Turbine Generator and Torque

1. Mar 2, 2012

hollyhiccups

I am making a small wind turbine using a generator to charge a battery.

I have chosen a generator in relation to the battery and ultimate output requirements of the LEDs.
However - I need to determine the amount of power I need to put generate for the system to work effectively.

The generator is rated at 10W. However I understand that due to Torque... To actually achieve this, the turbine design (and wind speeds) will need to produce more Watts than this.
But just how much is what I struggling with - is there a formula to use?

Theoretically achieving an RPM of 2800 and there is a constant wind speed of 15 m/s.

Many thanks :)

2. Mar 2, 2012

OldEngr63

There are a lot of numbers in your post, but not much information as to what you know, what you don't know, etc.

You say, "The generator is rated at 10W. However I understand that due to Torque... " Well, "due to torque, what?" Are you making a statement, asking a question, or just fading out?

You also say, "Theoretically achieving an RPM of 2800 and there is a constant wind speed of 15 m/s." This is not a sentence; there is no verb. Would you care to tell us what you had in mind here?

3. Mar 2, 2012

hollyhiccups

In theory my generator will achieve 2800 rpm.
At this speed the generator I am running will power 10W.

I need to design the wind turbine that will run with this generator to achieve 10W.

With wind speeds of 15m/s and an rpm of 2800 a turbine blade size of 0.13m x 0.05m would produce 10W.

However - from my limited understanding - Torque will mean that designing a turbine to produce 10W will not result in a 10W output from my generator.

How does Torque relate to this? Is there any equation? Any information or knowledge would be appreciated. :)

4. Mar 2, 2012

OldEngr63

That is a whole lot better.

Power (watts) = ω T
where
ω = shaft speed (rad/s) = 2 π (rpm)/60
T = torque (N m)

There is also the matter of conversion efficiency. Ten watts of mechanical power into the generator will not give you 10 w electrical output. It depends on the design of your generator as to what the efficiency actually is.

There are also efficiencies to consider in the transmission between the turbine and the generator. Generally speaking, there is some power lost at every step, so part of the answer is to minimize the number of steps, and the other part is to minimize the losses per step.

It would not be surprising if you needed 50 or 60 w of power from the wind to get 10 w electrical output.

5. Mar 2, 2012

pantaz

Have you looked at the various websites dedicated to DIY wind turbines? Many of them have excellent examples and plans for generators that they have actually built and tested.