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axial flux pma help

Discussion in 'Renewable Energy' started by dropthetailgate, Feb 3, 2013.

  1. dropthetailgate

    dropthetailgate New Member

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    I built my first ten inch 24 N42 magnet and 9 coil 16 ga 257 grams each +/- 4 grams. It is not perfect I know but!!! It is making 24 volt at about 140 rpm. It is star configured by the way and two of the phase terminals measure 2.4 ohms and the run to the house is about 75 feet of 12ag. It is on a 69 sq ft VAWT using a belt drive. What I am confused about is that at an estimated calculated based on gear ratio speed of 500 RPM it only produces maybe 0.5 to 1.0 amp. The gap is probably 1/8 inch which I understand is wide due to my errors but still it brakes hard when shorted. It crosses my mind that the belt could be slipping but I don't think it is. At about the charging point of about 140 rpm it is making .o6 amps. Do you have any thoughts on this to share with me?
     
  2. dropthetailgate

    dropthetailgate New Member

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    Well the belt was slipping. I reduced the gear ratio 9:1 to 5.5:1, used a longer belt at lower angle and tightened the belt up and am up to 2 to 3 amps at about 150 RPM so that is a little learning experience relief. I'd still like some input on peoples experiences with belt drives etc in a similar situation. And what you think about going to an 18 awg stator direct drive or at least much more reduced gear ratio say 2:1 maybe. I don't think in that case I would have to put as much tension on the belt and axle that way to keep it from slipping.
     
  3. Mr RB

    Mr RB Well-Known Member

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    Photos?

    What is the max power output supposed to be? 24v at 3A does not sound a lot of power out considering the trouble of building your own generator.
     
  4. dave

    Dave New Member

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  5. dropthetailgate

    dropthetailgate New Member

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    Don't give up on me. I will try to get you a decent pic. I know the power is low. I'm disappointed but will figure it out I hope maybe with your help. I had figured that I would see about 150 watts at 10 or 12 mph winds.
     
  6. bryan1

    bryan1 Well-Known Member

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    ok how many turns did you do for each coil as that will dictate the voltage per each RPM. Generally one will do a one coil test before casting the stator then doing a sum to work out the cutin rpm. Basically the more turns on a coil will produce more voltage per 1 revolution. Now VAWTS aint the most efficient so don't expect too many amps out as once the current starts to flow the torque required will soon bog down the VAWT.

    On the fieldlines forum a few years was a competition for anyone to show a VAWT producing more than 100 watts on a continuous basis and that prize was never won.

    Now go make a HAWT and say put a 3 metre prop on and watch the performance difference....

    Anyway I'm not trying to rain on your parade but 2.4 ohms does sound too high as DIY builders do like to keep the resistance under 1 ohm for each phase.

    A pic of your VAWT would be nice to see and I do think a new stator wound to suit direct drive would perform much better.

    Regards Bryan
     
    Last edited: Feb 4, 2013
  7. dropthetailgate

    dropthetailgate New Member

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    It is about 125 turns but as stated it cuts in around 140 rpm hitting 24 volts that is. I am going to need some time to become comfortable with all the proper terms. It is around 2.4 ohms across each pair of the three coils. So 1.2 ish ohms per phase. I think better out loud if you know what I mean so this helps. When I tested the stator voltage by hand with no load I don't recall much surging. I will double check that. Today some buddies discussed it at work with me. Helped me think. The amperage is surging under load. Makes me think that even though I can't see or hear the belts slipping I think it still is. I am going to go to an even smaller gear ratio and see if it does not help some more. It could be stalling because of what you said the VAWT is not so efficient. I based everything designing it on 80% efficient turbine being it spins at about 80% of the speed of the wind with no motor or gears etc..

    [​IMG]
     
  8. dropthetailgate

    dropthetailgate New Member

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    The clapping is a just a spacer bushing that needed adjusted. It runs nearly silent.
     
  9. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    69 ft square for 150 watts sounds rather inefficient to say the least. :eek:

    Not to be rude but for that small of unit and for the time effort and costs of materials and to only run at a few hundred RPM tops why didn't you just go with a larger direct driven stepper motor or PM AC servo motor for the generator?

    I never have figured out why so many people want to spend a pile of time effort and money to make 'roll your own' generators when there are loads of pre made commercial grade AC and DC motors that will walk all over any home made design for output, durability, efficiency, and size for the same or less costs. :confused:
     
  10. dropthetailgate

    dropthetailgate New Member

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    tcmtech, Please provide me with a link to the AC motor you feel would best suit my needs. I think the only data you really need is that the turbine is 4' dia. and runs roughly at 80% the speed of the wind at wing tip at average wind speed of about 11mph in the winter here and as you know it is currently 69 sq ft. Thanks.
     
  11. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Just watch the online auctions like eBay. All you need to do is some basic math to find a motor that has power specs and related speed and torque numbers equal to or greater than what your rotor will be working at and call it good enough.

    What you would be searching for would be stepper motors, PM AC servo, PM DC servo, or PM alternators. Given those search criteria I guarantee you will be overwhelmed with the choices you will find! :D

    Personally I am a fan of using the multi KW Getty's, GE, and Fanuk industrial servo motors for my wind generator projects being they are nearly indestructible but I guarantee you wont like the prices! $$$$$$$

    From what I saw earlier today a good low speed PM DC servo motor that could put out at least 150 watts at 150 RPM or close to it is around $100 new. Used are even less.
     
  12. Mr RB

    Mr RB Well-Known Member

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    I would deal with the belt slipping first, try something like a toothed belt (timing belt) and pulleys, or even a small well-oiled bicycle chain and two sprockets, which is probably cheaper and easier in the early stages as you can try different gear ratios.

    The gear ratio will be important, to optimise the generator output power for your typical wind conditions.

    A photo of the home made generator showing size of the rotor and number of poles etc would also be a big help. :)

    If buying a motor the Fisher Paykel washing machine direct drive motors can make an excellent low-speed generator.
     
  13. dropthetailgate

    dropthetailgate New Member

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    Thanks that is what I am doing. I have made my second adjustment to the gear ratio now and switched to a 5/8" belt from a 1/2" belt for better traction. As soon as I get some wind I will see where I am. The rotors are 10 inch. 24 1.5"x 0.5" inch round n42Mags and the stator is 16 AWG three phase 9 coil 1.2 ohms per phase around 125 turns as I recall. The gap is about 1/8". It hits the 24 volt load charge level at about 120 to 130 rpm. The wind was lite today about 5 to 10 closer to 5 mph today just barely enough with the newest smaller gear ratio used so far of 4.5:1 to give me a pretty steady 0.06 amps. I will let you know if I see any improvements as soon as the the wind picks up better. I forgot to mention I think that I did see improvement already when I made my first gear change going to 5.2:1 It then surged about 1 to 3 amps so there seemed to be less slipping then.

    pma.jpg
     
    Last edited: Feb 6, 2013
  14. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Any chance you can reduce that?
    What magnetic material are you using for the coil cores?
     
  15. dropthetailgate

    dropthetailgate New Member

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    I went out and turned the motor by hand with it under load to get a better feel for what I was dealing with. What a lesson that was. They taught it in school but that is a whole different story on paper isn't it. My gosh it amazed me the torque it required. I'm a physical chemist of about 23 years now in the steel industry and related fields. So you probably are thinking what a dumb one I must be when I tell you this. I have seen some amazing and powerful things. Been close enough to almost touch steel that was so hot it was white. Seen Blue flashes in electric arc furnaces that are guestimated with high probability of accuracy to be electrons converting from mass to energy. I never dreamed I would feel power like that in my hand made from what say you about 8 pounds of nothing but metal assembled in my kitchen by hand with glue. WOW!
     
  16. Mr RB

    Mr RB Well-Known Member

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    It should freewheel with no effort at all, until you get the 130 RPM where it will finally put current into the battery. Under that RPM there should be no current flowing and no electrical load, and there should be no mechanical load as your coils (the stator) has no steel? From what I have seen of these generators the coils are just wire glued into a plastic or wood former to make the stator.
     
  17. dropthetailgate

    dropthetailgate New Member

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    Where I am now. The belt slip is a big factor. I changed the motor to mounted bearings but most important reduced the pulley ratio to 2.7:1. and went to a 5/8" belt as opposed to 1/2" My new record is now upwards of 300 watts. The wind was probably 25 mph maybe plus some then. I know it's not perfect but I feel I am on my way. I am going to change to a stator that will allow me to direct drive the motor or close to.

    [​IMG]
     
  18. bryan1

    bryan1 Well-Known Member

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    G'day,
    If your going to use a direct drive alternator then it will be handy to know what RPM the VAWT spins at for your desired cutin. Then you'll have the RPM figure to do the one coil test on the bench.

    It has been a while and the grey matter is a tad rusty but off memory here is the calc for the one coil setup

    Say at 150 RPM you get 4.95 volts off that single coil and your using 9 coils in the stator so 3 coils for each phase.

    So 4.95 x 3 = 14.85 x 1.414 (star connected) = 20.9799 - 1.4 ( Rectifier Diode Drop) = 19.59 volts.

    Now less turns will produce less voltage and more turns will increase the voltage, for holding the single coil I just use the famous Hot Melt Glue onto some wood board to hold the coil between the mag plates. By trying out each wound coil you'll be able to find the sweet turn number to suit your genny and not have too many stators being used as tea cosies....

    Cheers Bryan
     
  19. summitville

    summitville Member

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    TCM Tech,
    What size (diameter) wind turbines are you flying ?
    What Model generators are you using ?
    Thanks,
     
  20. dropthetailgate

    dropthetailgate New Member

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    Here is a vid of the turbine and a pic of my controls. The turbine is 17.25'X4'. It spins about 85% the speed of the wind without the motor and pulley on it. So it spins about 60 rpm at 10 mph and should spin 70 in a perfect world. At this time I am happy with the direction things are moving. I just got 18 AWG wire in the mail for a new stator. I will see where I end up then go from there. I have another question. Is it really that bad to add newer batteries to the older ones to increase the size of the bank. If not then would there be any advantage to put newest batteries in one parallel and older ones in the second parallel set. The batteries are 12 volt and the system is 24. Also should I put fuses on each and every wire going to a + post? I read it is good idea but I don't see people do it.

    [​IMG]
    [​IMG]
     
  21. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I prefer to run the standard three blade horizontal style up to around 9.5 feet in diameter going direct drive to large Gettys DC servo motors.

    Here is one of mine from a while back. http://www.electro-tech-online.com/threads/wind-generator-up-and-running.93158/

    Then the crash and burn. http://www.electro-tech-online.com/threads/wind-generator-no-longer-up-or-running.93321/

    Then the rebuild. http://www.electro-tech-online.com/threads/wind-generator-up-again.104543/

    Then it crashed again and since then I have gotten married and have a regular job plus am building a house so I have not worked with anything serious relating to wind power for almost two summers now. :(

    Here is the one of the big Gettys DC servo motor I use for a direct drive generator still attached to the the last system that crashed. It had a weak blade root due to insufficient resin in the fiberglass and snapped off. The other two blades then hit the tower when it broke off it base while it was still spinning.
    It fell over 20 feet but the motor came out unharmed!

    DCP01978.JPG

    So far my number one failing point has been crappy factory made fiberglass blades. :mad:

    However I now have some new steel blades ready plus several more servo motors and towers all waiting to go up this spring and if they don't hold up I am going back to carving my own out of wood again. :D

    I have had several homemade sets that I carved out of common 2' x 6" construction lumber that had great aerodynamic characteristics plus ran at insane speeds unloaded without ever failing for many years before they simply weathered to the point they couldn't fly any more. That was when I started trying the supposedly better factory built fiberglass ones which have been absolutely junk and a wast of my time effort and money in the long run so far.
     
    Last edited: Feb 21, 2013

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