Servo Motor Controllers, VFDs, and teco-electric: A Buyer's FAQ

I've been buying motion components for a 120-person automation shop for six years. It's not a giant operation, but we push about $180,000 a year through our procurement system. This FAQ is built around the questions our maintenance team and sales engineers actually ask. Plus one or two they didn't know to ask.

Here's what I'd tell anyone comparing servo motor controllers, VFDs, or older Century AC motors:

• What's a VFD?
• Why do servo motor controllers cost more?
• Servo or stepper — which one do you need?
• Is "Century AC motor" a brand?
• How do I contact teco electric and use the teco electric login?
• What's the hidden replacement cost?
• Does a better controller change customer perception?

1. What's a VFD?

VFD stands for variable frequency drive. It controls the speed and torque of an AC motor by changing the frequency and voltage feeding it. Think of a dimmer switch, but for a motor. If you only need speed control and soft starting, a VFD is usually the lowest-cost answer.

As of January 2025, my distributor's quote for a 1 HP sensorless vector VFD was $168. That's a real quote, not list price. Prices for drives have been shifting with component costs, so verify current pricing before you budget.

2. Why do servo motor controllers cost so much more than VFDs?

Because they're solving a different problem. A VFD varies motor speed, but a servo motor controller closes the loop around position, speed, and current using feedback from the motor's encoder. That means faster processing, more I/O, and tuning software.

In Q2 2024, we priced a 750W servo package: motor, controller, and cables came to $1,840. A comparable 1 HP VFD plus AC motor was $520. That gap looks outrageous until you watch a servo hold position while a machine pushes against it. That's what you're paying for.

And don't forget the motor itself. Servo motors have higher-grade magnets and a feedback device. The controller is only half the equation.

3. How do I choose between a servo motor and a stepper motor?

Short answer: if you need high torque at low speed and absolute holding torque, use a stepper. If you need speed, acceleration, or closed-loop feedback, use a servo.

The old line was "steppers are cheap, servos are expensive." That's not true anymore. We've standardized on closed-loop steppers for a lot of simple axis moves — they're a solid middle ground. But when a customer says an axis has to stay in position under a cutting load, I stop looking at steppers. We go straight to the servo motor controller and budget for it.

4. Is "Century AC motor" a brand? Can I run it with a teco-electric drive?

Yes, Century AC motors are a brand. They're part of Regal Rexnord now, and they show up a lot on HVAC blowers, fans, and pumps. A Century AC motor is usually a general-purpose single-phase or three-phase motor, not a precision motion product.

Can you run it with a teco-electric VFD? If it's three-phase, usually yes, as long as the drive is sized for the motor's full-load amps. But don't ignore the nameplate. In March 2023, I did exactly that on a 2 HP Century motor and ordered a VFD that was too small. When the motor stalled under load, the drive tripped. Had 2 hours to decide on the replacement before the line restart, so I went with a stocked unit instead of the ideal one. That mistake cost us a rush order and two nights of overtime.

5. How do I contact teco electric and use the teco electric login?

To contact teco electric, the official Teco Electric & Machinery site (teco.com.tw) lists regional sales offices. That part's easy. What surprised me is that the teco electric login is separate from the general contact system. If you're a distributor or long-term customer, you need the portal login for manuals, order status, and warranty claims.

Set that up before you need it. In 2022, our only purchaser left in a hurry, and nobody knew the teco electric login password. It took two weeks to regain access to documentation we needed for an audit. Now the login is in our company password vault, with a note for the next person.

6. What's one hidden cost nobody budgets for when replacing a Century AC motor?

Mounting and shaft dimensions. A Century motor that's been in service for years may have a shaft extension or bolt pattern that doesn't match a teco-electric replacement. The motor quote might look great — say, $1,240 for three motors. Then you pay $540 for adapter plates, $310 for couplings, and $1,000 in labor. That's the hidden cost.

In Q1 2024, that happened to us on a three-motor swap. The motors were the cheapest part of the project. Now we add a 25% contingency to any like-for-like AC motor replacement until we physically verify the frame dimensions. It's an easy way to protect your total cost of ownership.

7. Does a premium servo motor controller actually change how customers perceive our equipment?

Yes, more than I expected. I used to think torque is torque. Then in Q2 2024, we swapped a budget servo drive for a mid-tier servo motor controller on a labeling line without changing anything else. The customer's operator said the "new machine just feels tighter." Vibration numbers on our test log were lower, and commissioning took 15% less time because the auto-tuning worked better.

The controller cost $280 more per axis. That's real money. Even after approving it, I kept second-guessing. What if the customer didn't notice? I didn't relax until their maintenance lead called to ask what we'd changed.

I'm not saying you have to buy premium everything. For pumps and simple fans, the VFD is plenty. But when a machine is the face of your product, that's where quality perception pays.