Homebrewed Electricity > Wind
Appropriate generator characteristics for small wind turbine
JW:
thinking about these motors. Check this out- I have a GE electric riding lawn mower.
I think my motors (3) on the mower deck. Meet the specification you guys are talking about.
Im having a problem posting pictures, I have to fix something. Ok will get some pictures up.
JW:
leheim:
Isn't the RPM area for a given turbine only determined by the rotor size? I understand that a wind turbine harvests the most energy from the wind if it operates at the optimum tip speed ratio (typically around 7 for a three-blade HAWT). If the wind speed is 10 m/s, the tip speed should ideally be 70 m/s, which corresponds to a specific RPM for a given rotor size. A small turbine would have to spin faster to operate at TSR=7. This logic is further elaborated in my original post. I think this is the core of my problem, so please tell me if I'm missing something here.
Thank you for the generator suggestion MagnetJuice. I have also been looking at this one:
ebay.co.uk/itm/235042332008?chn=ps&_ul=GB&var=534977374051&norover=1&mkevt=1&mkrid=710-169684-097358-0&mkcid=2&itemid=534977374051_235042332008&targetid=293946777986&device=c&mktype=pla&googleloc=1010976&poi=&campaignid=20649918451&mkgroupid=151788312862&rlsatarget=pla-293946777986&abcId=&merchantid=6995734&gclid=Cj0KCQiAw6yuBhDrARIsACf94RV3voAhQUyhNRR0LcWsCQCp3uWbPtWYMEVdzHyCNEoHbJthoCFvIxwaAqJVEALw_wcB
I have also another question. Some of you are talking about the cut-in speed where the generator will output 12V. Is there a problem with just using a buck-boost converter?
Greetings,
Lars Erik
Mary B:
--- Quote from: leheim on February 16, 2024, 02:18:32 AM ---Isn't the RPM area for a given turbine only determined by the rotor size? I understand that a wind turbine harvests the most energy from the wind if it operates at the optimum tip speed ratio (typically around 7 for a three-blade HAWT). If the wind speed is 10 m/s, the tip speed should ideally be 70 m/s, which corresponds to a specific RPM for a given rotor size. A small turbine would have to spin faster to operate at TSR=7. This logic is further elaborated in my original post. I think this is the core of my problem, so please tell me if I'm missing something here.
Thank you for the generator suggestion MagnetJuice. I have also been looking at this one:
ebay.co.uk/itm/235042332008?chn=ps&_ul=GB&var=534977374051&norover=1&mkevt=1&mkrid=710-169684-097358-0&mkcid=2&itemid=534977374051_235042332008&targetid=293946777986&device=c&mktype=pla&googleloc=1010976&poi=&campaignid=20649918451&mkgroupid=151788312862&rlsatarget=pla-293946777986&abcId=&merchantid=6995734&gclid=Cj0KCQiAw6yuBhDrARIsACf94RV3voAhQUyhNRR0LcWsCQCp3uWbPtWYMEVdzHyCNEoHbJthoCFvIxwaAqJVEALw_wcB
I have also another question. Some of you are talking about the cut-in speed where the generator will output 12V. Is there a problem with just using a buck-boost converter?
Greetings,
Lars Erik
--- End quote ---
Watts generated is determined by rotor size... that is where you need to start. Just because it says it will do 200 watts doesn't mean it will do it with a 3 foot rotor. Research power available vs rotor size.
You start with determining how much power you need, then start looking for an appropriate alternator that reaches that at the lowest possible RPM because high speed on a wind turbine is SCARY. Rotor blades can explode from the forces... tossing shrapnel for hundreds of feet. That is why the axial flux alternator is so popular on this site, it can be designed with low cut in speeds... I for one would not want a set of blades up there spinning at 750RPM at cut in speed!!!!!
SparWeb:
Hello Lars,
Have you set up with wind turbine outdoors in the wind yet?
The explanations you've received so far are excellent, so the only improvement possible is for you to take that thing outside on a windy day and observe it, and take measurements of what happens. You should run it without the MPPT controller at first.
Set it up on a rigid post, pole, or structure. Being a temporary set up for test I won't direct you too much but just make sure it won't flip over with a 100 Newton push against the blades. Be mindful of your own safety doing this, however, and if you stop reading now, ignore the warnings below, and carry it outside and hurt yourself - it's your fault, not the anonymous stranger on the internet.
First make sure you have shorted the output wires together and expose it to a strong wind in that condition. If there is a terrible mis-match between the rotor and the motor you will find out quickly enough. Shorting the wires permits the maximum current to flow, which usually means too much torque for the blades to turn. This is a brake. You want a brake, for safety. If this brake works, it will help ensure your WT is safe in the future, too. It should turn very slowly in this condition even in a strong wind. Any other behaviour is not acceptable.
If it does spin uncomfortably fast with leads shorted, don't try to grab the blades! Regain control by turning the tail by hand until the rotor is facing sideways to the wind. Then bring it back indoors or in the lee of a building to sort out why shorting the leads did not restrict the blades. If shorted leads can't make the blades turn slowly, then stop now, redesign this WT, or start fresh.
When you are certain it will not spin out of control with the wires shorted, then you can allow it to turn with resistance or battery charging loads. I would do this to characterize the behaviour of the WT before installing the MPPT. You will not be able to demonstrate the effectiveness of your MPPT device if you don't know what the characteristics of the WT were before you installed it!
NEVER RUN A WIND TURBINE UNLOADED.
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