B&K Precision 1745A User Manual

MANUAL

Model 1744A & 1745A

0-35 V, 0-10 A

DC POWER SUPPLY

With Dual

Displays

TEST INSTRUMENT SAFETY

WARNING

Normal use of test equipment exposes you to a certain amount of danger from electrical shock because testing must sometimes be
performed where exposed high voltage is present. An electrical shock causing 10 milliamps of current to pass through the heart will stop

most human heartbeats. Voltage as low as 35 volts dc or ac rms should be considered dangerous and hazardous since it can produce a
lethal current under certain conditions. Higher voltages are even more dangerous. Your normal work habits should include all accepted

practices to prevent contact with exposed high voltage, and to steer current away from your heart in case of accidental contact with a
high voltage. Observe the following safety precautions:

1. There is little danger of electrical shock from the dc output of this power supply. However, there are several other possible test
conditions using this power supply that can create a high voltage shock hazard:

a. If the equipment under test is the “hot chassis” type, a serious shock hazard exists unless the equipment is unplugged (just turning

off the equipment does not remove the hazard), or an isolation transformer is used.

b. If the equipment under test is “powered up” (and that equipment uses high voltage in any of its circuits), the power supply outputs

may be floated to the potential at the point of connection. Remember that high voltage may appear at unexpected points in
defective equipment. Do not float the power supply output to more than 100 volts peak with respect to chassis or earth ground.

c. If the equipment under test is “off” (and that equipment uses high voltage in any of its circuits under normal operation), discharge

high-voltage capacitors before making connections or tests. Some circuits retain high voltage long after the equipment is turned
off.

2. Use only a polarized 3-wire ac outlet. This assures that the power supply chassis, case, and ground terminal are connected to a good
earth ground and reduces danger from electrical shock.

3. Don’t expose high voltage needlessly. Remove housings and covers only when necessary. Turn off equipment while making test
connections in high-voltage circuits. Discharge high-voltage capacitors after removing power.

(continued on inside back cover)

2

TABLE OF CONTENTS

Page

TEST INSTRUMENT SAFETY --------------inside front cover

INTRODUCTION ------------------------------------------------- 4

FEATURES --------------------------------------------------------5

SPECIFICATIONS ------------------------------------------------6

CONTROLS AND INDICATORS-------------------------------8

OPERATING INSTRUCTIONS --------------------------------10

Safety Precautions ---------------------------------------------10
Equipment Precautions ----------------------------------------10
Hook-Up -------------------------------------------------------- 10
Typical Constant Voltage Operation-------------------------13

Setting Current Limit ------------------------------------------14
Typical Constant Current Operation-------------------------15

Constant Voltage/Constant Current Characteristic---------16
Connecting Two Power Supplies in Series------------------16
Connecting Two Power Supplies in Parallel ----------------19

Page

APPLICATIONS------------------------------------------------ 20

General -------------------------------------------------------- 20
Electronics Servicing ---------------------------------------- 20

Electronics Manufacturing ----------------------------------20
Electronics Design Lab --------------------------------------20

Electronics Education---------------------------------------- 21
Battery Charging --------------------------------------------- 21

MAINTENANCE ----------------------------------------------- 22

Fuse Replacement -------------------------------------------- 22
Line Voltage Conversion------------------------------------ 22

Adjustments---------------------------------------------------22
1743B Calibration-------------------------------------------- 23
Instrument Repair Service----------------------------------- 23

WARRANTY SERVICE INSTRUCTIONS ----------------- 25

LIMITED TWO-YEAR WARRANTY -----------------------26

SPANISH MANUAL ------------------------------------------- 28

3

INTRODUCTION

B+K Precision

The

Supplies are high quality, general purpose dc power sources.
They provide 0-35 volts dc output, adjustable with both coarse

and fine voltage controls for precise settability. The current
output is 0-10 amps, adjustable with both coarse and fine current

controls (model 1745A). Two large LED meters continuously
monitor the output voltage and current (model 1745A). The
VOLTAGE meter is green, while the CURRENT meter is red

(model 1745A).

These models exhibit excellent regulation and low ripple
characteristics. The circuit design incorporates a pre-regulator,
which greatly reduces internal power dissipation at low output
voltages. The styling is both attractive and functional.

These instruments may be used in constant voltage or constant
current applications. The crossover from constant voltage to

constant current modes is smooth and automatic. LED’s indicate
the “CV” (constant voltage) or “CC” (constant current) mode of

operation. In constant voltage applications, a current limit may
be preset. When load variations cause the current to reach the
preset limit, the unit then regulates output current rather than

output voltage.

Models 1744A &1745A DC Power

Current limits are adjustable from 5% to 100% of maximum.
In constant current applications, the maximum voltage may

be preset. When load variations cause current to drop below
the regulated value, the unit reverts to regulated voltage
operation at the preset value.

Reverse polarity protection prevents accidental damage to

the power supply from improper connection to an external
voltage, and current limiting protects the equipment being

powered, as well as the power supply.

The output is isolated from chassis and earth ground,

which permits full flexibility of connections. When needed,
the (+) or (-) polarity may be strapped to ground, or either

polarity may be floated to an external voltage. Two supplies
may be connected in series as a 0-to-70 volt power source, or

two supplies may be connected in parallel, with suitable
balancing resistors, for up to twice the output current.

These power supplies are well suited for a wide variety of
electrical and electronics applications, including service
shops, engineering labs, production testing, school

laboratories, and home use by hobbyists.

4

FEATURES

0-35VOLTS

Continuously variable over 0-to-35 volts with coarse & fine controls.

0-10 AMPS

0-to-10 amps current rated for continuous duty at full output current.
Coarse and fine current adjust controls.

LABORATORY QUALITY

Excellent regulation, low ripple.

CONSTANT VOLTAGE ORCONSTANT CURRENT

Provides regulated dc voltage output or regulated dc current output.
Crossover is smooth and automatic.

LEDDISPLAYS (model 1745A)

Two large, easy-to-read LED digit displays monitors output voltage
and output current, and provides good visibility in bright or low

light.

TwoCurrent Ranges (model 1744A)

High-Low switch selects full output (0-10A), or on quarter
output (0-2.2A). Low range improves current settability and

meter resolution.

LEDINDICATORS

Act as pilot light and identify mode of operation and metering.

PRE-REGULATOR

Limits internal dissipation for higher reliability.

ISOLATEDOUTPUT

Either polarity may be floated or grounded.

OVERLOADPROTECTION

Fully adjustable current limiting (from 5% to 100% of
maximum output current) protects circuit under test and the

power supply.

REVERSE POLARITYPROTECTION

Prevents damage to power supply from external voltage of
reverse polarity.

STYLING

Modern functional styling. Logical, convenient layout of
controls.

5

SPECIFICATIONS

OUTPUT VOLTAGE: 0 to 35 VDC, coarse and fine
adjustment.

OUTPUT CURRENT: 0 to 10 A, coarse and fine
adjustment.

CONSTANT VOLTAGE OPERATION

Voltage Regulation
Line (108-132 V): ≤0.2% +2 mV

Load (no load to full load): ≤0.04% + ≤0.04% + 2 mV

Recovery Time: ≤100 μs typical.

Ripple Voltage
RMS: ≤1 mV.

Temperature Coefficient

(0° to +40 °C): ≤300 PPM/°C

CONSTANT CURRENT OPERATION

Adjustable Current Limits: 5% to 100%
Current Regulation

Line (108-132 V): ≤0.4% + 5 mA
Load ≤0.4% + 5 mA

METERING

Model 1745A
Voltmeter 4 digit Green LED Display

Range: 0 to 99.99 V.
Accuracy: (0.5% + 9 digits)

Ammeter 4 digit Red LED Display
Hi Range: 0 to 9.999 A.
Accuracy: (0.5% + 9 digits).

Model 1744A
Voltmeter Range: 0 to 40 V

Accuracy: +2.5%

Ammeter Hi Range: 0 to 11 A
Lo Range: 0 to 2.2 A.
Accuracy: +2.5%

POWER REQUIREMENTS:

Domestic: 120 VAC ±10%, 60 Hz
International: 120/220/230/240 VAC - 10%, 50/60 Hz

POWER CONSUMPTION: Approximately 420 W or less at

full load.

PROTECTION: Reverse polarity protection,

Current limiting.

6

SPECIFICATIONS

TEMPERATURE RANGE

Operation: 0° to +40° C, ≤75% R.H.
Storage: -15° to +70° C,≤85% R.H.

DIMENSIONS (HxWxD): 5.7” x 10.5” x 15” (145 x 267 x 38 mm)

NOTE: Specifications and information are subject to change without notice. Please visit www.bkprecision.com for the most current

product information.

Note 1:
Important: Even with noticeable Thermal Drift, this high resolution power supply will be considerably more accurate than any standard
three digit display bench power supply.

Thermal Drift: Since this power supply has greater resolution than standard bench power supplies they are more susceptible to Thermal
Drift. Thermal Drift occurs on almost every type of power supply but is more apparent on high resolution types. Thermal Drift results in the
metering of the power supply to either slowly increase or decrease with the change in the power supply’s internal temperature. As the power

supply outputs more power its internal temperature will increase causing the metering (primarily the current) to slowly increase. As the
power demand is deceased the power supply will cool causing the metering (primarily the current) to slowly decrease. If the power supply
remains with a constant output of power for more than fifteen minutes the power supply metering will remain constant and should not

continue to drift.

WEIGHT: 27lb. (12.25 kg)

ACCESSORIES SUPPLIED: Instruction Manual,

Spare Fuse

7

CONTROLS AND INDICATORS

INDICATORS

Either the “CC” or “CV” and the LED indicators will be lit

whenever the unit is operating, thus serving as a pilot light. The unit
automatically changes from CV to CC operation when the preset
current limit is reached.

1. C.C. (Constant Current) Indicator. Red LED lights in constant
current mode. Unit regulates output current at value set by CUR-

RENT controls.

2. C.V. (Constant Voltage) Indicator. Green LED lights in constant
voltage mode. Unit regulates output voltage at value set by

VOLTAGE controls.

3. GREEN LED Display (1745A). 4 digit display continuously
monitors voltage.

4. RED LED Display (1745A). 4 digit display continuously
monitors current.

VOLTAGE CONTROLS

5. Coarse Control. Coarse adjustment of output voltage. Read value
on GREEN LED display.

6. Fine Control. Fine adjustment of output voltage. Read value on
GREEN LED display.

CURRENT CONTROL

7. Coarse CURRENT Control. Adjusts current limit in
constant voltage mode. Adjusts constant current value

in constant current mode. Current can be read from
RED LED display.

8. Fine Control (1745A). Fine adjustment of current limit
or current value. Current can be read from RED LED
display.

OUTPUT TERMINALS

9. “+” Terminal (Red). Positive polarity output terminal.

10. GND Terminal. Earth and chassis ground.

11. “-” Terminal (Black). Negative polarity output

terminal.

REAR PANEL CONTROLS

12. Fuse

13. Power Cord

8

CONTROLS AND INDICATORS

7. Fuse.

8. Power Cord.

9. 110/220 Line Voltage Conversion Switch.

Figure 1. Front Panel Controls and Indicators.

Figure 2. Rear Panel

9