Axial Flux turbine at 10,000' with Clipper and Classic - setup questions

[wbuffetjr1]

Hello!!

I recently had an axial flux turbine built. Very frustrating process to say the least. I WISH I had the tools, skills and time to build one of these myself. Unfortunately, I do not. I also do not have a 100% grasp of the equations or electric theory behind these turbines. Some of y'all are amazing BTW!

Here's what I have:
48V 680AH battery bank, 4,000 watt AC clipper from Midnite and a Midnite Classic 250.

Stator is 15 coils of 15 gauge wire. 72 turns per coil. 40 - N42 magnets

Transmission wire is 80' of 6 gauge wire

8.2' diamater rotor

My site is at a remote location at 10,000' in the mountains. IMO we have some fantastic wind that can be downright ferocious in the Winter. I have tried to stay very conservative with this turbine and setup, but now (after a lot of reading on this site) I am afraid the 8.2' rotor may be to small for this generator and stalling. However, I am afraid the 9.2' rotor might get out of control in the Winter when no one is there. I don't need max power from this rig, consistent usable output would be nice. Hoping someone might have a similar setup to mine and some insight. The builder never discussed TSR or any of that kind of stuff with me and doesn't seem to have any first hand knowledge of setting up the wind curves in the classic. It is built very well, but now I need some help dialing it in.

It seems like what ever I set the Step One to in the wind curve the turbine has a hard time making it past that initial setting.

Also, the tail that came on the turbine is WAY to small. It currently takes a 15mph+ wind to turn the turbine into the wind. I am building a much bigger tail for it. Are there any negatives, besides early furling, to having an oversized tail??

Youtube video is up - just search for axial flux at 10,000'

[MagnetJuice]

Welcome to the Forum.

I am assuming that the size of the magnets are 2 x 1 x ½ inches. If that is not the case, can you tell us what the size is?

If you provide that information, we can estimate the output power of that alternator at different RPM's.
That would make it easier for someone here to recommend the size of the rotor.

Ed

[wbuffetjr1]

Thank you! Wonderful forum, full of info!

Yes sir, magnets were 2" x 1" x .5"

Thanks for the help!

[MagnetJuice]

Your turbine is capable of producing about 1800 Watts.

It was designed to cut-in (start charging your 48 Volts battery bank) at around 100 RPM.

Someone else here can help you with the size of the rotor. I have some knowledge about that but I don't feel comfortable giving advice in that area.

Ed

[bigrockcandymountain]

What voltage are you trying to cut in at? The nice thing about the classic is you can make pretty much any rotor work within reason.    You should be able to make your 8.2' work.

The tail size doesn't affect furling directly.  The weight though will affect furling.   Heavier will make it furl later not earlier.
 Make it about 6 sq ft or more should be good.  Mine is 9 sq ft for a 13' diameter.

Even if you have to run to 150v before cut in that is ok on the classic.  Let us know what you have programmed now and we will give you some advice. 

[bigrockcandymountain]

What was the wind speed in your youtube video?  Was it trying to charge or just freewheeling?

Good looking setup.  Hopefully we can get you sorted out. 

[wbuffetjr1]

Thanks for the input.

What approximate wind speed would equal 100 rpms?

Wind speed in the video was about 6 mph and it was just freewheeling. I started out the curve with the Step 1 at 60V and never saw voltage go over that. I moved it to 70V, then 80V and then to 100V and finally saw it make a little power at 100V. Current power curve looks like this:

Step    A    V
1         0     100
2         2     105
3         5     111
4         8     116
5         11   122
6         14   128
7         17   134
8         20   139
9         23   145
10       26   152
11       29   160
12       32   167
13       35   171
14       38   174
15       39   179
16       40   180

I arrived at this curve through a combination of recommendations from Midnite and experimentation. I feel like maybe the amps come on a little too strong? I have the Classic connected to MyMidnite and can monitor remotely. A couple times since I have been home the turbine has peaked at 100.2V and produced no amps. I know I can raise the voltage from here, but like I said I was trying to be conservative especially with me being gone for 6 weeks.

Unfortunately I only had about a week of messing with the power curve before I had to leave. In that time I didn't get as much useful experimentation done as I would like because it was taking quite the wind to even turn the turbine into the wind. PLUS it seemed like as soon as I stood the thing up the wind completely quit blowing!!!  Figures...  I am going back up for two weeks in September and plan on spending that time getting it dialed in.

Current tail is approximately 550 sq inches of 10 gauge steel. I have doubled the sq inches and used aircraft aluminum for the new tail - should be equal in weight to old tail. One cool feature the turbine has is a telescoping tail to supposedly adjust furling. Make the tail longer and it HOPEFULLY furls later. We will see what happens.

[bigrockcandymountain]

At 100 rpm the tips of an 8.2' rotor are 2576 fpm.  (8.2 × pi x 100) .

2576 x .0113636 is 29 mph tip speed. 

So at 10mph cut in your tsr is only 2.9.  That is assuming  cut in is at 100rpm.  Your builder should at least be able to tell you volts / rpm.  That would be a helpful number to know.

I would suggest you let this thing spool up to tsr4 at least before cut in.  That would be about 137 rpm at 10mph. 

I would start by upping the cutin voltage to say 130v. Do the first few steps less amps so maybe
Step 2.   1a.   135v
Step 3.    2a.   140v
Step3.      4a.    145v
Step4.      6a.     150v
Etc

Experimentation will be best.  Don't be afraid to run a high voltage.  It will be more efficient for everything along the line.  Easier on the coils in the stator, rectifier, etc. 

A larger rotor sure seems like it would work well at the rpm the generator works at.  The one you have should be fine though. 

[SparWeb]

OK
First off, at 10,000 feet elevation, you have only 75% of the air density to work with.  Any power curve based on sea level will lose 25% of its power just by your altitude.
I'll pass by a little later for more thoughts about power your 8' rotor can give you.  It's not 1800 Watts.

[MagnetJuice]

On my post above, I said:

"Your turbine is capable of producing about 1800 Watts"

I made a mistake. What I meant to say is:

Your alternator is capable of producing about 1800 Watts.

And I believe that is a correct estimate.

Ed

[MagnetJuice]

These are my calculations for the alternator OPEN VOLTAGE.



Maybe the cut-in voltage should be higher than 48.8 Volts.

Ed

[SparWeb]

Here's a rough idea of the power curves you are working with for a 8-foot rotor.
Lots of assumptions built into this one - it can vary up and down depending on a lot of things.
In the video the blades look like they have both twist and taper.  That should mean this is fairly close.



To use the graph, take a constant wind speed.  If the generator limits the turbine to turning at a certain RPM in that wind speed, then the power arriving at the rotor is matched with the power taken by the generator.

Cut-in at 100 RPM is much too slow for a 8-foot rotor.  I didn't extend the curves down below 10 mph but it looks more like 200 RPM.  This also suits my experience with my 8-foot WT, which does not suffer as much altitude effect and I still believe is stalled, yet cuts in at 160 RPM.  You really need to be cutting in at 150-200 RPM to get any useful power.

Shaft power is not electrical power. The generator wastes some energy as heat.  This is calculated as (R*I^2).  The loss to resistance isn't bad at low power, but it gets worse at higher power.  I can only guess at the resistance of your stator wiring, and note that there's an added resistance in the buried 80' wire to the tower (perfectly normal).  Let's say for the sake of argument that it's 5 ohms.  If you get 10 Amps to flow then (R*I^2) = 500 Watts lost to heat, while the output power will be about (10A * 100V) = 1000 Watts.  To drive the generator, you need 1000+500 = 1500 Watts of mechanical power at the rotor shaft.  That can only happen at...  consulting the graph...  25 mph wind.

YMMV.
It will help to measure the resistance per phase of the alternator.  If for some reason the rectifiers are at the top of the tower, and all you get is DC at the terminals you can access, then let us know and we can suggest a different way to measure system resistance.

It will also help to tell any details about the blades that you can.  I made some assumptions to get the graph above.  It's a bit "perfect" if you know what I mean.  Any number of realistic factors could reduce the available power at the rotor to drive the generator.

[wbuffetjr1]

Wow! Thanks all for the information and suggestions.

Builder didn't provide any voltage per RPM data. He did post videos measuring the resistance of each phase and they all came in at 1.7-1.8 ohm.

Just to clarify I am correct with the terminology, understanding, etc. So to raise my cut in RPM I need to raise the voltage setting for Step 1, correct? Assuming so, will raising Step 1 to the 135V that BigRock recommended get the cut in closer to 200rpm? What would y'all be comfortable with for the final step (16) voltage and amp settings? Builder says the stator can handle up to 300V?? I don't think I need that much power and like I said, I don't want to run this thing at max capacity. 

The blades are from CMS Magnets. They are the blades the builder suggested. I am assuming you guys are all familiar with them. If not, I already have the 9.2' set at my house and could post a pic of one. It sounds to me like the 9.2' set would make this thing much more productive, no?? Would bigger blades with a toned down power curve be easier on equipment? Would anyone be concerned with the Classic/Clipper not being able to keep 9.2' blades under control in a severe storm - say 50-60+mph wind?? Hopefully the furling will work properly and it won't be 100% up the the electronics. Up there I have learned to plan for ABSOLUTE worst case.

[bigrockcandymountain]

You are correct.  Raise step 0 to 130v or so. 

Those cms magnetics blades are high tsr blades so yes, we are on the right track. 

I would be comfortable with 200v for a final step, but that is up to you.  Maybe ask midnite what their clipper is good for.  I am not too sure what it has for safety circuits in it.  High voltage should not hurt anything.  All things being equal, it will reduce amps and therefore reduce heat in the stator. 

The 9.2 blade set i think would be a better match but furling would.have to be very early to avoid burning up the stator. 

[wbuffetjr1]

10-4

I know the Clipper is rated for 250V max. The Classic 250 is the same.

[SparWeb]

Yeah it's the rating of the stator to be worried about, not the Clipper.
The wire in the stator rated for 300V is good, and important, but heat loss is usually the limiting factor in an axial-flux alternator.
That's a much harder rating to determine - not something one would normally ask a custom builder, either.

Getting the MPPT dialed in for the set-up you have is a much better thing to work on now, rather than changing blades.  Maybe we can prove that bigger blades will help, but not until the power curve is optimized.  You may have a diamond in the rough, just need polish.

[kitestrings]

as soon as I stood the thing up the wind completely quit blowing!!!

Oh course, that's a more solid law than Betz limit.

Welcome to the board.  We are also using the Classics.  Our application, size, etc. is all different, but I agree that the Classic is  user friendly, and you can pretty easily try, and save alternate wind curves until you get close.  I think MS even has a tutorial video.

Check the specs, but I believe the upper limit at 48V on the Classic is 52A, so you have plenty of room there.  IIRC you also have another ~50V within their "hyperVOC", which supports Spar's thought that the alternator will be the thing you'll need to protect.

Doesn't appear you have near enough wind in the video to make any informed decision/design changes, so I'd keep experimenting.  Find the cut-in, wake it a little below that and build from there.

I'll check back when I've a bit more time, but good luck.  ~ks

[MagnetJuice]

This mystery is beginning to make sense. I believe this turbine was designed, on purpose, to ignore the low winds that the average turbine strives to get power from. It was designed to get power from the high winds that blow on those mountains.

If that is the case, the alternator was designed to be able to take the high RPM without burning up. The way to do that is by building an oversized alternator and making the gap between the magnets and the stator bigger than normal. That will make the alternator less efficient and that explains why the builder chose the 8.2 Ft blades. That is why the winds have to be blowing quite strong before cut-in. So the alternator, which could produce 1800 watts with a normal air gap, will be producing only enough to match the power produced by the smaller blades.

I calculated with a wider air gap and came up with 49 open volts at 120 RPM and 61 volts at 150 RPM.

One of the turbines from Hugh Piggott's book has 8 Ft blades and is designed with a TSR of 7 and to cut-in at a TSR of 8.2. That is at 7 MPH winds and 205 RPM. The alternator for Hugh turbine only has 24 magnets and is rated conservatively at 700 watts.

So the trick is to find the sweet spot with the Classic controller and MPPT.

I think that SparWeb is right when he says; “You may have a diamond in the rough, just need polish” But forget about trying to get 1800 Watts with those blades.

Ed

[wbuffetjr1]

Thanks again for all the help. It is much appreciated.

Actually, the builder told me over and over again this was a low wind turbine. I told him I would like to furl the thing out of the wind slightly prematurely to play it safe in my harsh conditions. Again, I think he did a decent job building it, but don't think he has the first hand knowledge of running one with a classic, TSRs, clipper, tuning wind curves, etc, etc. So thank God for this forum and you folks.

First and foremost I need to get this new tail installed. Over my last 5-6 days up there we had 10, 12, 14 mph winds but the turbine wouldn't even turn into the wind. That made experimenting difficult and was frustrating. I ended up casting a fishing line over the tail, pulling up a small rope and turning the thing into the wind myself to try to gather some data.

I can't wait to get back up there and try the new tail and new curve.

[MagnetJuice]

That's interesting. I wonder what the builder meant by “low winds”. If you tell me “we have some fantastic wind that can be downright ferocious in the Winter” I would consider 20 MPH to be low winds.

It probably would be a good idea if you talk to the builder and ask specific questions using numbers. When you say that you told him that you want the turbine to “furl slightly prematurely” that could mean different things to different people.

I think you should ask him these specific questions:

* The RPM or wind speed that the turbine should cut-in.
* At what wind speed it will start furling with the tail that you have now
* The thickness of the stator
* The width of the air gap

Maybe others here can suggest other questions to ask that are important to help troubleshoot the problem.

By the way, air gap is the distance from one magnet on one rotor to the other magnet on the opposite rotor. The stator sits in the air gap, between the two magnet rotors.

Specific answers to those questions would be good to have, to be able to troubleshoot problems.

Also, what makes you so sure that the tail is undersized? It could be something wrong with the yawing mechanism. Maybe it is snagging or it doesn't have a good washer or needs grease. I would check all that before altering the original design.

Ed

[bigrockcandymountain]

Your existing tail 550 sq inches.  How long is it? It almost seems like it should  work better than it is.   I would second the idea to grease the pivot. 

It will be good to have the larger tail though too. 

[Mary B]

Check the bearing seals, some are really tight when new and act as a brake...

[kitestrings]

I tend to agree with Ed that talking with the builder might be worthwhile.  Even if he's unfamiliar with the Classic and Clipper, he clearly had some basis for decisions.

I'd also second (third?) looking at the yaw bearing before making changes.

Lastly, I should have probably said that the HyperVOC, as I understand, it offers additional protection, where the equipment is preserved, but it does not actually operate in that range.  I don't think then that the controller will continue to operate the Clipper above 250V (250-298V range). It's kind of like pulling your head in your jacket until things clam down.  My point hasn't changed though, that it will be the turbine and not the controller that will likely fail first.  ~ks

[wbuffetjr1]

That's interesting. I wonder what the builder meant by “low winds”. If you tell me “we have some fantastic wind that can be downright ferocious in the Winter” I would consider 20 MPH to be low winds.

It probably would be a good idea if you talk to the builder and ask specific questions using numbers. When you say that you told him that you want the turbine to “furl slightly prematurely” that could mean different things to different people.

I think you should ask him these specific questions:

* The RPM or wind speed that the turbine should cut-in.
* At what wind speed it will start furling with the tail that you have now
* The thickness of the stator
* The width of the air gap

Maybe others here can suggest other questions to ask that are important to help troubleshoot the problem.

By the way, air gap is the distance from one magnet on one rotor to the other magnet on the opposite rotor. The stator sits in the air gap, between the two magnet rotors.

Specific answers to those questions would be good to have, to be able to troubleshoot problems.

Also, what makes you so sure that the tail is undersized? It could be something wrong with the yawing mechanism. Maybe it is snagging or it doesn't have a good washer or needs grease. I would check all that before altering the original design.

Ed

Ed - thanks for all the input.

The winds CAN be ferocious in the Winter, BUT we don't ALWAYS have 20mph winds. I was clear that I was thinking furl at ~25mph. Clear about trying to be conservative and think about durability/longevity. 

To be honest I am done asking the builder questions. He told me I would have to experiment with the tail/furling to figure it out. Stator is almost 1" thick. Air gap is 1/8".

There is no yaw bearing. He built a bracket that clamps to the yaw shaft. The bracket has two roller blade wheels that the flange from the turbine rides on. It works pretty slick when spinning the turbine by hand and seems easy to replace the wheels when they wear out. The yaw shaft is 2" x 1.25" mechanical tubing with an od of 2.00". That slides into a 2" schedule 40 pipe (od of 2.067") the turbine is built around. Fits like a glove.

[wbuffetjr1]

I would start by upping the cutin voltage to say 130v. Do the first few steps less amps so maybe
Step 2.   1a.   135v
Step 3.    2a.   140v
Step3.      4a.    145v
Step4.      6a.     150v
Etc

Experimentation will be best.  Don't be afraid to run a high voltage.  It will be more efficient for everything along the line.  Easier on the coils in the stator, rectifier, etc.

Folks-

I have a question about this curve. If I follow these steps for the rest of the points on the curve, I wind up with some HUGE numbers towards the end of the curve. It seems like I will be trying to pull way more power than the turbine can possibly produce. Is this normal? Should I slow the amp increases down like 1, 2, 3, 4, 5 then 7, 9, etc for example? Should step 16 be a power number the turbine can actually possibly produce or no?

[bigrockcandymountain]

Hmm i will let the folks that know axial flux generators better answer that question. 

My classic definitely has the upper steps set beyond what the turbine will produce.  That way, you have some cushion room for those really quick gusts that spin the turbine up before the furling can react.  Whether this is a good idea with an axial i don't know.

[kitestrings]

We're using two Classics, so you have to ignore the little 'wiggle' in the middle of the chart, that just helps to wake and transition load to the second one.  Our voltage is much lower; this is a 15' turbine, and we cut-in at about 92 rpm, 59 volts.  Overall though, it is lighter loading early to let it get up spinning without early stall, or constantly cycling above and below cut-in, then pretty linear, with a bit sharper curve at the upper limit.  I don't know if it helps, but this approach has worked well for us.


 

[wbuffetjr1]

What do you guys think of this??

[bigrockcandymountain]

Looks great to me.  Give it a try anyway. 

[wbuffetjr1]

Will do! Thanks BigRock!

[Boondocker]

what is the present battery voltage? and what is it set at in the classic.  Once  the batteries reach float stage,  the classic/ clipper  will hold the turbine back.  why let it  run when not necessary.
also here is a setpoint  max voltage turn-pod in the clipper to Hold back the turbine operating voltage 

bd










o

[wbuffetjr1]

48V flooded LA battery bank. Classic is set to 48V battery bank. Float Voltage is set to 55.4V. The Clipper turn pod is currently set to 200V. Will raise that setting slightly when I put in new curve.

I have the wind classic set via a relay to power a diversion load when in float. Diversion load is a 1/2HP pump. The 1/2HP pump  provides supplemental aeration to a lake. Will help keep fish alive through Winter.

[Boondocker]

 curious to know what voltage the 'air-pump' is operating?

 suggest troubleshooting one part of the system    at a time.  disconnect the diversion load, get the  classic&clipper  working first   with turbine charging batteries.

bd