Week 10 - Output Devices

Group Assignment

This week we had to measure the power consumption of an output device.
We decided to test a stepper motor since we had one available in our lab and wanted to understand how much power it actually uses.

What we did

So basically we took this stepper motor (model 17HS4401S) that we found in the lab and tested how much electricity it uses under different conditions. It was pretty interesting to see the differences!

Quick explanation of terms (for those who don't know)

What it is	What it means
Power Supply	The thing that gives electricity to other stuff. Ours can be adjusted to give different amounts of voltage
Voltage (V)	Think of it like water pressure - higher voltage = more "push" for the electricity
Current (A)	How much electricity is actually flowing (like how much water is coming out of a hose)
Multimeter	Tool for measuring electrical stuff - voltage, current, resistance, etc.

The Motor We Used

We picked the 17HS4401S NEMA 17 stepper motor. These are pretty common in 3D printers and CNC machines, so it seemed like a good choice for testing.

What the motor specs is:

• Rated Voltage: 12V
• Rated Current: 1.68A per phase
• Step Angle: 1.8° (which means 200 steps = 1 full turn)
• Holding Torque: 4400 g·cm

Power Supply Setup

We used this adjustable DC power supply that we have in the lab. It's pretty nice because you can control both voltage and current, plus it shows you what's happening in real time on the display.

The display shows both voltage and current at the same time. There are two sets of controls - "coarse" (moves fast) and "fine" (for precise adjustments). We looked at the motor Specs to figure out we needed 12V.

One thing our instructor told us - always set current limits! If you don't, LEDs can get hot and pull more current until they burn out. Same goes for other components.

How we set it up:

1. First, set voltage to 12V using the coarse and fine knobs
2. Turn everything off and short the test leads together
3. Turn back on and set current limit to about 1.5A (bit under the motor's rating)
4. Connect the motor and see what happens

Our Test Results

Test 1: Motor just sitting there (not moving)

What we measured: 12.0V, 0.85A, so that's about 10.2W

Test 2: Motor spinning freely

What we measured: 11.330V, 0.92A, so about 11.0W

Test 3: Making it work harder

Then we tried holding the motor shaft while it was trying to turn, making it work harder. As expected, it needed more power to fight against our resistance.

What we measured: 12.0V, 1.22A, so about 17.0W

Summary of our measurements

What the motor was doing	Voltage	Current	Power
Just sitting there (holding position)	12.0V	0.45A	4.8W
Spinning freely	12.0V	0.92A	10.8.0W
Working against resistance	12.0V	1.22A	14.64W

What we learned

Some interesting things we noticed:

• The motor uses quite a bit of power even when it's not moving! This is because stepper motors maintain "holding torque"
• When you make it work harder, it draws more current (and uses more power)
• Setting current limits on the power supply is really important for safety
• Both the power supply readings and multimeter gave us similar results, which was good
• Now we know how to size a power supply properly for projects using these motors

Overall this was a pretty useful exercise. We didn't expect the motor to use so much power just sitting there, but now we understand why stepper motor drivers often have features to reduce holding current when the motor doesn't need to move.