The source file of the CNC meter is open source LiChuang EDA. The HEX file of the meter program and the power board PCB are in the attachments. You can download them directly.
The measurement range of the meter; voltage 0-100V current: 0.1A-30A, two DAC outputs, 0-5V with strong load capacity set by the software, and the circuit uses MOS to expand the current. CN2 is the power supply for the meter, within 10-30V, VOGE of port CN3 is the voltage control output 0-5V CUNT is the current control 0-5V VIN is the voltage detection input, the range is 0-100V.
How to use the CNC meter: Press the middle button on the meter to switch the voltage and current adjustment mode, the up key + down key - adjustment step 0.1V/0.1A supports continuous pressing, and continuous pressing is also 0.1V/0.1A step fast addition and subtraction. Press the middle button again to exit the voltage and current adjustment mode. At the same time, remember the current setting value. Press the up key and down key at the same time to enter the voltage and current calibration mode.
In the calibration mode, the voltage and current are two points, one low range and one full range. In the calibration mode, press the middle key to save the current AD value, press the key to calibrate the next point, exit the calibration mode, and press the middle key twice to exit. If you do not need to measure the current of 30A, you can change the sampling resistor to a larger one, enter the calibration mode and calibrate it.
The power board is designed to have a power of 750W, with an adjustable voltage of 0-150V and a current of 0-5A, and a 494+MOS tube solution. The board developed this time has been verified, and it is now open source. Friends in need can directly download the attached board.
Set two cooling fans, turn on fan 1 at 45°, turn on fan 2 at 55° to enhance heat dissipation, overheat protection at 75°, LED and buzzer alarm, and stop output at the same time. The temperature is lower than 75° to recover.
The voltage and current are adjustable. The power board presets 0-5V to control the voltage and current. Set the maximum output limit potentiometer and adjust it as needed. The output filter capacitor withstands a voltage of 250V. It is recommended to set the maximum voltage to within 200V.
The main control chip of the power board is TL494, and the totem drives the MOS tube. The measured power is 550W. The conditions are limited and there are no test tools. Theoretically, it can reach about 800W.
CNC meter The CNC
part of the power board samples the STM32F0 series microcontroller, uses the on-chip 12-bit ADC to collect voltage and current, and two DACs are used to set the voltage and current respectively. The display is a 12864 monochrome screen, which displays voltage, current, power, and sets the voltage and current values. The voltage measurement range is 0-150V and the current is 1A-35A. The overall accuracy is OK.
The whole machine picture CNC meter + power board
picture is the CNC meter PCB.
The current uses OP07 differential amplification, and the accuracy is a little worse in the milliampere range. The precision of using resistor amplification to measure below 1A is OK. The sampling resistor currently used is 2.25mΩ 2*5mΩ constantan wire in parallel. When passing 30A current, the value can be stable and not adjusted.
Milliamperes were not considered when designing. The main current is used for charging electric vehicle batteries. When programming, the minimum current is directly set to 1A and the maximum is set to 30A. The 100V shown in the picture header is for testing the power. Adjust the voltage limiting potentiometer to 100V.
The maximum current (short-circuit current) of the open-source power board is limited to 6.1A. The charging indication is program-controlled, and the preset 0.5A light turns on.
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The meter head also uses the open source meter head this time. 1000W real thing!
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The temperature of the transformer should be lower, about 40 degrees. The transformer is of EI55*2. The output end uses 50 wires in parallel. The overall performance is OK. To test long-term full load, you still need to use iron phosphate batteries. Lead-acid batteries are not good. They will reduce power after charging with high current for a period of time. Iron phosphate and lithium batteries can test the temperature rise of various components under long-term full load operation. I have made several versions of the charger, and I am basically satisfied with this version. I will revise the version again when I have time, and integrate the CNC part into the power board.
The 4 MOS tubes of the finished product have been replaced with IGBTs. The driving circuit part of the 1000W version is different from that of the 750W version. The heat sink temperature is estimated to be around 55°C-60°C. The specific temperature is not clear, but it will not be hot to the touch for a long time. Fan 2 is set to start at 55°C, and it stops after starting for a while. Fan 1 has been running at full speed. I made the holes by hand. I originally used a drill to drill a row of round holes for the air inlet, but my hand shook and the drill went off-center. I simply made slots, but the result was even worse. I couldn't bear to look at it, so I used a machine to make holes later. Or use PCB as a baffle.
The 1000W meter software has been changed to coulomb meter mode, which can display the total charging AH from the start to the end of charging, as well as the charging time from the start to the end of charging, and the power is reset.
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The shell is still made of aluminum alloy. It has not been installed yet. It is troublesome to drill holes manually.
The shell size is 120*200*69. The shell length is too short. It is easier to assemble it with a length of 230. The CNC version with a length of 200 can be installed on the front of the shell.
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