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12V Wind Turbine - Voltage question

  1. Feb 23, 2015 #1
    Hi,

    I have this wind turbine (http://m.ebay.co.uk/itm/251320008073?nav=WATCHING_ACTIVE&skus=Output:12V&varId=550270984212) in the UK, wall mounted about 18ft, its not in the best position, but it still turns pretty fast, enough to hear the blades spinning from inside, and for it to generate 17VDC (Even though its only rated for 12v).

    The issue is, when its spinning quite fast, its only generating about 5-7 volts, 7volts plus is when you can start to hear the blades making a noise. I'm just wondering why it has to spin that fast to generate anything? It seems like it needs Arctic winds constantly just to get any use out of it.

    Is there anything I can do? It generates three-phase AC. If I had a 24v turbine, I'm presuming it wouldn't need to spin as fast to generate about 12-14v?

    Thanks,
    Owen.
     
  2. jcsd
  3. Feb 23, 2015 #2

    sophiecentaur

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    Perhaps it is faulty in some way. If the alternator has some open circuited turns, you would expect it to under perform. Or else, the bearings may be worn or the blades distorted so it makes a lot of noise even at low speed (I have had that). IS there a published spec of output volts and current for different wind speeds? My 12V, 2A turbine needs a lot of wind to give any more than the 2A claimed - but that is to spec.
    I read the (your) advert and it is a presented in a rather 'quaint' way. Have you any reason to expect it to work as well as they claim? Not everything you can buy on eBay is what it claims to be. OTOH, my Rutland 503 turbine is very low power but does exactly what the makers claim - it cost more than yours when I bought it a few years ago. Perhaps you get what you pay for?
     
  4. Feb 23, 2015 #3
    Since I was a lad, I dreampt of building one of these for my grandfather. But, my studies have shown that you really do need quite a wind speed to produce the advertised power, and lesser speeds just produce dribbles of energy.
    Another frustration, and this is on the part of folks such as yourself, is that these machines produce a varying amount of optimal voltage versus speed. That presents a challenge regarding power conversion. I know any number of people who would start scratching out a design for a switching power converter, but having something on the napkin is a long way from having something in your home that won't start a fire...
    If you substituted a 24 volt alternator, you'd simply have scaled the problem to a different range. I suspect someone has dealt with this and produced a power converter to change the varying source voltage to a fixed voltage for use. If not, perhaps it's a good time to use the phone and ask why not.
     
  5. Feb 24, 2015 #4
    Hi,

    Thanks for your replies. I have seen the turbine reach 8A, not sure at what voltage, but most likely 17v, which gives us about 130watts (from the top of my head). That was only for about a second before the massive gust of wind died down and dropped it to 6A and back down to 0. That was by putting an analogue Amp metre in series with the output of the charge controller I have.

    It seems like its working fine, but until I see some sort of graph showing the voltage or amps versus wind speed, I don't know what to think.

    Could you tell me what sort of problems i might have if I went for a 24volt instead?

    Thanks.
     
  6. Feb 24, 2015 #5
    A 24V, 300 W machine gives the same power as a 12V, 300W machine when each is running at rated speed, voltage, and current. Tying a 24V alternator into a 12V battery will allow it to charge at 1/2 of rated speed, but it will only deliver 1/2 of its rated power.
    The 24V machine has thinner wire to accommodate more windings. Thus, it's made to deliver less current in return for delivering a higher voltage. With a strong wind, you may damage the alternator or blow fuses / breakers.
     
  7. Feb 24, 2015 #6
    Ah I see. When you mean damage the alternator, is that because its spinning too fast? It has electro magnetic breaking built in (unless thats down to you for breaking it manually).
     
  8. Feb 24, 2015 #7

    sophiecentaur

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    There is no point in trying to beat the system in this way. The windings will have been designed with (hopefully) the right number of turns and the right gauge of wire for 12V operation. That will be the optimal design for a 12V battery bank. Working a 24V alternator into a 12V battery bank could roast the wire or, most likely, bring in the Current Limiting regulator (Electromagnetic brake). That, of course, would mean that you get less peak power to your battery.
    It may be possible to choose a better site for the turbine than the one you are using (?). A small, hand held anemometer (as used for sailing etc) could be used to test all points in your property. An in-depth survey like that could give you a good return on your effort, in the same way that you would (more obviously) choose the best site for a PV array to avoid shading.
    Height can make a big difference.
    P.S. Is it too late to send the unit back? I don't like to be too negative but, after the experience of having run my wind turbine for several years*, I would not buy another one. PV has become much cheaper since I made my original choice and, in moderate Latitudes, and not in the "Arctic" winds, the Wind solution for low powers may well not be the best. But the price you paid is surely not too much to spoil the fun of your experiment. It can supplement a PV array if you want a reliable supply.
    *They are very noisy in the confines of a small boat!
     
  9. Feb 24, 2015 #8
    Hi,

    Thanks for your reply. I was wondering sending it back and try to find another turbine that generates around the same but at a lower RPM, although I don't think I will without the price getting higher and higher.

    As for the turbines current position, its not in a good place like I said before, its close to the house and only has proper access from three directions. Its not in the middle between the two houses. I originally wanted it wall mounted at the side of the house so the turbine is above the roof, but I'm not sure how much the planning permission will cost on a normal UK house in a culdesack.
     
  10. Feb 24, 2015 #9

    sophiecentaur

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    I think it's down to swept area. If you can go twice the diameter (will look massive, I expect) then you can probably use less than half the wind speed. If you look at Websites of 'professional' installers you can get an idea of what's needed for a seriously workable system. It's no wonder that everyone is not doing it. They are very costly.
    Is there another wind turbine in your locality? There is only one near me (high on a hill in Brighton) and that is on a School campus.
    If you look upon this as a bit of entertainment then you will get good value out of your money but any truly useful system would create howls of objection from neighbours. It could be well worth while doing a bit of a survey, as I suggested. It's seriously hard work to move a support mast to another part of the house, chasing the prevailing wind.
    Good luck with it.
    (Look at the local Government site to find planning applications for one.)
     
  11. Feb 24, 2015 #10

    jim hardy

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    Well, your statements about speed and volts are confusing.
    Are you getting ~6 or ~17 volts?

    I note "rated " speed is 1850 which will look mighty fast for a near four-foot propeller.

    They claim in paragraph "Introduction"
    15 m/sec is 33moh. edit> make that mph
    But the user manual says
    And specifications say
    Inconsistent at best. 12.5m/s is about 29.8 mph.
    Let's take the instruction manual's number of 30 KWH per month with wind at 5.8m/sec
    that's ~ 1 kwh/day = 412/3 watts, which at 12 volts is ~3½ amps.
    at wind speed of 5.8m/sec = 13 mph.

    The quick test for a permanent magnet generator is to plot unloaded volts versus RPM and compare to design.
    If you're not getting design volts
    You could have a defective generator or a defective rectifier.

    If you are getting correct volts for a known RPM,
    then we need to put a number on your perception of "arctic wind".

    old jim
     
    Last edited: Feb 25, 2015
  12. Feb 25, 2015 #11

    sophiecentaur

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    Yes Jim. The devil is in the detail and that spec is not one that should be used in deciding whether or not to invest a 'lot of' money. At that price, we are dealing with a 'fun project' and nothing more. I am sure it is written in the hope that not-too-technical people will buy it as a serious addition to their home electricity supply. In my experience, you really do need pretty high wind speeds for a small wind generator to do its stuff and that involves noise.
    eBay would help in any argument about the seller's responsibility to replace the unit if it is not doing what it claims. (As long as the unit is returned soon after the transaction.) If a replacement does the same thing then you should get your money back. But you will need to be able to measure wind speed reliably.
     
  13. Feb 25, 2015 #12

    jim hardy

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    Decades ago Mother Earth News printed designs for home-made turbines using car alternator and bicycle sprockets.
    In those days a 30 amp Chrysler alternator cost only $19 new.
    The simple ones without internal regulator are still cheap, probably around $39..
     
  14. Feb 25, 2015 #13

    sophiecentaur

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    Then you need to design and build a suitable turbine which will not shake itself to death and also deliver the required torque at reasonable wind speeds. Getting the balance right would be beyond many home constructors.
     
  15. Feb 25, 2015 #14
    I actually have two vehicle alternators, but can't get past the issue of it causing a high amount of torque when it's trying to excite is magnetic field. I thought they'd only be useful for hydro, since after it's got past that 'high torque', it carries on rotating easily while generating electricity. I can get access to alternators at my college, so if there's a better one for wind, tell me which one and I'll see if there's one on the shelf.

    As for the turbine, I only wanted something to charge batteries, not something to 'reduce bills'. I have currently got my turbine connected to this rectifier (although proven to be inefficient to it's 2v+ drop on the diodes), and then connected to a 'boost buck' which 'steps up' the voltage to 14.4v which I variably set. I then had the output connected to my solar charge controller so I can see if it's outputting any power when it's spinning, and it reached 14.4v @ 1A - though there was barely any wind at that moment, so it didn't rotate as fast as it did before.

    Obviously I dislike this method, as it's like having a power station capable of generating MW of power, and you're unable to fuel it, so you're only able to generate a kW (poor example).

    Thanks for the replies though.

    PS: jim hardy, remember my previous thread on alternators for wind turbines?

    Also, is this the article you meant when on about Mother Earth News?

    I found this article as well on this guys alternator-based wind turbine. How does this even work?
     
    Last edited: Feb 25, 2015
  16. Feb 25, 2015 #15

    jim hardy

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    I recall that there was such a thread but dont remember it very well... "Sometimer's" syndrome i guess, can remember details of conversations from 40 years ago but not 40 minutes....

    The Mother Earth News article that i remember was from around 1970
    it described a far more primitive machine using mostly bicycle parts
    i think the blades were plain flat boards more like traditional windmills in western movies.

    That article is short on data. I believe he needs a LOT of wind to make electricity.
    He appears to use a "one wire alternator" which we didn't have in 1970... they must be revved up to a thousand or two RPM to start generating, as explained here:

    http://bob_skelly.home.comcast.net/~bob_skelly/alternator_conversion/wiring_alternator1.html [Broken]

    I have not built such a gizmo myself so cant give you an informed opinion.
    His pictures look to me like a high wind location - observe how the trees in background lean...
    Should you undertake to build one of these, plan on some testing. Friends of mine mounted their wind turbine on a flatbed trailer and took it out on lightly travelled roads to test its performance.

    old jim
     
    Last edited by a moderator: May 7, 2017
  17. Feb 25, 2015 #16

    jim hardy

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    errrr,,,ummm... not sure i understand the concern over torque.
    dont forget energy is conserved
    if you expect electrical energy to come out of an alternator , you must put mechanical energy into it as torque X rpm .

    decent layman's explanation of excitation here



    that's why the first article included a centrifugal switch for the field.
     
    Last edited: Feb 25, 2015
  18. Feb 25, 2015 #17

    sophiecentaur

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    A vehicle alternator is designed to rotate at 3000+RPM at least so using it for wind generation will always require some gearing / chain / belt arrangement to multiply up the speed. That will make the starting friction effects worse and be a serious problem unless some sort of centrifugal clutch (or equivalent) is used to allow the turbine to get going, in order to get over the initial torque needed. It seems a very unsuitable candidate, to me - despite being cheap and available.
     
  19. Feb 26, 2015 #18
    If you get an alternator and begin to rotate its shaft by using a drill for example - making sure that there is a bulb in series with the input where the dashlight connection would go, then when it gets up to speed, you'll feel a big torque in which the bulb will begin to go out, since its trying to excite the rotors magnetic field. And of course, it will be inducing a current in the stator, so that will have a magnetic field.

    That's why I said I'd only really use an alternator with some sort of water wheel, so I can get a wheel from an old bicycle let's say, and attach that to the water wheel, and you have your ratio. This is because once you've got past that 'excitation torque' it'll freely spin again like it does when you spin it by hand, but it will be generating this time. I only know from experience and experimenting around with them.
     
  20. Feb 26, 2015 #19

    sophiecentaur

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    But what about the rotation speed requirement? A car alternator doesn't produce much power at ticker - at which speed the alternator will be doing not far short of 3k rpm. Surely what's needed is an alternator with many more poles.
     
  21. Feb 26, 2015 #20
    You're absolutely right, I'd still be stuck with a high speed requirement, in this case, a lot higher. The easiest would be to just get a PMA or build one. I actually have an alternator disassembled and just needs the claws being opened to fit a donut magnet in there.
     
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