 Buck boost transformers
These 4 coil dry-type distribution transformers are used for
single-phase or 3-phase.
When delivered from manufacturer, the Buck Boost is wired as
an insulation
transformer ... also called isolation transformer. In this
configuration, Buck–boost
transformers 'are used to power low voltage circuits including control,
lighting circuits, or applications that require 12, 16, 24, 32 or 48
volts."
For
example, a commercial building might have 480 volt lights, but the
switching is 24 volt. For this application, a buck boost transformer
would be used to change 480 volt into 24 volts for the switch(es).
Choosing the correct model, and wire connections depends on your incoming voltage (120-240-480 volt) and output
voltage
(12 to 48 volt). Resource:
Wiring chart
When the Buck Boost is re-wired onsite as autotransformer,
it will step
up (increase) or buck down (lower) voltage by 5-20%. This
would be the correct use of a Buck Boost if voltages are lower or
higher than standard.
For example if a motor is rated for 240 volt, but actual
voltage at the location is 206 volt, then the undervoltage will
damage the motor. To solve problem, a Buck Boost would be selected
based on the voltage needed, then wired
as
autotransformer so the 4
coils will boost 206 nearer to 240 volt.
Other commercial uses would be to step up 240
volts to 277 volts etc. For example the commercial building has 240 volt service, but wants to use 277 volt lighting.
Selecting the right transformer is done using
charts that show a range of input and output voltages ... for example
input of 240 volt and output of 277 volt ... the electrician would use
the charts to select the nearest voltage ... then use a
second set of charts for correct wiring. Resource:
Wiring for buck boost transformers start pg 6
Typical
household use for a Buck Boost would be to step 120 or 240 volt down to
12 to 24 volt AC.
Another
use would be to correct a voltage drop (frequently caused by long run
of
wire) up to standard voltage
All inputs and outputs are AC not DC
Note if voltages vary, then the transformer does not stabilize voltages
... nor protect from surge events, uneven voltage across each leg etc.
Buy:
150
watt Square D 120-240 volt to 24-12 volt
Square
D buck boost
Buck boost transformer
Siemens transformer at Amazon
240-120
buck boost transformer
Note: If 12-24 volt DC current is needed instead of AC, then
an LED driver is used. Buy: LED
driver
 More detail
How transformers work. Inside each transformer are the primary and
secondary coils (windings). Transformers can have two coils or
multiple coils. Buck boost transformers have 4 coils, 2 on primary side
and 2 on secondary as shown Fig B-1.
Each coil of wire is wrapped
around an iron core that is shared by both primary and secondary sides.
The iron core is represented in Fig B-1 by the two horizontal lines
located between the primary and secondary, and is a source of grounding
for transformers. All transformers must be grounded.
When power is applied to the primary coil(s), it
magnetizes the iron, which induces power on the secondary coil(s) of
wire
even though the primary and secondary share no wire in common. This is
called magnetic induction. If the number of
turns of wire on the primary side are exactly twice as many as on
the secondary side, then the voltage is lowered by 1/2. Varying the
turns ratio lets transformers deliver a variety of voltages.
The typical transformer described above is called an
insulating
transformer because
the primary windings are electrically separated (or insulated) from the
secondaries and the primary and secondary share no wire in common. This
ensures that the
lower voltage wires can never be energized with the higher voltage.
Example of insulating transformer is a cell phone charger, or a
doorbell
transformer, low voltage pathway light transformer etc. When delivered
from factory, buck boost transformers are wired as insulating
transformers, but they can be rewired as autotransformer where the
primary and secondary windings are not insulated from each other.
A 4-coil
buck boost transformer can be wired as an autotransformer to
buck up (raise) or buck down (lower) single phase or 3-phase voltages
by 5-20%. This is accomplished by connecting all 4 coils together to
form a single coil, and then pulling a wire off center connection point
as illustrated in Fig B-2.
Autotransformers are sometimes prohibited by local electric codes
because
voltages are not electrically separated or insulated from each other
like you have with insulating transformers ... except buck boost
transformers only change the voltage by a small percent, which means
only a small risk.
Contrast
buck boost with industrial transformer that is designed to step 480
volt down to 240 volt. If the industrial transformer is wired as
autotransformer, and transformer suffers an internal failure, then the
240
volt wires could be unexpectedly energized with highly dangerous 480
volt. The buck boost transformer does not pose same level of danger
when wired as autotransformer.
Overall, the buck boost wired as autotransformer helps solve problems
encountered in commercial electric wiring.
1)
Non-standard voltages. Voltages are generally stable, but
they vary, and can be different at
each location, especially with longer distance from service box. Low
voltages and high voltage affects operation and efficiency of
electrical
equipment. The buck boost can bring voltages into standard.
2) When higher or lower standard voltage is
needed.
Commercial electric services offer a variety of
standard voltages, including 120, 208, 240, 277, 480 etc. If
the service is 120-240-208 high leg delta,
but 277 volt is needed for the lighting, then a buck boost transformer
can solve the problem.
3) Need more kVA than the rating plate.
Autotransformers can deliver up to 10 times more kVA than the
transformer rating
plate, and run quieter, and cooler with less heat loss and with higher
efficiency.
Note: Buck boost cannot create a
Neutral, like industrial transformers shown lower on page.
Resources: Buck-Boost can deliver more
kVA than rating plate Siemens Buck boost pdf
"Why can a buck-boost transformer operate a kVA load many times larger
than the kVA rating on its nameplate" when wired as autotransformer?
Note: when wired as insulating or isolation transformer, a
transformer can deliver only the rated kVA and shouldn't be overclocked
without risk of overheating and damage to transformer.
Resources: Buck-Boost can deliver more
kVA than rating plate
Resources:
kVA is Kilo watts: 1 kilo watt is 1000 watts, so .5
kVA is 500 watts
Va = volts x amps = watts
Siemens transformers/ pdf
Read about household single-phase electricity
Difference single-phase and 3-phase
What is 3-phase
How to wire 3-phase timers |
Example
wiring diagram for transformer
