Fortsätt till huvudinnehåll

[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. 












Kommentarer

Populära inlägg i den här bloggen

[VAWT] Plausible improvements of the Savonius windmill

Cut a barrel in half, mount it on a shaft and you have a windturbine. If the barrel is used, then what else probably would end up on a scrap heap is instead used for converting renewable energy.

Simplicity and low cost makes this an attractive option especially for societies with limited economy and a malfunctioning or non existing electric grid. Small off-grid electrical networks can be built and people who perhaps most needs electricity get that. Isn't that neat?


Savonius (from http://solarvan.co.uk/savonius)

An overlooked potential?
The Savonius though has a widespread reputation of having low effiency and is often dismissed as a credible option around forums and in formal litterature. However, when looking at the graph below from a publication Wortman did 1983, the effiency can be realtively high provided that the TSR(Tip-to-Wind-Speed-Ratio) is held at a correct value and the windmill should work quite nicely. In practice this could probably be done by controlling the generato…

[VAWT] Affordable wind measurements

The shop Clas Ohlsson in Sweden sells a spare anemometer for the  WH-1080 weather station for a hobbyist friendly price around 15 euros. This anemometer can probably be found in other countries too.


The WH-1080 spare anemometer

Here  you can read about how to use this anemometer together with an Arduino or any other embedded system.  As we couldn't find any data on the characteristics of this sensor, we did our own calibration in a wind tunnel and the results are presented in the report above. This anemometer was used in a Bachelors Thesis project related to the devlopment of optimization of the Savonius Turbine, here tagged [VAWT].

[Cubex] First corner balancing of Cubli based hardware

You shouldn't judge a book by a cover they say, and likewise you shouldn't judge a project by what just meets the eye. During our current master thesis work I had the chance to get better acquainted with some of the works of among others Leonhard Euler and Joseph-Louis  Lagrange. These people spent thousands of hours on things that have been  beneficial to even the whole human race. Few people know this though.Why? Because the works consist of truckloads of books full of equations, and it is not as easy to see the use of this as for instance painting a wall or something that is easily recognized and valued. 



This stands in contrast to Cubli. It makes use of abstract science in a way that is perceivable more easily. Although it is a great deal of fun to use the results of among others Euler and Lagrange for various things  it is useful to also demonstrate the concrete use and validity of it for ourselves and others. Therefore we choose to do our master thesis around a Cubli base…