Need help! Please!

[Danny Helms]

Hello, I'm new to green energy and I'm having some problems/questions. I'm an inventor and really haven't dabbled in green energy much until now. I have a few questions if someone could please help.

1. The biggest questions is, Do coreless Axial Flux generators cog when they're charging a battery bank or do they spin freely? I've had that question answered both ways, yes and no, so I still have no idea.

2. Can you wire several axial flux generators in series? If so, can someone give me a diagram of how to do it?

3. How do you figure the power rating of a axial flux generator?


I understand that it's aggravating dealing with newbies and I'm sorry. I've researched a lot online and I just cannot seem to find rock solid answers to these questions. A simple link to an answer will be more than appreciated! Thanks in advance!

[Rob Beckers]

Hi Danny,

1) Is a matter of how you want to define "cogging". Normally (at least from my reading) it's about a freely spinning generator. It cogs when force is needed to turn it, due to magnets lining up with the steel core in a way that makes some positions of the rotor more favorable than others. Makes it feel like the thing is binding.

When any alternator is producing power it WILL take force to turn it. That is how power is produced (takes energy input to get something out). I've not heard of cogging used in that context but could imagine some talking about the force not being the same as it makes a 360-degree turn. That would be caused by the way windings and magnets line up.

Normally axial flux alternators have just a steel backing plate that holds the magnets. There is no change in position between magnets and steel when you spin the rotor, hence no cogging in that regard.

2) I'm sure you can. Not tried it personally, but was involved in a project where each was rectified to DC and then put in series to increase the Voltage. The same can likely be done in AC too (for a 3-phase or multi-phase alternator) but I've not tried to wrap my head around it.

3) That's a moving target... Maybe best defined as "right before it melts down". :eek:

I suppose a more reasonable way is to define an efficiency that you can live with, and use that as the limit for output power (the more you try to get out of any alternator, the lower the efficiency gets due to various losses). In the case of alternators that is also very much dependent on the RPM you're spinning at.

-RoB-

[Danny Helms]

Thanks for the reply. I'm just having a hard time understanding how these generators work. I'm not very knowledgeable when it comes to electronics. I have more of a mechanical mind I guess. I found a fair amount of information on radial generators and I know they bind significantly when charging batteries. I haven't been able to find a whole lot on Axial Flux.

I'm working with a low torque source to turn these generators. There are ways to overcome that, but I think I've about pushed it as far as I can. That's the reason why I'm asking about the generator binding when it's charging. It will turn the rotor pates with the magnets attached easily, but I haven't finished the stators yet, so I have no idea if it's going to work or not. Some people say it does bind while others have said that it spins freely. I don't know what to expect. I guess I'm just expecting another hurdle.

I wish someone had more research on these generators because from what I've been able to find, it's all a guessing game. I'm using 16 gauge wire for the coils, 9 coils, 24 magnets, because, from what I understand, it will carry more amps, but produce less volts. I would love to produce a generator that gets around 600-1000 watts, but not sure if my design will do that or not. I guess if it produces electricity at all, it's a success, but I would love for the generator part to really kick out some decent power. I guess I'll just have to finish it to see. This has definitely been the hardest part of the whole project for me.

[Dave Lahar]

Hi Danny,

I would say no, axials do not have cogging, because of the the lack of iron cores as Rob’s suggested. When you short the windings is the only time they cog (usually for braking)

Regarding putting two, or more, in series it probably can be done, but wouldnt be neccessary to get 600-1000w, and would probably add, unneccessarily to the weight, cost & complexity. We have a 15’ axial that I would call a 2.5 kW turbine. We regulatly hit 4+kW

You can calculate output based on rotor dia. & match alternator design.
I would recommend you check out fieldlines forum, and also books by Hugh Piggot or “the Dans” on Otherpower.

Good luck Dave(aka ‘kitestrings’)

[Danny Helms]

Hi Dave, I wish I could say more about what I'm doing, but the short story of it all is that I'm trying to design a setup that uses several ( somewhere between 3 and 6) 12" Pancake Axial Flux generators run in series. I'm trying to get the output up to about 5-6kw by using multiple generators. I can't really use one big generator because I'm limited on torque (it's not a wind generator). I got the coils in the stator today and hopefully will get it wired up tomorrow. All of this is 3d printed, so there's no fiberglass in the stator. It all snaps together.

How much power can I expect from a 12" stator, 9 coils of 16 gauge wire (110 turns), Dual 9" rotors with 12 each, 3/4" x 1 1/2" x 1/4" N52 magnets. Should be able to turn at around 5-600 rpm. Turning around 700 rpm right now so should easily do 600. The suspense is killing me!

[Rob Beckers]

Danny, not to highjack this thread, but I would love to hear more (and see pictures!) about a 3D printed alternator! Maybe start a new thread about it?

Sounds very interesting!

-RoB-

[Danny Helms]

Sure, let me get some pictures this afternoon and I'll post them. It took a lot of work and it's really neat, but I don't mind showing it. Well, if it works, it's neat anyway. I can't show all of the pieces and how they fit together, but I can show the stater and the rotor pieces. I didn't invent those. I wish I could show the whole thing, but that's not a good idea at this point. I'll post pictures tonight. Thanks!

[Danny Helms]

This is my 3d printed Axial Flux generator. Still working on it so I'm not sure how much power it will make.

[Rob Beckers]

Very nice Danny!
Now I want to build one too...:love:

-RoB-

[Danny Helms]

Well, I got the stator all wired up last night and got everything put together. I've got to build a brace to keep the stator straight, but turning it by hand at about 220-230 rpm, I'm getting about 45-55 volts. Haven't tested the Amps yet because I have no idea how to use a multi-meter and I can't find anything on youtube that tells me how to test Amps. Braces are printing right now, so maybe tonight I can figure out how much it's going to put out. I have to say, I'm well pleased so far because I have no idea what I'm doing....lol When it first showed 36 volts, I said, "that's can't be right. I've got to be doing something wrong", but it was right. I'm thinking at full speed, this thing is going to put out a lot of power. Fingers crossed!

[Ralph Day]

A good clamp multi meter is indispensable. Clamp goes around one dc wire and reads the amps passing through the wire. And owner's manuals are handy too.

Ralph

[Danny Helms]

96 volts at 430 rpm, which is about how fast it's going to run. Still don't know the amps yet.

[Dave Lahar]

I'm not sure how thick the spacer/retainers are that are between the stator coils and the magnets, but you'll get the most power by reducing the air gap as much as possible. You also would get much more power by adding another magnet rotor on the opposite side, but I know you are planning to put multiple layers on this thing.

It is not a axial, but there is a guy named PhilB on the Back Shed forum that put several F& P alternators together on a single wind turbine. I think he called it "the beast". Might be something of use there, and he's pretty knowledgeable.


We built our axial using a individually potted stator coils. Similar to your approach it yields a very uniform wind and stator:
https://www.fieldlines.com/index.php/topic,148058.msg1026285.html#msg1026285
https://www.fieldlines.com/index.php/topic,149124.msg1038950.html#msg1038950

[Danny Helms]

I'm guesstimating that there is probably 4mm between the copper wire and that magnets. That's really as close as I could get it with 3d printing. I'm satisfied with the amount of power that it's putting out. Started on the 2nd generator now. Coils are finished.

[Bill von]

Well, I got the stator all wired up last night and got everything put together. I've got to build a brace to keep the stator straight, but turning it by hand at about 220-230 rpm, I'm getting about 45-55 volts. Haven't tested the Amps yet because I have no idea how to use a multi-meter and I can't find anything on youtube that tells me how to test Amps. Braces are printing right now, so maybe tonight I can figure out how much it's going to put out. I have to say, I'm well pleased so far because I have no idea what I'm doing....lol When it first showed 36 volts, I said, "that's can't be right. I've got to be doing something wrong", but it was right. I'm thinking at full speed, this thing is going to put out a lot of power.
A few notes.

1) If you don't know how to use a multimeter get someone local to show you. Not knowing how to use such a tool indicates a pretty deep lack of knowledge, and that's not a good position to start from when working with high voltages. I would recommend NOT learning via the Internet for safety specific items like that.

2) Voltage does not equal or imply power. Power is current times voltage, and if you get your generator working, you will need to sweep its load to find its actual output curve - and then you will want to operate near the knee of that curve.

3) Axial flux vs radial flux doesn't mean much in terms of electrical design. They both act similarly electrically. Much more important are things like winding, phase connection and synchronization. Are you getting wild AC out of them? Then you cannot directly parallel or series them. You'll need rectifiers, at which point you can parallel them. To series them you'd need to also mechanically couple all the shafts so they cannot spin at different speeds.

4) You say "I can't really use one big generator because I'm limited on torque (it's not a wind generator)." Then you are limited on power. Your power is determined by torque times RPM; you cannot "get more" out of a given prime mover by using multiple smaller generators.

[Danny Helms]

Hi Bill, and thanks for the response,

I realize that I may sound ignorant from these posts, but I'm really not. I'm just limited on what I can say. I've never used a multi-meter because I've never had a need to use one. I'm an inventor. Most of my knowledge is mechanical, not electrical, so I ask questions. That's how we learn.

You're right. I guess you could say that I'm not building a machine with multiple generators as much as I'm building a single generator with multiple rotors/stators. There is a single shaft turning the entire machine and each stator is rectified. And I understand and agree with what you're saying about Torque. Torque........well, there's just so much i can say at this point. I'll just say that I agree with you.

[Danny Helms]

"if you get your generator working, you will need to sweep its load to find its actual output curve" Could you explain this in detail please?

[Dave Lahar]

Hi Danny,

Bill has it right. You are going to want to connect to a load at some point - sooner rather than later if you are reproducing other layers as you've proposed. You can either put a balance 3-phase resistive load on it, or connect it to a battery bank, after rectifier(s), in turn with a means of loading the bank, plot the output. Spinning it up will tell you if you have the right number of turns for the desired voltage, but not much more.

You mentioned a few conflicting things earlier: spinning up around 700 rpm and producing 600-1,000w. I suspect you'll ease into it, but on a single stator/mag rotor (one unit without stacking) you probably are going to be limited by the ampacity of the single strand #16 wire; somewhere around 22 amps IIRC. My sense is that you will hit this way before 700 rpm.

You haven't really provided the voltage or application, so it is hard to offer much. To that point, I'd encourage you to consider that most of the forums you're poking at are builder/tinkerers, like yourself, with a multitude of varied experiences and skills. I doubt anyone is trying to infringe on any future patent(s). You've asked for help - freely given by contributors - but don't seem to be sharing much. Not real cool IMHO. Take that out and you will learn infinitely more.

[Danny Helms]

Hi Dave,

I understand what you're saying and I agree. I'm definitely paranoid, but it's just not a good idea to release too much information.

It looks like it's going to be running around 3-400rpm with the stators installed. I'm guessing that there is some drag between the stator and the rotors, because I was getting around 700 rpm originally when I only had the rotors installed. That's still a decent speed I think. I'm assembling the second stator today and after it's installed, I'll definitely do what you guys suggested before I go any further. Or heck, I may just stop there. I really don't need to build the generator because there are other people than can do that way better than me. This is just my curiosity pushing me to do it. I'm just interested to see how much power I can get out of it and if producing power is going to slow it down significantly. I guess I just like building things and wanted to see if I could do it.

The application of this project is merely to charge a battery bank just like a wind or solar system does.

[Dave Lahar]

So, I’ll venture a WAG at what you might see –

With 110 turns of #16. Did you weigh or measure the wire in a coil? I’d estimate that your coil resistance might be about .16 ohms. This would put your L to L at about .97; and phase resistance at .48 ohms. Let’s assume that – big variable here (as you haven’t stated the voltage) - you were tied to a 48V bank, and from your preliminary numbers were cutting in (reaching nominal 48VDC) at about 230 rpm, then:

To get output into the bank we have to be above cut-in.

Voltage is pretty much linear with respect to speed.

At 350 rpm we might have E = 73V, so the “forcing volts would be (73 -48 =) 25V. With a stator resistance of .48 ohms we should see current of (25V/.48 * 1.3 =) 40 amps, or an RMS voltage of 31 amps. This would be in the range of 1800-1900 watts, and with losses likely closer to 2500w.

The potential problem might be that at an AC line voltage of about 40VAC you would be pulling about 40 amps, and the one strand off 16# CU won’t sustain this very long. A solution might be to wind two strands in hand if space allows, or just not spin it that fast…or if you can split the load across the two stators with your current thinking.

Others, can check my math. This was just trying to ballpark based on the known parameters...and there are quite a few variables.

P.S. Did an earlier post get edited? I would have swore you were talking earlier about patents - which I reacted to - and now I don't see it.

[Bill von]

Hi Bill, and thanks for the response,

I realize that I may sound ignorant from these posts, but I'm really not. I'm just limited on what I can say. I've never used a multi-meter because I've never had a need to use one. I'm an inventor. Most of my knowledge is mechanical, not electrical, so I ask questions.
No worries, and I don't think you're ignorant. You just don't have much practical experience with electricity if you've never used a meter before. And at high voltages/powers, that's a VERY dangerous thing to try to learn.

I'd try to:

1) Get someone with experience to teach you / do it for you (best)
2) Get some formal education on it (circuits course with a lab)
3) Learn on your own on MUCH smaller motors/generators

[Bill von]

"if you get your generator working, you will need to sweep its load to find its actual output curve" Could you explain this in detail please?

Let's take a simple example.

You have a DC generator generating 100 volts. It has the capability of generating up to 100 amps when supplied with enough torque - but your prime mover is limited to 1 kilowatt.

Now suppose you measure power by measuring the open circuit voltage. You measure 100 volts. 100 volts * 0 amps = 0 watts. Hmm, that's not helpful.

So you get a resistor. Say it's 10K. Current = V/R so current =.01 amps. Now total power is 100 volts * .01 amps = 1 watt. Seems wrong to you!

So you try another resistor. This time it's 1 ohm. Current = V/R or 100 amps. But the prime mover can't supply that much torque so the generator starts to bog down. Now you measure 100 amps but only 1 volt because the generator is barely spinning. Now you are generating 100 watts. What's wrong? Why is your well designed generator giving you only 10% efficiency?

The answer is that you didn't get the load right. Another way to say this is you had an impedance mismatch. If you had a 10 ohm load, then you'd get V/R=10 amps. And the prime mover can handle that, since it's not over 1 kilowatt - so you get 100*10 amps = 1 kilowatt. (A little less due to resistance losses and the like, but you get the idea.)

So how do you know to choose 10 ohms? You can use the process above and get close. But a better way to do it is to sweep the load, from say 1 ohm to 10,000 ohms. At some point you will get peak power.

Note that there are devices out there designed to do this for you, called peak power point trackers. They are used primarily on solar power systems to match the load to the output of the panels.

[Danny Helms]

I’m following what your saying, but again, I know very little about electronics and electrical language. I follow your math, but that’s about as far as I go. That’s why I like YouTube. Show me how to do something and I get it the first time. Talk to me in a foreign language and I have no idea. I appreciate the explaination though.