3 or 5 blade

i have a 36v 350 watt motor geared up to 6 to 1 for a generator. i am in a zone 2 wind speed. i plan on a 12 v sysytem
what size rotor do i need?

 

Hey John welcome. What is the RPM rating on your motor? I would guess that with the 6-1 gearing you would want to go with a big 5 blade. Its going to take some torque to get it going. The RPM rating will have a lot to do with it to see what the cut in speed will be.

 

it is a my1016, 12.8 amp and 2750rpm

 

ok so your motor will make 1volt per 76.4 RPMs. So to charge a 12v battery @14.4v you will need 1100 RPMs. Thats way to much normally. Now you have your ratio of 6-1 so now you will need about 184 RPMs. Now that is very do-able. I would say go with the 35" wind grabbers. now to 3 or 5 blades?? If you were in a higher wind zone I would say 3 blades but I would lean more to the 5 blades just for the torque that you need for the gearing. I am sure that Windy will see this soon and should be able to give you a good answer but I hope this helps ya.

 

I agree. Five 35 inch blades are the way to go. There is some inefficiency/mechanical resistance with using gears so you will need the extra torque that the five blades will provide.

I will also say that I am not a fan of geared wind turbines. If you can pick up a used motor or generator (or a new one) for a reasonable price that will allow you to build a direct drive unit, I would strongly suggest doing it.

 

Whats wrong with geared drives windy? Once mastered they will be the staple of true high powered home units :idea: Just have to have big blades and a sound infrastucture.. :ugeek:

 

as i checked in my engineering books, a properly desgned gear box is 98% efficent, sure seems the way to properly match torque and rpm to load.
ever try to start out a car in high gear?

 

does anyone have a graph , chart or math equation of the torque and rpm vs wind speed for the ready made turbines?
john b

 

i calculate that a 80 in dia turbine in a 20mph wind will probably generate about 320watts. i used power=1/2pAVxVxV and betz rule of 59% and efficiency of 40% for the turbine design. Where did i go wrong? i tried to put my calculations in the reply but sponsor rejected it. too many characters
john b

 

I think 320 Watts is about right. We see around 350ish (24 volt bank) and 200ish (12 volt bank) in 20 mph wind for the 750 PMA. On an extremely optimized wind turbine, you could theortetically get about 475 watts but in the real world that is going to be difficult.

So, it seems that there is nothing wrong with your calculation.

 

My opinion is the Windtura 750 performs just fine in low winds with the 3-blade WindGrabbers. You can watch the videos of it making power in low wind conditions in the product description:

http://www.windynation.com/products/wind/generators-and-pmas/windtura-750-complete-wind-turbine-kit