Measuring votlage from a DC motor

Im hoping someone can help me, im a high school teacher and one of our projects is for students to design and build a wind turbine. The issue im hoping someone can help with is we need to measure the voltage produced from the motor. I was planning on using a simple circuit with a LED and having the students measure the voltage with a volt meter however this requires the blades to be spinning very fast, hence some students don't get to make any readings. This is where I thought an arduino could help but I am new to using them and not sure where to start.

Is there a way to get an Arduino to measure low and higher voltages coming from the motor using an Arduino?

WIN_20250404_08_48_39_Pro2560×1440 469 KB

Use a multimeter with peak-hold. Low = 0vdc.

Welcome to the forum!

Do you have any estimate of the magnitude of the voltages that need to be measured?

Are the voltages so small that you cannot read them with a multimeter, even at its smallest scale (mV)?

Tried set the DMM to AC?

Could You give more information about the motor and its wiring?

Which motor? What is it's rated voltage at what speed?

How fast does the motor spin when it is powered by an appropriate power supply? That will tell you the peak speed required to generate the same voltage from the motor.

Only if armature resistance and rotational friction are negligible.

Sure, but for all we know the motor could be AC synchronous. I am concerned about a 3 bladed prop. That would produce a lot of torque. To be similar to a real wind turbine, there needs to be a gear drive that multiplies the output speed and reduces the torque.

Possible, but I'm assuming OP's topic title is accurate.

All the more reason not to assume that the rotor is frictionless.

Thanks for all the input so quickly.
Regarding the motor, im un sure of any specifications as it is a lot of motors left over from previous projects.

When I attach a multi meter to the LED i get readings between 2 and 0.5V.

Does any one know of a tutorial that can allow me to log the voltage outputted from the small motor?

That is in the range of an Arduino's ADC.

If it goes above 5 or goes negative (when turned backwards), it could harm an Arduino Uno.

Maybe try a resistor instead of a LED so you don't get the diode's non-linear response.

Did you work through:

or these:

What readings do you get with the LED connected the other way?

There's more than one kind of DC motor, not all will function as a generator, what exactly do you have? You need to know what type they are.

Permanent magnet? Series or parallel wound field? Brushless? What?

Of those I'd say only permanent magnet gives you any chance of success and brushless is a none starter as they are not really DC motors, they are AC motors with a built in inverter.

To stand any chance of getting a decent output from the slow speed of rotation I imagine you have from the wind turbine you really need something with multiple poles of permanent magnets for the field.

Exactly what I'm getting at except some points. Most of them actually. But a DC motor that can be used as a generator will output AC, or are there exceptions, other types? Permanent magnets are the only ones I can think of.

That doesn't sound right to me, the commutator will rectify the output, although, as @t_brown_86 is finding, getting a meaningful output to rectify is proving elusive.

Can you at least post a picture of the motor with something in the picture for scale (like your hand or finger).?

You may be thinking of an alternator. A DC motor will output DC current, unless the shaft rotation changes direction, or you get a resonance due to energy exchange between the armature inductance and the rotor inertia.

Or a banana