Variable Transformers
Product Design & Engineering Data
Product Design & Engineering Data
tions, two 120-volt units are ganged for 120-volt line-to-line
usage. For 240-volt open delta applications, two 240-volt
units are ganged with the open delta assembly. In any of the
above voltage applications, higher current requirements are
met by paralleling two or more units in the ganged assembly.
EFFICIENCY & REGULATION
In contrast to inefficient, wattage-burning resistive-type controllers such as rheostats, STACO Variable Transformers have
an extremely low power loss and efficiencies as high as 98%.
STACO Variable Transformers deliver any desired voltage
(within the transformer rating) with negligible variation in output
voltage from no-load to full-load current. Voltage drop tables
and a sample regulation curve are provided in this section.
DISTORTIONLESS V OL T A GE CONTROL
STACO Variable Transformers produce an accurate transfer of
input wave to output circuit, providing distor tionless voltage
control (a requisite of many sophisticated electronic applications).
Type 1010B Cutaway
General Information
STACO ENERGY PRODUCTS CO. is a leading manufacturer
of variable transformers, the most versatile and reliable voltage controls available. Variable transformers have many
industrial and laboratory applications as basic components to
control voltage, current, power, heat, speed, light, and
electromechanical force.
A basic STACO Variable Transfor mer consists of a single
layer, magnet wire, winding on a toroidal core of laminated silicon steel. A carbon brush, connected to an output lead, is
rotated over a precision ground, plated commutator track to
tap off voltage at any turn from zero to the maximum output
voltage of the winding.
STACO research has developed design features and proprietary processes providing longer lasting, more reliable products. Particularly impor tant is the high-temperature foundation material bonding the coil securely to the core assembly.
This material, which has a high thermal transfer characteristic, dissipates heat from the brush contact area, increases the
heat-distribution of the core itself and provides the transformer with greater tolerance to transients and short-term
overloads.
VOLTAGE RATINGS
Basic single STACO Variable Transfor mers are rated either
120 volts or 240 volts. Higher voltage requirements are met
by combining or ganging 120-volt or 240-volt units. A 480volt, single-phase application can be met with two 240-volt
variable transformers ganged in a series connection. In threephase applications, three 120-volt units are ganged in a wye
connection to result in a 240-volt line-to-line three-phase
assembly. Similarly, three 240-volt units are ganged in a wye
connection to result in a 380-volt or a 480-volt line-to-line
three-phase assembly. In each of these instances, the individual transformers, or coils, are identified with the basic voltage rating, either 120 volts or 240 volts. When variable transformers are connected in open delta for three-phase applica-
PLATED COMMUTATOR SURFACE
The commutator surface of each coil is specially plated with
precious metal, giving STACO commutators longer life,
increased resistance to corrosion and the capacity to withstand greater overloads (while maintaining a constant contact
voltage drop).
SIMPLE INSTALLATION AND CONNECTION
Mounting and hook-up of STACO units is convenient and
easy. Most series units are designed with an adjustable shaft
to accommodate either bench or panel mount (adjustable to
accommodate varying panel thickness). Terminals are easily
accessible: screw, lug, quick-connect or solder design.
Connections deliver increasing output voltage with either
clockwise or counter-clockwise knob rotation. Manually operated units have standard dials graduated 0-100 (percentage
of output voltage).
LONGER LIFE WITH NEGLIGIBLE MAINTENANCE
Precise design assembly of the brush (at a constant pressure
to a smoothly finished and securely bonded commutator surface) provides excellent mechanical performance, long life,
and low-driving torque. Brush replacement is seldom needed, but it is easily performed. High safety margins of voltage,
current-carrying capacity and dielectric strength are why you
can expect longer life from STACO Variable Transformers.
SMOOTH AND LINEAR VOLTAGE CONTROL
STACO Variable Transfor mers are designed with a fraction of
a volt per turn. Close adjustment of output voltage is easy
because the brush always contacts one or more turns. Coil
turns are evenly spaced, and output voltage is proportional to
angular rotation. Full angular travel is approximately 320
degrees on all Series.
VOLTAGE DOUBLER (DUAL INPUT)
Most 240-volt models have an additional input voltage tap permitting normal overvoltage output, with half normal input voltage.The output current must be reduced when the output voltage exceeds 125% of the input voltage as shown in Fig. B on
page 6.
????Product Design & Engineering Data
TEMPERATURE & RATING
The low loss of STACO Variable Transformers allows operation at full current rating @ ambient temperatures up to 50
degrees C (122 degrees F). In locations above this temperature, the output current must be reduced according to Fig. A
on page 6. On single-transient loads and on-off cycled loads,
output currents up to 10 times normal may be carried for brief
intervals, as shown in Fig.C on page 6.
MILITARY SPECIFICATIONS
All STACO Variable Transfor mer models are available on special order to meet certain militar y specifications. Typical of the
requirements which can be met are:
ALTITUDE PHENOLIC PARTS
CONNECTING WIRE SHOCK
CORROSION VIBRATION
HUMIDITY
RUGGED MECHANICAL CONSTRUCTION
STACO Variable Transfor mers are precision built to exacting
mechanical tolerances using the finest materials available.
Quality assurance inspections are performed to insure that
the high designed-in quality is maintained throughout the
manufacturing cycle. A STACO Variable Transformer provides
accurate, reliable and lasting voltage control for a broad variety of applications.
General Definitions
The following words or phrases are commonly used to
describe characteristics of STACO Variable Transformers.
INPUT VOLTAGE : The supply voltage to which a STACO
Variable Transformer is connected.
FREQUENCY: All units in this catalog operate in the range
of 50 to 60 HERTZ unless otherwise noted. These units may
be used on higher frequencies within the limits shown in the
tabulations in the section “Operation at Higher Frequency,”
page 5.
OUTPUT VOLTAGE : The range of voltage available at the
output terminals.
CURRENT RATING TERMINOLOGY: To permit maximum
utilization of STACO Variable Transfor mers, output ratings are
given for both constant current and constant impedance
loads.
CONSTANT CURRENT RATING: Output current that
can be carried regardless of output voltage setting.
(Reduce, for output above 125% of input voltage, on voltage doubler connection.)
CONSTANT IMPEDANCE RATING: Output current that
can be carried with loads such as incandescent lamps or
resistance heaters in which the current drawn is approximately proportional to the applied voltage, increasing to
maximum current at line voltage. This rating applies only
to applications where maximum output voltage is limited
to line voltage.
KVA R ATING: The maximum output current at maximum
output line voltage multiplied by that maximum voltage and
divided by 1000 for single phase. Divide by 577 for three
phase (1000/ 3).
OVERVOLTAGE CONNECTION: Output voltage from zero to
17% above line voltage (10% for 171 through 291 Series).
LINE VOLTAGE CONNECTION: Output voltage from zero to
line voltage.
VOLTAGE DOUBLER CONNECTION: Unit gives full overvoltage output with half normal input voltage. Available on
most 240- and 480-volt units. Reduce output current when
output voltage exceeds 125% of input voltage.
REGULATION: VNL - VFL
VNL
VNL = Output Volts No Load
VFL = Output Volts Full Load
DRIVING TORQUE: Torque required to turn the STACO
V ariable Transformer shaft.
ROTATION: Rotation of STACO Variable Transformer shaft
gives increase in output voltage (as viewed from referenced
end).
SINGLE UNIT TAP AND TERMINAL DIAGRAM: Input connection is shown for normal overvoltage output. Optional line
voltage and voltage doubler input are indicated. Winding section voltages are for a normal overvoltage (or voltage doubler)
connection at input voltage shown. Line voltage connections
give 85% of these voltages (90% on 171 through 291 Series).
Cased units with line cord may omit several coil taps.
CONNECTION — SINGLE PHASE UNIT: Terminals are provided on most models for zero to 117% of input voltage (overvoltage connection) and zero to 100% of input voltage (line
voltage connection).
CONNECTION — SINGLE PHASE PA RA LL E L: Up to nine
units on the same shaft may be paralleled by using suitable
chokes and circuits to multiply the current and KVA rating.
Parallel operation of smaller ganged units is not recommended because it is usually more economical to handle rated
loads with the capacity of larger single units. (See specification charts in each transformer series section.)
CONNECTION — SINGLE PHASE SERIES: By jumpering
the common connections, two equal single units (or two equal
groups of paralleled units) driven by the same shaft may be
used at double voltage (line-to-line) in single phase series
with external connection only to the input and output terminals. The load must be grounded. If an input neutral is connected to the common, an output neutral may be used.
Transformer or loads need not be balanced to neutral.
CONNECTION — THREE PHASE OPEN DELTA : By
jumpering the common connections, two equal single units
(or two equal groups of paralleled units) driven by the same
shaft may be used at normal voltages (line-to-line) in three
phase open delta. One power line, identical on input and output, connects to the common. The other input lines connect
to the two input terminals, and the two output terminals feed
the other output lines. (This connection is the same as single
phase series with neutral, except that here voltages on all
input line pairs are equal and out of phase.)
X 100 (percent)
Product Design & Engineering Data
CONNECTION — THREE PHASE WYE: By jumpering the
common connections, three equal single units (or three equal
groups of paralleled units) driven by the same shaft may be
used at double voltages (line-to-line) in three phase wye. The
load must be ungrounded. Input lines connect to the three
input terminals, and the three output terminals feed the output
lines. If ganged units are used in a system that ordinar ily has a
common neutral or ground between source and load, then the
neutral or ground must also be connected to the common point
of the ganged variable transf ormer assembly. If the system has
no neutral, then the loads must be balanced. Because of the
115.5% voltage on the individual single units, there are 50
HERTZ restrictions. See specifications for each Series.
BENCH MOUNTING: Mounting of STACO Variable
Transformers on floor, bench, or wall where the knob and
brush rotors of single units (and most multiple units) are at
the same end of the coils.
UNCASED (OPEN CONSTRUCTION) MODELS: The basic
models of all series are uncased designs. The type number
contains no prefix or suffix letter. These models do not have a
protective housing for coil or terminal board. Adjustable shaft
design on most manually operated models permits back-ofpanel or bench mounting.
PORTABLE CORD & PLUG MODELS: Cased plug-in models have a ventilated steel case, line cord, receptacle, illuminated on/off switch and fuse. A three-conductor (3PN prefix)
line cord and matching receptacle are available on these
units. Plug-in models are connected for output voltage in a
clockwise rotation and are available in each Series through
the 2510/2520 units.
CASED MODELS: All 1010B to 6020 Series models are
available in cased designs (identified by the suffix “C,” “CT” or
“E” in the type number). “C” styles enclose only the coil, while
“CT” models provide protective housing for both coil and terminal board. Knockouts are provided in the terminal board
housing to accommodate conduit or cable connections. “E”
styles include our NEMA 1, drip-proof, fully front accessible
enclosures for our 5000/6000 Series.
BACK OF PANEL MOUNTING: Mounting of STACO
Var iable Transformers with shaft passing through a panel.
The knob and brush rotors of single units (and most multiple
units) are at opposite ends of the coils.
ISOLATED VARIAB LE TRANSFORMERS: An Isolated
Var iable Transfor mer consists of two (primary and secondar y)
magnet wire windings on a toroidal core.The primar y winding
is electrically isolated from the secondary winding. The input
winding has 82% of the turns of the output winding so the output voltage can be varied from 0-122% of the input voltage.
L SERIES: A selected grouping of variable transformers
packaged in a deluxe aluminum enclosure, three-conductor
line cord, plug, matching receptacle, pilot light, switch and
fuse. An ammeter and voltmeter are available on the 10 amp
model.
????Product Design & Engineering Data
General Design Specifications
The table below lists general design values for each standard
unit on a per coil basis. The DC resistance is as measured
from start to finish of coil winding, no load losses are actual
core losses, and the torque values are the driving torque
required to move the rotor and brush assembly. Using per
coil values listed, total DC resistance and core losses can be
calculated for parallel or series connected ganged units, and
total torque requirements can be determined.
Type DC Res. 60 Hz Losses Torque
171 23.6 1.5 6 max
201 23.8 1.5 6 max
221-B 14.5 1.8 6 max
252 115 2.0 6 max
291 8.0 2.2 6 max
501-B 4.4 3.0 10-30
511 4.4 3.0 10-30
1010B 1.2 5.4 15-35
1020B 11.4 5.2 15-35
1210B 0.6 6.4 15-35
1220B 4.4 6.4 15-35
1510 0.3 13.2 15-35
1520 1.4 18.0 15-35
2510 0.21 14.7 60 max
2520 1.7 14.5 60 max
5011 0.090 28.0 105-160
5021 0.353 28.0 105-160
6011 0.144 7.5 105-160
6020 0.478 7.5 105-160
Coil No Load Driving
(Ohms) (Watts) (oz-in)
Per Coil Value
EFFICIENCY
Efficiency curves are available from STACO or can be drawn
similar to the efficiency curve shown below for any units by
starting at zero, passing through the knee point, and reaching
98% efficiency at rated voltage.
Knee Point Data
Model Number % Efficiency Volts
171 62 23
201 67 24
221-B 73 23
252 65 50
291 67 24
501-B 77 18
1010B/1210B 80 30
1020B/1220B 80 17
1510 86 10
1520 83 20
2510 90 30
2520 87 40
5011 82 27
5021 75 40
6011 87 30
6020 82 38
Efficiency
OPERATION AT HIGHER FREQUENCY
All STACO standard Variable Transfor mers are designed to
operate within a frequency range of 50 to 60 Hertz unless
otherwise noted. While designed to operate at 50/60 Hz,
Staco Variables can be operated at frequencies up to 2000
Hz. The table below lists unit maximum output current rating
at 50/60, 400, 1500, and 2000 HZ.
Maximum Output Current (Amperes)
Type
171 1.75 2.2 1.75 2.2 1.75 2.2 1.75 2.2
201 2.0 2.5 2.0 2.5 2.0 2.5 2.0 2.5
221-B 2.5 3.2 2.5 3.2 2.5 3.2 2.5 3.2
252 0.8 1.0 0.8 1.0 0.8 1.0 0.8 1.0
291 3.0 3.5 3.0 3.5 3.0 3.5 3.0 3.5
501-B 5.0 7.0 5.0 7.0 5.0 7.0 5.0 7.0
511 5.0 7.0 5.0 7.0 5.0 7.0 5.0 7.0
1010B 10.0 13.0 10.0 13.0 9.0 11.7 9.0 11.7
1020B 3.5 5.0 3.5 5.0 3.5 5.0 3.5 5.0
1210B 12.0* 15.0* 12.0 15.0 3.2 4.5 3.2 4.5
1220B 5.0* 7.0* 5.0 7.0 4.5 6.3 4.5 6.3
1510 15.0 20.0 12.5 17.0 5.0 7.0 5.0 7.0
1520 7.5 10.0 7.5 10.0 3.5 4.3 3.5 4.3
2510 25.0 30.0 18.6 30.0 9.0 11.5 9.0 11.5
2520 10.0 13.0 9.3 13.0 3.3 5.0 3.3 5.0
5011 50.0 — 22.5 22.5 — — — —
5021 28.0 — 14.0 14.0 — — — —
6011 60.0 — 25.0 25.0 — — — —
6020 35.0 — 17.0 17.0 — — — —
50/60 Hz 400 Hz 1500 Hz 2000 Hz
Constant Constant Constant Constant
I ZIZIZIZ
* 60 Hz only
Product Design & Engineering Data
OUTPUT CURRENT LIMITS
Continuous brush output current of STACO Variable
Transformers, at normal ambient temperatures, must be limited to the rated amperes. The constant current rating may be
drawn at any brush position except in voltage doubler circuits.
For satisfactory life, the br ush output current of STACO
Var iable transformers operated in hot enclosures, or other
locations of high ambient temperature, must be limited as
shown in Fig. A. Close exposure to radiant heat should be
avoided or loading should be reduced accordingly.
For voltage doubler connections (at output voltages above
125 percent of the input voltage) the continuous brush output
current must be progressively limited (as shown in Fig. B)
down to 44 percent of rated amperes at maximum output voltage. Protection of this type of usage may be approximated
with a dual-element lag fuse in the lead to the the input terminal and with either a quick or slow blow fuse in the br ush output lead.
SHORT-TIME CURRENT OVERLOAD
Although STACO Variable Transfor mers are small and light
weight for the large power ratings which they handle, brush
currents up to 10 times normal may be drawn for a brief time.
The maximum on time curve of Fig. C shows the duration of
surge on transient currents which may be absorbed by a cold
unit on motor starting or similar service. Protection for this
level of service may be approximated by hydraulic-magnetic
circuit breakers with trip coil in the brush output lead. If the
unit is hot from previous loading, such as repetitive overloads,
it must also be allowed sufficient off time as indicated on the
minimum off time curve of Fig. C to prevent excessive temperatures. If the time on is less than allowed by the “on”
curve, the minimum time off may be reduced in accordance
with the following equation:
)
2
1
–
OFF TIME
ON TIME RATED CURRENT
Protection for this level of ser vice may be approximated by a
dual-element lag fuse in the brush output lead.
OVERLOAD CURRENT
=
(
Figure A. Max output current for high temperature
Figure B. Max Output Current — Dual Voltage
Figure C. Max On Time and Min Off Time for Various
Overload Current Conditions
MOT OR-DRIVEN V ARIABLE TRANSFORMERS
Motor-driven models permit remote control of large amounts
of power. A STACO motor-driven Variable Transformer can be
installed in any out-of-the-way space and the control station
placed where desired. Extreme flexibility in system design is
possible because the control location does not have to
accommodate the variable transfor mer assembly. Motor-driven units have the same electr ical ratings as their corresponding manually-operated types.
The motor drive is a compact integral unit mounted on top of
the assembly. On cased models, the motor-drive assembly is
enclosed and is provided with knock-outs for cable or conduit
connections. The permanent magnet synchronous motor
operates on 120 volt, 50/60 Hertz single phase lines.
Because synchronous motors are frequency sensitive, they
operate slightly slower at 50 Hertz.
????Product Design & Engineering Data
the STACO Variable Transfor mer shaft. Limit switch control at
the lower and upper limits of travel prevents overtravel. The
limit switches may be adjusted if desired. Additional limit
switches may be added for operation and control of auxiliary
circuits as required, STACO Auxiliary Switch Kit P/N 9640057 (available separately).
To specify, prefix the desired time of travel in seconds, and
the letter “M” for motor-drive to the Type number. For example: 5 seconds speed travel = 5M1010B.
Normally, one switch is used to operate each Motor-Driven
STACO V ariable Transf ormer. Any momentary contact switch,
whether lever action or push button, may be used. If desired,
additional switches can be provided to permit control from
any of several locations. Master control of two or more motordriven units is also possible using relays or multiple-pole
switches.
TYPE FRC-20 AND MP CONTROLLERS
Standard motor-driven models are available in speeds of 5,
15, 30 and 60 seconds at 60 Hertz for full range travel from
zero to maximum output voltage. A smooth, quiet planetary
gear unit is used for proper speed reduction from the motor to
For our Motor Operated Variable Transformers, we offer the
FRC-20 and MP Controllers, which both position and regulate the variable transfor mer. For complete information refer
to section on controller types, pages 38 and 39.
Regulation
These tables provide the voltage drop at selected
points at the corresponding model’s regulation curve.
This is the variation in the output voltage from no-load
to full-load current. A sample regulation curve for the
6000 Series is illustrated below.
120 Volts - Voltage Drop At Full Rated Output Current
Type
171 0.2 4.2 7.1 8.5 7.0 4.0 0.2
201 0.2 4.9 7.8 9.0 7.5 4.2 0.3
221-B 0.3 3.0 5.1 6.0 5.0 2.9 0.3
291 0.4 2.5 4.1 5.2 4.2 2.3 0.4
501-B 0.3 3.9 5.2 5.8 5.2 4.0 0.3
511 0.3 3.9 5.2 5.8 5.2 4.0 0.3
1010B 0.2 2.8 4.2 4.5 4.2 3.0 0.8
1210B 0.2 1.3 1.8 2.0 1.8 1.4 0.4
1510 0.1 0.8 1.4 1.7 1.5 0.9 0.2
2510 0.5 1.8 2.2 2.5 2.2 1.9 0.1
5011 3.0 4.2 4.8 5.4 5.2 4.1 3.0
6011 1.9 2.5 3.3 5.7 4.8 3.7 2.0
240 Volts - Voltage Drop At Full Rated Output Current
Type
252 1.0 13.0 17.5 20.6 17.0 12.5 1.4
1020B 0.2 5.4 6.7 7.0 6.5 5.0 0.4
1220B 0.2 4.5 5.8 6.1 5.6 4.3 0.4
1520 0.2 2.2 3.6 4.0 3.3 2.1 0.3
2520 0.5 4.2 5.2 5.5 5.2 4.2 0.4
5021 2.5 4.2 5.8 7.0 6.6 4.6 2.6
6020 1.4 3.9 5.9 7.0 6.2 4.5 1.6
020406080100120
0 40 80 120 160 200 240
Brush Setting (No Load Volts)
Brush Setting (No Load Volts)
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