"STRANGE" home electrical problem -- pop and spark -- sometimes

The spark is caused by the laptop charger, not by the outlet. Over the years, several of my household's chargers have been frequent offenders, no matter where at home or on the road that I'm plugging them in.

 

Pretty much all little chargers of that sort nowadays use a theory of operation called switched-mode.

Your outlet is supplying 120 volts AC. That's not what the laptop wants. So the charger has to reduce it.

In the olden days the charger might have a heavyish transformer in it, followed by a linear regulator that would trim the transformer output down to what the laptop needs, with the rest going off as heat (making the charger somewhat inefficient). You could think of trying to get just the right water pressure out of a faucet by turning the faucet to somewhere part-open, part-closed, hearing that hissing sound of the water being throttled through the part-closed faucet.

The new ones are smaller and lighter, and kind of work on the principle of a bucket. The laptop power comes from the spigot at the bottom, and as long as the height of water in the bucket is right, the pressure out the spigot will be right.

There is no longer a throttling, part-closed valve on the input. Instead there's just a big, open-or-shut gate. Whenever the bucket gets a little below the target level, the gate dumps a big glug of incoming water into it, then shuts. In the laptop charger, this may happen thousands of times a second. (The faster you can do that, the smaller the bucket you can get away with.)

It's more efficient as it avoids the energy loss of throttling through a part-closed valve. When the gate's closed there's no flow and no loss, and when it's open it's so open there's very little loss, just rushes right through.

When you first plug it in, the bucket's empty, and that first gate opening makes a great big glug. Pop!

That's just the way they work.

Some switched-mode supplies will have something on the input to tame the rush a little when they first turn on. The supplies for my basement LED lighting are like that: they have a negative-temperature-coefficient thermistor on the input, that resists the initial flow and heats up, and once it's warm it resists less. So there's no big rush when I turn on the basement lights ... instead, there's just a half-second or so delay before they light up.

 

What @fuzzy1 and @ChapmanF said. One simple and one much more complete explanation.

Most of my power supplies make a big pop, too. Especially the charger for my mower battery.

 

You can tell the genuine Apple ones from the counterfeits because the real ones have a fairly distinctive spark/pop.

 

Could the counterfeits have lower quality capacitors with higher internal resistance, in turn reducing that inrush surge and pop?

The pop is more likely from filling the input filter capacitor, in front of that gate (or "chopper" in the wiki description), before operation even starts.

That is the original way, there are more ways now to tame that inrush. But they all add a bit of extra cost, which the manufacturers often avoid if think they can get by without it.

Yes. The clock radio draws far less power, so they can more easily and cheaply keep its inrush well below any noticeable spark.

 

I don't have the raw electronics chops to directly validate your theory but I think that sounds quite plausible.

Sometimes you only need to be a smell-lectrician.

*sniff sniff* "Yeah, we're gonna unplug that now."

 

When I first saw the title....my first thought Based on your previous posts was “Grab the pooches and RUN!!!”
Maybe get the hubby out too if there’s time.

However (Comma!) Fuzzy and Chap are right.

Power supplies can arc a little when you plug them in - something you can sometimes mitigate by plugging in the cord first and then the brick if the plug is detachable (HP powder supplies for example often have separate cords.)
Other times you can plug the power supply and then plug in or power up the ‘puter.

If your power supply has an LED unplug it and watch to see how long it takes for the LED to wink out.
Sometimes they will remain illuminated for a few seconds.
This means that when you plug the brick back into your outlet, the bucket(s) have to be filled back up even when nothing is attached to the power supply.
Not much you can do in this case.....

OPs Normal....

 

That brought a chuckle. When I was supervising electricians, I would usually send motors back for repair with one of two trouble tags. "Bad bearings, please replace bearings." or "Blue smoke escaped. Please reinstall blue smoke." The motors always came back fixed up just right.

 

Kris buy a plug in ac phase tester. Cheap. Check all your outlets.

Using your dvm check the ac voltage across the plug. What is that? Should 120.

Check the ac voltage from the small slot on the outlet to the ground hole. What ya got? Should be 120.

The in ohms check the resistance from the big slot side of the outlet to the ground hole on the outlet. What ya got in ohms? should be a dead short or very very low ohms.

Everything is switch mode supply from the last 40 years. Should not see any pop or spark when you plug it in. Cant remember the last time I saw something arc when I plugged it in.

 

Ah...the famous 'magic smoke'!

BT
DT.

It's not just motors that run on smoke.
I find that semiconductors have a slightly off-white variant of the same substance.

They will not function without it.
Capacitors won't either.
Back in the 'long ago' sometime in the Mesozoic era (Global Warming 1.0) I used to see magic smoke escaping from time to time, and sometimes even caused it myself......at least once by troubleshooting with a jumpered out fuse.

Sadly....telecommunications seldom offers me the opportunity to troubleshoot down to the component level......

 

3-prong outlet tester, on general principles? Yes. But likely not relevant to the OP question.




AC phase sequence tester? No. In fact, hell no! Normal residential service is single phase, not 3-phase, so a phase tester is useless.

No yet that long.

Where have you been hiding out? A spark when plugging in SMPS power bricks is quite common. See previous explanations.

 

I've done that with a lightweight jumper to find out which oil pressure switch had a short in the return wire. "Not that one. Not that one." POOF! "There it is!" LOL!!

 

I just did a gig where one of those simple receptacle testers saved the day.

I briefly joined a crew installing some temporary remote networking equipment in a football stadium in Indiana a few weeks ago. One of the other guys was merrily setting up computer and network gear and plugged in a surge-suppressed power strip.

*BOOM*

It sounded like a shotgun shell going off. He was fazed but fine. The power strip wasn't. I guess the varistor was unhappy about opposite polarity inrush.

I grabbed my tester out of my bag and the device answered "Hot & Ground Swapped"

Hmm...

We called the site electrician in and we let him work it out. Eventually, another happy customer.

 

^ Give warmest regards to my beloved home state!
In a week or so I will be making one of my semi-occasional journeys back to the home sod where I will revel in sub-90 percent humidity, leaves that are not all green, ground that is not all flat and.....REAL PUMPKIN PIE!!! (although Sam's comes fairly close ).

Haven't decided on a book for the journey, although I am in possession of a (virtual) pre-release copy of Grisham's "A Time for Mercy" so maybe a detour through Mississippi's Ford County is in order while I drive.....or I might see if I can finally divine Austen....

 

I know what you mean. I'm on the front porch at my wife's ancestral farm enjoying low humidity and 70º weather. Just finished doing some siding repairs on one of the old out buildings and hanging some decorations on the wood shed. I'm hoping for some ... REAL APPLE PIE!!! while we're here.

 

It could be ants. I don't know why but I always see ants coming out of my electrical outlets. They do cause pops and sparks. Just my thought though.

 

This sounds like 'inrush current' described here: Prius - UPS Project

Here a hot thermistor has a switched power supply plugged in. Notice the huge current spike in the first power cycle as the capacitor draws a huge current:

In some cases, this can result in a surprising but harmless spark like someone suddenly shouting "BOO!"

In this case, there is a cold thermistor which presents a high resistance so it takes multiple power cycles to charge the capacitor:

It took at least 3-4 power cycles to charge the capacitor at a substantially lower current. There is no spark or sudden inrush to trigger a spark. It is the functional equivalent of smoothly releasing the clutch versus popping the clutch.

Inrush thermistors are a little tricky. They start cold with a high resistance and warm up as the current flows through them causing their resistance to decrease. But they remain in the circuit generating the heat that lowers their resistance ... they get hot. You don't want your power outlet in the wall of the house getting hot as heat is the enemy of wires and walls.

Another approach would be an outlet with an integrated power switch. With the switch off, no spark. Then flip the switch and the spark will be masked by the switch "click." But like many problems, it can be over engineered.

Early X-ray machines has huge transformers and power requirements. So ON/OFF was handled by a two-contact, relay. Powered ON, the first contacts with a power resistor would engage first followed by the larger power contacts. Powered OFF, the power contacts would open putting the power resistor in the circuit. Then these contacts would open with a substantially reduced arc. This was done to avoid arc burning or even welding the contacts.

Bob Wilson