DC Electronic load

More info about this project can be found on my channel:

https://youtu.be/NScaRQj53l0

Used tools:

                           

Project status: ✔️ ready for construction!

The project is poised for construction and operational use. However, ongoing development persists, addressing minor bug fixes and introducing new features. Stay tuned for updates!

Project overview

Commercially available electronic loads often come with a hefty price tag, so I decided to build my own. This project was inspired by many electronic loads, with the primary inspiration being Scullcom's Electronic DC Load. You can view it here.

   

Project goals:

• 300 W power dissipation

• up to 8A and 50V (obeying the 300W limit)

• Remote voltage sensing option

• Easy to input values: you can use an encoder as well as a keypad

• 5 modes of operation

  • Constant current mode

  • Constant power mode

  • Constant resistance mode

  • Transient response mode

  • Battery testing mode

• Nice to look at: doesn't look like a poor DIY build

Electronics:

Block diagram

PCBs:

• Main board: responsible for main funcionalities of the load

• Front board: responsible for user input with the rotary encoder and switching the voltage measurement circuitry between the main and sense terminals

Mechanical construction:

The case for this project is made with 1mm thick bent sheet metal, with a 3D printed front panel.

PC remote controll battery mode app

The app is currently available for Windows only. To run it, simply double-click on

\desktop_app\release\windows-64bit\electronic_load_control_app.exe

Accuracy measurements

Click to learn more

The precision of the electronic load's current and voltage measurements, as well as its set current accuracy, were tested against the Sanwa PC7000 multimeter. The following tables present the results of these measurements.

Accuracy of set and measured current values

Set Value [A]	Load Measurement [A]	Multimeter Measurement [A]
0.1	0.104	0.1032 ± 0.0029
0.2	0.203	0.2024 ± 0.0037
0.3	0.300	0.3000 ± 0.0044
0.4	0.406	0.4051 ± 0.0053
0.5	0.500	0.4997 ± 0.0060
0.6	0.602	0.6020 ± 0.0069
0.7	0.702	0.7020 ± 0.0077
0.8	0.800	0.8000 ± 0.0084
0.9	0.904	0.9038 ± 0.0093
1.0	1.007	1.0065 ± 0.0101
2.0	2.007	2.0070 ± 0.0181
3.0	3.006	3.0057 ± 0.0261
4.0	4.003	4.0022 ± 0.0341
5.0	5.002	5.0007 ± 0.0421
6.0	6.001	5.996 ± 0.068
7.0	6.998	6.997 ± 0.076
8.0	7.998	7.990 ± 0.084

Accuracy of voltage measurements

Load Measurement [V]	Multimeter Measurement [V]
1.002	1.0022 ± 0.0006
2.002	2.0029 ± 0.0009
3.004	3.0043 ± 0.0012
4.004	4.0039 ± 0.0015
5.006	5.0058 ± 0.0018
8.004	8.004 ± 0.006
10.01	10.007 ± 0.007
12.01	12.008 ± 0.007
14.01	14.010 ± 0.008
16.01	16.004 ± 0.009
18.01	18.007 ± 0.010
20.01	20.008 ± 0.011
25.01	25.011 ± 0.013
30.02	30.016 ± 0.015
35.02	35.019 ± 0.017
40.02	40.019 ± 0.019
45.02	45.023 ± 0.021
50.01	50.012 ± 0.023

Conclusion: ✅

The current values measured by the electronic load did not deviate from the set value by more than 7 mA. All measurements taken by the electronic load are within the range of values measured by the multimeter, considering the multimeter's measurement error.

Uploading the code using USBASP

Click to learn more

Add the following code to the platformio.ini file

upload_protocol = custom
upload_port = usb
upload_flags = 
    -C
    ${platformio.packages_dir}/tool-avrdude/avrdude.conf
    -p
    $BOARD_MCU
    -P
    $UPLOAD_PORT
    -c
    usbasp
upload_command = avrdude $UPLOAD_FLAGS -U flash:w:$SOURCE:i

Uploading the code this way will reduce the boot up time.

Note: Since this method removes the bootloader, in order to program the uC via UART next time, you have to burn the bootloader.

What could be improved in the next version:

• Add reverse polarity protection
• Higher resolution DAC

Special thanks

Special thanks to Eryk Możdzeń, who helped solving a software problem with a memory leak.