# Variable frequency drives - proper settings.

#### Gailileo

Joined Jun 8, 2020
10
I am studying variable frequency drives.

I figured out how to set the basic parameters for a particular VFD to control a 3 phase motor (name voltage, amps, frequency, RPMs, etc.). Basically I can make it move forward and in reverse, and wire it up to external controls.

My question is about torque. There are a lot of settings regarding torque and I have no idea what to set them for or why. Can anyone suggest some reliable reading or resources to help me cut down on research time? I get one week of access to this equipment and I want to make the most of it.

I know how to change the settings, so I am more interested in the math and physics used to calculate a desired value for a setting (and the purpose behind the value).

#### BobaMosfet

Joined Jul 1, 2009
2,121
Yes, get a datasheet for it and read the datasheet - that will tell you everything you need to know.

#### GetDeviceInfo

Joined Jun 7, 2009
2,198
Once you describe to the VFD what the physical motor attributes are, you then describe the application, which of course is too broad to generalize. My best resources have come from manufacturer technical documentation, driven by real time applications.

#### LowQCab

Joined Nov 6, 2012
4,228
Three Phase Motors have absolutely BRUTAL Starting Torque,
and a HUGE Start-Up-Current-Spike,
because of the standard nature of how 3-Phase Motors work.

That massive Start-Up Torque, and Current Spike, is very seldom a desirable attribute,
so smoothing it out is usually a bonus,
and it can cut-down on shrieking V-Belts, and broken Gear-Reduction-Boxes.

However, some applications "must-have" a "minimum" initial "Bump" in Torque when first started,
for the Machine to function reliably.
So, there is a minimum instantaneous Starting-Torque Setting,
and a "Ramp-Up-Time" that increases Torque over a set Time-Period, from that "Starting-Point-Torque".

In other words, you don't have to start from "zero", you can start from 5, 10, or even 50% Torque,
then Ramp-Up over XX Seconds to 100%.

You may also have the option to limit the Start-Up-Current to a
fixed "Maximum-Current", or "Maximum-Torque" setting, ( basically the exact same thing ).
This will tend to be "self-tuning" to some degree,
as the character of the Load that the Motor is driving
will directly affect the "Acceleration" "Character" of the Motor and all of the attached machinery,
because there is a virtually linear relationship between the
Motor's Torque Output, and Current Demands, measured in Amperes,
so you're basically putting a hard limit on the Maximum-Peak-Torque that the Motor can produce.
This is very useful for extending the expected life of the Machinery being driven,
because 3-Phase Motors can "HIT" hard and fast, like a sledge-hammer.

You may also have the option of RPM-based-Ramp-Up vs Time, ignoring any Torque/Current Limits.

Or it might be possible to implement all of these at the same time, under varying conditions.
.
.
.
.

#### strantor

Joined Oct 3, 2010
6,817
My question is about torque. There are a lot of settings regarding torque and I have no idea what to set them for or why. Can anyone suggest some reliable reading or resources to help me cut down on research time? I get one week of access to this equipment and I want to make the most of it.
You'll need to get all that from the users manual for your drive (hope it's a good drive with a good manual!) And any further information from that manufacturer's supplemental documentation. Because all the brands are a bit different in what they call things and how they implement the features. When you're used to one drive and you switch to another, there is a bit of learning curve like learning a new programming language. Not as extreme as that, but just for example. You would not learn much about C++ by studying Java documentation. Probably a better analogy is cars. If you're a Volkswagen mechanic you can still work on a Toyota but you're going to be in consulting the manuals quite often because things will be different than you expect. You need to study Toyota documentation to learn Toyota systems effectively. Volkswagen documentation won't be much help.