Siemens Motor Control: Electric Motor Starters vs. Brushless DC Motors for Linear Actuator Kits

Two Ways to Control a Siemens Motor in a Linear Actuator Kit

I am a quality and brand compliance manager at a company that sells and supports Siemens motors and drive components. I review every motor package before it reaches customers — roughly 200 items a year. Maybe 180, I would have to check our audit log. In 2025 I have already rejected 7 percent of first deliveries because the spec on the purchase order did not match the spec on the motor nameplate or the control scheme.

The most common question we get is not about maximum torque. It is about which Siemens motor control approach belongs in a linear actuator kit. And when people talk about Siemens electric motor starters, they usually mean the direct-on-line or star-delta contactor assemblies that give an induction motor one speed. The other option is a linear actuator kit built around a Siemens brushless DC motor with an integrated speed controller.

Both can work. They are not interchangeable.

Here is the comparison framework I use:

• Option A: a Siemens AC induction motor with a gear reducer, started by a Siemens electric motor starter (direct-on-line or star-delta). Speed is fixed by the gearbox and by the motor rated rpm.
• Option B: a linear actuator kit built around a Siemens brushless DC motor and an integrated controller. Brushless DC motors of this class give you electronic speed adjustment, soft start, and stop behavior that a starter cannot provide.

I am not including servo systems with position feedback, because that is a different decision. I am focusing on the boundary between simple electromechanical starting and electronic variable-speed control.

How Fast Can a Linear Actuator Move? It Depends on Control

The first question I hear is: how fast can a linear actuator move? The honest answer is that in a ballpark sense, small electric linear actuators run from about 0.5 to 4 inches per second under normal loads. Maybe 3.5, I would have to look at the specific kit. High-speed, low-load units can reach 8 to 12 inches per second. I can only speak to the small actuators we have tested.

But the exact speed depends on the motor speed and the screw lead:

speed (in/s) = motor rpm ÷ gear ratio × screw lead (in/rev) ÷ 60

With Option A, motor rpm is essentially fixed by line frequency and the number of motor poles. To change speed, you change the gearbox or the belt. There is no field adjustment unless you add a VFD, and that changes the whole comparison. With Option B, the controller changes the motor voltage or the commutation timing, so you can adjust speed without changing hardware.

So when someone asks me how fast a linear actuator can move, I ask them to first decide what speed they need at what load. A starter-based actuator gives you one speed for one design load. A brushless DC motor package gives you a speed range, but you still have to verify that the Siemens SIMOTICS motor data sheet shows enough torque at the lower end of that range.

Start-Stop Duty: A Red Flag for Many Starter Installations

Linear actuators cycle. They start, move, stop, reverse, and then start again. The duty cycle of that motion is the most under-specified value in the orders I audit.

Option A with a Siemens electric motor starter is simple. The contactor pulls in, the motor gets line voltage, and the actuator runs until the limit switch stops it. That is fine for occasional starts. But every across-the-line start creates inrush current and a mechanical shock. At 20 starts per minute, the contactor, motor, and gearbox all take wear.

Option B with a brushless DC motor is different. The controller ramps current, which limits the mechanical shock. In the lab, we ran a linear actuator kit with an AC motor and a starter against a brushless DC kit with the same screw lead. The BLDC unit completed roughly 50 percent more cycles before we saw measurable wear on the lead screw nut and mounting plate. That was one test, and our test actuator was small. But it matches the physics.

Never expected the starter-based version to need service first, honestly. I grew up with 3-phase induction motors and assumed they were indestructible. The surprise was not the motor. It was the contactor and the mechanical coupling that wore out. The motor survived, but the system did not, and the customer saw the whole thing as a system failure.

Starting Current and Torque at Low Speed

A direct-on-line starter can draw six to eight times the full-load current during start. That is the price you pay for the simplicity of Option A. A star-delta starter reduces the current, but it creates a torque step when it switches from star to delta.

Option B limits starting current to roughly 100 to 150 percent of rated current while still producing enough torque to move the load. For a linear actuator that has to break away from a static load, that is often the better choice.

The counterintuitive part is what happens when the actuator jams. If a limit switch fails, a starter-driven induction motor will keep pushing until the overload relay opens. A brushless DC controller may fault out or cycle instead. Which behavior is better depends on your production line. I would rather see a controlled fault than a broken bracket, but a maintenance team that knows contactors may prefer the brute-force approach.

Installation Simplicity vs. Configuration Control

Option A is easy to install. Siemens SIRIUS starters are designed to IEC 60947-4-1, and their wiring diagrams are standard knowledge for plant electricians. If a coil burns out, you replace it. If an overload relay trips, you reset it. There is very little hidden state.

Option B has more hidden state. The controller has parameters for acceleration, speed, current limit, and fault behavior. One wrong parameter can make the actuator run at half speed or trip on overload during a normal start. In my audits, I have seen returned controllers labeled as failed, but the hardware was fine. The file simply had an incorrect current limit. That is why I treat configuration as part of quality control.

That said, once the BLDC controller is correctly set up, it is usually trouble-free. It also gives diagnostics that a starter cannot provide, such as current history and fault counts. From a quality standpoint, diagnostics are valuable because they turn a vague complaint into a measured issue.

Total Cost: More Than the First PO

I am not going to give you specific prices, because motor prices vary by frame size, efficiency class, and lead time. But in a ballpark sense, a starter package costs less up front than a brushless DC motor with an integrated controller. Starters also have low repair costs and long availability.

However, if you need adjustable speed, the starter is not a lower-cost alternative. You would have to add a VFD or change the gearbox, which changes the initial quote. The BLDC package can look more expensive until you add up the hardware that a fixed-speed design needs for speed changes.

Plus, energy matters. For a linear actuator that runs at partial speed for most of the cycle, a brushless DC motor can be more efficient than an induction motor running at full speed and then hitting a limit switch. But then again, if the actuator runs at one speed continuously for hours, an induction motor with a starter is efficient, simple, and easier to maintain.

Bottom Line: Which Siemens Motor Control Should You Choose?

I went back and forth on this for a long time, and I have changed my recommendation as field feedback came in. The answer depends on the application, not on which controller looks better in a brochure.

• Choose Siemens electric motor starters if: the speed is fixed, the actuator cycles only occasionally, and your maintenance team is already comfortable with contactor logic. This is a no-brainer for a simple push-pull station with one or two starts per hour.
• Choose a linear actuator kit with a brushless DC motor if: you need to change speed on the fly, you have frequent start-stop cycles, or you want soft motion and diagnostics. This fits automated inspection stations, packaging adjustments, or material handling setups where product sizes change.
• If the requirement is still up in the air, I would start with the brushless DC kit. It gives you more room to tune motion during commissioning and avoids swapping hardware later.

This worked for us, but our situation was specific. We are a mid-size Siemens-specialized supplier with an application engineering team. If you are in a plant with limited drive commissioning experience, the starter may be the safer call. Your mileage will vary if your actuator loads are very heavy or your production schedule is unpredictable.

If I had only two hours to make this decision before an order deadline, I would start with the duty cycle. If the application starts fewer than five times per minute and always at the same speed, use a starter. If it starts more often or needs speed adjustment, use brushless DC motor control. That rule will not cover every corner case, but it covers a lot of them.

And please, whatever you choose, document the speed, torque, duty cycle, and controller settings. That is the part that makes quality control possible.