This that famous harmonic distortion?

[tom66]

Most of the cheapest meters have a diode peak detector so they are only accurate for pure sine wave that has no DC component.

[Behemot]

Enjoy, APC BE550-FR. I guess active-PFC PSUs won't like this stuff…

[Behemot]

Originally Posted by Kiriakos GR

New glossary terms for you.
what's coming out from all those al cheapo UPSes.
Modified sine wave with passive PFC.

my cheap multimeter can only make like 160 V from it
Average measuring meter = Non - True RMS

OK, there was nothing new for me.

New information for you: „modified sine wave“ can mean all types of strange and sometimes pretty terrible wave types, which have absolutely nothing in commong with sine wave, other than maybe carying +- the same energy. Waves definitelly not healthy for hunreds od devices out there people often use them (or try to use them) with. And I am not talking about PSUs here but things like pumps.

My plan is to map some of it and do some experiments with it.

[Kiriakos GR]

People the man become expert in just 24 hours.
Do no post further messages.

[Behemot]

Let me ask, who are you telling me not to post anything else in my own thread? Aren't you somewhat too self-important lately?

Don!t get it wrong but as quite often, especially from you, when I ask something, I get no answer but everybody telling me how wrong I am doing it and what moron trying to kill myself I am. Thank you very much, very helpfull. I did not get the answer till now BTW.

Now when I checked different phase, distortion-free, I got pure sine wave so my idea was confirmed, thanks for making me find it myself, which is the best possible solution by the way.

So I am sorry, but such input as yours I don't really need

[Kiriakos GR]

Just take a camera and show your face.. I do not do... me..you...me...you.. dialogs with ghosts and kids.

[Behemot]

What?

[budm]

"I told ya several times already, I am no idiot." Who is calling you idiot, from what we see, the measurement is not done right so what you see is not truly represent the real AC wave form you are trying to look at without using the diff probe as others have pointed out or float the scope (which is dangerous and the input of the scope has to be able to handle the voltages). If you are going to get mad when we pointed out the method you are using is not right, then good luck.
Draw up the 3 wires you have on your outlet, the Phase, the Neutral (return), the safety Ground. if the Neutral is not tied to safety ground at the circuit breaker panel, then your reading between the Phase and Ground will not be valid since you will be reading the voltage through the stray capacitance of the wiring/ main transformer that supplying the power to the outlet. That P-P reading as shown that I see also tells us the reading is not done properly.
If you put AC meter between Hot and Ground, if the Neutral is tied to Ground, then you should read 230VAC. Reading of 160VAC between Phase and Ground indicates that the Neutral is not tied to safety ground or the wiring problem.

[joshnz]

Hi Behemot, Do you have the scope isolated?
if so that is wrong. What you are measuring should isolated.
You should measure the output of the transformer but it will filter some of the noise from the grid.

[Behemot]

Neutral is tied to ground, before breakers, that's the norm around Europe, did not see important to mention that.

I told ya what the O-scope was measuring was not important by that time - I am not doing measurements now! Simply looking how the wave looks; probably multiplier was not set right but that does not matter. That 160V was what DMM was showing when running on battery - that made me somewhat think the output is some crap so the meter is not even able to measure it. Also wattmeter got nothing from it. So I looked at it with O-scope, you can see the result in post #22.

Differential probe seems to me like some wonderfull mantra which will save everything. Generations managed without it and I also won't buy differential probe expensive like hell for simple looking at waves and taking orientation measurements.

Another phase without any load looked OK so that confirmed for me the technique is fine and I really saw harmonic distortion by the power supplies (display has no PFC at all, ATX PSU only passive one), maybe lights (don't really know where the lights are connected in here).

joshnz: yes, would you ppl at least mind reading what I wrote? It is in the very first post, O-scope is isolated by 2kVA isolation transformer. Jeez, that's the first thing to do when measuring things like this.

[tom66]

It's a bad idea to isolate the oscilloscope. Always isolate the load instead.

[Behemot]

There was no load.

[tom66]

Well, always isolate what you're testing anyway. Never the oscilloscope.

[Behemot]

Been using it for load but can do for empty socket as well I guess. The question is if it won't smooth some of the waveforms?

[joshnz]

Originally Posted by Behemot

Neutral is tied to ground, before breakers, that's the norm around Europe, did not see important to mention that.

I told ya what the O-scope was measuring was not important by that time - I am not doing measurements now! Simply looking how the wave looks; probably multiplier was not set right but that does not matter. That 160V was what DMM was showing when running on battery - that made me somewhat think the output is some crap so the meter is not even able to measure it. Also wattmeter got nothing from it. So I looked at it with O-scope, you can see the result in post #22.

Differential probe seems to me like some wonderfull mantra which will save everything. Generations managed without it and I also won't buy differential probe expensive like hell for simple looking at waves and taking orientation measurements.

Another phase without any load looked OK so that confirmed for me the technique is fine and I really saw harmonic distortion by the power supplies (display has no PFC at all, ATX PSU only passive one), maybe lights (don't really know where the lights are connected in here).

joshnz: yes, would you ppl at least mind reading what I wrote? It is in the very first post, O-scope is isolated by 2kVA isolation transformer. Jeez, that's the first thing to do when measuring things like this.

My understanding is the ociliscope is getting it's power from the isolating transformer and probe is connected to to the mains?

[Behemot]

Yep.

[joshnz]

I also understand that you have the ground clip of the scope connected to the neutral of the power point?

[Behemot]

Nope, to the ground as well. I say as well because the O-scope ground is connected to earth ground directly. I see what you mean but I am not really sure if it would be safe to ground the neutral of running UPS - I cannot be really sure the neutral is not flowing so there may be some (not low) currents flowing through, no?

[tom66]

The reason it is not safe to isolate a scope is because it's a single insulated device, which means one failure is permitted, a live-to-chassis fault. With a properly earthed instrument, this will simply trip the RCD/GFCI or blow the fuse. Isolating it removes this protection. In addition, if you happen to connect the earth of the scope to a live circuit, the scope chassis is now floating live. If you touch it, you could be electrocuted.

So, always isolate the load/DUT only!

[Behemot]

Originally Posted by tom66

In addition, if you happen to connect the earth of the scope to a live circuit, the scope chassis is now floating live. If you touch it, you could be electrocuted.

Nope - it is directly donnected to earth ground so it will go to short and trigger breakers. Besides, there almost nothing metalic besides connectors on it…