# privatier

• privatier commented on deba168's instructable Arduino Energy Meter - V2.02 months ago

As a fellow electrical engineer, and after a cursory review of the Arduino code, I think you created an instrument which measures peak to peak value of the current flowing through. You make then assumptions on the value of the mains voltage, on the waveform of the current (sinusoidal) and on the power factor to calculate and display the energy consumed in the device under test. In a real world situation, the mains voltage is not constant, due to the varying voltage drop on the wires from the generator to the user; also it is not sinusoidal, due to all the rectifiers in most electronic gadgets, which charge filter capacitors at the peak of the line voltage. The waveform of the current is not sinusoidal either for many appliances. The diagram in step 3 shows an example of non-sinusoidal w...

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As a fellow electrical engineer, and after a cursory review of the Arduino code, I think you created an instrument which measures peak to peak value of the current flowing through. You make then assumptions on the value of the mains voltage, on the waveform of the current (sinusoidal) and on the power factor to calculate and display the energy consumed in the device under test. In a real world situation, the mains voltage is not constant, due to the varying voltage drop on the wires from the generator to the user; also it is not sinusoidal, due to all the rectifiers in most electronic gadgets, which charge filter capacitors at the peak of the line voltage. The waveform of the current is not sinusoidal either for many appliances. The diagram in step 3 shows an example of non-sinusoidal waveforms for voltage and current. The power factor, unless measured by other means, is only known for purely resistive, capacitive or inductive loads, certainly not for motors or electronic appliances.A technically correct solution requires calculating the root-mean-square of the instantaneous values of voltage and current through integration (remember calculus?). The procedure can be approximated by sampling voltage and current at a rate which is relatively high with respect to the line frequency, and then calculating the RMS value from the samples over an integer number of periods of the line voltage. With a change in hardware, you have to sample two quantities : the mains voltage (through a voltage divider) and the current (through the ACS712 module).

• privatier commented on Ana Quadros's instructable Homemade Delicious Almond Milk5 months ago

I make my almond milk with creamy almond butter - no straining necessary.

• privatier commented on MarcusW44's instructable Build a 3D Printed Curta Calculator11 months ago

amazing! I own the real thing, bought at a deep discount when the electronic scientific calculators from HP and TI came out. In some technically oriented schools students learned to operate the levers of these marvelous devices rapidly with their thumbs - like people using smartphones today.

• privatier commented on KJMagnetics's instructable World's Simplest Electric Train1 year ago

Ingenious - how long does the battery last? (The external circuit has very low resistance; thus a high current is flowing, discharging the battery rapidly.)Keep the magnets away from small children, who might swallow them!

• Go to a place where they recycle electronic equipment and look for two UPS. They contain transformers you can connect back to back, with lot of power if you find big ones.

• While you get three times the voltage, which is not surprising if you understand how solar panels work, it's the power in watts, voltage times amperes, which is of interest, just look at your electricity bill. On commercial solar installations, there is an inverter which optimizes the watts by adjusting the loading on the array. In your case you have to find the optimum power manually by adjusting a load resistor. The angle with which the sun shines on a solar array changes in the course of a day. For example I get 2.4kW at 12PM, 1kW at 5PM for my rooftop array. Your proposed arrangement of the panels is at a significant disadvantage in this respect, unless you install an automatic mechanical gizmo to track the sun.

• privatier commented on Into the Dirtshop's instructable DIY Truck Bed Camper!2 years ago

I built something similar for my Mazda5 minivan. I built a platform by fitting a plywood sheet to the interior shape of the car, cut in half, with hinges across the middle. The second row seat is removed, and the front part of the platform rests on 6 milk creates with camping stuff. The crates are sturdy and easy to carry from the car to the camp site.

• privatier commented on jenfoxbot's instructable How to Use (and Choose) a Multimeter!2 years ago

When measuring current, the current flows through a resistor inside of the multimeter, and the instrument actually measures the voltage across, which is proportional to the current. The internal resistance should be small, in order to have a small influence on the behaviour of the circuit which you want to measure. Consider that some auto-ranging meters have a relatively high resistance, with voltages across the instrument terminals approaching 1V at full scale.When measuring small resistance, on the order of 1Ohm, consider the resistance of the probes. Short the tips to read the resistance of the leads, and subtract this value from the one displayed when connected to the resistor under test.