The ones I have seen are belt-driven with varying ratios from the engine. Perhaps 2:1 or 3:1, so if they reach a voltage to start charging when the engine is at 500 RPM, then they are spinning about about 1000 RPM or more. So on a 12V system, they need more than 1000 RPM to put any current into the battery. To get to 100 Volts, then holding the truck engine to 5000 RPM would get you the 10,000 RPM on the alternator you’d need.
I get that this works on your truck when you need it in an emergency, but these are ludicrous speeds for a wind turbine. I’ve been going to great lengths to keep the RPMs of my wind turbine down to 400 RPM and below. Ever.
Gearboxes and belt-drives are the best way to make a terrible wind turbine worse.
The power of a wind turbine is determined by the blades and the wind speed, not the alternator.
Automobile engines run for maybe 1-2 hours a day. Trucks do more in this regard. Wind turbines should spin 24/7. Any auto alternator used in a wind turbine will suffer bearing failure in less than a year.
FYI
my WT has just started showing signs of bearing failure, mostly because it’s -25C. The 6206 bearings have lasted 4-5 years or so, minus one year of inactivity.
Also:
I went to e-bay looking for alternators anyway, in some ways just for fun and also in hope that maybe something comes onto the market that will change the game for me. Nothing yet.
Thank you for your reply.
OK I’ll forget automotive alternators for wind turbines.
Understood. The alternator should be capable of extracting the power produced by the wind turbine. The point is a lot of capacity in a small package due to the high frequency.
Re; eddy currents.
It takes AC to generate eddy currents.
In an auto alternator, the rotor is not laminated.
AC is induced in the stator and the stator is laminated.
The old DC generators used solid field poles.
The voltage induced in the armature windings was AC but the brushes were continually changing the connections to extract DC. The armature was laminated.
An illustration of this is the conversion to brushless excitation that was done on a large number of diesel generators.
Originally these had a DC exciter mounted on the generator shaft.
The DC was taken off by conventional brushes and fed back into the rotating field windings by conventional slip rings.
Then some genius grooved the main shaft so that three wires could be passed past the bearing.
He removed the brushes and connected the wires to three commutator segments 120 degrees apart. Now he had three phase power.
He mounted rotating diodes and fed the resulting DC to the field windings.
In later conversions the commutator was removed completely.
I installed, serviced and repaired quite a few of these converted sets.
The point is, AC,will induce eddy currents even at low frequencies.
DC, basically no eddy currents.
A synchronous motor will have a squirrel cage winding for starting.
When running, a synchronous motor may be subject to a speed oscillation of plus and minus a few degrees.
That is enough to generate enough current and counter- torque in the squirrel cage winding to dampen the oscillations.
I am not inclined to worry about eddy currents in a PM rotor until I get a conflicting explanation.
Some out of the box thinking.
What about a stator parallel to the shaft rather than parallel?
I am thinking about a fairly large magnetic plate turned by the shaft.
A series of magnets mounted on one side of the plate.
They may be surrounded and supported by an aluminum plate.
The stator would face the magnets.
I am thinking possibly a series of small transformers with one side of the core removed and that side facing the rotating magnets.
Cogging; We can rectify the output of each coil and then combine the outputs in parallel.
That way we can have the ratio of magnets to core as N+1 or N-1. That should greatly reduce cogging.
One advantage is with a greater diameter we will get a greater voltage for a given RPM.
One disadvantage is that a large diameter behind the wind turbine may not be good.
I have quite a few old mercury vapour ballasts. It’s 20 below in my shop just now.
When it warms up a little I will cut one open and see if it has any possibilities.
I’m trying to visualize that but probably not getting it.
Unless you’re talking about an axial flux alternator, in which case I know exactly what you mean. I’ve built some and they suck.
If it’s something else, can you come up with a diagram?
It may be more informative to explain the concerns driving my thoughts and the parameters that I am trying to optimize.
The voltage induced is a function of the strength of the magnetic flux and the speed at which the flux is cut.
No matter how strong your magnets are, you won’t get the field strength much past the saturation of the iron.
You can rewind a motor for a higher voltage but the available space in the slots means that more turns must be a smaller wire, limiting the safe working current.
With the strongest magnets available, simple math indicates that an 1800 RPM, 480 Volt motor running as a generator at 450 RPM will develop 120 Volts.
One way to increase the speed which the flux is cut, is to increase the diameter of the rotor.
But, before I try to re-invent the wheel. are you satisfied with the performance of the re-purposed motors or would you like something better?
One of my faults is a tendency to try to increase efficiency past the point of diminishing returns.
ps. Working on a drawing. I sometimes don’t use my CAD program for years at a time and I was never very good to start with. It’s slow. grin
Yup, we’re on the same page there. The way you’ve put it is accurately describing my goals. Get the flux in the stator teeth up to the saturation point of the iron. The V/RPM analogy is interesting - something I’d wondered about before but really didn’t have any reason to believe it made sense. And it’s not a subject I can easily just look up in a book because nobody writes books about converting motors, of course.
So if it really is a realistic guide, then:
480V/1800RPM = 0.267 VAC / RPM is the baseline in series, and 0.133 VAC / RPM in parallel
If that’s converted to DC by rectifying, then it’s ( * 1.41)
0.376 VAC / RPM in series and 0.188 VAC / RPM in parallel
When I converted the previous Baldor 3HP, I tested its open-circuit voltage: 37.3 VDC @ 100 RPM
which is exactly the same! So I’ve always believed the V/RPM relationship, but never really could explain it like you can.
The diagram in my last posting has about 1.8T peak flux in the stator teeth, so I’ve pretty much got it to the saturation point now. I’ve done a few other combinations since then, trying to get the same field intensity using magnets 3/8" thick rather than 1/2" thick, and getting close. The gap clearance has to be really tight.
Bill,
That really worked. Your suggestion made a lot of things clear, and last night I was able to crunch through calculations that make complete sense. I can take the V/RPM from normal operations, and then by measuring the stator tooth arrangement inside the motor, the number of wire turns per coil, plus the number of poles, phases, and coil groupings, can get approximate flux per coil per pole. About 1.6 Tesla. This lined up really nicely with what’s being predicted in the FEMM simulations, and also gives me an upper limit to the mass of magnets I need to put on before getting diminishing returns.
It turns out I can get what I want with magnets 3/8" thick instead of 1/2". This saves money and is easier to fit on the rotor. Thank you again for sticking with me and my (probably confusing) explanations of what I’m doing.
How much extra weight can a wind turbine tower support.
I am thinking along the lines of a 1:4 speed increase,
That will give 4 times the voltage and four times the kW for a given size of generator.
Will the saving in generator size compensate for the weight of the gearbox?
The differential from a small car with independent suspension or the front diff from a 4x4 pickup will last forever.
Block the spider gears and shaft drive the generator below the turbine axis.
Has anyone done this?
Comments?
Of course people put gearboxes on wind turbines.
The giant Vestas and Siemens machines run at synchronous speed with the grid and rely on gearboxes to make it possible to use a reasonably sized generator.
In medium size projects, there have been a mixture of not only gearboxes but also variable pitch in all combinations. Here’s an example of that: http://www.wind-works.org/cms/index.php?id=625&tx_ttnews[tt_news]=4331&cHash=98b15e22e0afd78640c43a3d8979433a
The reasons that these larger machines have gearboxes is because right-sized off-the-shelf generators exist and are economical to employ in the machine, provided that the speed mismatch can be dealt with. A 4-pole generator is easy to find, and the gearbox that can handle the ~50kW mechanical power with a step-down ratio of about 20:1 is also available. That lets the blades run at 100 RPM then variable-pitch can be used to capture a decent power curve in a wide range of wind speeds. Build this well and the machine will work.
Many of the components listed above will need some customization to make them serviceable together in a medium-size wind turbine (20 - 200 kW). There are lots of examples of these. But they certainly all require maintenance. A statement that “it will run forever” ignores the need to replace and replenish oil in the gearbox, and to monitor for leaks that could lead to catastrophic failure. Many times, the assumption that maintenance will be done has been made, and successfully so, allowing these wind farms to run productively for a long time. You can see the work platforms on the towers etc.
In very small wind <10kW the assumption of maintenance is not a sure thing at all. You are selling to rich people, home owners, greenwashers. Speaking for myself, I absolutely do not want to have to maintain an oil reservoir that’s 50 feet up on a tower. Lowering and raising the tower is not a delightful experience. It is a chore and exposes my equipment to risk - the lower process is an order of magnitude more dangerous to my equipment than anything the weather can throw at it.
I’ve seen people post stories and photos about their WT projects with gearboxes. Those were fun to watch, and certainly some of these builders succeeded for a while. But in comparison to my machine that has run 10 years with 2 tower moves to replace bearings, every single one of them say that they “do not have a wind turbine any more”.
Back to my current project.
Bill, your tip about the flux in the stator really works. I can do back-of-the envelope calculations and get a number that seems reasonable.
It was many years ago when I was doing some calculations for electromagnets.
Lines of force rather than Tesla.
I checked Wiki.
Wiki
“high permeability iron alloys used in transformers reach magnetic saturation at 1.6–2.2 [tesla]”(https://en.wikipedia.org/wiki/Tesla_(unit))
and
“Saturation puts a practical limit on the maximum magnetic fields achievable in ferromagnetic-core electromagnets and transformers of around 2 T”
Yes, 1.6 sounds very reasonable.
As for gearboxes, my 19 year old pickup with about 500,000 klics is on the second motor, third transfer case and the tranny is getting shaky. No leaks or any issues with the differentials.
The front diff has drive flanges, one of which could support a fairly large blade.
4.11:1 so at a turbine speed of 438 RPM the generator will be spinning at 1800 RPM.
Those diffs will withstand wheel slip forces.
By the way I followed a link you posted in another thread: http://www.scoraigwind.com/
I looked at a couple of DIY generators.
I was surprised to see that apparently they don’t realize the value of iron cores.
Both generator types that I looked at used air core stator coils.
If the combined thickness of the magnets is roughly equal to the thickness of the coreless coil, they are throwing away about 1/2 of the possible capacity.
That does not mean that the units are inefficient as far as work out/work in.
It means that they are using about twice the amount of material than is needed for a given capacity.
At a given current the IsqR losses will be about the same on both machines but the percentage loss will not be the same.
Example:
Capacity without cores = 2 kW.
Capacity with cores = 4 kW
Losses, both machines = 100 W.
(2000W - 100W) / 2000W = 95% efficiency
(4000W - 100W)/4000W = 97.5%
Fun with numbers.
Agreed on the axial-flux generators. I don’t build them for a whole raft of reasons. They aren’t very robust. I refer people to Scoraig wind because it’s about as organized as you can get for a home-built wind turbine kit and the guru there really deserves to sell those great books he wrote.
Without an iron core the air gap is reallllllly big. The trouble is where to put the iron if you wanted to add it. It would have to be central to the wire coil, and ideally you would make it laminated. But as the magnet passes by, it changes the forces between magnets and the smoothness of its motion, so the magnet rotor disks need to be much more stiff. Everything gets heavier. As each magnet passes a block of iron there’s a pulse of force so we also get vibration. The original goal was to make something simple and cheap, so iron cores were discarded as too difficult for the “homebuilder” to deal with.
It can be done. I’ve seen it done, but it’s much more complicated.
Hey - putting a tranny on a wind turbine is possible if you want to. I’m just listing the things you’ll have to overcome if you want to do it. And I’m not done my list yet. I chose to keep mine as simple as possible. I’ve met homebuilders who tried gearboxes and others who’ve tried pitching blades, too. They don’t have wind turbines any more, but I still do. Does that make mine better? I think it does. Do you want to prove me wrong? The winner is judged by the machine that puts the most kilowatt-hours into the grid or the batteries.
OK I am about to click the BUY button on CMS Magnets but just can’t quite convince myself that my new complicated idea to make the rotor is actually easy to assemble. Putting together multiple wedges with magnets pulling on them and getting everything aligned - just so - doesn’t look easy to do right now.
The winner is judged by the machine that puts the most kilowatt-hours into the grid or the batteries. 