# Choosing a generator for mini wind turbine

1. Oct 24, 2013

### carbs

Hello physics forum,
I am currently trying to figure out how to pick a generator for a horizontal axis mini wind turbine based on specs. I plan on buying a DC motor to use as a generator with blades directly attached to motor shaft. My goal is for the motor to be most efficient at 25mph wind speed, but also be able to generate power at lower wind speeds.

Wind speed from 0 to 25mph

My calculations so far:
Max power = 9 watts @25mph wind speed w/ perfectly efficient blade using equation: P=0.5*0.593*ρ*A*v^3
where P is power (W), 0.593 is Betz limit, ρ is air density (kg/m^3), A is swept area of blades (m^2), and v is wind speed (m/s).

Is there any way to approach buying a generator mathematically?
Some specs sheets on motors I see have voltage/torque/rpm/current@max efficiency, and stall torque/current.
Thanks!

2. Oct 25, 2013

### Simon Bridge

The motor will make the blades spin slower than the same conditions without the blades.
You want to assess how much the motor with load the blades against he sort of winds you expect to operate in.

The motor ratings are for driving the motor.

Also see: