ABB VFD vs Siemens PLC Starter Kit: Why I Stopped Comparing Apples to Oranges (and What to Buy Instead)

The Comparison That Doesn't Make Sense (And Why I Made It Anyway)

In 2022, I was tasked with sourcing automation hardware for a new packaging line. I had two line items on my list: an ABB VFD for a conveyor motor and a Siemens PLC starter kit for the control logic. My boss, who isn't an engineer, looked at the two line items and asked the killer question:

"Which one is better? Can't we just buy one and use it for both?"

And I, in my infinite wisdom (circa year one of doing this), spent an entire afternoon trying to compare them. I checked specs, watched YouTube reviews, and even tried to see if the ABB VFD display could be programmed like a PLC. It cannot. (Ugh.) I ended up ordering a Siemens PLC starter kit thinking it would handle the motor control too. The result? A $3,200 order that sat on the shelf for three weeks because it couldn't drive the 7.5kW motor. The VFD I should have ordered arrived late, and the line started a week behind schedule.

Here's the first lesson, learned the expensive way: These are not competing products. They are complementary components. Comparing an ABB VFD to a Siemens PLC is like comparing a car's engine to its steering wheel. You don't choose one; you need both. The real comparison readers should be making is different entirely.

Dimension 1: The Function (What It Actually Does)

The Assumption: Both devices control motors, so they must be competing for the same job.

The Reality: They control completely different aspects of the system.

An ABB VFD (Variable Frequency Drive) is a power converter. Its job is to take incoming AC power (usually 3-phase, 380-480V) and vary the frequency and voltage going to a motor. This controls the motor's speed and torque. The ABB VFD display shows real-time parameters like speed, current, and fault codes. It's a closed-loop device primarily concerned with the physical movement of the motor shaft.

A Siemens PLC starter kit is a logic controller. It takes inputs (sensors, buttons, limit switches) and executes programmed logic to determine outputs (relays, contactors, and sometimes signals to a VFD). It doesn't drive the motor directly. It tells the VFD when to start and stop and at what speed. It's a decision-making device.

Comparison Conclusion: The VFD is the muscle. The PLC is the brain. You can't compare them on function because they don't overlap. The conflict only arises when you have a very simple application where a VFD's built-in programmable logic (PID controllers, simple start/stop sequences) is sufficient, eliminating the need for a separate PLC.

Dimension 2: The Cost Breakdown (Not Just the Sticker Price)

This is where I made my crucial mistake. I saw the price of the Siemens PLC starter kit and the price of the ABB VFD and tried to do a value comparison.

ABB VFD Cost:

• Hardware: A basic ABB VFD for a 5-10 HP motor (like the ACS355 or ACS580) costs between $400 and $1,500, depending on features and enclosure type.
• Installation: Requires a qualified electrician due to high voltage. Line and load reactors may be required.
• Programming: Parameter setting via the ABB VFD display (keypad) is usually straightforward. Basic tuning takes a few hours for a novice.

Siemens PLC Starter Kit Cost (e.g., S7-1200):

• Hardware: The starter kit (CPU, power supply, digital I/O module) costs $300 to $700. You may need additional analog modules.
• Software: TIA Portal (the programming software) is not free. A basic license is ~$500, but full versions can cost thousands. This is a hidden cost many miss (I sure did).
• Programming: Ladder logic, FBD, or SCL. Requires training. A simple start/stop sequence might take a day to learn and implement for a first-timer.

The Hidden Cost Comparison (The Part No One Talks About):

People think the VFD is more expensive because the hardware price looks higher. The reality is the opposite if you factor in the software and engineering time. For a single-motor speed control application, the VFD is almost always the more cost-effective solution. The PLC's value is in managing complexity—multiple motors, sensors, recipes, and data logging. If you are just trying to replace an air filter in a house (or run a single pump), you don't need a PLC.

Comparison Conclusion: The VFD wins on hardware cost and ease of deployment for simple tasks. The PLC wins on value per unit of complexity. The real comparison isn't price-to-price; it's price-per-function-complexity ratio.

Dimension 3: The "I Can Use This For Everything" Trap

This is the dimension that surprised me. I assumed the PLC could eventually replace the VFD if I bought a more powerful one. It's a common industry misunderstanding (causation reversal).

The Misconception: "If I buy a more advanced PLC, I can control the motor without a VFD."

The Truth: A PLC cannot vary the frequency of power delivered to a motor. Period. It can only send analog signals (like 0-10V or 4-20mA) to a VFD to tell it what frequency to output. You cannot bypass the physics of motor control with better logic. The ABB VFD is an absolute requirement for variable speed AC motor control.

Conversely, a VFD's internal PLC is incredibly limited. While modern ABB VFD displays allow for some programming, it's nowhere near the capability of a Siemens S7-1200. The VFD is a terrible solution for managing a complex process sequence.

Comparison Conclusion: Each device is locked into its physical role. The VFD handles power. The PLC handles logic. There is no overlap at the hardware level. The choice isn't 'VFD vs PLC'; it's 'How much logic overhead do I need on top of my power control?'

So, What Should You Actually Compare?

Here is the 'A vs B' that actually matters for your buying decision:

Scenario A: You are controlling a single motor (e.g., a fan, pump, or simple conveyor).

• Buy: An ABB VFD with good parameter programming (like an ACS580). Use the built-in PID and start/stop logic.
• Don't Buy: A Siemens PLC starter kit. It's overkill and adds cost and complexity. You'll spend $500 on software and a week learning it needlessly.

Scenario B: You are coordinating multiple motors and sensors (e.g., a packaging line or machine tool).

• Buy: Both. A Siemens PLC (or similar) for the logic and multiple ABB VFDs for the muscle. The PLC communicates setpoints to the VFDs via fieldbus (Profibus, Profinet) or analog signals.
• Don't Buy: Just VFDs with fancy programming. You will hit a wall with complexity and lack of debugging capability. The PLC pays for itself within the first week of troubleshooting.

Scenario C: You are replacing a car part (e.g., a TIPM fuel pump relay bypass kit).

This is a completely different world. A TIPM fuel pump relay bypass kit avoids the integrated circuit board in a Jeep or Chrysler to ensure fuel pump power. This has zero to do with industrial VFDs or PLCs. Don't conflate the terms. If you are working on a car, you're looking for a relay and a fuse, not automation hardware.

Scenario D: How to replace an air filter in house.

Also unrelated. This is residential HVAC, not industrial motor control. The motor in a furnace fan is often a simple PSC or ECM, not controlled by a standard VFD. Stick to the correct domain.

Bottom Line: Stop Comparing Wrong Things

Here’s where I landed after the $3,200 mistake: I created a simple decision tree for my team. It has saved us from repeating that error (we've caught 12 potential mismatches using it in 2024 alone).

1. Is the task 'make this thing spin'? → Buy a VFD (like ABB).
2. Is the task 'decide when to spin, how fast, and what to do if it jams'? → Buy a PLC (like Siemens).
3. Is the answer 'both'? → You have a real project. Good luck, and invest in a proper controls engineer. (Note to self: I should have done this in 2022.)

The vendors who list exactly what their product doesn't do are the ones I trust more now. A transparent vendor tells you upfront 'Our VFD cannot replace your PLC' instead of hoping you buy both and figure it out later. (Pricing as of January 2025; verify current rates.)