Is there a formula?

BilljustBillBilljustBill Solar Expert Posts: 212 ✭✭✭
In 1980, I learned about wind power by rebuilding an old 6 volt Wincharger. Later, I put up an Entertech 1800 and lived with it for several years.

Then about ten years ago, I bought two 50 volt Ametek motors when a surplus dealer scrapped old tape drives from the old computers of the 1990's... and shelved them until now....

I've found the bargain of an auction on six 29" blades made of carbon fiber like these:

http://cgi.ebay.com/6x-64-Wind-turbine-generator-blades-for-AMETEK-motors_W0QQitemZ200409553431QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea9571a17

The main question is that I'd like to run a front set of blades for one Ametek and rear set for the other Ametek while they are on the same pivoting frame and use the same slip rings. I remember that when Biplanes were designed, the formula for the space between the bottom wing and the top wing was based on 1-1/2 times the width of the wind (cord).

If I build this type of wind turbine to use both generators, and make the rear boom longer and further back acting like a tail, how much space between the two sets of rotor blades? Or use a 3-blade rotor in the front and the six blade rotor for the back to get the best of low and medium wind speeds Using a 45' sissors tower and guy wires, do you think this turbine design will work?

Ideas for a charge controller on a 12v battery bank?

Thanks for your opinions and observations,
Bill
Bill

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is there a formula?

    You may find there's some problems with running two sets of blades within one 'airstream path'. The turbulence created by passing over the first set of blades will greatly reduce the effectiveness of the 'rear' set.

    I have a vague recollection of an attempt to increase harvesting capacity and reduce vibration by using a similar set-up which involve the rear set operating in reverse direction of the front set. I can't remember the specifics, but you may note you don't see such a set-up offered commercially anywhere these days. That could be a clue to its viability. :p

    Charge controllers for wind turbines is another issue. MPPT type controllers are often used for their ability to 'down convert' high output Voltages and to automatically engage diversion loads, but they have issues keeping up with ever-changing output of turbines in varying winds. PWM type controllers don't have this problem, but generally can't 'down convert' or handle diversion loads. Picking the right controller is a matter of your turbine's specific output characteristics and what you need to do with it.
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: Is there a formula?

    Coot,

    How long of a length would it take to offset the turbulence on the rear blade, if any ?

    And what if you can set the pitch on the rear prop to offset the airflow difference and make it spin faster or easier ?


    BillJustBill,
    This is overkill, however I use a Morningstar TS-60 for my 3 turbines. It's got all the features mentioned earlier.
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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is there a formula?
    Coot,

    How long of a length would it take to offset the turbulence on the rear blade, if any ?

    That is a very good question. The answer is: it varies with the wind speed.
    If you've ever seen images of 'wind tunnel testing' where they stream smoke into breeze to see how air flows across a car or plane you get an idea of what's going on. Think about billions of parallel streams of air flowing towards the blades. Some of it hits the blades, and in accordance with Newton's Laws imparts some of the mechanical energy to the turbine causing the blades to turn. This air is then deflected off at an angle with somewhat less energy in it. Other streams miss the blades entirely, and go past without energy loss until they run into the deflected streams. Slight deflection of the 'straight' streams and slight 'correction' of the angled ones. Eventually the streams will exchange energy and resolve themselves into relatively straight airflow again.

    How far back this happens is dependent on the speed of the wind and the characteristics of the turbine. Basically, the faster the wind the greater the turbulence and the longer it takes for the air streams to resolve.
    Take a look at how far apart commercial wind turbines are, as in this pic by great a professional photographer: http://thaumadzo.deviantart.com/art/Grounded-145251171
    Even the install instructions for small-scale wind always wants no obstacles for hundreds of feet around. Here's a view from TLG's site which shows many small turbines:
    http://www.tlgwindpower.com/
    And what if you can set the pitch on the rear prop to offset the airflow difference and make it spin faster or easier ?

    Another very good question. Again the answer is that the variables are such that the rear blades would probably have to be variable-pitch to maximize 'harvesting'. It'd take a really good aerodynamics expert to figure this one out. Not my forte, but I bet someone somewhere is working on it.
    BillJustBill,
    This is overkill, however I use a Morningstar TS-60 for my 3 turbines. It's got all the features mentioned earlier.

    Darn good charge controller, that.:D
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: Is there a formula?

    Just had another epiphany. What if......

    The front prop was about half the size of it's rear one, and the rear prop acted like a tail ?
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  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Is there a formula?

    There are multi-prop wind turbine designs... Here is one that can have a dozen mounted on a long shaft. More here. Available for sale over there.

    There is an assumption though that they sit at an angle to the wind (notice that the "tail" is at an angle to the rotor axis)--not in direct shadow of the blade set in front.

    Interesting design--not quite sure I am thrilled with the alternator 100% exposed to weather and the large lever arm of the main shaft if anything goes south.

    They have even done a tandem prop aircraft too (Cessna Skymaster for one). As I recall, I pilot I used to know flew those in the Vietnam war and told me that the fuel flow (which is directly related to horsepower) was something like 60/40 front:rear engine...

    If you intent is to pull maximum energy from a particular air flow--multiple props can do that--and that is what a classic turbine (jet engines, pumps, steam turbines, etc.)--sometimes with multiple stages.

    However, I would guess that if the 60:40 rule works out... To get that last 40% you have to spend quite a bit of money for that... You may be better off increasing diameter by 30% (larger swept area) or installing a second turbine...

    You will avoid the issues of vibration as the trailing prop hits the wake of the tower, and the turbulence of the first prop.

    I think, years ago, I read an article about a proposal to put two counter rotating propellers on a a turboprop aircraft for higher efficiency... Ah, found something about that here.
    f it is well designed, a contra-rotating propeller will have no rotational air flow, pushing a maximum amount of air uniformly through the propeller disk, resulting in high performance and low induced energy loss. It also serves to counter the asymmetrical torque effect of a conventional propeller (see P-factor). Some contra-rotating systems were designed to be used at take off for maximum power and efficiency, and allowing one of the propellers to be disabled during cruise to extend flight time.

    Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers[1]. However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 db, and tangentially 10db[1]. Most of this extra noise can be found in the higher frequencies. These substantial noise problems will limit commercial applications unless solutions can be found. One possibility is to enclose the contra-rotating propellers in a shroud. It is also helpful if the two propellers have a different number of blades (e.g. four blades on the forward propeller and five on the aft).

    The efficiency of a contra-rotating prop is somewhat offset by its mechanical complexity. Nonetheless, coaxial contra-rotating propellers and rotors are moderately common in military aircraft and naval applications, such as torpedoes, where the added maintenance is not as much of a concern to government budgets.I][URL="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed"]citation needed[/URL][/I
    It is a Wiki--but it seems to conform to my, limited, memory of what I have read over the years. Notice that this setup can be more common on ships.

    Not to say that it cannot be done (it has)... It will take some work and experimentation to figure out the optimum setup.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: Is there a formula?

    Is there anything out there that will "Funnel" the wind down a short tunnel to increase the air pressure and speed ?

    Why not forget the extra prop and find a mini-shroud in front that narrows the wind path into the blades ? Theoretically, the cut-in speed could be much less than 7mph. It's kind of like that homemade box fan setup mentioned a month or so ago.
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  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Is there a formula?

    The problem is with 6-7 MPH wind--there is very little energy in it. Even if you can collect the energy, there will not be much.

    Regarding the Ducted wind turbine--it has been done many times (from NAWS's Wind Turbine page), follow this link:
    Shrouded Wind Turbines
    So far--not very many successes (unless you include separating people from their money by fraudsters).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is there a formula?
    Is there anything out there that will "Funnel" the wind down a short tunnel to increase the air pressure and speed ?

    Basic physics problem; when you funnel that wind into a smaller space with increased pressure, some of the mechanical energy in that wind will be converted to heat from the compression. Net result; energy loss.

    There's simply no way to take "X" amount of energy and turn it into "2X" energy without adding energy from some other source. Even then there is an energy loss from combining the two.
  • BilljustBillBilljustBill Solar Expert Posts: 212 ✭✭✭
    Re: Is there a formula?

    Looks like some good thinking and questioning going on here!! I thank each of you; keep going!!! My idea of this dual rotor comes from a memory of a company in Florida that tried to design one twenty years or more ago. I haven't been able to find any old info on them.

    So far, what I think I've learned is four things:

    The centerline of the rotors should tilt downward (maybe 15 degrees?) to get the front rotor's propwash somewhat out of the back rotor's way.

    Give some distance between the rotors; maybe 15% more that the span of the front rotor.

    Offset the tail to allow the rotors to furl and rotate out of the wind direction for overspeed protection.

    Use a good solid controller like the TS-60 to control the varying voltages of the Ametek motor/generators with the excess switching to a dump load into the heating element(s) of a second hot water heater tank when the batteries are full or the wind turbine has extra amps.

    Now, let me ask this: If one generator is being rotated by a 3-bladed, 65" rotor and the identical voltage back generator is rotated by a 6-bladed, 65" rotor of the same type blades, Can I wire these in parallel, even though they will be running at different speeds?

    Being wired together the voltage/amp/watt output could be increased, but then, I could use one set of slip rings. What do you think?

    I'd be using these blades:
    http://cgi.ebay.com/18x-64-Wind-turbine-generator-blades-for-AMETEK-motors_W0QQitemZ360213379441QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item53de63f971
    Bill
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is there a formula?

    Identical generators turning at different speeds produce different Voltage. Parallel wiring wouldn't work. To get maximum harvest you'd need two controllers of the MPPT type so both varying generator outputs could be down-converted to the same Voltage with varying current levels as available.
  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Is there a formula?
    The centerline of the rotors should tilt downward (maybe 15 degrees?) to get the front rotor's propwash somewhat out of the back rotor's way.
    Down, left, right, does not matter. The angle will be somewhat proportional to the length of the shaft/offset. Shorter shaft, more offset to avoid blanking. Notice that the rotor blades are well offset from each other in the couple designs I posted.
    Give some distance between the rotors; maybe 15% more that the span of the front rotor.

    Your choice, but again the examples I posted showed a much larger offset (scale the pictures but 2x the diameter was closer in some of them.

    To a degree, you will have to experiment and see what is optimum for your design. Note that the farther you point your blade axis away from the wind, the less power you will generate.
    Offset the tail to allow the rotors to furl and rotate out of the wind direction for overspeed protection.

    Two different effects here... One duel rotor design had an offset tail to avoid the first blade set blanking the second.

    Furling or an adjustable tail offset (up to 90 degrees) would allow automatic or manual shutdown and protection against high winds (depending on how you design your mechanics).
    Use a good solid controller like the TS-60 to control the varying voltages of the Ametek motor/generators with the excess switching to a dump load into the heating element(s) of a second hot water heater tank when the batteries are full or the wind turbine has extra amps.

    Just to be clear, the output voltages of the Ametek generator is set by the battery. The current output of the generator is set by the rotational speed and torque.

    A diversion controller simply looks at the battery voltage and, when it decides the battery is fully charged, just turns on a "dump load" to divert excess current (power) to the resistor bank.

    There are MPPT type charge controllers for Wind Turbines that find the optimum I*V maximum point for a generator/alternator (similar function to that of a Solar PV based MPPT Charge Controller), but the MorningStar is not one of them (not sure there are many MPPT wind controllers out there yet... Midnite Solar has their "Classic" controller design in testing--but is not available for purchase yet (as far as I have read here).

    A MPPT Wind Controller has the potential to dramatically increase harvest. Should be interesting to read other's testing when the controller becomes widely available and specifications are released.
    Now, let me ask this: If one generator is being rotated by a 3-bladed, 65" rotor and the identical voltage back generator is rotated by a 6-bladed, 65" rotor of the same type blades, Can I wire these in parallel, even though they will be running at different speeds?

    The dual units I have seen just use one alternator and 2 or more blade sets. Are you planning on one alternator per blade set?

    Notice that Ametek are true DC Servo Motors (as far as I know) and generate DC voltage/current. Connecting in parallel should be OK (can be other problems--fusing, side loads from gearing/blades, weather resistance, etc.).

    Many turbines use Car Like Alternators... These are 3 phase devices and you have the choice of bringing down the three phase or using the internal rectifier (diode) bridge to convert to DC and tie to the battery bank.

    Paralleling rectified DC output to the battery bank is fine. Paralleling the three phase output will not work.
    Being wired together the voltage/amp/watt output could be increased, but then, I could use one set of slip rings. What do you think?

    If you use DC output and appropriately sized slip rings--should be OK. Make sure you secure the wiring to the slip rings appropriately. Many slip ring assemblies will fail if the wire is simply hanging on the slip ring connection and suspended down the center of the tower.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BilljustBillBilljustBill Solar Expert Posts: 212 ✭✭✭
    Re: Is there a formula?

    The dual units I have seen just use one alternator and 2 or more blade sets. Are you planning on one alternator per blade set?

    In thinking out the design, it is built around two Ametek 50v DC motors. Each one is being driven by separate sets of blades; three blade rotor on the front for mid to higher winds, and 6 blade rotor on the rear to use mid to lower wind speeds with extra drag on the longer downwind boom that keeps both rotors into the wind. .

    The front rotor will be about 14" from the tower pole centerline. The speed control is based on this front rotor and operates like the old 1920's Parris Dunn design where the generator and rotor tips up and back. As it furls, this should scatter the wind to the rear rotor, too. (We'll see... ;>)

    To keep the assembly from being tail heavy, yet allows a longer distance between rotors, the rear 6-bladed rotor runs through two sealed pillow block ball bearings with a 3/4" diameter, long shaft. The pitch of the blades would use the adjusting tab that comes with the set and allows a coarser pitch for more torque and lower RPM. The rotor shaft is coupled to the second Ametek with a cushioned-splined coupling used to connect a engine/motor to a water pump. The generator is mounted on top of the centerline of the tower pole's pivot bearings where its weight is carried. (Copyright concept BZ).

    I'm in the wind zone rated 1.5 as we are close to the beginning line of #2 zone , so winds do get high, but average windspeed is relatively low. Plus these Ametek motors have an original intake hole and exhaust hole where air must have been pumped through them for cooling. I've not seen these on the Ebay Ametek's....

    Thanks for your ideas and comments,
    Bill
    Bill
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