FR-F800 (FREQROL) Inverter Drive series – Selection between two (or more) drives based on Duty requirements

Selection of a suitable inverter drive. The following points are useful for such a process;

Suppose you are required to select a VFD amongst two or more selected options based on output capacities – in order to avoid classical selection mistakes, here are the ponts to consider:

When it comes to the selection process for a suitable VFD – two important prerequires are required;

  1. Detailed information on the application.
  2. The motor nameplate, with all of its information.

The first (and one of the most important) fact to point out is that one CANNOT select an inverter drive accurately based on the kW value on the motor namplate. This kW value is applicable ONLY to the motor’s mechanical power output.

Taking into account the law of energy conservation, along with the fact that there are always energy losses when converting energy from one form to another – it becomes clear that this kW value is not suitable for motor input capacity selection. This is because a motor converts electrical energy to rotational mechanical energy – and losses in the form of heat, noise etc are not being taken into account with such decision making.)

So what do you look at when selecting a suitable inverter drive for your application?

The application itself. There are 5 main inverter models available in the Freqrol range – in short:

FR-CS80 – this an entry level – compact VFD for small applications.

FR-D700 – this is a slightly higher level than FR-D700 – compact VFD for basic applications

FR-E700 – an all-rounder semi-modular VFD.

FR-F800 – the specialized Energy Saver for fluid reticulation applications (fans, blowers and pumps). Also a specialized drive for control systems (flow and pressure).

FR-A800 – the top of the range, flagship FREQROL VFD. It has all the features and functionality as the FR-F800 inverter, but is, in addition, also equipped for high torque applications (conveyers, crushers, crains, etc) and also intended for Factory Automation applications (positioning capabilities).


After the drive has been selected based on the application – it is time to refer to the motor nameplate to select the VFD class and size.

To select the class of VFD – one as to look at the Vac value on the VFD. (usually falls in the 200Vac or 400Vac ranges – but can also fall outside these ranges). It must be taken into account that the class will also be affected by the motor’s configuration connection (Delta vs Star). and therefore should also be taken into account.

After the class has been selected – the size is to be selected. Now here is where most engineers make a mistake by looking at the kW value of the Motor on the nameplate. As mentioned before, this value refers to the mechanical power output of the motor – and can ONLY be used to size select a VFD in a world where there is zero energy losses.

So how does one select the size of a VFD? Well through the FLA (Full-load current) value of the motor. This is the current (A) rating on the motor nameplate. (Once again the motor’s configuration connection (Delta vs. Star) is to be taken into consideration here).

Lets look at a practical example. Suppose the user has a pump with a 1.5kW,3ph 380Vac motor and a suitable VFD is to be selected.

From the application we can immediately see that a FR-F800 is to be used (especially if advanced control systems and extended energy savings requirements are to be applied). 

We also see that a 400Vac class (3ph) VFD will be selected, As for the size selection – we need to look at the FLA value on the motor nameplate. 

Let’s refer to the table below for more clarity;

​So how do you know if the drives you purchases will be able to run your application?

Based on the table above; look at the Motor nameplate FLA value;