Buck Boost Transformers are small, single phase, transformers designed
to reduce (buck) or raise (boost) line voltage from 5 to 20%.
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Buck Boost Transformer
The most common example is boosting 208 volts to 230 volts. usually to
operate a 230 volt motor such as an air-conditioner compressor, from a
208 volt supply line. They have a dual voltage primary and a dual
Buck-boosts are a standard type of single phase distribution
transformers, with primary voltages of 120, 240, or 480 volts and
secondary typically of 12, 16, 24, 32 or 48 volts. They are available in
sizes usually from 50 volt amperes to 10 kilo-volt amperes.
A buck boost transformer is the ideal solution for changing line voltage
by small amounts. The major advantages are their lost cost, compact size
and light weight. They are also more efficient and cost less than
equivalent isolation transformers. When connected as an autotransformer,
they can handle loads up to 20 times the name plate rating.
When a buck boost transformer has the primary and secondary windings
connected, it becomes an autotransformer. Now only the secondary
windings are transforming voltage and current. The majority of the KVA
load passes directly from the supply to the load. This is why they can
supply a load with a larger KVA rating than the nameplate indicates.
They are ideal for low voltage lighting control applications. They are
designed to supply power to low voltage lighting circuits, control
panels or other systems requiring 12, 16, 24, 32 or 48 volts. They are
also suited for low voltage landscape lighting. They are UL listed for
outdoor service and their compact size makes them the perfect solution
for providing power to accent lighting application .
There are two basic types of buck boost transformers, self adjusting
(active) or passive designs. The active types monitor incoming voltages
and will adjust the outgoing voltage to be within an acceptable range.
This is typically between 115 VAC and 225 VAC for computer UPS systems.
The system will either lower or boost voltage if it senses a variance in
the incoming voltage.
Passive transformers are used for larger equipment where the amount is
fixed. This is commonly used when someone wants to use a piece of
equipment that is made for European power (220VAC to 230VAC) in the
United States, which has both 208V and 240V service available.
The passive transformers are rated in volt-amperes and are rated for a
percent of voltage drop or rise. For example, a buck boost transformer
rated at 10% rise at 208VAC will raise incoming voltage of 210VAC to
231VAC. A rating of 5% drop at 240VAC will yield the result of 233VAC if
the actual incoming voltage is 245VAC. The ratings of 208VAC for
business class three phase power, and 240VAC for residential class
electrical power are approximate, and will vary by several volts
depending on the location and even the time of day and local demand.
Buck Boost transformers only adjust the voltage, not the frequency, or
cycles of the electricity, so you can't use it to adjust equipment that
requires 50Hz in the US. All US power plants use a 60Hz systems. Some
equipment is designed to run at 50Hz or 60Hz, and would work fine.
Most passive transformers come semi-wired, where you complete the last
internal connections to have the unit perform the amount of buck or
boost needed. They have multiple taps on both the primary and secondary
coils to achieve this flexibility. They are designed for hard wired
installations (no Plugs) and allow the same transformer to be used in
several different applications. The same transformer can be rewired to
raise or lower by 5%, 10%, or 15% for either 208VAC or 240VAC
applications, depending on the final wiring done by the electrician.
In the tanning industry (and for use in other industries) there are new
fixed transformers that cost about the same but are configured
differently. They are already prewired, so you must purchase them with
the exact amount of buck or boost you need for your application. Rather
than being hard wired units, they have plugs and receptacles
making installation very quick and easy. This eliminates the need for an
electrician if you can determine your exact incoming voltage. To further
make them easier to use, they offer rating in amps rather than volt
amps, which makes it easier to match up the right transformer for the
task. These are used almost exclusively in light to moderate
applications that require 240VAC 40 amp or less.
Not all 240V equipment needs a transformer to buck or boost the voltage.
These types of transformers are used when a piece of electrical
equipment has an electrical requirement that is slightly out of
tolerance with the incoming power supply. This is most common when using
240V equipment in a business with 208V service or vice versa. It is also
common for electronics that are made in a different country than where
they are being used.
Often equipment will be rated with a voltage range, such as 220VAC to
230VAC, requiring a buck boost transformer if the incoming power is not
within the range. It is important that you use a buck boost transformers
that is rated equal to, or greater than the rated load of the equipment, or you can damage the transformer and
If a piece of equipment needs a buck boost transformer but one is not
used, it can cause damage to the equipment. Running the equipment at a
voltage that is lower than the rated amount can cause the amperage load
to rise, in order to meet the total wattage requirement of the
equipment. This can result in damage, including melting of wires or
parts. Running at a voltage too high can cause other types of damage.
The type of damage that can happen depends on the type of equipment and
it sensitivity to improper voltages, but in most circumstances, it will
at least greatly reduce the service life of the equipment and make it
more prone to failure. Buck-Boost transformers are an economical way to
correct this potentially very serious problem. Anytime a line voltage
change in the 5-20% range is required, a buck-boost transformer should
be considered as your first line of defense.
When the amount of rise or drop in the incoming voltage is more
than 15% to 20% then this is usually out of the boundaries of
what a buck boost transformer is designed for, and a line transformer is
required. Line transformers are basically the same, but with different
tap points to provide grater rise or drop in voltage, such as 240VAC to
Application Use of Buck-Boost Transformer:
A typical application is 120 volts in, 12 volts out for low
voltage lighting or control circuitry. In most applications, this
low voltage transformer is field connected as an auto transformer.
Low supply voltage exists because equipment is installed at the
end of bus system.
When the supply system is operating at or over its design
Where overall consumer demand may be so high the utility cuts
back the supply voltage to the consumer causing a "brownout".
These transformers provide tremendous capacity and flexibility in KVA
sizes and input/output voltage combinations. Basically you get can get
75 different transformers all in one convenient packaging.
Output KVA available at reduced voltage can be found by:
Actual Input Voltage Rated Input Voltage
x Output KVA = New KVA Rating.
Most Common Ask Question About Buck-Boost
1. How does a buck-boost transformer differ from an insulating
A Buck-Boost transformer is an insulating type
transformer when it is shipped from the factory. When it is connected at
the job site, a lead wire on the primary is connected to a lead wire on
the secondary-thereby changing the transformer's characteristics to
those of an autotransformer. The primary and secondary windings are no
longer "insulated" and secondary windings are no longer "insulated" and
its KVA Capacity is greatly increased.
2. What the different between a buck-boost
transformer and an autotransformer?
When a buck-boost transformer primary lead wire and secondary lead wire
are connected together electrically, in a recommended voltage bucking or
boosting connection, the transformer is an
autotransformer. However, if the interconnection between the primary and
secondary winding is not made, then the unit is an insulating type
3. Why do Buck-Boost transformers have 4 windings?
To make them versatile. A four winding has 2
primary and 2 secondary windings and can be connected eight different ways
to provide a multitude of voltage and KVA outputs.
4. Will a buck-boost transformer stabilize voltage ?
NO, the output voltage is a function of the input voltage. If the
input voltage varies, then the output voltage will also vary by the same
5. Are there any restrictions on the type of load that can be
operated from a buck-boost Transformers?
There are no restrictions.
6. Why can a buck-boost transformer operate a KVA load many times
larger than the KVA rating on its nameplate?
The transformer has been auto-connected in such a way that the 22V
secondary voltage is added to the 208V primary voltage, it produces 230V
7. Can buck-boost transformers be used on motor loads?
Yes, either single or three phase.
8. Can buck-boost transformers be used on three-phase systems as
well as single-phase systems?
Yes, a single unit is used to buck or boost single phase voltage. Two
or three units are used to buck or boost three phase voltage. The number
of units to be used in a three-phase installation depends on the number
of wires in the supply line. If the three-phase supply is 4 wire Y, use
three buck-boost transformers. If the 3-phase supply is 3 wire Y
(neutral not available) use two buck-boost transformers.
9. Should buck-boost transformers be used to develop a three-phase
4 wire Y circuit from a three-phase 3 wire delta circuit?
No, a three phase wye buck-boost transformer connection should be
used only on a 4 wire source of supply. A delta to wye connection does
not provide adequate current capacity to accommodate unbalanced currents
flowing in the neutral wire of the 3 wire circuit.
10. Why are buck-boost transformers shipped from the factory as
insulating transformers and not pre-connected at the factory?
A four winding buck-boost transformer can be connected eight
different ways to provide a multitude of voltage and KVA output
combinations. The proper transformer connection depends on the user's
supply voltage, load voltage and load KVA. It is more feasible for the
manufacturer to ship the unit as an insulating transformer and allow the
user to connect it on the job site in accordance with the available
supply voltage and requirements of his load.
11. Are buck-boost transformers as quiet as standard isolation
Yes, the isolation transformer would have to be
physically larger than the buck-boost transformers, and smaller
transformers are quieter than larger one.
12. How does the cost of a buck-boost transformer compare to that
of insulating transformer - both capable of handling the same load?
The dollar savings are generally greater than 75% compared to the use
of an insulating type distribution transformer for the same application.
13. What is the life expectancy of a buck-boost transformer?
It is the same as the life expectancy of other dry-type transformers.
You should have the following information before selecting a
Line voltage - The voltage that you want to decrease or
increase. This can be found by measuring the supply line voltage
with a voltmeter.
Load Voltage - The voltage at which your equipment is designed
to operate. This is listed on the nameplate of the equipment.
Load KVA or Load Amps - You do not need to know both- one or the
other is sufficient for selection purposes. This is usually
found on the nameplateof the equipment.
Frequency - The supply line frequency must be the same as the
equipment to be operated - either single or three phase.
allows signal or power to be taken from one device and fed into
another without electrically connecting the two.
are devices that transfer electrical energy from one electric
circuit to another, without changing the frequency, by
are designed to meet certain performance specifications and size
requirement that you require. There is a wide range of custom
Buck Boost Transformers
is a ideal solution for changing line voltage by small amounts.
Often used to buck (lower), or boost (raise) the voltage from 208v
to 240v for lighting applications.
Pole Mounted Transformers
are mounted to poles for overhead electrical lines. Used in various applications.
Are available in single phase or three phase transformers.
Medium Voltage Transformers
are used with a medium range of voltages. They come in a full
range from liquid-filled, convention dry type as well as cast coil.
Pad Mounted Transformers
are a excellent choice for commercial and industrial such as
manufacturing facilities, refineries, office buildings, schools,
hospitals, restaurants, and retail stores. They come in various
sizes and can be used underground as well.
typically these voltage transformers are used in power transmission
applications. High voltage transformers are also used in microwave.
- With Acme Electric being in business
over 80 years, they have always believed in offering there customers superior service, quality and technical expertise in the
AMVECO Transformers -
AMVECO designs and manufactures toroids
transformers, current transformers, and auto transformers. Most
AMVECO products are custom designed utilizing their state-of-art proprietary
CAD programs. The AMVECO engineers can quickly generate designs in a
matter of hours, if needed.
Federal Pacific Transformers -
Federal Pacific is a division of Electro- Mechanical Corporation, a
privately held, American owned company founded in 1958. Federal
pacific offers dry-type transformers from .050 KVA through 10,000
KVA single and three phase, up to 34.5 KV, 150 KV BIL with UL
approval through 15 KV.
Marcus Transformer - Ever since they opened their doors for business a half a century ago,
they have been a leader in innovative transformer design. As a
family-owned company they are proud of the reputation they have
earned for making quality-built transformers that deliver
exceptional performance and savings.
Hammond Transformers - Hammond Manufacturing was founded in 1917 in Guelph, Ontario,
Canada. In the last 3 decades it has expanded to the US and the
international markets offering many types of power transformers.
- TEMCo Transformer, a family-owned business which has been
manufacturing and distributing electrical products since
1968. They focus on transformers that significantly
reduce power consumption over 30 percent compared to competitive
GE Transformers - GE has been a key player in the energy industry for
more than a century. Since the installation of
their first steam turbine in 1901. They have become
number one provider of high-technology power generation
and distribution equipment.
Jefferson Electric Transformers - Jefferson Electric has
been a pioneer and innovator of magnetic products since 1915.
Jefferson broad line of dry-type transformers are backed by quality
assurance systems so stringent that each and every unit gets
thoroughly tested before it goes out there door.
Distribution Transformers - Distribution
transformers are generally used in electrical power
distribution and transmission power. This class of transformer has
the highest power, or volt-ampere ratings. and the highest
continuous voltage rating.
Substation Transformers - Substation Transformers are large
devices which usually weigh tens of thousands of pounds. They are
filled with tens of thousands of gallons of heat transfer fluid.
Although they are typically 99.8% efficient in the transforming of
electricity from one voltage to another, processing hundreds of Mega
Volts-Amps of electricity force the liberation of hundreds of BTUs
Medical Grade Isolation Transformer -
Medical Grade Transformers generally refer to the transformers
used in medical devices as well as hospital, biomedical and patient
care equipment. There are a number of strict safety rules,
guidelines and laws governing the design, construction and the test
of these transformers.
Drive Isolation Transformer -
They are used to isolate a drive from a main power line to
prevent the transmission of harmonics that the drives produce back
into the power line. They stop drive harmonics from disrupting
computers and other sensitive equipment.
Toroidal Transformers -
Toroidal Transformers are more efficient than the cheaper laminated EI types of similar power level. Some of the advantages are smaller
size, lower weight, less mechanical hum, (making them superior in
audio amplifier), low-off-load loss.
Step-Up Transformers - A Step-Up Transformer is one whose
secondary voltage is greater than its primary voltage.
This kind of transformer "steps up" the voltage applied
to it. -
- A Step-Down Transformer is designed to reduce voltage from primary to
They can range from sizes from .05 KVA to 500 KVA
Isolation Transformers -
An Isolation Transformer is a device that transfers energy from
the alternating current (AC) supply to an electrical or electronic
load. It isolates the windings to prevent transmitting certain
types of harmonics.
Buck Boost Transformers - Buck Boost
Transformers make small adjustments to the incoming voltage. They
are often used to change voltage from 208v to 240v for lighting
applications. Major advantages of Buck boost transformers
include; low cost, compact size and light weight.
High Voltage Transformer - There are many different types of
voltage transformers. A High Voltage Transformer operates with high
voltages. Typically, these voltage transformers are used in power
transmission applications, where voltages are high enough to present
a safety hazard.
Medium Voltage Transformers -
A Medium Voltage Transformer can be connected directly to a primary
distribution circuit and generally has the most load diversity.
These voltage transformers have installation practices that are
generally in accordance with application recommendations from the
Institute of Electrical and Electronic Engineers (IEEE).
Low Voltage Transformers
- A Low Voltage Transformer is an electrical device that transforms
120 volts (line voltage) into 12 volts or 24 volts (low voltage).
Some uses for low voltage transformer are in landscaping lighting.
Single Phase Transformers - In electrical engineering, single-phase electric power refers to the
distribution of electric power using a system in which all the
voltages of the supply vary in unison. Single-phase distribution is
used when loads are mostly lighting and heating, with few large
Three Phase Transformers - Three
Phase Transformers must have 3 coils or windings connected in
the proper sequence in order to match the incoming power and
therefore transform the power company voltage to the level of
voltage needed while maintaining the proper phasing or polarity.
Custom Transformers -
Custom Transformers are designed for a certain performance
specifications and size requirements. The company works with
your engineering specification.
Industrial Control Transformers -
Industrial Control Transformers are used to convert the
available supply voltage to the required voltage to supply
industrial control circuits and motor control loads.
Pad Mounted Transformers - Pad
Mounted Transformers are usually single phase, or three phase, and
used where safety is a main concern. Typical applications;
restaurant, commercial building, shopping mall, institutional.
Pole Mounted Transformers -
Pole Mounted Transformers are used for distribution in areas
with overhead primary lines. Outside a typical house one can see one
of these devices mounted on the top of an electrical pole.
Oil Filled Transformers -
Oil Filled Transformers are transformers that use insulating oil as
insulating materials. The oil helps cool the transformer.
Because it also provides part of the electrical insulation between
internal live parts, transformer oil must remain stable at high
temperatures over an extended period.
Dry Type Transformers - Dry-Type
Transformers are available for voltages up through 34.5 kV
(although the most common upper limit is 15) and KVA ratings up
through 10,000 (with 5000 as the usual limit). Dry-type use air as a
coolant, lowering health and environmentally concerns.
Auto Transformers -
An Autotransformer is an electrical transformer with only one
winding. The winding has at least three electrical connection points
called taps. Autotransformers are frequently used in power
applications to interconnect systems operating at different voltage
classes, for example 138 kV to 66 kV for transmission. Another
application is in industry to adapt machinery built for 480 V
supplies to operate on the local 600 V supply.
Electrical Transformers are devices used to raise or lower the
voltage of alternating current. For instance, power is transported
over long distance in high voltage power lines and then transformers
lower the voltage so that the power can be used by a business or household.
An Isolating Transformer is a transformer, often with
symmetrical windings, which is used to decouple two circuits.
An Isolation transformer allows an AC signal or power to be taken
from one device and fed into another without electrically connecting
the two circuits. Isolation transformers block transmission of DC
signals from one circuit to the other, but allow AC signals to pass.
Power Lines - A Transmission Line is the material medium or structure that forms
all or part of a path from one place to another for directing the
transmission of energy, such as electromagneticor acoustic waves as well as electric power
transmission. Components of transmission lines include wires, coaxialcables, dielectric slabs, option fibers,electric power lines, and waveguides.
Transformer Voltage - The measure of the amount of force on a
unit charge because of the surrounding charge.
Transformer Frequency -
The transformer cannot change the frequency of the supply. If the
supply is 60 hertz, the output will also be 60 hertz.
Transformer K Factor - Some transformers are now being offered
with a k-factor rating. This measure the transformer's ability to
withstand the heating effects of non-sinusoidal harmonic currents
produced by much of today's electronic equipment and certain
Primary Voltage - The coil winding that is directly connected
to the input power.
Harmonic Cancellation -
Harmonic cancellation is performed with harmonic canceling
transformers also known as phase-shifting transformers. A harmonic
canceling transformer is a relatively new power quality product for
mitigating harmonic problems in electrical distribution systems.
This type of transformer has patented built-in electromagnetic
technology designed to remove high neutral current and the most
harmful harmonics from the 3rd through 21st.
Enclosed transformers come with a weatherproof standard set by
Epoxy Encapsulated -
A process in which a transformer or one of its components is
completely sealed with epoxy or a similar material. This process is
normally preferred when a unit might encounter harsh environmental
Voltage Regulators - A
Voltage Regulator is an electrical regulator designed to
automatically maintain a constant voltage level.
It may use an electromechanical mechanism, or passive or active
electronic components. Depending on the design, it may be used to
regulate one or more AC or DC voltages.
AC Line Reactor -
AC Line Reactors is a three phase transformer used in
conjunction with AC variable frequency and DC motor drive.
They are a bi-directional protective filtering device.
Line Power Conditioners -
Power or Line Conditioners regulate, filter, and suppress noise in
AC power for sensitive computer and other solid state equipment.
DC Power Supplies -
Conversion of one form of electrical power to another desired
form and voltage. This typically involves converting 120 or 240 volt
AC supplied by a utility company to a well-regulated
lower voltage DC for electronic devices.
Rotary Phase Converters -
Rotary Phase Converters are commonly used in home or small
commercial or industrial settings. Rotary phase converters convert
single-phase power into three-phase power. This is a very
cost-effective way to power three-phase electric motors and other
three phase equipment.
Frequency Converters -
A Frequency Changer or Frequency Converter is an
electronic device that converts alternating current (AC) of one
frequency to alternating current of another frequency.
Voltage Converters -
A Voltage Converter changes the voltage of an electrical power
source and is usually combined with other components to create a
Magnetic Motor Starters - Magnetic Motor Starters are
essentially heavy duty relays mounted in boxes, often equipped with
heater/thermal overloads matched to the motor they start.
Motor Starting Auto Transformers - An Auto
Transformer starter uses an auto transformer to reduce
the voltage applied to a motor during start. The auto transformer
may have a number of output taps and be set-up to provide a single
stage starter, or a multistage starter.