You want to know a secret? I don’t like AC. When in doubt, he’s not doing my heart any good, and besides, he’s acting weird anyway. Nevertheless, the power supply modules must also be installed and wired, so off they go. As specification of the switching power supplies I decided to use the following parameters:
- Input voltage: 230V AC
- Output voltage 12V DC
- Output current: 12.5 amps
- Total power: 150 Watt
- Efficiency: 87.5% at 25°C
In order to guarantee an output power of 300W for the measurement equipment, we have to run two of these power supplies in parallel, because the maximum TDP value, which Igor assumed for me, is 240W. Minus the thermal resistances and possible later scalability, I prefer to install 60W reserve.
Then after the power supplies were wired in parallel and settled into the case, it looked like this:
The cold appliance connection, the fuse and the power button are also already installed. The fuse used is a fine-wire fuse of 5 amperes with the tripping characteristic fast. In this step it is important to calibrate the power supplies. Since not every household has 100% accurate 230V AC at 50 Hertz, it is possible to calibrate the output voltage with small adjustment potentiometers directly on the power supply module. In this case I decided to use 12.05V.
Next, I need to tap the primary circuit amperage so I can accurately set the TDP after the fact. It is important to note that the power supplies only have an efficiency of 87.5%. This means that if the primary circuit converts power X, then only 87.5% of X comes out on the secondary side. This circumstance must be compensated with a measuring resistor, since the display of the current intensity is located on the primary side. In practice, I use a Rogowski coil here. L, i.e. the 230 V phase, is fed through this wire coil. The alternating current determines the magnetic field strength, which in turn induces an electrical voltage in the coil, which we then use to measure the current.
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