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[VAWT] Second test

There were some issues during the first tests due to that the output voltage from the generator was too low. The generator voltage can be raised by using a gearing factor n that increases the rotational speed and therefore the EMF voltage by 

EMF = n*k*w

where k is the motors voltage constant and w is the wind turbine's rotational speed. The generator will spin faster and therefore generate more voltage, simply put. 

When a gearing is introduced the torque on the generator's rotor is also decreased. This reduces the copper losses 

Ploss,copper = r*I^2 ~ r*(T/(k*n))^2 

as the current I is directly proportional to the torque T, and inversely proportional to a theoretical motor constant k, in theory. Lower rotor torque thus means that the copper losses are reduced. 

Reluctance effects
However, the BLDC motor used is affected by quite a lot of  reluctance effects. An initial torque of a certain level is needed to overcome the reluctance effects and the motor then rotates a step. This wasn't an issue without gearing, but with gearing not not even pressurized air could get the rotor to spin. 

The solution could be a larger rotor that could exert a higher torque, and/or more sophisticated electronic control with lower voltage drops. Reducing the gearing isn't an option with the current electronic circuit as the this gearing ratio is needed to get a proper voltage a the moment. 

First power measurements
An Arduino board was connected to the setup and measured rotational speed, output voltage and output current. The current was measured by using the ACS711EX current measurement IC that does measurements based on the hall effect. 

I think Arduino is great for quick prototypes like this. Earlier I used several other boards, including boards I made myself and did regular low level programming in Eclipse with plugins, and similarily. Sometimes such approaches are needed, but many times it just takes more time than when doing the same thing with   Arduino and alike. 


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