Variable Speed Drive FAQ
(Frequently Asked Questions)
Joliet Technologies is dedicated to providing our customers and
website visitors with quality information about our products and services. As
well as helpful information you can use to make well informed decisions
regarding your drive needs.
Below is a list of questions that are common to our products and services. In
addition we will make every effort to provide hard to find information you can
use on a daily basis. If you are
looking for specific information regarding AC variable
frequency drives, DC variable speed drives and/or adjustable speed drives in
general and did not find it, let us know and we will
do our best to find it and publish it. All questions and comments are
Q. What makes Joliet
Technologies different, compared to other variable speed drive integrators?
you can tell from our website, we are committed to providing as
much information as possible regarding the products and services
we provide. We have done our best to give you the information about
the drives we use in our systems, so you can make clear and informed
decisions for your particular application.
From the moment you contact us (and you can contact us in a multitude
of ways, by phone, fax, e-mail, RFQ form
a Pro form) you will realize that our sales staff and engineers
have the knowledge and resources to provide the drive system solutions
you need. We will work one on one with you to make sure all your
questions are anwsered and all application issues are addressed.
Our goal is to give you the best products & services at the best
price, it's that simple.
Q. What's the difference
between a non-regenerative dc drive and a regenerative dc drive?
difference between these two types of DC drives is explained on
this page, DC Drive Types.
Q. What's the difference between a variable frequency drive
(vfd) and a variable speed drive (vsd)?
variable frequency drive (VFD) refers to AC drives only and a variable speed
drive (VSD) refers to either AC Drives or DC Drives.
VFD's vary the speed of an AC motor by varying the frequency to the motor. VSD's
referring to DC motors vary the speed by varying the voltage to the motor.
Q. What is the difference between
a VSD and a Soft Start Starter?
difference is the speed that the motor can run, when at full speed. With a
soft start starter, the motor is reduced voltage started, and then when the
motor is at full speed, or a timing circuit has timed out, a "running
by-pass contactor" pulls in and the motor continues to run at
full base speed. With a VSD (Variable Speed Drive) or VFD (Variable Frequency
Drive) (these are the same thing, just different names for the same unit),
The motor will soft
start, and you can vary the speed of the motor, by varying the output frequency
from the VSD or VFD.
So, if you don't need to vary the speed of the motor,
once the motor is up to speed, then the correct solution is a soft start starter
for that motor. If
the process requires the motor speed to vary at anytime, the correct solution
is a VSD / VFD.
The cost for a soft start starter is much less than a VSD
Q. Can a variable frequency drive replace a softstart?
A. Yes, a variable frequency drive can replace a soft start starter, since most drives give you a current limiting ramp to start and stop your motor. BUT, if you do not need to vary the production speed of your motor, then the soft start starter is still the correct product for the application. This is because the cost of the soft start starter is less than the cost of a variable frequency drive.
Q. Are the variable frequency drives phase sensitive?
A. No, variable frequency drives are not phase sensitive. You can adjust the direction of rotation of the motor, through the software of the drive.
Q. Can a variable frequency drive be used for a fan application, blower application or a pump application?
A. This is one of the best applications for an AC drive. In most fan/pump applications, there is a need to vary the output of the fan/pump. This is very easy to achieve with an AC drive. Plus you get the benefit of reduced energy cost of running the motor!!!
Suitability of VFD for pumps.
VFD’s are well suited to pumping applications. Many are manufactured
to include motor speed/torque profiles specifically intended to optimize pump
performance. However, there are some issues which must be considered before
deciding on the use of VFD’s:
- Suitability of the motors – the motors must be rated for inverter-duty
to withstand the higher electrical stresses drives can impose. Some older
motors were not built to withstand these stresses and may fail prematurely.
of motors from VFD’s - the VFD’s will induce voltage
transients on the load connectors. If these connectors are too long
(manufacturers often suggest keeping motor lead length to 50m or less),
at the motor terminals may increase to several factors above nominal, which
also cause premature motor failure.
- VFD installation location and environmental
conditions – this will
determine the type of enclosure and conditions under which the VFD’s
will operate. VFD’s which must withstand severe moisture, temperature
swings, or dust can fail prematurely and must be protected by suitably
Q. How can a variable speed drive improve our production?
A. The drive can be "tuned" to the application to achieve maximum output of the equipment. Sometimes this is slightly under the base speed of the motor, and sometimes, it is over the base speed of the motor. Since every application is different, contact us through an email or the phone to discuss your application in detail and discover how we can help improve your companies' production output.
Q. What is the percentage of
operating cost reduction after installing a VFD?
A. This question
is a very open-ended one which depends on many factors - load, incoming
supply voltage, utility costs, and several others - and so cannot be
simply answered. A good place to start customizing the inquiry for your
use would be at ABB's web site; they have tools for rough calculations
for energy savings using VFD's.
Q. Can I run a 230V, 3Ph motor with 230V, 1Ph input?
A. Yes. Joliet Technologies is pleased to announce that we have the solution to run most 230V, 3Ph motors with only 230V, 1Ph input!
Call for more information.
Q. What is the best drive for my application?
A. This is not an easy question to answer. Before we can give you a comprehensive answer to this question we will need to know more about your application and specifications. Simply call (815)
725-9696, toll free (866) 492-9888, fax (815) 725-9393 or e-mail us with your application and specifications and we will recommend the drive that's right for you.
Q. Can I convert my DC Drive application to an AC Drive?
A. Yes, You can convert your DC drive system; to an AC drive system by replacing both the motor and the drive. Consideration must be given for the torque and speed range of the DC motor, when converting to AC. You will need to
consider using a "Vector" AC drive for this conversion.
Q. Will a variable frequency drive or variable speed drive save me money?
A. Yes, the AC drive can save you money on operating cost, when the load and motor speed can be varied. By reducing the speed of the motor, you will consume less energy, which will reduce your electric bill.
Q. What is the cost of a VFD?
varies widely based on manufacturer, voltage, ampacity, enclosure type, torque
requirements, quantity of analog and digital inputs/outputs, and communications
options. One example: a standard wall-mountable, NEMA 1 , 3-50/60-380/480
volt, 30Hp, variable torque/normal duty, general purpose drive, with 2AI/2AO,
6DI/3DO, and Modbus RTU protocol from ABB will cost approximately US$2,700
(Oct. 2011). We also sell drives from Siemens, WEG, Control Techniques, Schneider,
Q. Should I replace my old analog equipment with new digital equipment?
A. DEFINITELY!!! For so many reasons. . . difficult and costly to get spare parts, Hard to find Tech. Support / serviceability, no communications, little flexibility, etc.
Q. Will Joliet Technologies train our staff to operate and maintain our equipment?
A. We can develop a training program that is tailored to your companies' needs and location. So, when it makes sense, we can train your personnel in our facility, or bring the classroom to your factory, for hands on training.
Q. What is a line reactor and what will it do for my application?
A. A line reactor is an impedance device. Its benefits are reduction of drive cross talk, and interference.
Input reactors will limit the waveform distortion and harmonic voltages. This will help to improve the power factor due to a reduction of the RMS currents in the system.
Output reactors are generally good up to 100 feet is distance (drive to motor). The benefits are the damping of peak voltage overshoots, which will reduce internal motor heating and lessen the "noise" that a motor can produce when it is run by a drive. On installations where the distance is greater than 100 feet, filters are recommended for motor protection.
Q. What filters are used for
filters are sometimes installed to reduce EMI, although modern PWM drives
are much less likely to generate significant noise.
On the load side, output
chokes can be installed to reduce drive generated harmonics in the motor
leads. Many drives have some output filtration already installed and harmonics
are generally not a problem as long as wiring is correctly segregated, properly
grounded, and the motor leads are not excessively long (typically less than
Q. What is the best drive manufacturer for my application?
is a difficult question to answer. Our sales engineers are knowledgeable of what products are available from well-known manufacturers. They will recommend the best drive for you based on your application and specifications. There maybe several products that will meet your specifications, we will recommend the one that is best based on price and performance. Simply call (815) 725-9696, toll free (866) 492-9888, fax (815) 725-9393 or e-mail us with your application and specifications and we will recommend the drive that's right for you.
Q. What are the maintenance
requirements of a VFD?
normal operating conditions, VFD’s generally require little
maintenance once properly set up. Spare parts can be obtained readily,
and some are replaceable by maintenance personnel. In other cases, qualified
service technicians are required.
Also see How To Maintain a VFD?
Q. Is it possible
to use the same soft starter to start two MV induction motors?
it is possible to start multiple motors from a single soft-start. Typically,
the motors are started sequentially and are identically rated. In a typical
MV application, additional contactor cabinets are connected and control-tied
to the soft-start. Once the first motor comes up to speed, the soft-start "Switches" to
control the next motor in the sequence.
In the case of only two motors, some soft-starts are manufactured with
dual settings to permit starting of motors that have different starting
characteristics, but actual motor output during ramp-up may not differ
much, being limited
by the inherent performance characteristics of the soft-start.
Multiple simultaneous starting of motors requires that the motors be identical
and that the soft-start be sized for the total load and supplied with supplemental
Q. What is exactly the difference
between AC and DC capacitor in functionality and manufacturing? Why a DC
capacitor is required to connect across the alternator terminals?
essence, a "capacitor is a capacitor", although there are differences
in design based on topology, type, and materials of manufacture. Sometimes
capacitors will carry a dual rating, for AC and DC - the AC rating for
a capacitor of the same capacitance is typically much lower than its DC
rating (often at least 3-4x less since AC max voltage peak-to-peak is ~2.8x
rms), to accommodate the significant heating internal to the cap caused
by frequency/alternating polarity. Some manufacturers manufacture AC caps
which are essentially two DC caps in series back-to-back; these limit current
flow through either cap but their internal resistance is somewhat high,
which can lead to eventual break down due to heating as well.
Use of a DC cap across alternator terminals is often done to filter alternator
whine (noise) caused by voltage ripple, the "AC" component of
rectified DC output. When the capacitance is properly installed and matched
to the frequency of the noise, it provides a low-impedance path to "divert" the
voltage ripple to ground.
As always feel free to contact
us with any questions and/or comments you may have.
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