iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
A variable frequency drive (VFD) changes motor speed while it runs; a soft starter makes starting gentler but normally runs the motor at fixed speed; and a contactor switches motor power on or off. Choose based on whether you need ongoing speed control, a less abrupt start, or simple switching—and include the protection the motor requires.
How do the three motor-control options differ?
| Option | What it controls | Typical fit | Key limitation |
|---|---|---|---|
| VFD (AC drive) | Motor speed and torque during startup and normal operation | A process that needs adjustable speed or torque | Must be matched to the motor, load, supply, and controls |
| Soft starter | The voltage and current during acceleration, and sometimes deceleration | A fixed-speed load that needs a gentler start | Normally does not control speed once startup is complete; reduced starting current also affects torque |
| Contactor-based starter | Whether power is connected to the motor | Simple on/off operation where full-voltage starting is acceptable | A contactor alone is not overload protection |
These are different functions, not interchangeable names for the same device. In a conventional across-the-line start, the contactor applies full line voltage to the motor. A complete starter arrangement commonly pairs a contactor with an overload device: the contactor switches current, while the overload device protects against excessive current and overheating. Eaton explains the distinction between contactors and overload protection.
When should you choose a VFD?
Choose a VFD when the motor needs adjustable speed or torque during normal operation—not merely a controlled start. A VFD varies the frequency and voltage supplied to an AC motor. In a basic drive, incoming AC is converted to DC, then an inverter synthesizes adjustable AC output using pulse-width modulation. This lets the drive control motor speed and torque during operation. Danfoss describes how a variable frequency drive works.
A VFD can suit a variable-load fan or pump when the process does not always need full output. Lowering output may reduce energy use, but the result depends on the driven system and its operating profile; it is not a guaranteed saving. Choose and configure the drive for the motor, load, supply, and control requirements.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
When is a soft starter the better fit?
Choose a soft starter when the process runs at fixed speed but benefits from a less abrupt start. It reduces applied voltage and current during acceleration, which can limit starting inrush and mechanical stress. Some models also provide a controlled stop. Once acceleration ends, the motor normally runs at supply frequency, so a conventional soft starter is not a substitute for ongoing speed control. AuCom compares soft starters and VFDs.
Check torque as well as current
Reducing voltage and current also affects starting torque. The motor still needs enough torque to break the load away and accelerate it. A lower current limit is not, by itself, proof that a soft starter is suitable. Consider a pump where pressure surges matter or a conveyor where abrupt acceleration stresses the mechanism, but verify the load’s torque and acceleration needs before selecting equipment. AuCom’s motor-starting guidance discusses this trade-off.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
When does a contactor-based starter make sense?
A contactor is an electrically operated switch that repeatedly makes and breaks a motor power circuit. Use a contactor-based starter for straightforward on/off control when the electrical supply and driven machine can tolerate the starting event associated with full line voltage. Include appropriate overload protection: a bare contactor does not provide the same protection as a complete starter.
How do you decide which starter to use?
Work through the application requirements before choosing a device. The supply, motor, driven machine, and process all affect the decision.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
- Decide whether speed must change after startup. If the process needs adjustable speed or torque while running, evaluate a VFD. If it runs at fixed speed and only needs a controlled transition, evaluate a soft starter. For simple switching, consider a contactor-based starter.
- Assess the electrical supply. Determine how much starting current and voltage disturbance the supply can tolerate. As AuCom’s motor-starting guide puts it, “The electrical supply determines how much starting current and voltage disturbance can be tolerated.”
- Check the load’s startup needs. Establish the torque required to break away and accelerate the load, its inertia, and how often it starts. For a soft starter, confirm that reduced-voltage starting still provides adequate torque.
- Match equipment to the motor and supply. Gather the motor nameplate voltage, phase, horsepower or kilowatt rating, full-load amps, and service factor. Confirm compatibility with the available supply and the selected control equipment.
- Specify protection and installation details. Identify the required overload type, control voltage, reversing function, auxiliary contacts, enclosure, and environmental protections. Check applicable electrical-code and hazardous-area requirements, product listing, and safety needs with a qualified electrical professional.
These details are needed to size and specify equipment; without the motor and application data, there is no sound basis for recommending a particular device rating or model.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
