Wind/hydro alternator design

[Rob Beckers]

Between Stew and me we may be able to find a source for custom made alternators. I have no idea at this time if this is going to go anywhere, but we may have a chance to start with a clean slate and come up with a set of 'ideal' specs for an alternator that enough people here would be interested in purchasing to make something like a group-buy possible.

The place to start is with the specs. Those are needed to get a price. Therefore the purpose of this thread is to come up with specs that would be interesting to a group of people.

To get this started, here is my stab at it: A sealed rare-earth permanent magnet alternator, with a somewhat oversized bearing (given the yaw loads wind turbines have to endure). Something around 3 or 3.5 kW at 300 RPM (makes for a 2.5 or 3 kW turbine), 120 Volt, so it's easy to cross some distance and be able to use the upcoming MidNite Solar MPPT controller or WindyBoy, at least 60 Hz (which dictates the number of poles).

As I said, this may not get anywhere so I certainly don't want to get anyone's hopes up. It's just that if I'm getting pricing from places I might as well use realistic specs. We'll see what comes out. Maybe it's way too expensive, maybe not.

-Rob-

[Mark Parsons]

Hi Rob.

My spec's.

I'm figuring on building a 10 - 12' HAWT. My cottage site shows 30m tower height wind atlas average of 4.3 m/s = 9.6MPH. Not a very good wind resource. The wind gets lost in the hills and trees. Hey, you gots' what you gots'...:(

For a 12' bird with a loaded TSR of 4 at 9.6MPH, calculator says = 90RPM. Stew's handy spreadsheet shows 508W max available for that swept area and wind speed. Assuming a Cp of 25% would mean harvesting about 130W average for my battery charging purposes.

For my purposes, an alternator with at least 1.25kW capacity should be fine for me to set the furling reasonably. The RPM vs Volts response is the most critical sizing criteria without a MPPT controller. If it means a larger alternator to ensure 130W and over 26VDC at 90RPM, so be it. At this low level of power, I would likely lose more to MPPT (in)efficiency than it would provide in extra watts.

Of course, I'm always interested to hear any concerns that my assumptions, expectations or math above is out of whack.

Thanks,
Mark

[Stewart Corman]

Rob,
I agree with most of your preliminary ballpark specs.
My needs are more in line with slower rpm speed, but that could be easily accomodated with gearing.
Let's presume a 12ft diameter, TSR=5, start furling at 20mph
The raw numbers are 4.5KW x 35%eff = 1.35KW @233rpm

Something around 3 or 3.5 kW at 300 RPM (makes for a 2.5 or 3 kW turbine)
I would say to design for 2KW, with overspeed current capacity at 3KW
The difference is that you want maximum efficiency at the rpm point where it gets used the most. (I've seen numbers like 90%)

120 Volt, so it's easy to cross some distance and be able to use the upcoming MidNite Solar MPPT controller or WindyBoy, at least 60 Hz (which dictates the number of poles).Why not DC??
Those are very expensive toys you are quoting above ...KISS
With AC you have to decide single or three phase.
Three phase requires extra wires.
To charge batteries, you need DC ..resistance heaters don't care.
Tie to the grid ..not worth the $3K in extra hardware ..never get payback.

REALITY CHECK: did a quick calc that to heat a 2K sqft house in midstate NY requires about 3KW/hr but this is avg ...more like 4.5 peak dead winter and 1.5 spring/fall ..so unless you are putting up an 18footer and have 18mph avg WS ...you will consume everything you can make


Mark can correct me, but there is no such thing as 60Hz except as a design point ..it will vary with rpm AND ..it is voltage that determines number of poles ...higher voltage = more poles ...I would vote for 230v.
I have 300 ft to house, would love to use smaller wire at considerably less cost. Wire could cost more than the generator!

Mark,
For a 12' bird with a loaded TSR of 4 at 9.6MPH, calculator says = 90RPM. Stew's handy spreadsheet shows 508W max available for that swept area and wind speed. Assuming a Cp of 25% would mean harvesting about 130W average for my battery charging purposes.
firstly, conventional designs will have higher than TSR=4, so your rpm should be higher
secondly, 25% efficiency is low if you do have TSR=4 ...laminar flow in low WS = best eff ...35% is better overall number with a commercially built axial (low loss) generator, no drive train
thirdly, you missed the Weibull distribution that doubles the avg output to 355w ..peak has to be calc at 18mph = 1.25KW... agree here

IMHO, I am in a quandry on sizing a mill for low WS as well ...going with 18ft rather than original 15 ft ...lower rpm, earlier cutout ..design for 2KW

For those who need my xls calculator:
http://www.greenpowertalk.org/attachment.php?attachmentid=93&d=1173805675
use sheet 1

Stew Corman from sunny Endicott

[Rob Beckers]

A few comments:

The whole point of a PM slow-speed custom designed alternator is to avoid gearing! Gears or other RPM conversion methods are weak links, and they cost money (so does a PM slow-speed alternator, but you don't want to pay for both). If one is planning to use gears it's a whole lot cheaper to use an existing motor/alternator (washing machine, induction motor etc.).

3 kW starts to get pretty sizable, and probably expensive (heavy too). My impression is that the majority of gennies that go up are in the 1 kW size, hence a 2 kW alternator so you get more out of the lower RPMs. Well, we'll see, it's easy enough to get quotes for a few sizes.

DC requires brushes, and they need periodic replacement. Something to avoid if possible.

3-phase is done to keep wire gauge small (energy has 3 wires to spread over vs. 2 for single phase), higher voltage is done for the same reason. 3-phase also helps make decent quality DC by simply using a bridge rectifier. Single phase makes atrocious ripple, this may or may not be an issue depending on what you hang behind it.

The expensive toys (inverter, MPPT charge controller) depend on what you want to do with it. If the objective is to charge batteries then the cheapest would be to have an alternator directly at battery voltage, from there just rectify and charge, using a diversion controller to keep things from overcharging (Higher voltage alternators would require a transformer, not cheap). However, this method of charging has piss-poor efficiency, word is that you're loosing about 50% of potential turbine output because for most of the wind regime there is no match between power draw and RPM. You pay more for an MPPT controller, but it will get 90% or so out of that same turbine. If you need grid-tie, then there no avoiding the expensive toys because of the UL1741 list requirement.

60 Hz was meant at rated power. The underlying idea is to have a reasonable frequency, so if a transformer is required it won't be a huge and expensive beast.

Voltage wise, a 220 or 240V alternator limits the toys: The MidNite controller won't work with it. Higher voltage is beneficial for wiring through. Maybe get a few quotes for various voltages.


-Rob-

[Mark Parsons]

Stew thirdly, you missed the Weibull distribution that doubles the avg output to 355w ..peak has to be calc at 18mph = 1.25KW... agree here

Please explain. Wind Resource Atlas gives average wind speed and direction rose. Why does Weibull double the average? Will change my plans, if so.

3 phase AC brushless is my vote. Direct coupled with a RPM to Voltage response to design into direct battery charging a 24V bank with a low WS cut-in around 7MPH. Each output in a 3 phase system carries SQR3 of the total amperage. Amperage (and Hz) is the source of power cable losses. Power losses in cables can be offset through larger conductors and / or parrallel conductors. With our size of only a few kW to transfer, I expect this alternator will cost lots more than the home run cable(s) unless you are mounting the bird hundreds of feet away.

RPM, number of Poles, and Hertz relationship. Hz = RPM * Npoles / 120

Rob 60 Hz was meant at rated power. The underlying idea is to have a reasonable frequency, so if a transformer is required it won't be a huge and expensive beast.

Going to be tough to find a happy medium with the Hz for everyone. As swept area, TSR and required voltage changes so does design RPM. Hopefully, someone designs a MPPT unit that handles a wider range of input voltages and has a good algorithm for wind energy harvesting. I'm still not convinced that a solar PV MPPT algorithm is any benefit for wind other than the DC-DC voltage converting for battery charging or grid tie to fix mismatched components.

Thanks.
Mark

[Rob Beckers]

Going to be tough to find a happy medium with the Hz for everyone. As swept area, TSR and required voltage changes so does design RPM. Hopefully, someone designs a MPPT unit that handles a wider range of input voltages and has a good algorithm for wind energy harvesting. I'm still not convinced that a solar PV MPPT algorithm is any benefit for wind other than the DC-DC voltage converting for battery charging or grid tie to fix mismatched components.


The real wind MPPT units, as for example Magnetek/Power-One makes them, have a table with many points (16 or so) that are programmable to follow the power curve of the turbine. The MidNite charge controller will do the same. Those are very good at harvesting power from a wind/hydro turbine. If you have that table set correctly it will get the maximum power out of your turbine, at any wind speed.

Not so good is the WindyBoy (and any other solar derived controllers/inverters). It has only two points to program (3 for the smaller units) and linearly interpolates between them. It makes for poor low-wind performance. On top of that the WindyBoy has a very high cut-in voltage, and therefore small operating range (making it even worse for low winds). Still, it'll probably do a whole lot better than direct battery charging (I know, the WindyBoy is an inverter and not a charge controller, just making the comparison).

As an aside, I can't for the life of me understand why SMA would design the WindyBoy the way it is. All the electronics are there to make an excellent MPPT inverter, and it very likely has a microcontroller inside. So why not have a decent size table for doing MPPT?

To get back once more to the frequency issue: This is a design choice, so it seemed to me one might as well shoot for reasonable frequencies. Yes, frequency drops with RPM, but wind power does so even more rapidly. Therefore, by and large it's the rated power and its frequency that determines transformer core size (if a transformer is needed). That is where my number of 60 Hz @ rated power came from. Frequency is completely irrelevant when it comes to direct battery charging or programming an MPPT controller, it's just for when a transformer comes into the picture.

-Rob-

[Stewart Corman]

from Rob:

DC requires brushes, and they need periodic replacement. Something to avoid if possible.

not true:
http://www.allproducts.com/manufacture97/allen101/product4.html

most new design "pancake" generators are PM/brushless and high efficiency
and no diodes to get zapped from lightening voltage spikes

BTW, what happens to all those fancy electronic gizmos when you get a lightening surge nearby?

from Mark:
Please explain. Wind Resource Atlas gives average wind speed and direction rose. Why does Weibull double the average? Will change my plans, if so.

simple statistical item ...since turbine power is proportional to WS^3, there is an accepted Weibull distribution of WS that says simply ...in order to have an "average" of 10mph, then some is higher and some is lower and the higher gives a disproportionately higher amount of power ...the exact number is about 1.9x, so I round off to "double", since it is an inaccurate determination of your real WS vs the official numbers anyway.

http://www.windpower.org/en/tour/wres/weibull.htm

correllary: if you have an avg 10mph WS, design your hardware for 2x power ie 12.5mph max efficiency, since that is the highest power density distribution ...
Look at the distribution ...if you furl out low ie 18mph, you lose very little opportunity, but larger blades will give more useable power at the lower speeds. Stretching the blades is a very small increase in cost/weight compared to everything else (keeping tower, wiring, and generator same).

Stew Corman from sunny Endicott

[Mark Parsons]

Thank you Stew for the explanation of the Weibull effect on power harvesting. It should have clicked for me prior. DUH :o

Brushless PM DC motors require a amplifier / controller to chop the DC into PWM (Pulse Width Modulated) AC phases to get the motor to turn. A Stepper Motor is somewhat similar other than each phase is connected to DC for a short period for the rotor to turn a small bit and lock to the stator field. Both of the above are classed as Synchronous motors. The rotor stays synchronous to the stator field. If anyone has any other Brushless DC tech that I'm unaware of, please post.

Be sure to ground the tower and use lightning arrestors on the generator outputs and surge supressors before your fancy electronics.

From Rob:To get back once more to the frequency issue: This is a design choice, so it seemed to me one might as well shoot for reasonable frequencies. Yes, frequency drops with RPM, but wind power does so even more rapidly. Therefore, by and large it's the rated power and its frequency that determines transformer core size (if a transformer is needed). That is where my number of 60 Hz @ rated power came from. Frequency is completely irrelevant when it comes to direct battery charging or programming an MPPT controller, it's just for when a transformer comes into the picture.
Agreed.

[Mark Parsons]

One option in harvesting wind energy that should be considered if the budget permits, or you are lucky enough to find these motors used or surplus, is AC PM servo motors. Almost all are 3 phase and come in large enough sizes to collect a few kW of energy. Another advantage should be the lower rotor inertia as compare to an axial flux design. The disadvantage is price over DIY costs and somewhat higher RPMs than a dual rotor axial flux. Here are the specs on a unit from Baldor. MSRP is about $3,400. The key data to use for alternator purposes is the Vpk/kRPM - peak volts it generates as an alternator per 1000RPM and the max current limit. These motors are rated up to 155C, and in wind applications which should rate as blower attached, providing an additional 60% of rated torque (current) drawn on a continuous rating basis.

Rob is looking for something in the 2-3kW range under 400RPM. The BSM100N-4250 produces 90Vpk at 400RPM (225.1Vpk/kRPM*0.4kRPM) muliplied by 17 amps continuous, times 1.6 for cooling in application should let this motor provide about 2.4kW continuous. Intermittent gust power available of 3 - 4 times that without damage could be expected. It weighs 77 pounds and is only 5.8" diameter by 10" long. Options include holding brake, gearheads, and encoders / resolvers.

Anyone in the group have direct experience with this option?

[Paul Bailey]

Who is looking for the servo????:)

[Mark Parsons]

Hi Paul,

Got one around the size shown above? I would take one for testing and then publishing some empirical data if you can get your hands on a surplus one - if cheap.

Thanks.
Mark

[Rob Beckers]

It's been a number of weeks, and I've been hunting for PM alternators during that time. I thought an update of what I've found so far is in order.

After looking long, wide, and hard, it turns out there are actually only two sources worldwide that sell PMAs suitable for wind/hydro off the shelf. These are Ginlong in China (http://www.ginlong.com/) and Alxion in France (http://www.alxion.com/). Both are used by a number of wind turbines (the 6kW Scirocco uses an Alxion), and both have an excellent reputation as far as quality is concerned, with the word on Alxion being "expensive, though the best you can buy" for wind PMAs. I'm quoting others, since I've not done business with either of them I can't personally vouch for them.

I've sent all manufacturers the following specs:


2.5 kW max. output @ around 300 RPM
Sealed (so it can be used 'in the weather')
Permanent magnet, low cogging
Two versions: 24 V for direct battery charging, and 120V
Around 60 Hz @ rated power (so a transformer doesn't have to be huge)
3 phase AC
Rugged, ie. two bearings instead of 'hinging' it at one side etc.


The pricing I've received is as follows:

Ginlong: They don't actually make anything that produces the requested output at that RPM. Closest is their GL-PMG-1800, which produces 1800 Watt at 480 RPM. Possibly their upcoming 5kW PMA will come closer. In any event, for their GL-PMG-1800 the cost is US$528 each in quantities of 10. This does not include additional cost of importing them, they'd be closer to $660 once all is set and done.

Alxion: They do make a model that produces 2600 Watt at 300 RPM, their 300STK2M. Pricing for this is a whopping US$2201 each in quantities of 10. Again before shipping and importing, so final price will likely be US$2900 when including all of that. That buys one a top-of-the-line sealed PMA that would last a very long time out on a tower, but it obviously comes at a price.

Then there's one other manufacturer of PMAs, though they only do custom designs, Precilec in France (http://www.precilec.com/). Their price for the above alternator came to an astounding US$6564 each in quantities of 10, before shipping and import. Not an option.

So where do all those alternators in the many small wind turbines come from? I've talked to a number of wind turbine makers about this, and besides using Alxion or Ginlong, all the other I've talked to make their own PMA. That probably means (for most) that they contract this out to a motor shop that can do laminations and windings, according to their design. I'm still talking to a shop in Baltimore that makes alternators. They are looking if they can manufacture a PMA according to the specs above, no pricing available yet.

That's where things are at. It looks a lot like there's little option for one that wants to produce a small wind turbine (and be competitive) but to roll their own alternator...

-Rob-

[Mark Parsons]

Thanks to the generosity of a fellow GPT member, I've had the pleasure of verifying my suspicions on servo motor use for micro Wind / Hydro applications.

Three used motors were sent to me that are no longer able to perform adequately for their intended applications. Inspection of them reveals mechanical issues with each. Bearings in 2 of the three need replacing and the third has a slightly bent shaft. These motors were saved from the dumpster. Electrically these 3 motors are still in excellent shape. Environmentally they are still in excellent shape.

The motors were 2 sizes of Allen Bradley 1326AB series. 1 -1326AB-B430E and 2 - 1326AB-B515E. The following link provides a document with full technical specifications of the product family.
http://support.elmark.com.pl/rockwell/Literatura/1326a-2_9.pdf

They exhibit zero cogging. The only running resistance at no load is bearing friction. I mounted them in the lathe and gave them a spin. Confirmed the 120VACrms per 1000RPM as specified. 3 phase sinusoidal output. Also confirmed the line to line resistance is as stated. Dismantled one to check the holding brake. These motors are very robust. With the bearings tightly embedded and locked into the machined end cap housings with the long rotor, the axial and radial withstand loads are enormous. Efficiency is not stated but suspected to be very high - over 90% due to a small air gap and tight tolerance construction.

Consider the following wind application using a B515E. Mount a hub with 3 - 48" long TSR=5 blades directly onto the 24mm motor shaft. RPM range for 10mph to 30mph is then 175 - 525 RPM. This results in motor output voltage range of 21 - 63 VAC rms. If an overall Cp of 35% is met then harvested power at 15mph would be 300 Watts with 260RPM producing 31 volts and close to 10 amps. This motor is not stressed for MPPT systems. For direct 24V battery charging situations in this application the motor should provide up to about 500 Watts into the batteries without stress. Cut-in RPM for 24V would be 140, this relates to a 8 mph wind speed.

I haven't bought one of these servo motors new in a while. I know prices have been coming down. I suspect a new B515E is worth about C$ 2,000. Finding one surplus can be down in the tens to a few hundred dollars. Finding one in a dumpster would be priceless...:cool:

Mark

[Joseph OLall]

Stew

Please explain. Wind Resource Atlas gives average wind speed and direction rose. Why does Weibull double the average? Will change my plans, if so.

3 phase AC brushless is my vote. Direct coupled with a RPM to Voltage response to design into direct battery charging a 24V bank with a low WS cut-in around 7MPH. Each output in a 3 phase system carries SQR3 of the total amperage. Amperage (and Hz) is the source of power cable losses. Power losses in cables can be offset through larger conductors and / or parrallel conductors. With our size of only a few kW to transfer, I expect this alternator will cost lots more than the home run cable(s) unless you are mounting the bird hundreds of feet away.

RPM, number of Poles, and Hertz relationship. Hz = RPM * Npoles / 120

Rob

Going to be tough to find a happy medium with the Hz for everyone. As swept area, TSR and required voltage changes so does design RPM. Hopefully, someone designs a MPPT unit that handles a wider range of input voltages and has a good algorithm for wind energy harvesting. I'm still not convinced that a solar PV MPPT algorithm is any benefit for wind other than the DC-DC voltage converting for battery charging or grid tie to fix mismatched components.

Thanks.
Mark


"RPM, number of Poles, and Hertz relationship. Hz = RPM * Npoles / 120"
Does this mean that we can calculate the RPM of say a wind turbine generator (PMG) by monitoring the Hz on one of it's 3 phase AC legs? I am trying to develop an accurate way of measuring the RPM of my wind turbine. Is this the right direction?
Thanks
:suspicious:

[Rob Beckers]

Hi Joseph,

That's correct: RPM and frequency of the voltage coming off the alternator are proportional. We use it with the Aurora inverters to do MPPT for wind turbines. It uses a table with frequency vs. output power, where frequency stands in for turbine RPM.

-RoB-

[Joseph OLall]

Thanks.

Do I have to build my own circuit or is there a configurable electronic module out there that I can buy?

[Rob Beckers]

Here's a schematic of one (well, most of one, it needs a power source for the opto-coupler and a resistor in the collector line):

[Joseph OLall]

Thanks for the response. Could you explain "it needs a power source for the opto-coupler and a resistor in the collector line" ?
Could the power source be 12vdc or 48vdc?
What does the wind + and - connect to? Can it be connected to a cycle meter..line the ones used by INSPEED anemometer?

[Rob Beckers]

Joseph, here is a link to the full datasheet for the TLP627 (http://www.semicon.toshiba.co.jp/docs/datasheet/en/Opto/TLP627_TLP627-4_en_datasheet_071001.pdf). The circuit as I showed it was taken from a commercial box, the output hooks up to an inverter to provide it with a frequency signal. For your own use, the optocoupler handles up to 300V collector voltage, so you can make any frequency signal voltage up to that by choosing the power supply voltage accordingly (with a 12V voltage supply it'll make 12 Volt square waves, with a 48 Volt supply the output frequency signal will be 48V square waves). For general use, you can drop the two 10 Ohm resistors (they are for protection and don't serve any particular electronic purpose), hook the emitter up to ground, and choose the collector resistor so it runs around 50 mA in current in the "on" state. So, for a 12V supply voltage that means a collector resistor of around 220 Ohm, for a 48V supply it works out to around 1 kOhm. It's not terribly critical.

-RoB-

[Vitruvian Wind]

Hey, just came across this thread. I'm an engineering student and did order the GL-PMA 1500 for a small vawt we're building. It gives about 1.5 kW at 500 rpm, which we thought was pretty good. It is high quality.

Here's what I'm posting for. You dont need to ship from China etc. TLG windpower (www.tlgwindpower.com) supplies these in the US, along with the inverter/controller for it. It was going to cost us $900 to get from China, and god knows what custom duty/import etc we'd have to pay. Yet from TLG we got it for a cool $650. There's a supplier for Ginlong, somwhere in Denmark who supplies sometimes to places in the US. TLG is one of them.

I hope these things get much much cheaper. 1 kW in 3-12 mph hour winds is just what third-world nations need, if it cant get better. Our whole turbine, a 2 X 1 m variable pitch VAWT, gives just that, but it cost $4000-5000 to make. Who's gonna afford that!:rolleyes:

[Rob Beckers]

Hi Vitruvian,

I'm familiar with the Ginlong alternators. By all accounts they are of good quality, at a reasonable price (as you can see from the other posts in this thread these PM alternators do not come cheap!). The main problem with Ginlong alternators is that they deliver rated power at a voltage that is far above the 600V DC limit (after rectifying) that UL/CSA listed grid-tie inverters such as the Power-One Auroras accept. That means you would have to run them at a fraction of their rated power, and that throws away part of your investment. One of my customers has been talking to them and is supposed to receive a delta-wired alternator shortly (their default is wye-wiring). The voltage of such an alternator would fall exactly in the sweet spot for the Aurora inverters, making it much more interesting.

If there's enough interest I could bring them in from China a dozen or so at a time, and get a much better price than you would get for single quantities. From the comments on Green Power Talk and the Fieldlines lists it would seem there are enough people looking, but it's hard to judge and I don't want to end up sitting on $10K (or more) of alternators that don't move...

-RoB-