Unsure what to make of this distortion - Page 1
Forum section: electronics / beginners

author: givitallawy
author_rank: Newbie
timestamp: February 27, 2023, 04:26:57 pm
content: Hey!First time posting but always love coming here. Lately I been having some issue with lights flickering.Sometimes my computer monitor would just turn off by itself.I've always been a low voltage tinkerer and decided to have a go at troubleshooting my home mains.I appreciate any and all feedback / suggestions. I am aware of the dangers of scoping high-voltage and have the appropriate equipment.One image is from my home and the other from my neighbors for comparison.I completely unplugged everything in my household and still have the same waveform.What do you think this could mean? Any advice on what I should look for?Sample from my neighbor is the top image.Sample from my home is the bottom image.Thank you for your time.

author: Zenith
author_rank: Frequent Contributor
timestamp: February 27, 2023, 04:58:48 pm
content: Lights flickering in your house but not your neighbour's house. I'm inclined to think it's a connection not screwed down properly or a faulty breaker. In most cases there's a part of the wiring in the building which is the supply company's responsibility and has seals on, before the meter. If it's outside, it will be the supplier's responsibility.It might be something obvious.I do feel obliged to say you ought to call in a qualified electrician to sort it out.

author: givitallawy
author_rank: Newbie
timestamp: February 27, 2023, 06:27:47 pm
content: Thank you, Zenith, I have an electrician coming out in the next few days.I am curious to know / understand what this pattern means? Or is this a typical waveform?

author: Zenith
author_rank: Frequent Contributor
timestamp: February 27, 2023, 08:54:17 pm
content: The mains supply should be a pretty good sine wave, however there are various things that can distort it, such as welders which use thyristors, mains born interference from devices with badly designed or faulty power supplies, and so on. As a guess I'd say that if you took an accurate average responding (sine) voltmeter, and an accurate true RMS voltmeter, and applied them to your supply and your neighbour's supply, you'd see little or no difference.An oscilloscope is not the first thing which would occur when tracking down a problem like this.It would be at least unguarded and a disservice to our host, to give anything but the most cautious advice on the subject of messing with a mains supply. Advice which could be lethal by electrocution, or causing a fire.You might have a look round using your senses, especially round the distribution box. This could guide the electrician.Sight. Is anything obviously burned?Smell. Do you pick up that nasty burned smell?Sound. Are there sizzling sounds?Taste and touch, we can safely leave out.Years ago friends of mine were lying in bed and noticed something flashing from the ceiling. They also heard noises from the loft. The next day they investigated and found squirrels had gotten into the loft, bitten holes in the ceiling and chewed the insulation off cables, which caused arcing as they ran about and caused a partial contact.

author: Bud
author_rank: Super Contributor
timestamp: February 27, 2023, 09:27:47 pm
content: Switch your scope to FFT mode and see what the specrum chart indicates.

author: jonpaul
author_rank: Super Contributor
timestamp: February 28, 2023, 04:45:29 am
content: The flat top sine is common for most home mains due to all the electronics loads drawing current to charge bus caps on the mains peak.Resistance or induction loads will not,cause this,distorted sine.A UPS running on the backup battery will make a,perfect sine.I see exactly the same distorted mains.No defect and no ill,effectUse a power Analyzers to check the PF and harmonics.AVOID ANY CONNECTION of a,Spectrum Analyzer to the mains.Use a 240 or 120V mains>< 5..24 V stepdowwn transformers to 7solate,and reduce,mains voltage to a,safe,level.Bon SoiréeJ

author: bdunham7
author_rank: Super Contributor
timestamp: February 28, 2023, 04:50:57 am
content: Quote from: givitallawy on February 27, 2023, 04:26:57 pmWhich is which? The first looks fine, so if that's yours I'd say your issue is intermittent and you aren't seeing it there. The second has some pretty awful noise on it that appears at first glance to be synced with the line frequency--so some sort of triac drive or something.

author: givitallawy
author_rank: Newbie
timestamp: February 28, 2023, 02:22:41 pm
content: Thank you all for the valuable input!@Zenith I am not perceiving anything out of the ordinary. However, the transformer which is fed by the main transmission line is located on my property seems to be buzzing louder than I remember. It is also buried in about 6 feet of snow. An electrician is due to be here this Friday.@Bud I will take a look at it in FFT mode once I get stepdown transformer.@jonpaul I looked at purchasing isolated probes, but they are very expensive. I'll be picking up a stepdown transformer.@bdunham7 The bottom figure (MicrosoftTeams-image (1).png) is from my home.

author: bdunham7
author_rank: Super Contributor
timestamp: February 28, 2023, 03:13:57 pm
content: In that case, that looks like some interesting interference but I can't guess the source offhand. As far as FFT and step-down tranformers, there's no need. If you can set up and view the waveform with the scope, switching to FFT mode won't change anything about the inputs or overall safety.jonpaul'sstatement about not connecting a spectrum analyzer to mains (which is definitely correct!!) refers to a different instrument, not a scope in FFT mode.What devices or appliances do you have that consume a lot of power? That really looks like a large heating device or something being turned on and off in a noisy manner.

author: TomKatt
author_rank: Frequent Contributor
timestamp: February 28, 2023, 03:15:18 pm
content: Quote from: Zenith on February 27, 2023, 04:58:48 pmSince I switched to led bulbs I've noticed that the ones in my bathroom appear to be very sensitive to power fluctuations caused by high current appliances such as my washing machine and well pump. Even my coffee maker heating element switching on & off causes a visible flicker in the led bulbs. Coincidentally, the bulbs in that circuit seem to fail more frequently than all the others in my home. In fact, the original ceiling light was one of those self contained led fixtures, but after replacing it twice due to failure I swapped it with a fixture that takes standard socket bulbs so I don't have to replace the whole thing again.I'm confident that I don't have any loose connections - moreso that led lighting is just more sensitive to power fluctuations.

author: givitallawy
author_rank: Newbie
timestamp: February 28, 2023, 03:27:48 pm
content: Quote from: TomKatt on February 28, 2023, 03:15:18 pmEvery light in my house is led, three of them failed prematurely over the last year.@bdunham7 Most notably, a well pump, furnace, chest freezer, washer/dryer and a few ceiling fans.

author: wasedadoc
author_rank: Super Contributor
timestamp: February 28, 2023, 03:40:14 pm
content: Quote from: jonpaul on February 28, 2023, 04:45:29 amMany, if not most, UPSs sold to provide short term power backup for home and small business computers do NOT produce a perfect sine wave. Instead they produce a "modified sine wave" which is a stepped waveform with as few as only 3 levels. One positive, one negative and zero.

author: Zenith
author_rank: Frequent Contributor
timestamp: February 28, 2023, 03:46:03 pm
content: Quote from: givitallawy on February 28, 2023, 03:27:48 pmIf this is cause by a faulty appliance, you should be able to track it down by turning them all off and turning them on one at a time. It could could be an intermittent fault.

author: jmelson
author_rank: Super Contributor
timestamp: February 28, 2023, 03:49:15 pm
content: Quote from: TomKatt on February 28, 2023, 03:15:18 pmBathroom bulbs are subjected to condensing humidity, and that is bad for anything that is mains-powered. Possibly dimmable bulbs may flicker more as they sense that as dimmer waveforms.Jon

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 28, 2023, 09:47:29 pm
content: Quote from: TomKatt on February 28, 2023, 03:15:18 pmGood LED lamps are designed with kind of constant current drivers so they typically are less sensitive to voltage fluctuations.If you have fluctuation-sensitive LED lamps just get rid of them, they are possibly not fine.

author: Zenith
author_rank: Frequent Contributor
timestamp: February 28, 2023, 10:23:35 pm
content: Does this show any pattern?Has it always happened but has become worse? Does it correspond to a new appliance such as a washing machine?Does it only affect lights in a certain room or part of the house? I recall you said it affected the computer. If you have a hifi or mains radio, do you hear crackles and pops when the lights flicker? If you have incandescents, say in a cooker hood or oven light, or just there because you haven't had to replace them, do they flicker too?Does it only happen when it's windy or wet?Does it correspond to work being done in the street?Roughly, how often does it happen? All the time? More or less every half hour? Once a day? Once a week? Every night between 7pm and midnight?And so on.

author: givitallawy
author_rank: Newbie
timestamp: March 06, 2023, 04:23:54 pm
content: $300 service charge later, still no idea what is causing the issue.The electrician told me that it isn't anything in my house that is causing it because the noise is originating before the meter.He recommended that I call the power company to come out and investigate.

author: MathWizard
author_rank: Super Contributor
timestamp: March 13, 2023, 04:42:48 am
content: This winter I have 120V LED bulbs flicker off sometimes, IDK if they are a driver or are just in series and the mains V drops a bit. But yeah I don't have anything else shut off. If it's mains voltage drops, I guess everything else has enough caps to hold over.