Weight a minute - tail weight suggestions

[Dave B]

 I've been running my new 48 volt stator now on my 16' machine through some pretty good winds. As I suspected and planned for it is stalling (alternator overpowering the blades) just above 600-700 watts @ approx. 12-15 mph then will fully furl. With the batteries 90% or better I have seen at best slightly over 1KW in gusts before the furling catches up. With lower SOC it will of course stall a bit earlier. It is furling properly in sustained winds of 15+ mph and not just appearing to, I am familiar with the difference. My tail boom is 8' from tip back edge of tail to hinge. The hinge angle is slightly less (less steep) by a couple degrees than the "book" version suggests.

 I am quite certain that adding just a bit of weight to the tail is the way to go to tweak this up slightly and I don't really have a clue as to what would be a safe place to start. I hold nobody responsible but I am just asking for anyone who has experimented similar with weighting the tail to delay furling. I'm thinking as little as a pound at the very end could make a significant difference. Any Stories and thoughts on this are much appreciated.  Dave B. 

[just-doug]

a slide mount on the tail boom with pinch bolts  and threaded mounting holes so i can bolt various weights to the mount is how I'm going to do it.this way the weight and its center of gravity can be tuned with out having to build a whole new tail each time.

[Dave B]

Just an update. I lowered my machine and added washers for weight to the mounting bolt(s) for the tail. I am going to get an exact weight from adding up a few remaining washers of the same. They are stainless and a total of 18 washers. These are the thin fender washers but a couple inches in diameter. 9 at the very end of the boom and 3 each evened out for 3 more of the mounting bolts. Pulled it right back up again and it's ready to log more data. We are supposed to get some decent wind tomorrow, if so I'll be able to know exactly the change it made, if much at all. It's easy to go beyond safe when dealing with furling. Tweak a little at a time with plenty of observation time between changes, sure beats the self destruct mode. Updates to follow.  Dave B. 

I've been running my new 48 volt stator now on my 16' machine through some pretty good winds. As I suspected and planned for it is stalling (alternator overpowering the blades) just above 600-700 watts @ approx. 12-15 mph then will fully furl. With the batteries 90% or better I have seen at best slightly over 1KW in gusts before the furling catches up. With lower SOC it will of course stall a bit earlier. It is furling properly in sustained winds of 15+ mph and not just appearing to, I am familiar with the difference. My tail boom is 8' from tip back edge of tail to hinge. The hinge angle is slightly less (less steep) by a couple degrees than the "book" version suggests.

 I am quite certain that adding just a bit of weight to the tail is the way to go to tweak this up slightly and I don't really have a clue as to what would be a safe place to start. I hold nobody responsible but I am just asking for anyone who has experimented similar with weighting the tail to delay furling. I'm thinking as little as a pound at the very end could make a significant difference. Any Stories and thoughts on this are much appreciated.  Dave B. 

[Dave B]

We got some decent wind today compliments of left over Irene. I have confirmed that I have successfully turned my machine into a stall limited, well controlled, low rpm decent charger for up to about 15 mph winds. Adding the weight to the tail significantly helped to raise the fully furled wind speed mph but the new stator (with it's current air gap) continues to overpower the blades keeping them stalled and so far the output limited to about 1KW. I am going to watch this close now for different battery SOC vs. output at different wind speeds. Adding just that amount of tail weight really changed things, now it's time again to figure it all out. Fun stuff,  Dave B.

[Flux]

Be careful, this mode of operating is tame and quiet and easy on the blades but you are using stall control with a bit of back up from furling. If you add too much tail weight you may break out of stall at some point and it will run away and the furling wind speed will be above the alternator capability if you get a long sustained burst of wind.

If you must stick with stall control I think you will have to forget the big power in high winds or risk a burn out. Good power in 15 mph winds should give you most of the power you need. If you want much more I would reduce the tail weight and add some resistance or increase the air gap and get the thing to furl as the main method of control and not rely on stall. Stall operation needs special blades and I doubt yours will react that way.

I have never run machines hard stalled but it seems from comments here it is fine as long as long as your back up furling takes over when the alternator is in risk of loosing control, if you get out of hard stallbefore the control is mainly from furling and there is sustained wind it seems to result in melt down but this may be partly confused by the fact that some people really cant tell furling from a bent tail. If you are careful and do things in controlled steps you may be ok, I cant' remember if you have some additional means of stopping it in high wind but shorting the alternator is no use if you break out of stall, it will make burn out absolutely certain and it would be better to leave it. If you have a brake you can do your experiments safely as long as it is not left unattended before you have sorted it out.

At present you seem to be holding power in high wind , if you reach a state where power rises then watch out, if the main control is furling the power will drop as it goes into furl but I don't think you will get that if you are using hard stall.

You are also using different blades and they may have even more tendency to break a machine out of stall.

Flux

[Dave B]

Flux,

  I have an intimate relationship with this machine and I appreciate your input. Baby steps and one variable at a time with plenty of observation in between any changes is the way to learn about what you have. I was getting a bit tired of what I consider fast running machines and the slow reacting iffy at best furling tail. This along with the noise prompted me to wind another stator that I knew I could test the lower limits of the blades with and that's where I am now.

 The custom load controller I have designed has been tested successfully very hard for overspeed protection as a backup to or in conjunction with the furling so I am very comfident of my testing so far. The added weight to the tail helped with eliminating the wishy washy spilling of air in the 10-15 mph range (my hinge angle is less than most) and yet still allows the tail to fully furl in constant winds above 15 mph. We know the SOC (load) makes a huge difference on how the machine reacts and this is what I am logging data on now.

 I really like running a lower rpm machine but like everything it is a compromise. Resistive heating, piece of cake dialing in compared to charging batteries. The MPPT equipment for wind reported on here so far I am not impressed. Same old story, way too many variables to prove with any consistency that the formulas programmed will provide the calculated results. I think there is hope though for some to make things work pretty well by programming their own MPPT "curves" tweaked by experiment rather than assume you can pop in a set of calculated points and expect the hardware to make you happy from this. Sure, bench testing proves it works but Oh my if we could only get a few bench techs. to build and spin up and load down a few real world axial machines on the bench with these very expensive MPPT controllers ....  Pipe dream I know because tests already show it should work and they are promoting it as so. Started and ended a rant in one sentence.  Dave B.   

Be careful, this mode of operating is tame and quiet and easy on the blades but you are using stall control with a bit of back up from furling. If you add too much tail weight you may break out of stall at some point and it will run away and the furling wind speed will be above the alternator capability if you get a long sustained burst of wind.

If you must stick with stall control I think you will have to forget the big power in high winds or risk a burn out. Good power in 15 mph winds should give you most of the power you need. If you want much more I would reduce the tail weight and add some resistance or increase the air gap and get the thing to furl as the main method of control and not rely on stall. Stall operation needs special blades and I doubt yours will react that way.

I have never run machines hard stalled but it seems from comments here it is fine as long as long as your back up furling takes over when the alternator is in risk of loosing control, if you get out of hard stallbefore the control is mainly from furling and there is sustained wind it seems to result in melt down but this may be partly confused by the fact that some people really cant tell furling from a bent tail. If you are careful and do things in controlled steps you may be ok, I cant' remember if you have some additional means of stopping it in high wind but shorting the alternator is no use if you break out of stall, it will make burn out absolutely certain and it would be better to leave it. If you have a brake you can do your experiments safely as long as it is not left unattended before you have sorted it out.

At present you seem to be holding power in high wind , if you reach a state where power rises then watch out, if the main control is furling the power will drop as it goes into furl but I don't think you will get that if you are using hard stall.

You are also using different blades and they may have even more tendency to break a machine out of stall.

Flux

[halfcrazy]

 I really like running a lower rpm machine but like everything it is a compromise. Resistive heating, piece of cake dialing in compared to charging batteries. The MPPT equipment for wind reported on here so far I am not impressed. Same old story, way too many variables to prove with any consistency that the formulas programmed will provide the calculated results. I think there is hope though for some to make things work pretty well by programming their own MPPT "curves" tweaked by experiment rather than assume you can pop in a set of calculated points and expect the hardware to make you happy from this. Sure, bench testing proves it works but Oh my if we could only get a few bench techs. to build and spin up and load down a few real world axial machines on the bench with these very expensive MPPT controllers ....  Pipe dream I know because tests already show it should work and they are promoting it as so. Started and ended a rant in one sentence.  Dave B.   

I am not sure if that is geared directly at me or not but I will assume it is as we are about the only ones "Promoting MPPT for Wind to charge batteries" I have been actively running a MPPT controller with 16 user adjustable set points for over 2 years on a 10ft Axial Flux design and also on a 17ft machine that is a direct copy of Dan B's except it now has 16ft Royal Wind and Sun blades on it although we will be going back to the Dan / Hugh design as we find it much more productive in low winds. We also have had numerous Beta sights running these controllers all experiencing the same gain do to keeping TSR at its optimum spot.

It is pretty simple when a axial flux alternator is connected to a battery direct it will have one spot in RPM that it is at its peak efficiency and this will wander around a little based on battery voltage. Now with a MPPT controller we can make that same turbine efficient throughout its entire range. This is not to say you can not build a low speed turbine that produces nicely in lower winds but that one can use a controller like ours to allow the turbine to run at its optimum tip speed ratio in any wind speed instead of one specific point.

I guess I am at a loss as to why you could even think it does not work it is simple math. Take a turbine like the one you are discussing in this thread that is obviously running in a stall for instance. If this turbine is stalling from 15mph up than it would make more power on a controller that lets its voltage rise. You do not have to get carried away and let it spin 4 times its cut in RPM you can let it say double its speed at the top end this will close to double your power.

I guess I could go into the discussion on turbines like the Bergey XL it is something like 7.5kw as a battery charger do to the lack of MPPT and it is over 11-12KW on a MPPT controller or in there case an inverter.

I am sorry you feel our product is a gimmick.

Ryan

[Dave B]

Ryan,

  Sorry you took offense to my comments, non intended and I certainly do not feel your product is a gimmick. It's basic math true, running faster will produce more power and in theory running at the TSR throughout the rpm loaded following the power curve should get it done. The problem I see is that the homebrew "machines" will not take this range into the higher rpm where the math (and tests) show great power increases and then stay together. The speed must be limited, the discussion board is filled with overspeed issues, fried stators, tower strikes etc. Anyone can run their machine fast and see the peak outputs, an MPPT controller is not creating any magic for additional power output but rather is just allowing the machine to run fast in the top end as well as follow the curve reasonably well in the lower rpm range. The top end is the issue of course I am not telling you anything you don't already know. I have no doubt the electronics can do it and the software as well but things happen very fast when the machine takes off and starts flying. I understand not wanting to dial in a stall curve but lots of discussions on both this board and other discussion boards indicate the great concern for overspeed. It's a catch 22, again I opologize if you took my comments as personal against a certain product, non mentioned and non intended. Running fast and running safe is a tough nut to crack.  Dave B.

 I really like running a lower rpm machine but like everything it is a compromise. Resistive heating, piece of cake dialing in compared to charging batteries. The MPPT equipment for wind reported on here so far I am not impressed. Same old story, way too many variables to prove with any consistency that the formulas programmed will provide the calculated results. I think there is hope though for some to make things work pretty well by programming their own MPPT "curves" tweaked by experiment rather than assume you can pop in a set of calculated points and expect the hardware to make you happy from this. Sure, bench testing proves it works but Oh my if we could only get a few bench techs. to build and spin up and load down a few real world axial machines on the bench with these very expensive MPPT controllers ....  Pipe dream I know because tests already show it should work and they are promoting it as so. Started and ended a rant in one sentence.  Dave B.   

I am not sure if that is geared directly at me or not but I will assume it is as we are about the only ones "Promoting MPPT for Wind to charge batteries" I have been actively running a MPPT controller with 16 user adjustable set points for over 2 years on a 10ft Axial Flux design and also on a 17ft machine that is a direct copy of Dan B's except it now has 16ft Royal Wind and Sun blades on it although we will be going back to the Dan / Hugh design as we find it much more productive in low winds. We also have had numerous Beta sights running these controllers all experiencing the same gain do to keeping TSR at its optimum spot.

It is pretty simple when a axial flux alternator is connected to a battery direct it will have one spot in RPM that it is at its peak efficiency and this will wander around a little based on battery voltage. Now with a MPPT controller we can make that same turbine efficient throughout its entire range. This is not to say you can not build a low speed turbine that produces nicely in lower winds but that one can use a controller like ours to allow the turbine to run at its optimum tip speed ratio in any wind speed instead of one specific point.

I guess I am at a loss as to why you could even think it does not work it is simple math. Take a turbine like the one you are discussing in this thread that is obviously running in a stall for instance. If this turbine is stalling from 15mph up than it would make more power on a controller that lets its voltage rise. You do not have to get carried away and let it spin 4 times its cut in RPM you can let it say double its speed at the top end this will close to double your power.

I guess I could go into the discussion on turbines like the Bergey XL it is something like 7.5kw as a battery charger do to the lack of MPPT and it is over 11-12KW on a MPPT controller or in there case an inverter.

I am sorry you feel our product is a gimmick.

Ryan

[ChrisOlson]

Dave, I run my 12G machines at TSR 5 and they maintain that tip speed ratio pretty consistently above 12 mph.  Just be careful with overloading the rotor.  You're not "stalling" those GOE222 blades - you're merely running them below optimum TSR so they don't make as much power.  In high winds (40-60 mph) they will "come alive" and you're still going to have serious power - except now with a high-resistance generator that is not designed for it.  That's why I went to a geared drive.

The furling is not predictable when you're running the rotor too slow.

The thing with MPPT is a discussion of a different color.  I prefer to get my performance using mechanical engineering instead of electronic engineering.  The MPPT controller will definitely wake up a turbine that is running up against a wall with a "stiff" generator.  But I look at MPPT sort of like a tracker on a solar array - you can get more power from your panels with a tracker, but you can also throw an extra panel or two in the array and get the same results as a tracker at a fraction of the cost.

If those MPPT controllers were more reasonably priced I might try one.  But if I don't have enough power day in and day out I'll throw a bigger, or another, turbine at the problem before I'll throw some electronics at it.

With MPPT you could wind your stator to run at, say, 480-600 volts and still set the power curve so the rotor is running "stalled", and probably get some marginal gains even at the wind speeds your turbine is tuned for.  I had thought at one point about trying the Classic controller on one of my geared machines, but with the stock stator and gearing that machine will hit 244 open DC volts running unloaded in a stiff wind.  I'd like to try running one up around 600 volts and I could do that with the stock stator just by changing the gear ratio.  At 600 volts you only need 3.3 amps down the tower for 2 kW and a guy could realize some substantial savings on copper if that could be done.
--
Chris

[Dave B]

Hello Chris,

  Like you I have been running a turbine of some configuration for quite some time now. Weeks, months and years of "up time" give us a pretty good understanding of how the components of the system work for or against each together to produce power.

  I use the word stall or stalling here because it's used so often but being involved with aviation also you know as well this term is not always used properly or explains what the intent to explain actually is. That's another discussion all in itself.

  Looking at the swept area vs. windspeed curve it's easy to see the potential output of a given size machine. It's easy to hit bragging rights top end, just run the machine fast and hope. If I were selling MPPT I certainly would be promoting higher outputs using my controller. It's much more impressive to work the steep end of the curve stating additional thousand(s) of watts than to state maybe it gets you a few more hundred watts in the average wind speeds. I see both sides but I will give away the secret to these amazing top end figures, open the airgap and let 'er wind up. The numbers are already in the design, strap on a shunt and meter and wa lah, huge output for a fast running machine and no investment of hundreds of dollars to get it.

  Unfortunately the real "sell" should be the improved output possible with MPPT in the average wind speed for a given size machine. It's not as exciting and higher numbers people go ga ga over so again we run into equipment, marketing and money issues to make sales.

  MPPT can be a great tool and with enough testing on a mass produced consistant wind turbine I believe an MPPT controller could be designed specific as an improvement to the overall performance of a particular machine. There are just way too many variables in the homebrew market for a plug and play MPPT solution. Those familiar with all the equipment of the system have a chance for safe improvement of overall performance by experimenting with the curves. A plug and play MPPT that would protect your machine within the design limitations and allow for the output in the upper end of the curve would sell pretty well. Tough to market that for homebrew.

  I'm with you Chris, power over time wins out every time over high power bragging rights for short term. Tortoise and the Hare. 6 years spinning here,   Dave B.
 

Dave, I run my 12G machines at TSR 5 and they maintain that tip speed ratio pretty consistently above 12 mph.  Just be careful with overloading the rotor.  You're not "stalling" those GOE222 blades - you're merely running them below optimum TSR so they don't make as much power.  In high winds (40-60 mph) they will "come alive" and you're still going to have serious power - except now with a high-resistance generator that is not designed for it.  That's why I went to a geared drive.

The furling is not predictable when you're running the rotor too slow.

The thing with MPPT is a discussion of a different color.  I prefer to get my performance using mechanical engineering instead of electronic engineering.  The MPPT controller will definitely wake up a turbine that is running up against a wall with a "stiff" generator.  But I look at MPPT sort of like a tracker on a solar array - you can get more power from your panels with a tracker, but you can also throw an extra panel or two in the array and get the same results as a tracker at a fraction of the cost.

If those MPPT controllers were more reasonably priced I might try one.  But if I don't have enough power day in and day out I'll throw a bigger, or another, turbine at the problem before I'll throw some electronics at it.
--
Chris

[ChrisOlson]

If I were selling MPPT I certainly would be promoting higher outputs using my controller. It's much more impressive to work the steep end of the curve stating additional thousand(s) of watts than to state maybe it gets you a few more hundred watts in the average wind speeds. I see both sides but I will give away the secret to these amazing top end figures, open the airgap and let 'er wind up. The numbers are already in the design, strap on a shunt and meter and wa lah, huge output for a fast running machine and no investment of hundreds of dollars to get it.

Theoretically this is true.  If you build and tune a turbine for a specific wind speed range, then MPPT will show no real advantage at that wind speed range because there are losses in the DC->DC converter in a MPPT controller too.  So far, what I've seen, is only the bragging numbers that you can get in higher wind speeds with the MPPT, which doesn't mean much day in and day out.  My turbines, the way they are running with no MPPT, only dump power on good wind days.  I don't need to dump more power by making more yet with an MPPT controller - I need the power on the average days.  And that is what I have tuned my turbines for - and I suspect you are experimenting with the same thing.

Theoretically there should be some performance gains even on a turbine tuned for 12-15 mph because of lower line losses.  But I have seen nobody actually log this with an MPPT controller because whatever you gain in the line loss, you turn around and lose again in the DC->DC conversion in the controller at those lower outputs.  And that's why I have calculated that you need to get the generator voltage up to around 480-600 volts to actually get a decent enough gain at average wind speeds most sites have, and even then the gains are very very small when the converter itself is only 95% or so efficient.  At 12 mph, for instance, if the generator is already roughly 90% efficient, and assuming you can raise the efficiency to 93% by reducing line loss, then lose your 3% in the voltage conversion, there is no gains.  And the only way you'll get any gains at those low to medium wind speeds is by putting the MPPT on a turbine that is not designed and tuned correctly in the first place for optimum efficiency at that wind speed.

So until somebody shows me hard numbers that indicate more kWh at 12 mph average I will continue to do it the mechanical way and will not spend $900 on a controller.  But so far all I've seen is the bragging numbers when the wind picks up.  And like you say, I can tune for that too without using any electronics.
--
Chris

[Volvo farmer]

I know just about enough to sound stupid and get myself in trouble here..

One thing I used to notice when my turbine was tied straight to the batteries was that I used to get pretty good performance when the batteries were up around absorb (28.8V). My only measurements were seat-of-the-pants observations but it appeared to me that if I had some seriously discharged batteries, say 24.8V, I could not get the turbine to run fast enough to make the kind of power it made when the batteries were at 28.8V.

I don't know if I could have opened the airgap even more and make it run equally well at both battery voltages. I never tried that. However, wouldn't a theoretical bonus of MPPT be that the turbine could fly closer to optimum TSR at both low and high battery voltages? I know my voltages swing almost 4 volts on a daily basis, depending on what stage of the charge cycle I am in.

[ChrisOlson]

However, wouldn't a theoretical bonus of MPPT be that the turbine could fly closer to optimum TSR at both low and high battery voltages?

Absolutely.  Another advantage with MPPT is that you don't necessarily have to "tune" for one wind speed - the controller lets the turbine run at the optimum voltage no matter what the wind speed or "clamp" voltage, and should yield overall better performance.

What I have been working on for close to two years is achieving a better match of the generator to available input power without using any electronics.  And DaveB is doing somewhat the same thing - he is "tuning" more for low wind output and taking what he gets on the top end.  The low (or average) wind speed energy production is what's important to most folks because it's what gets the work done in your house day in and day out.  Few people live where the wind blows at 25 mph all day every day.

I think MPPT is a simple "bolt-on fix" for turbines that have generators that are too powerful for the blades because it lets them actually run, i.e. the blades are running at more optimum TSR so they make more power.  There are other ways to do this that don't involve an expensive electronic box, is all I'm pointing out.  And the electronic box is not the "silver bullet" because it has losses built into it too, which become more significant in the lower to medium range wind speeds Dave and I are tuning for.  And this is why I'd like to see somebody who has two identical turbines run one on one turbine and let the other one run straight up with no MPPT, log power on them both over the course of a month or two along with wind speed, and prove that MPPT can actually win out over a properly tuned machine side by side in the real world.

I have such a setup to do just that.  But I'm not going to spend $900 on an electronic box when I can build another turbine for that amount of money and get double the power that I get from one.
--
Chris

[Dave B]

 Here's my point. Take the standard book version 10' axial machine. The Dan's have said and other's have verified that running this machine at a constant 750 watts is probably tops for not burning it up. Certainly it can handle brief periods of much higher output but running much above 750 watts for an extended period of time such as when the good constant winds come (and they will) if it isn't set to furl properly it will burn up. Every design has limitations, this size and design has been tested by the hundreds now so it is a decent example.

  So, how much can an MPPT controller improve the output of this machine ? Lets say this 10' machine runs 100 watts in 10 mph wind and then 800 watts in a 20 mph wind with no MPPT. Very possible, very common reasonable figures. So, with an increase of only 10 mph we gain 700 watts. Averaging 70 watts per every one mph increase. We know the curve is not a straight line like this but for an example we at least have the range.

  Now, I have a hard time understanding why I would want to buy a $900.00 controller for this machine ? I am not trying to belittle the idea or any current MPPT equipment out there. If somebody can sell me on what this would do for a machine like this to justify the expense I will listen. Keeping in mind that 800 watts continuous will probably burn it up and without adding a dime to it's current configuration anybody can add a little weight to the tail and prove it as a peak machine of 1500-2000 watts easily. By By stator at best in the constant decent winds of 20+ mph winds and a heavy tail.

  Any of these book version axial machines from say 10' to 20' diameter are already capable of very high outputs. One quick look at the swept area vs. wind speed output curves shows why burnouts are very common for machines not set up properly to limit the upper end. Look at the curve, hundreds of watts increase for 1 mph increase in wind speed. At the upper end things happen very, very fast, this should be no surprise when you study the swept area vs. wind speed output curves. Burn up a few stators and or be near by as a machine immedialtely accelerates to run away speeds, this will get your attention and a respect for keeping the rotor speed under control.

  I am much, much happier with a slower running machine and Chris you are correct, I am working on more power from the real world average wind speeds and forgetting about the rare occasions of hight winds and peak outputs. It's not as exciting but it is very satisfying to hear people say I see your machine turning all the time. Yep, uptime is huge for wind turbines.  Dave B.   

[oztules]

Dave ,

It's not the 800 watts that will cause the problems...... but rather how those watts are made up.

It's the current in the coils that kills the stator, not the watts. So if we have a device that lets the rpm increase, and the voltage to rise, we can then use a converter to increase the current and decrease the voltage but keep ostensibly the same watts.

So look at it like this..... if we make a black box that holds the current at say a max of 10 amps, the stator can run cool..... if we let the rpm increase to triple (extreme indeed), then the watts can triple, but the stator is none the wiser re current..... it is still 10A.

It can be thought of as a dynamic transformer. Your house service transformer gives you your house voltage at high current, but only 110v. The HV  gets to the step down at very high voltages (22000v is usual), so a 1 amp fuse will run your house service for a 22kw  (200A/110v) house service..... low current high volts to high current low volts..... same power.

In normal cases, we actually chop the DC, not transform the AC.... but the result can be the same...... we convert a higher impedance power to a lower impedance power.... it is only about impedance matching in the end .... air to blade, and stator to battery.... both interrelated. Mechanical impedance mixed up with electrical impedance....... not resistance, as they are both frequency dependent, and so change dynamically as conditions (including wind )change.

Ideally it was thought to be possible with active mppt (real time tracking/fuzzy logic)... but no-one could get it to work, and they all appear to be back to jump tables..... which is not much trickier than transformer tap swapping... (relays or triacs perhaps). Thats why you need to put in the set points to describe the power curve. The things are not smart enough to actually do real mppt as that is too hard to control.

So there are real gains to be made, at the expense of RPM, blade wear and noise..... but the current can stay where ever we chose with the chopper ( buck converter)


Having said all that..... no I won't / don't want / not interested /couldn't care less about  MPPT for ME. It won't help a tuned mill greatly, it won't survive the storms on the 40th parallel without good furling, it cant be fixed locally (island in the ocean), and is a complete waste of my time. It is much more sensible to build it bigger, tune it to your area,and run it slow.....  it is easy to live with, and it  can't break down......... and  I don't want a mppt buzz bomb in the back yard.

Headline figures..... hmmm I did 5000w or more with my little 4meter mill in a fair blow.... but I let it go at 140v and it clipped near 40A........ and I don't ever want to do that again.

yes the stator was unharmed...... I don't figure a mppt would like that

As I see it from the boonies......just more  high tech rubbish to get in the way of a good "rustic" power plant...... next to my old pumper mill.





..................oztules

[Volvo farmer]

I can understand the concept of tuning for low and medium winds, and forget about trying to get 1.5KW out of a 10 footer in high winds. I even agree with the premise, despite owning and using a MPPT charge controller.

Dave and Chris, you have played with these things more than I have. Do you think I could have opened my airgap more on my machine and seen improvement in battery voltages at the 25V range? And how would that have affected the machine when the volts were 29V? Say I was having good 20mph winds, and I tuned for optimum performance at 24.8V. Would the machine just run faster and depend on it's furling mechanism more at 28.8V?  My first machine with smaller magnets and thinner stator wire burned out a stator in a storm. I thought Dan went to bigger magnets and thicker stator wire to make a more powerful alternator, less likely to run away in high winds. It seems opening the airgap defeats the purpose of stronger magnets and thicker wire and increases my likelihood of  another burnout.

Besides any conversion losses in a MPPT charge controller, I find that mine uses 5W 24/7, even when there is no wind.  Since we go days here sometimes with no wind, I find this to be a disadvantage in that regard. And lastly... The things do not cost $900. The 150V version is commonly available for less than $700 street price.

Chris, since you are so good at building wind turbines, I will buy you a brand new 150V Classic in trade for a nicely constructed 10' wind turbine of the DanB/Piggot design, I will even source my own blades and light blue paint.  Just something to think about

[ChrisOlson]

Dave and Chris, you have played with these things more than I have. Do you think I could have opened my airgap more on my machine and seen improvement in battery voltages at the 25V range? And how would that have affected the machine when the volts were 29V? Say I was having good 20mph winds, and I tuned for optimum performance at 24.8V. Would the machine just run faster and depend on it's furling mechanism more at 28.8V?

Yes it would, and the machine will just run a bit faster at the higher voltage.

You have the classic case of a generator way too powerful for the blades.  Get rid of those big round magnets and use 2 x 1 bars and you'll get a better match between the generator and available input power.  Guaranteed.  I knew that for a long time, but just confirumed it when I built my latest generator with ferrite magnets.  The neo mags are very powerful, and the trend has been to use way too powerful of magnets in the generator.  Then add resistance to the line or open up the air gap to get the thing to run.

This is what I said about MPPT being a simple bolt on "fix" for improperly designed and tuned turbines.

Chris, since you are so good at building wind turbines, I will buy you a brand new 150V Classic in trade for a nicely constructed 10' wind turbine of the DanB/Piggot design, I will even source my own blades and light blue paint.  Just something to think about

I'd be happy to build you one of my geared machines but I'm not all that interested in the Classic anymore.  If they had one I could run up to 600 volts, and it was priced reasonably, then I'd try one.  The way the things are now my geared machines would blow one all to hell in decent winds and the the last thing I need is a runaway turbine because an electronic box couldn't handle the power.
--
Chris

[Dave B]

  Here's a photo of my adjustable curve (non real time MPPT either) controller I built over 6 years ago. Briefly, AC in off a phase is rectified and knocked down (voltage divider is the high wattage resistors you see, these are not the load resistors) for DC in of a couple LM3914 bar graph drivers, adjustable 0-5 vdc full scale linear lighting of 15 LEDS that indicate RPM. Any LED selected triggers a solid state relay to a load. Shown here in it's simple version of basically 3 steps for unloaded start up and 2 clicks for heating water.

  Adding a bit of resistance really wakes up these machines by letting them run faster, how about that. Gee, what if we do that in selected steps and load based on the power curves ? My controller just became fancy and expensive. This is my MPPT controller, I'll let it go for a steal for $500.00 or I'll build these all day long for that price to anyone who wants to select where on the curve they want their machine to run faster. Sounds amazing I know but when I connected my MPPT controller with my own carved blades, I could get over 3000 watts from my 12' machine in 25 mph winds ! Maybe I shouldn't say I have the pieces to prove it.

  Dave B.

[oztules]

Yep, an MPPT in the making.

For heating I would go single phase, and use your bar graph light machine to drive stepped resistances to an opto isolated driver into a big triac (100a@1000v about $15) and control the element that way. (high powered light dimmer effectively) It would give you all the steps without all the relays. Each led output could then be routed through it's own voltage divider to drive the triac..... using the LM3914 in spot mode rather than ripple mode.

Nice work there.


..... oztules

[Dave B]

Thank you Oztules for the comments and suggestions. In it's original configuration and I believe in this photo I was running a 12' single phase machine heating water. I wanted a tool for stepping the load any number of times (up to 15 in this configuration) and any where along the RPM range automatically so I built this controller. It has been through many different changes for different machines and applications since and even if not used for load control it makes a nice light show as an RPM meter. About $80.00 in parts I believe.  Dave B.

       

Yep, an MPPT in the making.

For heating I would go single phase, and use your bar graph light machine to drive stepped resistances to an opto isolated driver into a big triac (100a@1000v about $15) and control the element that way. (high powered light dimmer effectively) It would give you all the steps without all the relays. Each led output could then be routed through it's own voltage divider to drive the triac..... using the LM3914 in spot mode rather than ripple mode.

Nice work there.


..... oztules

[kitestrings]

Good discussion here.

First off thanks to Dave for sharing your experiences.  My only caution, is proceed with caution as it appears you are.  I think the fact that your looking at both the blades, the furling and the loading all in combination indicates to me you'll get to a workable set-up.  As you know, stall limiting and well tuned furling still are only part of the equation if your batteries are floated and there's nowhere to put the excess.

I have some input on the variety of earlier topics.  I've got two of the unmentioned contollers sitting in their boxes, while we slog through our axial build, so I've clearly committed myself to move in that direction, for better or worse.  On the other hand, I also have a geared turbine that we've lived, maintained and gotten to know intimately, as Dave has described.  I've also been solely off grid since about '84-85.

The way I see it Chris would prefer a mechanical approach - and he seems more knowledgeable & better equipped than most contributors to that end - to the same basic load matching challenge that we all face.  Oz points out some of the potential benefits of MPPT, but also the risks.  I do think, long term there are also some trade-offs with introducing a gearbox of any type.  We've got more moving parts, bearings, lubrication (and potential for leaks), seals, wear, end-play and losses.  The mechanical losses I suspect will be comparable to the converter losses of the electronic approach.  And, with or without gearing, and fine tuning, you still are attempting to pick a narrow, workable range of windspeeds and make things efficient there.  You're still faced with matching up a straightline alternator output to a cube-curve prop output.  Until, or unless, you can do an automatic transmission or mechnical VSD of some sort, the challenge is still there.

We tend to talk about wind like it is more define-able than I think it is - light, steady, or moderate, 'averaging x-y at my site'.  And, while we can attempt to design for the norm, mother nature tends to inject her will at will.  In the wake of hurricane Irene, I supose an exclamation is in order.  My point is most turbine have to perform in a wide range of conditions that vary seasonally, with weather patterns and storms.  I fiully agre with the high percentage of 'up-time' being key.

The biggest concern I have with electronics approach is the risk of failure due to lightning.  I still don't like to relying soley on an inverter - though mine's been bulletproof for many years.  My waterpumping, refrigeration and lighting is still predominantly DC.

I do think MPPT has the potential to do something most of us mortals have been unable to do - match the power curve over a wider range of speeds (using some reasonable limits of the upper range), and allow for load diversion, metering, data logging and a variety of useful features.  When I invested in an mx-60 for my solar system, it seemed like a alot of money at the time, but it bought something that just adding panels couldn't replicate - and I've never regretted that move.

Just my thoughts,

~kitestrings

[ChrisOlson]

I do think MPPT has the potential to do something most of us mortals have been unable to do - match the power curve over a wider range of speeds

I fully agree.  The big question is whether or not it's necessary.  Folks who have flown turbines for any length of time know that low to midrange performance is more important than high wind performance, even though the most power is available from the higher winds.  For off-grid folks with battery charging machines the high wind performance is usually not even desired because it's usually too much amps.  For the grid-tie folks the high wind performance is "money in the bank" because they can sell more power to the grid and there's a place for it to go (assuming something doesn't blow and the grid stays online).

Oz summed it up pretty well by saying he doesn't want a MPPT bozz bomb on a stick in his back yard.  Some of us prefer to run more than one turbine, or bigger slower turning turbines, because of the reliability issues with high speed machines.  As always, wind power is about what you get for energy production day in and day out that makes it practical (or not) to use it as a power source.  And the bulk of that power is not generated at 20-25 mph.  It's generated at 10-15 on most sites, day in and day out.

So whether or not MPPT even works on a wind turbine to provide more usable energy to run your home has still not been proven.  So far all I've seen on it is that it will let the turbine produce more power when the wind blows hard, and most of us have enough power as it is on days like that.  We all the need the extra power on the other days.  How much power you can get from the wind is still a function of swept area no matter how many smoke filled boxes you throw at the situation.  You can increase the amount of swept area in the breeze by either putting up more turbines, or building bigger ones.  You can't increase swept area with an electronic box.

This is a good thread - Dave is experimenting with the same thing I've experimented with for close to two years.  And the kWh meter tells the story in the end on what works and what doesn't.
--
Chris

[halfcrazy]

Well lets put a little logic to this. Say you have a turbine like our 17ft machine it cuts in at 7mph and makes good power to about 9mph so the gain from the Classic at 7mph is probably 0% now lets say at 30mph we make 3 times the power that is a 300% gain so we can draw a line between these 2 points for fun and at 19mph we would gain 150% and at 13mph we would see a gain of 75% now lets say you do not want Chris's MPPT Buzz Box in your back yard we can program the curve to run up and keep the blades at there optimum TSR until we hit any speed you like and then flatten the curve to drive the turbine back into a stall from that point on up. This is exactly what we do with the 17ft machine to keep it slow and tame but what it does do is keeps the turbine making prime power between 7 and 17mph. This same turbine direct to battery's falls flat on its face above 9mph and seems to stall at 600 watts until we get good blows of 20mph or above. Now I understand as has been stated I can open the air gap and optimize it for say 12mph but now it is going to be unloaded so to speak below that and still stalled above that.

I live off grid with this stuff all day every day my welder my air compressor everything and I could care less what my peak wattage is I want KWH PERIOD and I can tell you that with a standard home brew it is a compromise and the MPPT controller eliminates that compromise. Top speed is truly user adjustable to whatever you prefer. I can tell you hard data shows that both my 10ft and my neighbors 17ft make at least double the usable KWH per month going through the controller instead of direct to battery.

I think the only legitimate argument I have heard so far is "I do not want electronics between my turbine and battery" As for Chris saying it is cheaper to build a bigger or second turbine I beg to differ I will gladly buy a 90ft tower and a 17ft machine every day for the street price of a Classic 150. Better start building Chris I think I can sell 20-30 17ft turbines a month for $750 with tower, guys and anchors oh and shipping.

Ok Rant off 

[Volvo farmer]

Well lets put a little logic to this. Say you have a turbine like our 17ft machine it cuts in at 7mph and makes good power to about 9mph so the gain from the Classic at 7mph is probably 0% now lets say at 30mph we make 3 times the power that is a 300% gain so we can draw a line between these 2 points for fun and at 19mph we would gain 150% and at 13mph we would see a gain of 75% now lets say you do not want Chris's MPPT Buzz Box in your back yard we can program the curve to run up and keep the blades at there optimum TSR until we hit any speed you like and then flatten the curve to drive the turbine back into a stall from that point on up. This is exactly what we do with the 17ft machine to keep it slow and tame but what it does do is keeps the turbine making prime power between 7 and 17mph. This same turbine direct to battery's falls flat on its face above 9mph and seems to stall at 600 watts until we get good blows of 20mph or above. Now I understand as has been stated I can open the air gap and optimize it for say 12mph but now it is going to be unloaded so to speak below that and still stalled above that.

I live off grid with this stuff all day every day my welder my air compressor everything and I could care less what my peak wattage is I want KWH PERIOD and I can tell you that with a standard home brew it is a compromise and the MPPT controller eliminates that compromise. Top speed is truly user adjustable to whatever you prefer. I can tell you hard data shows that both my 10ft and my neighbors 17ft make at least double the usable KWH per month going through the controller instead of direct to battery.

I think the only legitimate argument I have heard so far is "I do not want electronics between my turbine and battery" As for Chris saying it is cheaper to build a bigger or second turbine I beg to differ I will gladly buy a 90ft tower and a 17ft machine every day for the street price of a Classic 150. Better start building Chris I think I can sell 20-30 17ft turbines a month for $750 with tower, guys and anchors oh and shipping.

Ok Rant off 

While I largely agree with the sentiment of this post. The details of the comparison seem to be a wee-bit obfuscated. Doesn't it take two of them there Classics to have enough amp-rating for a 17 foot machine? That there's $1500, not $750. I might be mistaken, that's just what I seem to remember.

Chris won't even build me a regular old non-geared 10' axial flux alternator in trade for one Classic, so your point is still mostly valid though. 

I like Kitestrings analogy that we are trying to tie a straight line alternator output to a cube-curve prop output. To me that puts the whole argument into perspective. You can tune for a sweet spot anywhere along the curve you like, but you're going to lose something somewhere. Chris seems to think you can have all the low and all the middle if you sacrifice only the high output.  My limited experience has been more akin to what Halfcrazy has reported, with the most maddening aspect being a totally different wind speed performance depending on my batteries state-of charge.

I wonder if the fact that I have wildly varying wind speed and Chris seems to have nice steady wind for days on end has anything to do with our perception of the situation.

[halfcrazy]

Volvo good point you could use 2 Classics on a 17 foot or do what we did and use a 150 and flat line the curve near the top and limit the Classic. We have a triac fired by the Classic that pwm's the 3 phase into resistors to limit the Classic 150 to 4700 watts. We have tried it both ways and there is a definite increase in KWH with 2 so i may have to up my price on 17ft turbines complete with tower and anchors delivered to 1500 bucks

[oztules]

Halfcrazy,

I don't understand your argument as being useful to anyone interested in their turbine. Anyone designing a turbine to start at 7mph is not terribly serious about performance anyway. If your machine is dreadfully matched, then you need someone else's help to make it work decently.... like a mppt solution.

Logic..... working on a turbine starting to stall at 9mph ...........  "This same turbine direct to battery's falls flat on its face above 9mph and seems to stall at 600 watts until"..... more like a boat anchor.

I built my two 4M machines for less than 800 dollars for both (not one). I don't need a 90 foot tower, and I am not interested in a 7mph cut in (more like 13mph with boost).... in short, I don't have any where near the problems you would have  to match a fair part of the curve. We claim a linear to cubic relationship, but due to the nature of the tsr to wind, it seems nearer to a square function. There is a lot of slippage if you design for the right part of the curve. read Flux's matching the load to get a better perspective.

A 12m tower is far more than I need, and it still costs nothing for  12m irrigation pipes galvanised and 8" in diameter. For the cost of 2 classics I could easily build 4 mills.

I say again, a mppt will only help significantly if your matching is poor anyway..... yours clearly was. The AWP up on the hill is putting an easy 24kwh/day for 3.6m. It is 1000 feet above the surrounds, and does this easily each day (annoy's me down here really...) so every situation is different. It would not help the AWP, as it is flat out all the time anyway, it won't help mine much, as they are well matched and furl early, it will help you significantly, as your matching has to be poor for a 7mph cut in.

There are a lot of things that will dictate the viability of a classic or any other solution between the stator and the batteries. But if you deliberately design a mill for poor performance in order to have to use electrickery (and I'm familiar with that enough that it does not scare/faze me), then good for you. I suspect real windmill folks like Flux roll over in pain when they read of 7mph cut ins.....which by definition  is aiming for very very poor matching.

If you do this , it has to be for a reason......sedate mill, don't need more power as a big mill taking it easy puts out far more than a smaller mill running well as a rule..... or just copying someone else who had different needs to you apparently.

Your argument is fair comment for your case and others like it, but not useful for a lot of other cases.

In short.... I  think this is less than useful commentary: "I think the only legitimate argument I have heard so far is "I do not want electronics between my turbine and battery" As for Chris saying it is cheaper to build a bigger or second turbine I beg to differ I will gladly buy a 90ft tower and a 17ft machine every day for the street price of a Classic 150. Better start building Chris I think I can sell 20-30 17ft turbines a month for $750 with tower, guys and anchors oh and shipping."

For me.......... Chris is right. I can BUILD not buy... a decent mill for $400 including tower.  In my case you are clearly wrong. In other cases, if they built it properly and made it a foot bigger they could probably match a MPPT, and if they built a stalled machine, a mppt may be good option if they have no skills of their own.

Lastly, I can easily build a solution if I needed to (and I don't), and DaveB seems to have done a fair effort in that direction already. It would not take much to adapt his design to a full fledged mppt. If you read the capacitor  discussion on the backshed, it would seem that an electronic solution is not the only answer to the problem.... and that kind of money spent on caps would produce a better more stable device anyway.


Were not all helpless, and there are a lot of solutions that will work for a lot of different situations, your experience is just yours.... not mine.
Interestingly  a lot of folk who live off grid here, don't strike me as renewable energy gurus just because they do live off grid and have since the fifties.


When the smoke gets out (and it will.... I note your safety triac will help with surge, but the ripple will kill the caps eventually), no matter how good their backup is, once Australia Post gets involved, rubbing sticks together will be a better way to get power while waiting.

And Volvo, I urge you to read Flux's matching the load. If you design for the right part of the curve, you get a fair bit of the curve to play with. If you want good performance with minimal electronics, then  higher cutin with cap doubling as per Gwatpe (backshed) will give you your low and mid and high..... (or a booster.....but  seems less good than a good cap design)

GwatPe has managed to get as near as to perfect, the  cubic relationships between his mill and his batteries .... just with caps, and with very very good monitoring software to back up his claims.

So I don't share your all your views, and feel there is plenty of cause for the home mill builder to not despair and think he can only succeed with the help of your mppt solution..


Its all in the design..... and there are plenty of options around.



...........oztules

[ChrisOlson]

Its all in the design..... and there are plenty of options around.

oz, the above quote is an excellent summary.  It seems to escape folks that throwing the biggest most powerful magnets at a generator efficiency problem (due to past burnouts and trying to fit fewer turns of bigger wire, etc..) is not the way to get power out of a wind turbine.  And that's the problem the halfcrazy's 17.  I could build one hell of lot better machine than that in a drunken stupor with one hand tied behind my back and the other one holding a beer.

You can't take a up-front bad design, strap an MPPT controller to it and then make a blanket statement that MPPT doubles the power output, insinuating that it will do the same thing on every homebrew turbine built.  You don't design for cut-in.  You design for the average wind speed on your site and take what you get for cut-in.  Most blades are very forgiving and they'll cut in at a decent speed anyway, reach their peak performance curve at the wind speeds that matter most, then taper off towards the top end.  And that tapering off is not a bad thing because when you got a turbine pushing 100 amps anyway you don't need to strap an MPPT controller to it and try to get 150.

I like that statement - "it's all in the design".

but what it does do is keeps the turbine making prime power between 7 and 17mph.

You don't need MPPT to accomplish this.  In fact you don't need any electronics at all to accomplish this.

This same turbine direct to battery's falls flat on its face above 9mph

If you got a 17 foot turbine that cuts in at 7 mph and falls flat on its face above 9 you got a serious problem with the machine, like the blades are mounted on it backwards or something.  It wouldn't hurt to have an expert that knows something about wind turbines look at the machine to see what's wrong with it.

and seems to stall at 600 watts until we get good blows of 20mph or above.

I hate to say it, but this is getting worse.  If you got a 17 foot rotor stalled at 600 watts I KNOW the blades are bolted on backwards.
--
Chris

[ChrisOlson]

Chris seems to think you can have all the low and all the middle if you sacrifice only the high output.  My limited experience has been more akin to what Halfcrazy has reported, with the most maddening aspect being a totally different wind speed performance depending on my batteries state-of charge.

VF - your turbine really shouldn't do that.  If I remember right, didn't you burn up the first one and got a replacement stator?  And all the problems started with the replacement stator?  Your generator is just too powerful for the amount of power the rotor can make.  Just open up the air gap on that thing and let it run.  Opening up the air gap does the same thing as using weaker magnets.  You'll find that you won't lose any, if it all, low wind performance by opening it up.  The blades will just run faster prior to cut-in and it won't even change cut-in by maybe 1 mph.  But it will wake the turbine up and you won't need no electronic box to do it.

The machine will furl more reliably too.  I don't know what blades you got, but I suspect the flat faced Clark-Y/NACA 44-series.  Those blades need to run because they got no torque to speak of.  They need rpm's to make power.  If you'd try it you'd see what I'm talking about, then you could sell that Classic 150 and get rid of the parasitic power draw of the confounded thing when the wind isn't blowing.

I wonder if the fact that I have wildly varying wind speed and Chris seems to have nice steady wind for days on end has anything to do with our perception of the situation.

Our wind varies as much as anybody's.  During "dog days" of summer in August is the worst time of the year for us here as far as wind power.  The machines are either idling on the tower just practicing, or running balls out in a thunderstorm.  Once we get into fall and winter my 12 footers make 12 kWh per day on average.  I've had days when they make 30 kWh in a day.  And I've also had days when they barely make 1 kWh.

But what I do know is that you can not expect a turbine to make decent power if you got too big of a generator on it.  It's like using a Farmall Super C to run a 15 foot John Deere discbine and try to cut hay with it.  You can do it but you got no power and you're not going to get anything done.  Hook that Super C up to a 6 foot sickle mower and you'll get more hay cut than you will with the big discbine.  If the load isn't matched to the power source the rig is not going to work.

--
Chris

[kevbo]

Ideally it was thought to be possible with active mppt (real time tracking/fuzzy logic)... but no-one could get it to work, and they all appear to be back to jump tables..... which is not much trickier than transformer tap swapping... (relays or triacs perhaps). Thats why you need to put in the set points to describe the power curve. The things are not smart enough to actually do real mppt as that is too hard to control.

I'm sure Chris knows the issues, but for those following the thread:  Actively tracking MPP is very tough to do on a wind turbine.  There is so much stored energy in the spinning mass (flywheel) that it takes at least a second, if not several, to see the effect of a load change, and the turbine takes, again, several seconds to respond to wind direction changes.  So by the time your power measurement stabilizes the wind strength and/or direction has changed enough that the data gathered as a result of changing the load no longer applies.  As a result, feedback schemes are pretty much doomed, and you are left with the feed-forward schemes, (MPPT "tuning") that while not perfect, can still offer significant gains.

Though I am an electroniker and can see a lot of advantage in MPPT, I really can't fault Chris's KISS logic.  One thing to always be kept in mind is that with wind and solar the fuel is free.  Raising the efficiency is economic folly if you raise the total cost of operation more than gain, because your fuel costs don't ever decrease with improved efficiency.    Just be sure you are looking at total costs, including capital,  land, time, insurance, divorce or other legal fights, etc!

Now, that said, I sometimes see a bit of straw manning going on.  In order to run well with direct charging many alternators are deliberately made less efficient, with lower than possible magnetic flux and/or higher than achievable winding resistance.  To then evaluate how such an alternator will perform with the addition of MPPT is valid only if considering adding it to an existing machine where it is impractical to rewind, regap, reblade, or otherwise optimise the alternator for MPPT use. It doesn't really apply to deciding if MPPT are worth it in general.  A low resistance, small air gap, high flux, high voltage alternator will never work without MPPT, but that is exactly what you want to get the most bang for the buck if you choose MPPT at the outset.  I see that Chris obviously appreciates this, but not all seem to.  As he says, you can use MPPT as a band-aid if you missed on your direct charging alternator design, but to really make it really sing, you need a totally different "stiff" alternator designed for MPPT use.  This does make for an expensive plan B if your MPPT scheme doesn't work out as planned.

As for the efficiency of high voltage alternators:  Yup, you gain a lot in transmission.  BUT, this means that the converter has to present a high impedance to the alternator, and that means you need high inductive reactance, and that means you either need lots of turns of wire on your inductors/transformers, higher mu core materials, or you need a higher operating frequency, and all of those things hurt efficiency.  It actually gets easier to design efficient high voltage transformers for high power levels, than at low power levels...this is just one reason that power companies scale down the power line voltages in steps as it nears the end users:  A pole-pig sized transformer would not be doable at 100KV, and your power is going to have to come 5 miles from the nearest substation even if your house is right under the 500KV cross-country line that feeds said substation.  I'd be impressed if you could make a 600V input MPPT run at 90% efficiency, and 85% might still be a tough target.  Not to be taken as gospel, as it has been some years since I worked on such things, and there have been numerous advances.

[ChrisOlson]

...........As a result, feedback schemes are pretty much doomed, and you are left with the feed-forward schemes, (MPPT "tuning") that while not perfect, can still offer significant gains.

It was my understanding that this was one of the great challenges of wind MPPT, and that the guys with the Classic had solved the problems.  But evidently not, as is sounds now like they're using MPPT tables like the Aurora grid tie inverter uses?  Or did the Classic controllers always use this method?
--
Chris

[kitestrings]

I'll say again, good discussion.

A couple more thoughts/questions:

Chris had a good point...

For the grid-tie folks the high wind performance is "money in the bank"

It can be for 'off-griders' as well, if you can do something useful with it.  We started doing 'opportunity load diversion' as I think it was coined on another board a couple years ago.  Preheating water with what would be wasted PV output (once the batteries are full).  It off-sets propane costs with minimal additional cost, and no plumbing thru the roof, feeze protection, pumps, deltaT controls and the like.  When it replaces my next tank of gas is when I'll be happy - not an unreasonable expectation, I think.

I mean this with no sarcasm whatsoever, I wish I could buy or build a tower here for $400, or $800 or some such.  We do need towers 100' or more in this local to be effective.  I know a local installer who recommends 140'.  At least for me, most of the numbers below, you'd have to shift the decimal point one spot to the right.

I do find it interesting that most folks don't think twice about investing in a $500-upwards of $3k inverter - another black that creative folks probably don't need - box but find MPPT controller to be exorbitant .  

oztoules wrote:

it seems nearer to a square function. There is a lot of slippage if you design for the right part of the curve. read Flux's matching the load to get a better perspective.

Oz, can you expand on this?  I'm familiar with this post, but I didn't come away with the same conclusion I guess.  And, I agree it is relevant.

There's alot of ways to skin a cat.  It'd be pretty boring here otherwise.  MPPT will prove itself or be a passing fad, but I'm glad someone is attempting it.  And, they (the manuf) look to be here to stay.  There beta site is worth a look.  I'm glad there are others approaching things from other means.  Chris's last statement summarizes pretty well the challenge

If the load isn't matched to the power source the rig is not going to work.

.  I guess I would add that we want to do this all-the-while keeping the heat out of the stator, reducing line losses, protecting the batteries, not prematurely wearing out the blades and finding useful tasks for the power generated.  No small task.

Lastly, my apologies to Dave for getting a bit off track from his original post.  I'm away for a couple days, so don't take offense, if I don't take [a timely] offense to something said

~kitestrings

[Dave B]

 This is all great stuff, I didn't realize there would be so much discussion about the user adjusted stepped load control (UASLC). I'll take credit for this acronym if I can.

 For those who have yet to build one of these standard book version axial machines and plan to do so please realize the upper end output potential for the swept area vs. windspeed of the machine you plan to build. These machines can and will reach these high outputs if they spin up to or near their TSR in the higher winds
without proper furling to protect them from self destructing.

  There is limited information in regards to maximum peak and or maximum sustained output ratings for these home built machines. This is a problem as this is pretty much left to the builder's discretion as to what he/she feels is safe. As mentioned, these machines can easily reach very high outputs as built without any other kind of current wind versions of MPPT or more simply put user adjusted stepped load control (UASLC)

  There is a maximum amount of power available for a given swept area and windspeed, period. These axial machines can go fast and put out huge amounts of power and I have to admit this is exciting and even more so when you have proof and can share this excitement. Go back a few years on this board and you will see all kinds of this bragging and right along with it all kinds of catastrophies. All of this well before any kind of mention of MPPT. The box does not make more power for your machine but with UASLC of any kind it can help to tweak in a poorly matched alternator, blades, load combination.

  If realistic numbers for suggested maximum continuous output were available for these book version sized machines it would be very helpful for those ready to build or wanting to make sure they don't see a crispy critter become of all their hard work during the first good blow of continuous wind of 20+ MPH. Unfortunately these realistic numbers could also possibly limit some sales of homebrew and related equipment at the same time. From a marketing stand point it's a tough call and I can appreciate this.

  Just a quick example and food for thought when considering possibly investing in MPPT. A typical 17' machine reasonably built can run at 1000 watts in a 15 MPH wind. Look at the curve, this same machine if unprotected can accelerate to nearly 8000 watts in a 30 MPH wind ! No magic box, it's just physics and those of us who have tested this either by accident or on purpose know all to well of it to be true. You will destroy your machine if you ride on the upper side of the curve.

  I like uptime, peak ratings are for marketing, realistic continuous output ratings are for safe day in day out power production. Sometimes you have to burn up or break a few things to decide for yourself where you are satisfied. In general, the book version axial machines already have a V8 on a Pinto chassis. Chris has proven again and again that this is not necessary. It's taken me a while to accept this idea but thank you Chris for your persistance to indicate this to be true. I am now running my V8 on 4 cylinders and cruising past the pack with no smoke and mirrors of MPPT. I'll buy 400 watts of solar with my $800.00 thank you or maybe like you build another machine.  Dave B.

 

 

[ChrisOlson]

  If realistic numbers for suggested maximum continuous output were available for these book version sized machines it would be very helpful for those ready to build or wanting to make sure they don't see a crispy critter become of all their hard work during the first good blow of continuous wind of 20+ MPH

A lot of my early burnouts of the "book" turbines were due to the machine running at the max safe limit for the winding for hours on end, then a gust comes along and pushes it over the limit for just a brief time.  Because the winding was already at its max safe temperature it burned a coil and lost a phase in that brief instant it went over the limit.  If the winding was cold when it did that it would be no problem and it would develop that higher power for quite awhile before it overheated.

This was most often blamed on furling issues.  But the turbine was furling fine.  And as I found out later, furling is not an absolute way to control power.  All it does is reduce the swept area and in 70 mph winds it don't take much swept area to make 3 or 4 or 5 kW.

Pushing these machines harder yet by letting them run faster with MPPT is just a time bomb to my way of thinking.  They won't take it long term.  Slow turning heavy turbines last.  Light weight fast ones don't.  Bergey sums this up pretty well on their website with the following statement:

Wind turbines run up to 7,500 hours per year, which is the equivalent of putting 100,000 miles a year on a car. And during storms they have to endure tremendous forces. While it's cheaper to build a light-weight, fast-turning wind turbine, the history of the industry dating back to the 1920's clearly shows that light-weight turbines don't stand the test of time. The heavy-duty Jacobs turbines from the 1930's can still be found running today. Their light-weight competitors are long gone.
--
Chris