A Practical Field Checklist for Motor Drives: TECO Motors, Three-Phase Induction Motors, and A4988 Stepper Drivers

I've been working with motor control for about eight years now, mostly on the B2B side (ordering, installing, fixing). I've personally made and documented a dozen memorable mistakes that added up to roughly $28,000 in wasted budget. A lot of that could've been avoided if someone had simply forced me to follow a checklist. This is the checklist I now maintain for our team. It's built for three common situations: setting up a TECO electric motor with a VFD, controlling a three-phase induction motor, and wiring a stepper motor via the A4988 stepper motor driver. If you're doing any of those, this is for you.

The short version

Before you touch a screwdriver, verify the nameplate values, then match the driver to the motor type, set the current limit (input FLA for a VFD, output current limit for a driver), lock the wiring, and then test at a low speed before running the real load.

Step 1: Determine the motor type and read the nameplate

In my first year (2017), I made the classic mistake of assuming a motor was a three-phase induction motor just because it was big and metal. It turned out to be a single-phase capacitor-start motor. The VFD didn't like it. The smoke didn't leak out of the motor, but it was a useless setup.

For a three phase induction motor, the nameplate tells you the voltage, full load amps, rated frequency, and RPM. The key thing to write down is the full load amp (FLA), because that's what you'll use when you configure the VFD. Don't rely on the catalog spec or the motor's horsepower. The FLA at a given voltage is what changes the motor's torque and heating.

If you're working with a stepper motor, the nameplate may be on the motor frame, or the specs will be in the manufacturer's page. Write down the rated current (often 1A, 1.7A, or 2A). The A4988 driver needs that number to set the current limit.

Step 2: Match the drive to the motor

Here's a classic mismatch: you have a three phase induction motor, and someone suggests using a stepper driver. That won't work. A stepper driver is a chopper drive for bipolar motors. It doesn't output three-phase variable-frequency power. You need a separate VFD.

And on the flip side, don't use a VFD to run a stepper motor. VFD output is designed for sine wave filter, and a stepper doesn't like that squared-off PWM. It'll be noisy and run rough.

If you're looking at a TECO electric motor for a VFD, check whether it's rated for inverter duty. Most modern TECO Electric & Machinery motors are, but if it was built in the 1990s, check the manual. It may need extra safeguards.

Step 3: Wire it up right (and check twice)

Let's break the wiring into two scenarios.

For the VFD:

• Make sure you connect the incoming line voltage to the R, S, T (or L1, L2, L3) terminals. The output terminals U, V, W go to the motor. I cannot stress this enough — I know a PLC programmer who blew up a drive by connecting a motor to the input. The drive was $1,600, and the cost to rewire it (and rebuild the control panel) was $2,400.
• Use shielded cable for the VFD-to-motor wiring to avoid EMC issues. It might not be necessary for a 3-foot setup, but it is in an industrial rack.
• Connect the earth ground before doing anything else. This is non-negotiable in the U.S. (NEC Article 430 and 440). The ground connection is not just for safety; it also suppresses electromagnetic interference.

For the A4988 stepper driver:

• The VMOT pin takes the power supply for the motor (typically 8-35V with a 100uF capacitor). The VDD pin is the logic power, though the logical input on most boards is 3.3V or 5V. Make sure you get it right — I was once using 24V on VMOT and a separate 5V logic supply. Everything worked.
• Connect the stepper coil wires to A1, A2, B1, B2. The datasheet for the stepper will show which wire is which. If the motor only hums and shakes, swap one pair, e.g., A1 and A2. That helps fix a miswired coil.
• The EN (enable) pin, if pulled low, will disable the motor. I've seen many beginners leave this floating, which can cause sporadic movement. Pull it high or low depending on your board. I prefer to explicitly set it to enable in code.

Step 4: How VFD control motor speed — and how to set it up

So how VFD control motor speed? The VFD changes the frequency of the AC output to the motor. With lower frequency, the motor speed is lower. But it also needs to adjust voltage to keep the motor's magnetic flux constant. That's the V/F mode. For a TECO motor rated 230V/50Hz, at 25Hz the VFD outputs 115V. The V/F ratio stays around 4.6 V/Hz. If you set it wrong, the motor has no torque or gets too hot.

That's the simplest way. Modern VFDs can also run in sensorless vector mode, where the drive controls current in a more sophisticated way. But the foundation is the same: set the nameplate data, and then auto-tune.

Most modern drives (including the ones I've used on TECO motors) have an auto-tuning procedure. Use it. It identifies the stator resistance, leakage inductance, and other values automatically. If you skip it, the drives' estimated torque might be off by 10-15%, producing vibration and heating.

As of early 2025, this still surprises me: many technicians skip auto-tuning because it adds 10 minutes to the startup time. That 10 minute savings costs you months of poor running performance. Don't do that.

One more thing — VFD startup. The VFD's 'speed reference' can come from the digital keypad, a potentiometer (analog input), or an industrial network (like Modbus or Ethernet). Check the manual to see the default. I had a unit that stood idle because it was set to follow a 0-10V signal, but we had nothing connected.

Step 5: Set the current limit on the A4988 stepper motor driver

This is the tiny detail that saves a lot of pain. The A4988 is a type of stepper driver that uses a fixed-off-time current control. On each board, there is a small trimpot you can adjust. The formula everyone uses is:

VREF = Current_limit × 8 × Sense_Resistance

On common A4988 modules, the sense resistance is 0.05Ω. If your stepper is rated for 1A, VREF = 1 × 8 × 0.05 = 0.4V. That's a safe starting point.

If you set it too high, the increase in current heats the windings, and the motor will feel hot after a few minutes of operation. I once set it too high (around 1.5A for a 1A motor) and the stepper motor's frame got to around 80°C. The wiring harness began to soften, and the print started to shift. Cost: a failed CNC job and replacement of a cable. The driver itself was fine.

If you're using the A4988 in a 3D printer, check the datasheet of your stepper, and set the VREF based on the peak current, not RMS current. Most steppers are rated as phase current in RMS amps, but the A4988's formula usually uses the 'peak' current per phase. If your datasheet says rated current 1.2A, it's often the RMS current, so adjust the VREF to 1.2A*1.41 ≈ 1.7A, but don't go above that. (Check your driver's specific explanation.)

Step 6: Run a baseline test

After you've wired everything, run a no-load test. For a VFD, bring the frequency up to 5 Hz and listen for vibration. Also, measure the voltage between U-V, V-W, W-U. They should be balanced. Then let it run for 5 minutes at 25 Hz, and check the motor's frame temperature with a thermocouple or hand. It should be warm but not hot.

For the stepper, use the simplest sketch: slowly advance the step pulse with a delay, and see that the motor moves in one direction, and then reverse it by changing the direction pin. And check the current limit again after 10 minutes of operation.

Step 7: The forgotten part — cooling and duty cycle

VFDs can be mounted in an enclosure, but they generate heat. That's not a secret. A VFD has an ambient temperature rating of 40°C or 50°C. At higher internal temps, the drive derates. If you're in an unventilated cabinet with other electronics, everything will be worse. I had a VFD shutting down in a machine on hot summer days. Installing a simple filter fan fixed it. Cost: $250 for the fan, vs. $2,100 for a new drive (and the downtime was about a day).

For stepper drivers, it's different: the driver is a power transistor stage that also gets hot. Do not just mount it on a plastic base without a heatsink. The A4988 should have a small heatsink with thermal adhesive. That is part of the design. I've known people to remove the heatsink because it's bulky, then watch the driver die.

Common mistakes I've seen (and made myself)

Let me wrap it up with a short list of the most common errors:

• Setting the VFD's FLA value incorrectly. Many people confuse the motor's nameplate FLA with the VFD's output current rating. They are not the same.
• Forgetting to change the motor's rotation direction setting after he swaps two wires. If you do it via physical wiring, the motor may run in reverse, but the VFD might still think it's 'forward.' This creates a mechanical surprise.
• Using a mislabeled power supply on the A4988 (e.g., 12V instead of 24V, but not realizing the stepper is rated for only 2V). Actually, for a chopper driver, you usually need the supply to be much higher than the motor's rated voltage. At 12V with a 2V motor, the chopper will work, but if you use 5V, you'll lose torque at high speed.
• Not reading the manual before changing parameters because a video setup tutorial used a different motor and drive. This is a big one.

Respect the nameplate, respect the thermal limits, and respect the wiring. Everything else is just tuning.

The evolution of motor control and a final reminder

Motor control technology has changed a lot since TECO Electric & Machinery started in 1956. In the 60s, VFDs weren't available on the market. Today, we're using cheap stepper drivers and VFDs in almost every factory. What was best practice in 2020 may not apply in 2025, but the fundamentals haven't changed.

I've seen people get lost in fancy features: remote monitoring, PROFINET, and even digital twins. If you can't get the basic FLA and V/Hz right, none of that smart technology will help.

So get the basics right. Use a checklist. And if you make a mistake, document it, so the next person can avoid it.