The Truth About Power Cords and there "Real" Price to Performance

It is strange dynaquest4 how some people want to show their lack of knowledge. I guess I am just here to help them .. probably would have been smart for them to find out how I spent a good part of my career. Oh well.

https://www.allaboutcircuits.com/technical-articles/understanding-thd-total-harmonic-distortion-in-p...

Read this article again. It proves you still have it totally wrong about THD.

Figure 1 shows a 60 Hz sine wave under a resistive load. The voltage swings from positive to negative and the current (i ac) tracks it. This has a power factor of one. That means you don’t waste any power. 100% of the power you put in can be used for "work". There is also no noise / harmonics being fed back to the grid so it won’t pollute the power grid with noise.
Figure 6 shows how a linear power supply works. It is a non-linear load. The 60 Hz voltage still goes up and down but the current  (i ac) is drawn mostly at the peaks. This distorts the current and generates harmonics that are fed back into the grid (back to the plug).

Figure 7 Harmonics of current flowing into a linear power supply shows what the power looks like flowing in to the AC/DC converter. The harmonics you see were not in the original clean 60 Hz power supply but they were generated by the AC/DC converter and fed back to the grid polluting it. This caused a lot of distortion in the current and causes 280% THD. But (again) everything other than the 60 Hz signal is considered distortion and is not used for any work. The power factor for this AC/DC converter is only 0.33 showing the harmonics are just wasted power. Approximately 70% of the power you feed in is wasted and gets sent back to the grid as harmonics polluting the rest of your (and your neighbors) power.

If you have too many non linear loads on a grid this distortion can be a big problem to other electronics (look it up). One thing they can do is make transformers buzz and overheat. This distortion is what you want to filter out by using a power cord. Or even better a power conditioner that removes the harmonics and feeds your system a clean 60 Hz sine wave.

280% THD? That’s a lot of THD! 😩

280% THD? That’s a lot of THD! 😩

Yes......that is why 70% of the AC power you put in is wasted by the AC/DC converter. But that does not mean you will have 280% distortion in your audio signal. The 33% converted into clean DC power that makes it out is what is used in the audio circuit.

Simple Question delkal: What is the frequency of the power drawn by a battery? Is it DC or is it entirely load dependent? Keep in mind there are 0 frequencies in a Battery. It’s all DC.

"Voltage" is only the potential to do work. The voltage is oscillating in amplitude at 60Hz. But unless you draw current there is no "power".

Second Simple Question: What will happen if a basic linear power supply draws power with a frequency spectrum of only 60Hz or 50Hz? .... hint, the answer is it will not work and the output will just be a 120Hz half sine wave.

You do realize when you admit that THD on an AC line is an actual thing that a) You are admitting power is NOT delivered at only 60Hz, AND b) That power not being delivered at only 60Hz is ESSENTIAL for operation of a linear power voltage.

There is so much fundamentally wrong with what you have written that I don’t even know where to start. Let’s start with .... "But (again) everything other than the 60 Hz signal is considered distortion and is not used for any work."... This is not remotely right. The supplied AC is just a 60Hz oscillating voltage. Without current, nothing happens and that is defined by the load (or interaction of the supply and the load). Hence, for a linear power supply to work, the frequency spectrum of the delivered power, ---- which is what is required to make it work ---- cannot be only the line frequency.

You are also confusing, at some or many levels, the impacts of THD and power factor. THD is not an indication of how much real power is delivered. Power Factor indicates this. I can create a load with a very low THD, but poor power factor. I only need to phase-shift the current.

Figure 7 Harmonics of current flowing into a linear power supply shows what the power looks like flowing in to the AC/DC converter. The harmonics you see were not in the original clean 60 Hz power supply but they were generated by the AC/DC converter and fed back to the grid polluting it. This caused a lot of distortion in the current and causes 280% THD. But (again) everything other than the 60 Hz signal is considered distortion and is not used for any work. The power factor for this AC/DC converter is only 0.33 showing the harmonics are just wasted power. Approximately 70% of the power you feed in is wasted and gets sent back to the grid as harmonics polluting the rest of your (and your neighbors) power.

NO,
That is not what it means at all. Poor power factor does not indicate that power was wasted. It simply means that Voltage and Current are not in phase. The only thing "wasted" is generation capability and distribution capability, and a bit higher resistive losses due to higher peak currents and hence higher RMS currents for a given power delivery resulting in higher losses in the distribution system (i.e. wires).

delkal59 posts12-16-2019 3:50pm

280% THD? That’s a lot of THD! 😩

Yes......that is why 70% of the AC power you put in is wasted by the AC/DC converter. But that does not mean you will have 280% distortion in your audio signal. The 33% converted into clean DC power that makes it out is what is used in the audio circuit.