# Turbine Motor output

#### lenoplix

Joined Jun 11, 2020
31
Hi,

I am trying to measure the voltage output of a DC motor that is being turned by a wind turbine in order to calculate the torque generated. However as the turbine rotates the force on the blade is a function of the azimuthal position thus a regular voltmeter is not able to sample the readings in microseconds thus aliasing the profile. So i would like to know how to code an arduino or myRio (preferably arduino) to read the voltage output of the DC motor so I can plot the torque curve as a function of azimuth.

There is already in Arduino IDE a preset code that takes the voltage reference as that of the power supply, however in my case the power supply is not a constant value due to the aforementioned reasons. So please help.

Regards

#### Chris65536

Joined Nov 11, 2019
270
I'm not sure what you mean in your second sentence, but the voltage output will only tell you the RPM. The torque would be proportional to the current, and will be zero with no electrical load. Just reading the voltage with a DVM draws almost no current.

#### lenoplix

Joined Jun 11, 2020
31
I'm not sure what you mean in your second sentence, but the voltage output will only tell you the RPM. The torque would be proportional to the current, and will be zero with no electrical load. Just reading the voltage with a DVM draws almost no current.
I will load the generator with a resistor and get the voltage across the resistor using a voltmeter however the sampling time is an issue

#### crutschow

Joined Mar 14, 2008
27,707
the sampling time is an issue
Why is that an issue?
Does the azimuth position change that rapidly?

#### AlbertHall

Joined Jun 4, 2014
11,498
I haven't tried this, but I think that if you rotate a DC motor at a constant speed you won't get a fixed constant DC voltage out of the motor. The voltage would surely vary with the commutation of the motor, be it with brushes or hall effect or however.

#### lenoplix

Joined Jun 11, 2020
31
Why is that an issue?
Does the azimuth position change that rapidly?
yes it does we have RPM of 500-800 with a radius of 10cm

#### lenoplix

Joined Jun 11, 2020
31
I haven't tried this, but I think that if you rotate a DC motor at a constant speed you won't get a fixed constant DC voltage out of the motor. The voltage would surely vary with the commutation of the motor, be it with brushes or hall effect or however.
That I know, however I wish to visualize this variation using an Arduino... any idea how that can be done?

#### LesJones

Joined Jan 8, 2017
3,486
Are you trying to plot the output voltage and or current against the angular position of the motor shaft ?
By azimuth do you mean the angle between the turbine axis and the wind direction ? I am not clear of your setup. Can you post a picture of it.

Les.

#### mcardoso

Joined May 19, 2020
198
How about setting up a scope? Use a hall effect sensor to measure shaft angle on one channel and the voltage generated on the motor with another channel.

#### lenoplix

Joined Jun 11, 2020
31
How about setting up a scope? Use a hall effect sensor to measure shaft angle on one channel and the voltage generated on the motor with another channel.
what i did was the following:

I connected a myrio to the dc generator through the AI0 ports since the highest voltage i get is about 8.5V, however when i start acquiring the data what happens is that the readings are full of errors and the period i get are not synchronous with the expected period of the forces produced by the turbine.

What we should get is a curve that shows 3 peaks over a single rotation each peak showing that a blade of the 3 blades is at max force output. however at any rotational speed the waveform obtained is almost the same but has different amplitudes, so how would the hall effect sensor help in this matter?

I tried using the RMS palette but it does not work properly due to having negative values generated when the rotational speed is lower than 500rpm even though the dc motor is rotating the same direction as when it is rotating at 800 rpm. at 800 rpm the values are all positive but the frequency of the peaks do not represent that speed.

note that i am reading every sample at 150 microseconds