturate in some places and not in others.

The rotor which is a loop of wire, produces an alternating voltage as it rotates, follow the right hand rule around the wire and you will find the voltage adds up.


If you take a 2 pole motor and reverse the polarity of half of the stator, you have just made a 4 pole motor with just 2 coils. The field is opposed, and squirts out the sides. There are 2 speed induction motors that do this intentionally.

In fact, you can take a 1700 rpm fan motor from a bathroom fan or something similar, and take the 4 coils which are all in series, and reconnect them for 2 in series each across from each other.

Connect 2 of them with a capacitor in series with mains ac, the other 2 coils get mains as well. The motor will spin at 3500rpm.

And burn up in a few minutes because it actually needs 60v not 120 with the new connection.

[brandnewb]

I have updated a representation of the conundrum as I agree I was a little cryptic with my earlier image.


would not this result in electron flows counter acting each other. Basically resulting in 0 net flow. In practice only little output would be the result as the system is never perfectly in balance.

It is so counter intuitive when I apply the right hand rule to see the usefulness of the attracting field arrangement.

I guess I am asking if this feels totally valid to you guys and if so I will then just accept it as a given. My mental image forming will follow suit later down the line.

EDIT: I can confirm though that attracting fields do double the field strength. I did so using my Tesla meter. Stacking these particular bar magnets does increase the field but does not double it. So essentially it would yield less bang for the buck if we stack these.
I think the stacking suggestion is mostly applicable to circular magnets if I understood it correctly.

[joestue]

the loop below, if it is able to rotate on its major axis under the magnets, would produce zero voltage.

but that's not how motors are wound.

if you continue the series of magnets to the left or right.. and were to move the loop sideways through the magnets (the loop is not rotating) it would produce voltage.

harddrive magnets are 2 poles, with a single coil of copper, current pushes the coil left or right under the magnets.

[MattM]

The electrical flow is dependent on movement of the magnets relative to the loop, and vice versa.  No movement means no relative electron displacement.  The static position it is shown would net zilch.  Move the coil or magnets along the x,y plane and viola, electrons are displaced and a magnetic field, relative to the strength of both movement and flux, forms at a perpidicular angle.  The electrons would rotate around the loop, not in a straight line but in a spiral around the center of the conductive mass of your loop.  The coil needs to isolate that electron displacement to prevent eddy currents, which is why thin wire coil is far better than a monolithic ring, when creating electrical current.

[brandnewb]

Yes!!! thank you all, I finally see it how the above would work.

I got blinded by my own setup in where there is no attracting field. So in the context of the image above there would be only magnets above OR below the coil. That mental image stayed with me for too long.

This is a wink to my self that not everything was under-exaggerated when I said I have difficulties grasping stuff ;(

Anyway, I propose a field test.

What if I wind a coil to produce 3.2 volts at almost no rpm. And directly hook up one of my LifePo4 cells to the alternator after rectification.
And let the wind do some actual spinning of this turbine.

Can we (I actually mean me of course) learn some useful stuff that way? I have enough multi meters, an oscilloscope that I barely know how to use and what have we to see what happens.

Or is that a sure way to destroy a cell?

Any tips and tricks are massively welcome.

[Adriaan Kragten]

In chapter 9 of my public report KD 341, I give two ways how it can be understood that a voltage in generated in a coil. The first way can best be used to understand voltage generation for generators with an iron core in the coil. The second way can best be used for axial flux generators with no iron in the coils. The optimum coil pattern for a 3-phase, 8-pole axial flux generator is given in figure 5 of KD 341. KD 341 can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports.

[bigrockcandymountain]

If you wind a coil to have high voltage at "almost no rpm" that will mean small wire and lots of turns.

I suspect rather than destroying the cell, you will overheat and burn the coil. 

People usually do a 1 turn coil winding test, where each coil is wound with 1 turn, and the generator is spun up to see the open voltage. It will be some very low number.  From this you can calculate the number of turns required to reach your target voltage at your desired rpm.

Once you know the number of wires in your coil, you can calculate the max diameter of the wires based on the space you have for your coils to fit in.

That is how people usually go about designing a generator. 

[Adriaan Kragten]

Knowing the open voltage for a certain number of turns per coil and a certain rotational speed is not enough. For proper matching with a certain wind turbine rotor, the winding has to be loaded like it will be used in practice. You have to measure the Pmech-n curve for this load and compare it with the optimum cubic line of the rotor. For matching see chapter 8 of my public report KD 35.

[brandnewb]

I recently found out about the midnight classic 250 MPPT charge controller.

This makes me to believe that one does not need to design the alternator (and in the meantime I would like to also include the turbine, hence forth referring to both as the setup).

If I understood the marketing correctly this would mean I can charge a 12vdc to 72vdc battery array (in my case 48vdc) with the setup outputting 48+30%vdc to 250vdc.

So no need to precisely match the generator to the battery array.

Does anyone have any thoughts on this?

[SparWeb]

It's an old saw in engineering circles now "What we can't get right in hardware, we can fix with software"...
None of which is true, just a sad reality. 

So you still need to make an alternator somewhat closely matched to the turbine, and only then adjust parameters with a MPPT controller to fine-tune.

[JW]

https://www.fieldlines.com/index.php/topic,150664.msg1060713.html#msg1060713

[JW]

https://www.fieldlines.com/index.php/topic,150664.msg1060701.html#msg1060701

[JW]

 

Does anyone have any thoughts on this?

YES its called making/completing a magnetic circuit...
 
I give up
https://www.fieldlines.com/index.php/topic,143807.msg970255.html#msg970255