Laptop charged, house lights flicker. What's going on?
December 7, 2015 2:29 PM   Subscribe

I've just moved into a new (to me) house. (The house itself is old and quite funky.) I brought with me my extant Macbook Pro (most-recent vintage). I'm finding that when my computer is fully charged and the charging cable is plugged in (green light), the house lights flicker.

This happens with my standard charging cable as well as with the charging cable on my brand new Thunderbolt display.

What's going on? Is this a 'feature' of the house's power situation? Has something happened to my laptop?

Most important, is there anything I can do to fix it?
posted by wemayfreeze to Technology (16 answers total) 1 user marked this as a favorite
 
Does this happen with a single outlet or all of them? Is it only the laptop, or will another device do it, too?

If single and all devices, you probably just have a loose connection inside that outlet. You plugging it in acts to push something out of alignment. Pull the plug out, and it's back in alignment.
posted by Cool Papa Bell at 3:02 PM on December 7, 2015


Usually this kind of thing happens when a circuit is close to capacity -- i.e. running the microwave used to dim the lights in our old house because they were on the same circuit.

This is NOT a good thing and it indicates a possible problem with wiring and possible fire hazard.

In particular, laptop chargers are low current so if they cause lights to flicker the wiring must be really sketchy...
posted by mmoncur at 3:02 PM on December 7, 2015


only when fully charged? and the flickering is a continuous thing, or just when the cable is first connected?
posted by andrewcooke at 3:09 PM on December 7, 2015


Does this happen with a single outlet or all of them? Is it only the laptop, or will another device do it, too?

I've experienced it with multiple outlets in the house, though I've only tried it in maybe two. Once my compy is fully charged again I'll give it a whirl elsewhere for some more data points.

only when fully charged? and the flickering is a continuous thing, or just when the cable is first connected?

Only when fully charged, and continuous. Not just when cable is first connected.
posted by wemayfreeze at 3:13 PM on December 7, 2015


Only when fully charged, and continuous. Not just when cable is first connected.

to me, this sounds more like some kind of interference issue, rather than load-related (because it's drawing least current then).

the only thing i can think of is that maybe your lights have a dimmer switch, and somehow something in the laptop power supply is putting spikes on the line that upset the dimmer (the kind of noise your computer power brick might be putting out can't upset the lights directly - it's just not powerful enough - so it seems like it has to be some weird interaction with different electronics).
posted by andrewcooke at 3:24 PM on December 7, 2015


How about plugged in to a power strip with surge protection?

Since this is a new to you house with funky stuff going on, I'd be inclined to call an electrician. Frying your laptop would likely be more expensive than a consultation call.
posted by amanda at 3:39 PM on December 7, 2015 [1 favorite]


A dimmer switch would definitely explain it, those are really sensitive to interference. (Although if a dimmer switch and an outlet are on the same circuit... bad wiring.)

Are the lights fluorescent? Sometimes fluorescent ballasts have weird interactions too.
posted by mmoncur at 3:41 PM on December 7, 2015 [1 favorite]


andrewcooke: to me, this sounds more like some kind of interference issue, rather than load-related…
Yeah, my thought too - dimmer switch, halogens with an electronic ballast, LED lights with a switchmode 'ballast'/supply, etc, can tend to get upset by harmonics on the mains. Maybe CFLs, which have ther own inbuilt switching supply too. The switchmode converters in typical power bricks tend to be noisiest when they're most (charging from flat) or least (battery fully charged) loaded - and that's when they put the most hash back onto the mains.

That said, Macbook Pro? The Apple chargers are normally pretty good in that respect - the one for my last-model MBP is quiet enough that I can use it alongside my shortwave receiver (unlike most of the other power bricks in the house…). Unless it's a 3rd-party charger?
posted by Pinback at 3:41 PM on December 7, 2015 [1 favorite]


How about plugged in to a power strip with surge protection?

Same problem. Surge protection doesn't help.

Lights are not fluorescent — regular incandescent bulbs in pretty pedestrian fixtures — nor are there dimmer switches on these lights.

Thanks for all your thoughts! Hoping we can get to the bottom of this, because, yes, frying my laptop or burning down the house are not rly in my plans.
posted by wemayfreeze at 3:47 PM on December 7, 2015


Next step: find an outlet on a different circuit and see if it has the same problem.

Unless the wiring is out of code, the bathroom outlets are required to be on a separate circuit.

Then we can narrow it down to one breaker/fuse and see what else is on that circuit...

Also am I reading right that it isn't a single Apple charger causing the problem?
posted by mmoncur at 3:50 PM on December 7, 2015


Also am I reading right that it isn't a single Apple charger causing the problem?

Still happening with the charging cable on a brand new Thunderbolt display, yeah.
posted by wemayfreeze at 3:53 PM on December 7, 2015


The switchmode converters in typical power bricks tend to be noisiest when they're most (charging from flat) or least (battery fully charged) loaded - and that's when they put the most hash back onto the mains.

I too have noticed a lot of switching power supplies in chargers for various electronics i own spit out interference when not under load. Usually in the form of audible whining/static noises. A few cause things like this.

On preview, i see it happens with multiple power supplies(including the thunderbolt display one, which is much beefier since it doesn't have to be in a tiny portable shell).

I had issues with this in my current place with my turntable and yes, flickering lights. I never tracked it down or completely resolved it, but my friend(who is a brilliant mechanical/electrical engineer who fixes industrial robotics and things of that nature) was absolutely convinced something was fucky with either one of the legs of the two circuits coming in to the building from the pole, or a bad ground. I ended up rearranging my entire apartment with what things plugged in to what outlets to eliminate most of the issues i was having. One of the circuits is literally JUST lamps now.

Another friends house where we had lots of issues with audio gear and flickering lights/grounding turned out to have a bad structure ground. An electrician confirmed this and installed a ground spike in the yard. Lots of old places ground to plumbing, and various repairs/corosion/etc can make that ground really flakey.

Honestly this would annoy me enough that if i wasn't renting, i would call an electrician and tell them what i was experiencing and ask what they thought.
posted by emptythought at 3:59 PM on December 7, 2015 [1 favorite]


Bear in mind that battery charge indicators often don't exactly match what's going on in the battery. It's quite possible that the laptop claims it's charged, but that the battery is actually at 99% (or 89% if it's old and degraded) and is sucking a great deal of power to try to get completely charged.
posted by joeyh at 4:05 PM on December 7, 2015 [1 favorite]


You may have an open ground, a ground loop somewhere, or possibly a place (inside the house) where neutral and ground are connected*.

Most small power adapters for electronics now are switching power supplies, which regulate their output by turning on and off rapidly. While your battery is charging the adapter is pulling a pretty constant load, but off the charge it will just pull power at roughly the same rate your computer is consuming it, and as your CPU usage spikes so will your power use. The unpredictable nature of that load could be what's causing the variation in flickering you're seeing.

If it bothers you, have an electrician out. You could have one or more new circuits run with proper grounding and just make sure to plug the computer into those. Shouldn't cost more than a couple hundred bucks, notwithstanding the cost of patching up any new holes the electrician has to make in your walls to run the new circuits.

* In the split-phase system used in the US, the neutral wire is grounded at the source, but it's not supposed to be connected to ground in the house. In houses that are old enough, the outlets may just have just had two wires running to them, and when houses get rewired to provide grounded outlets, things have a tendency to get weird. Ask me about the time I electrocuted myself plugging in a printer cable. Or the house I lived in where you couldn't use any three of the coffee maker, toaster, and TV at the same time. Or the time I measured 70 volts AC across the terminals of the water heater when its circuit breaker was off.
posted by fedward at 5:50 PM on December 7, 2015 [2 favorites]


BTW the water heater thing was a symptom of a larger and weirder problem but none of the houses with those weird power issues have burned down and I'm alive to tell the stories, so … yeah. Getting an electrician out can't hurt, anyway.
posted by fedward at 6:10 PM on December 7, 2015


My first thought was also a grounding issue, especially in an older house.

Lights and sockets should be on different circuits, which suggests some weirdness going on at the main board.
If this is a grounding issue I wouldn't expect this to cause a problem with the laptop, because it's going through a transformer to charge anyway, but it's not safe and you never know where some random voltage might build up.

An electrician should be able to test this in a matter of minutes with good test gear, but the fix could be trivial or enormous. Electrical weirdness of any kind is worth checking out properly though.
posted by Just this guy, y'know at 3:13 AM on December 8, 2015


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