Topic | Weird voltage reading after nearby window AC unit kicks on

Home Forums Mooshimeter Support Weird voltage reading after nearby window AC unit kicks on

This topic contains 4 replies, has 2 voices, and was last updated by  ville 6 days, 22 hours ago.

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  • #22053 Reply

    Matt M

    Hi all,

    I recently purchased the Mooshimeter to do some long-running voltage logging on some outlets in my house to investigate potential (ha) under or under voltage issues in my house. I’m testing it out first in my office where I can keep an eye on things and get used to the Mooshimeter before deploying it in its desired location (where my TV and AVR were plugged in before they mysteriously died).

    I have the meter hooked up to the surge protector at my desk, which is plugged into a nearby outlet. C to ground, V to hot, omega to neutral – via multimeter leads that I’ve snipped at one end and wired into a GFCI replacement plug – set to measure AC voltage and aux AC voltage, with all the settings like ranging, frequency, and sampling set to auto. I have an air conditioner plugged into the other outlet on the receptacle that the surge protector is plugged into.

    The reading starts normal, with around 110-120V on hot-ground and ~500mV on neutral-ground. It seems that when the air conditioner compressor kicks on, the GFCI plug resets (this isn’t the Mooshimeter’s problem, but makes me think something is really wrong with this air conditioner), which brings the reading down to 0V neutral-ground and something like 2V hot-ground. When I reset the GFCI, the hot-ground reading spikes up to >200V, sometimes flashing something even as high as 600V. I simultaneously use my other multimeter to read the hot-ground voltage on another socket on the same surge protector and it reads a normal 110-120V, same with when I unplug the Mooshimeter’s GFCI and read from the same socket, and when I use the GFCI leads on the other multimeter, all looks normal. But the Mooshimeter is still reporting >200V. During this time, the graph with buffer mode on doesn’t show a normal sine wave shape, it’s pretty irregular. When I turn off the air conditioner, the Mooshimeter reading goes back to zero. Sometimes during this process, the Mooshimeter itself has seemed to reset, or maybe it’s just the app, where I get booted out to the device selection screen except it shows my device as “bootloader” and prompts me to install firmware, but killing the app and restarting it gets past that issue.

    Screenshot of graph

    What’s going on here? Is the Mooshimeter picking up on something that my other multimeter doesn’t due to a higher sampling rate or something? Or is it calculating the RMS/average voltage that it displays incorrectly? I’m not sure which multimeter to trust, and I’m trying to build up trust in my Mooshimeter readings before I deploy it for long term logging.

  • #22054 Reply

    Matt M

    The image didn’t seem to be included with the tag, here’s a direct link: https://imgur.com/Nx2hVOl

  • #22058 Reply

    ville
    Participant

    Measuring between ground and neutral with ohm-input sounds bad. Or at least I would not do that.

    I have no idea what happens when you overload that just over 1 volt input, but that might be the reason for strange readings on the actual voltage channel.

    Measuring current would be more interesting anyway. I have chinesium current transformers for that and i have made an extension cord with banana plugs in the middle (in a box, where i can have my mooshimeter safely) for easy installation to any device with a plug.

    If removing that connection from ohm-input still shows that same waveform, i would measure between neutral and live next.

    Is it possible to safely measure voltages (and current, preferably with a current clamp) at that ac-unit?

  • #22061 Reply

    Matt M

    Good catch, thank you – I had seen that the omega input wasn’t just for resistance but also a secondary voltage measurement, but I didn’t realize that the aux voltage was limited to 700 mV. Since the neutral-ground measurement reflects load on the circuit, and the reading was around 500 mV before the compressor kicked on, the inrush load of the compressor probably put it over that 700 mV threshold and perhaps measured with the primary reading. So it seems that I can’t measure voltage on the entire 3-prong outlet at once. But my main concern is really the hot voltage, so that should work fine.

    Your idea for measuring current is cool. Is your extension cord setup effectively equivalent to a line splitter with a CT clamped into the hole? But with banana plugs to continue the connection from one side to the other, disconnecting them to slide on CTs and then reconnecting for the measurement?
    https://www.amazon.com/Line-Splitter-Klein-Tools-69409/dp/B01B7RTNSO

    I’ll have to come back to the air conditioner measurements – the outlet near it has reversed hot/neutral from the previous owners that I need to swap, and my earlier tests were done with the air conditioner hooked up to an extension cord, which even though it’s heavy gauge was another variable I just didn’t want in the mix.

  • #22063 Reply

    ville
    Participant

    My measuring setup has also other connectors for the actual current path, banana plugs are just for connecting to multimeter.

    I remembered that i had those cheap Chinese current transformers for that, but actually it was a way nicer 125/5A one. As our household sockets go up to 16A (@230V) here in Finland, I had looped a wire 5 times through it to get 25/5A and could easily connect that to ampere input.

    I got stackable safety banana plugs, so i could have neutral and one wire of that natively potential free current transformer output connected to C-connector on the meter at once, but still being able to use them separately without tools. Just have to remember that I should not touch that current transformer while connected, specially as our schuko-plugs aren’t polarized and could be inserted in two ways to the sockets (which should be internally connected so that live is on the right or down side, but you could never trust it).

    With that setup it is quite easy and safe to log how different appliances behave on a little longer time periods.

    With the mentioned Chinesium ct-clamps (blue, split core, comes with audio-plugs on a lead, cheap) and my two mooshimeters I have logged my whole house consumption for months. One channel for some phase voltage and three channels for three phase currents. I got surprisingly clean signal from 30A/1V transformers (most houses/apartments here have 3x25A main fuses), even with one mooshimeter channel being actually for 60/600 volts.

    I have seen those line splitters on youtube etc, but those are not a thing here. It might help in some rare cases, but as an electrician I usually find some easy and safe place to stuck my current clamp anyway. And with that thing, you would have to measure voltage separately, so i think my extension cord with old lunchbox in the middle wins :D

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