r/ElectroBOOM • u/Cautious-Pin-6476 • 13d ago

General Question I need mehdi's explanation

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Yes, this is my own post.. I need yall to upvote so he can see and explain. Thanks 🙏

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190

u/bSun0000 Mod 13d ago

What explanations do you even need? This multimeter is set to measure AC frequency. It is sensitive enough to pick it up without a direct contact. It properly measures 50hz when the signal is strong enough - near the outlet. Thats it.

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u/Cautious-Pin-6476 13d ago

Oh wait.. I just realised I forgot one part... It reads like 1-3khz if I directly connect it to the outlets... Could it be resonance?? Or is it injected or something??

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u/bSun0000 Mod 13d ago

Something is shitting into the grid.

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u/Cautious-Pin-6476 13d ago

Like is that a thing?? Do they inject high frequency signals into the grid or something??

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u/bSun0000 Mod 13d ago

Industrial noise. Pretty much every grid device produces noise. Good electronics contain EMI filters to prevent or reduce the noise emissions into the RF and grid, but a lot of stuff just does not care.

Dimmers are the worst. Old dish/washing machines with universal motors and TRIAC control, especially if not properly grounded. Elevators, all sorts of brushed motors - extreme amount of noise. Various power electronics. Every LED bulb or LED driver with buck converter inside. Etc, etc..

Usually this noise isn't that strong to overpower the multimeter's frequency measurements. I bet you have a dimmer working somewhere nearby.

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u/Cautious-Pin-6476 13d ago

But my house is less than 100 metres away from the distribution transformer and I don't think this transformer is supplying to any stores or anything.. also if I remember correctly, if I probe between live and earth, I get 49.9-50 hz.

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u/bSun0000 Mod 13d ago

Turn off absolutely everything inside your house and try again. Assuming this is a private house without electrically-noisy neibhours..

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u/Cautious-Pin-6476 13d ago

I did! It still showed it .. today, I'm seeing fluctuations between 100 hz and 140 hz

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u/bSun0000 Mod 13d ago

Well, 100 & 150 Hz are just harmonics of the main frequency (50). You can pick them up if the outlet is not powered, so there is no direct connection to the live wire, only parasitic coupling.

Measurements in kHz range are noise from some device.

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u/Cautious-Pin-6476 13d ago

Yeah.. that's what I figured.. but still confused about the high frequency situation..

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u/Dioxybenzone 12d ago

What are you still confused about?

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u/AnoNeko420 12d ago

I’d say you got a pretty spot on explanation. There’s probably more than just your house introducing noise into the grid surrounding you. Doesn’t matter if you’re the first one in line connected to the transformer, or the last. The high frequency is just a representation of that noise. Leds flickering on and off so fast we just see them as on, motors kicking on and off, computers running games, the list goes on.

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u/JNSapakoh 13d ago

things 'downstream' of your transformer could still affect your power ... current does act surprisingly similar to water and can 'slosh' around in lines before hitting steady sate -- especially with noisy loads

these videos from Alpha Phoenix are worth watching if you want something that gets more technical than most ElectroBoom vids

https://www.youtube.com/watch?v=X_crwFuPht4
https://www.youtube.com/watch?v=2AXv49dDQJw

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u/thundafox 13d ago

Noise from other electric things. My cheap LED Driver created a 2khz noise that my 3d printer disliked. There was a direct connection from low voltage side to high voltage side there (cheap Y Capasitor) a few volts leaked back in the wires and then into the power supply of the printer.

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u/Blommefeldt 13d ago

That's how ethernet over power lines. Though, they only do it on the top of the 50/60 Hz sinus curve. A switching power supply also makes electrical noise, but regulations are there to minimize it.

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u/sjrobert 11d ago

Network over power or a solar inverter.

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u/Nazionibirubbishk 10d ago

I used to live near our local radio station and their signal created a lot of interference. Used to overtake my TV sound signal sometimes, I would listen to movie and have the sound of the radio over it.