Specifications

Setup
Connect the power supply in
parallel to the DC load. Set
the power supply to its rated
voltage and set a preset value
for current. The DC load
should display the rated
voltage if power supply's
output is on. Incrementally
increase the current drawn
from the load and observe the
behavior of the voltage in the
power supply. When the
current on the load gets close
to the power supply preset
current limit, observe before,
during, and after the crossover
point, where the power supply
switches from CV to CC mode.
DC Load Setup
Set the DC load to CC mode
by pressing I-set (for B&K
Precision 8500). You have
have to press twice. Turn on
DC load's input.
Results
A B&K Precision 9120A DC
power supply rated at 32 V
and 3 A was tested with a DC
load. The voltage from before
to after the current crossover
point was observed. Table 1
shows the data of some
measurements to demonstrate
the power supply behavior
before and after the crossover
point.
Power supply
measurements
(readings from power supply)
Voltage Current Mode
32.0001 V 0.00024 A CV
31.9999 V 2.65178 A CV
31.9999 V 2.99467 A CV
0.1569 V 2.99999 A CC
Table 1: Measured Data from B&K
Precision 9120A.
It follows that the
measurements demonstrate a
voltage vs. current curve
similar to Figure 4. Drawing
from the data, the voltage
drops immediately upon
reaching the crossover point,
which is at 2.99467 A in this
case. The power supply
changes to CC mode after this
point, and voltage remains at
0.1569 V, with current limited
to 2.99999 A. This behavior is
normal and expected for a CV/
CC power supply. There are
other types of power supplies
with different current limit
designs such as foldback
current and CV power supplies
(without CC mode). The
voltage versus current curve
will greatly differ from that of
CV/CC power supplies, so it is
advised to test their current
limit characteristics before
utilizing them in devices or
applications.
BATTERY TESTING
The forms and standards for
storing, renewing, and using
energy are evolving. New
methods for providing power
for electronic products have
been discovered and are far
more complex than they were
several decades ago. With
increasing need in our society
for clean and efficient energy,
engineers have now turned
their focus to develop
applications that utilize, for
example, fuel cells,
supercapacitors, and
photovoltaic energy. Due to
the complexity in the design of
these sources, it is useful to
have a programmable test
instrument that can verify
precise details of the sources'
behavior. This is often where
a DC load comes in handy
because of its programmable
flexibility as well as its
capability to run discharge
tests on power sources like
batteries. This section will
provide a basic overview that
demonstrate an efficient way
to perform battery discharge
and internal resistance testing.
Battery Discharge
Curves
When designing and testing a
battery for powering a device,
a great deal of attention
reflects on energy efficiency
and lifetime. For this reason,
a standard performance test
consists of analyzing discharge
curves that characterize the
behavior of the battery. By
observing these curves, the
battery life can be measured,
and its efficiency can be
computed. Some DC loads
provide this feature to allow
battery discharge
measurement, in which the
total charge is provided in Ah
(ampere*hour) to a specified
voltage. B&K Precision's 8500
DC load series all provide this
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