COMBIVERT F6 and S6: How the drives differ

The perfect drive controller for every application

The COMBIVERT Drive Controllers F6 and S6 are the powerful drive controllers from KEB and are often mentioned in the very same breath. After all, the devices are modern inverters, both drive a wide range of motor technologies and both feature safety directly in the drive. And yet COMBIVERT F6 and S6 differ in essential respects. What exactly separates and unites the devices? 

If plant and machine manufacturers are looking for frequency inverters that not only cover a wide power range, but also reliably drive synchronous, asynchronous, PM or IPM motors from KEB and third-party suppliers, the COMBIVERT F6 and S6 Drives are often the first choice. The F6 combines the advantages of a frequency inverter and a servo drive in just one device, controlling motors without an encoder or with an encoder - just as the machine or system requires. This is also possible with the S6, which was specially developed for servo applications.  

Both drives have scalable safety functionalities directly in the drive. Flexible utilisation of the safety functions and limit values via digital I/Os and/or the "Safety over EtherCAT" (FSoE) or PROFIsafe safety profile is possible as required. The COMPACT device version comes with STO as standard, while the APPLICATION and PRO versions feature STO, SBC and optional encoder-based speed/position-dependent safety functions. Precision and maximum repeat accuracy as well as functional consistency across the entire power range are further aspects in which the F6 and S6 are equal. 

What makes the difference

However, in addition to the many similarities, the drives differ in some aspects: 

Product range

The COMBIVERT F6 covers a range from 2.2 kW to 450 kW and is designed for a rated current of 9.5 A to 800 A. The S6, on the other hand, is designed for a rated current of 2.6 A to 16.5 A and, with a power range of 0.75 to 7.5 kW, is designed for applications that require comparatively lower power. With a high overload capacity, the S6 ensures optimum dynamics. 

Housing sizes

The S6 servo controller is available in two housing sizes. There is more choice here with the F6: users can choose between seven housing sizes for the inverter. 


The difference in size between the two devices is recognisable at first glance. This is because the S6 Servo Drives are only available in a compact book format, creating the ideal conditions for space-saving control cabinet installation. Thanks to their modular design, however, the F6 Drives are also ideal for efficient installation. 

Sub-mounted braking resistor

Starting with frame size 4 of the F6, sub-mounted braking resistors are available that are mounted on the rear of the inverter heat sink. This saves space in the control cabinet and eliminates the wiring work otherwise required by the user. The F6 also has an integrated temperature model that protects the braking resistors from overheating.

Different cooling concepts

They ensure that the KEB Drives are highly scalable. The F6 is available as an air-cooled or liquid-cooled built-in or push-through variant. The S6 is available to system and machine builders as an air-cooled built-in version. One of the advantages of liquid cooling is the particularly high efficiency and increased service life of the inverter, as it can be operated cooler and more evenly. The advantage of air cooling, on the other hand, is that the user can change the fans as required. 

All in all, the F6 and S6 are two powerful and flexible drive controllers that ensure highly efficient drives in numerous application areas. Due to the different power ranges and the variance in device sizes, users will always find the ideal drive solution in the KEB portfolio. 

20221216 img portrait geisler timo

Timo Geisler

Product Manager Drives

+49 5263 401-747
+49 151 46746515