DC Electronic Load Applications and Examples Application Note V 3032009 22820 Savi Ranch Parkway Yorba Linda CA, 92887-4610 www.bkprecision.
Table of Contents INTRODUCTION.........................................................................................................................3 Overview of software examples........................................................................................................3 POWER SUPPLY TESTING.......................................................................................................4 Load Transient Response..........................................................................
INTRODUCTION As technology is constantly advancing, demands for quality test instruments increase due to the need for making better and accurate measurements to accommodate newer technologies. For most electronic applications today, using energy efficient and reliable power sources is critical.
POWER SUPPLY TESTING For design testing and verification, the need for regulated power supplies are increasing with ongoing advancement in technology. More so, it has become a necessity in newer electronic devices to be tested with precise and sophisticated power supplies. There are some specifications that determine some underlying performance factors in typical power supplies. Particularly, the load transient response, load regulation, and current limit.
Objective Characterize the time it takes for a power supply to stabilize its output voltage after a step change in the load. transient response is observed during the rise time in the load with a step change from 1.5 A to 3 A. The output voltage dropped by approximately 1.6 mV. Approach Connect a DC load (B&K Precision 8500 DC load) to a power supply. Use the DC load's transient mode to apply a step change in load to the power supply.
Procedure 1. Turn on the power supply and set it to its rated output voltage. Ensure that the current adjust knob, if present, is set to its maximum value. 2. Write down the measured voltage of the power supply. Call this value V0. 3. Press I-set on the DC load to set to power supply's rated value. Turn on the input of the load by pressing On/Off. 4. Write down the measured voltage of the power supply. Call this value V. 5. Turn off the DC load's input by pressing the On-Off button. 6.
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.
useful built-in function for quick setup and testing. Battery discharge can also be tested with the provided program under the “Software Examples” section of this note. Additionally, small changes to the program will offer even greater control for the test, allowing measurements to be made under different modes and settings. The following describes the discharge test setup for a consumer “AA” size battery. Similar setups can also be used for other types of batteries.
the battery's chemical energy is used up. The internal resistance drops as the temperature increases. If VL is the voltage across the load, we have V L =Vo iR i python battery.py 5 cc 0.5 0.5 aa_test 78deg F Figure 7. Command Used to Run Program measured as: Ri = (2) V o−V 0.5 (4) Thus, R i= ∣V L−Vo∣ i (3) This gives us a way to evaluate the internal resistance using the DC load, either manually or by a program. For smaller batteries, a programming approach is an advantage.
the voltage (V) is 1.415 V. Using equation (4) gives an internal resistance of 0.16 Ω. Batteries are complex nonlinear electrochemical devices. The two common electrical measurements of batteries used to gauge their state are the DC internal resistance and the AC internal impedance. In the "old" days, AC characteristics of a battery were not terribly important for DC operation. However, modern digital electronic devices can draw sharp current spikes from their power source (e.g.
Figure 11. Connect the BNC to binding post adapter into a B&K Precision's 2542 oscilloscope. Follow the setup below for the DC load and oscilloscope. DC Load Setup 1. Setup transient mode with current levels from 0 A for 0.5 ms to 120 A for 1000 ms in pulse mode. 2. Set load to CC mode 3. Turn on input for a short moment. Turn off once oscilloscope setup is complete. Oscilloscope Setup 1. Set to single run. Figure 10.
change in time; that is the difference of the cursors. For B&K Precision's 8510 DC load, slew rate is measured to be 1 A/μs. OTHER DC LOAD APPLICATIONS rates of B&K Precision's 8500 DC load. This load can measure with a millivolt resolution before indicating an overrange. Refer to the section for detailed information on setting up and running the software application. Fuse DC loads can be very resourceful for various tests and applications.
Battery Discharge Test The objective of this program is to characterize the discharge curves of common household batteries. It can be used to monitor and log data when a battery is discharged by one of B&K Precision's 8500 series DC loads. Instructions There are two settings that can be modified in the code to cater particular test settings.
Usage() port = int(sys.argv[1]) mode = sys.argv[2] value = float(sys.argv[3]) cov = float(sys.argv[4]) filename = sys.argv[5] + ".dat" docstring = "" if len(sys.argv) > 6: docstring = join(sys.argv[6:]) # Check values assert(port >= 0) assert(mode in ("cc", "cv", "cp", "cr")) assert(value > 0) assert(cov > 0) from os.
Voltmeter Reading In this section, the codes provided below are used for the “voltmeter” application using the DC load. It provides a convenient and remote way to collect voltage readings into a data file to serve its purpose. Instructions Two settings must be configured correctly to run the script. They are port and baudrate. In the code of voltmeter.py, they are declared at the beginning as “port = 5” and “baudrate = 38400” by default.
default. Please change the values to match the port and baudrate settings used to interface on the PC. Here's an example to run the command: python fuse.py 5 The value “5” represents the fuse value to set. In this example, it is 5 A. With slight modifications to the script, the program can also monitor voltage and power. fuse.py import sys, dcload from time import time from win32com.client import Dispatch from msvcrt import kbhit port = 5 baudrate = 38400 def ReadCurrent(load): fields = load.
© 2009 B&K Precision Corp.
