AC/DC Plug Sparks When Plugged In - Page 1
Forum section: electronics / projects

author: bostonman
author_rank: Super Contributor
timestamp: January 06, 2022, 12:50:02 am
content: I have a 12V DC (single output) 20A AC/DC power supply, and, when I plug it into an outlet, it sparks.I'll use the word 'obviously' assuming this is just low ESR capacitors and inductors causing this and not anything else.Although it's not really a problem, I'm wondering if a way exists to reduce (or eliminate) this sparking.edit: I failed to mention that it sparks at the plug when it's being plugged into the wall

author: Vovk_Z
author_rank: Super Contributor
timestamp: January 06, 2022, 01:35:36 am
content: It is a usual thing. Capacitors cause this mostly. Huge film high-frequency filtering caps (if they are) but mostly the main reason is huge electrolyte charging current (if we are talking about AC/DC power supply). Of cause, there are ways to reduce this inrush current, but it may cost a lot, almost up to as much as the whole device costs. It is costly, so manufacturers usually use cheap simple methods - NTC resistors with as small rated resistance as needed to current was not too huge.

author: bostonman
author_rank: Super Contributor
timestamp: January 06, 2022, 01:50:08 am
content: This is a power supply for my 3D printer.My thought is that the sparking will cause carbon and/or burning inside the outlet. I have reduced this a bit because I installed a cover with an on/off switch. Now I can plug it in without the arching, but imagine the switch itself may develop carbon.I agree this is usual, but this power supply seems much worse than anything I've seen.

author: Vovk_Z
author_rank: Super Contributor
timestamp: January 06, 2022, 01:59:44 am
content: Of cause it is much better to use a switch than to use a plug. Because burned outlet is a problem.Switches are made to withstand those transients so it is ok for them. Just use a powerful enough switch, with a rated current of 10-16 A.If you turn it on and off frequently (several times a day) and worry about switch then change it after several years of duty.

author: themadhippy
author_rank: Super Contributor
timestamp: January 06, 2022, 02:33:10 am
content: QuoteAnd people laugh at us brits with our switched socket outlets

author: electr_peter
author_rank: Unknown
timestamp: January 06, 2022, 08:43:25 am
content: As mentioned above, there are ways to reduce inrush current and sparking, but they may be not trivial or cheap. In addition to linear PSU with high value capacitors, SMPS (both AC->DC and DC->DC) typically have huge inrush currents on start-up (even low power ones). More advanced ($$$) DC/DC converters have additional limited inrush current settings.To reduce inrush current, use soft-start circuit - from NTC thermistors, relays/triacs to more sophisticated ones.Switch may be more robust than plug/socket for inrush, depends on specs. Repeated plug-ins will damage contacts on both plug and socket (you can see pitted dark craters in metals) making it progressively worse.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 06, 2022, 11:49:18 am
content: Best plugs in the world mate, untill you tread on one in the night and try not to wake everyone in the house.Much worse than a lego encounter.My Swtiched 13A sizzles when I use the socket switch to turn on my media centre kit- but that might be becasue I'm using one of those crap 3 gangers.I fact. I'll repace that today with an MK, I only need 2 gang.

author: dmills
author_rank: Super Contributor
timestamp: January 06, 2022, 12:27:44 pm
content: MK actually offer 3 gangers, I was quite surprised.Gradually replacing all the contractor specials in my place with MK as the silly things fail.Regards, Dan.

author: themadhippy
author_rank: Super Contributor
timestamp: January 06, 2022, 01:07:22 pm
content: QuoteIf you look carefully you'll see its fused,that way it lets you use it on a spur off the ring without breaking the 1 single or 1 double outlet rule.

author: TheMG
author_rank: Frequent Contributor
timestamp: January 06, 2022, 07:23:05 pm
content: Decent quality receptacles and plugs are pretty robust, that small amount of arcing would likely take YEARS of plugging/unplugging several times daily to wear out the contacts by the arcing alone. In fact, the receptacle is more likely to fail from simple mechanical wear before this occurs.As for switches, a good quality switch should have a "snap action" to ensure the contacts open and close rapidly, minimizing arcing.

author: electr_peter
author_rank: Unknown
timestamp: January 06, 2022, 09:27:18 pm
content: Plug pins definitely suffer from inrush current, see examples hereburn-marks-on-apple-charger-plug-pinsThe problem with arcing/inrush current is that it occurs in low power devices (e.g. 5-20W charger momentarily draws >1-2kW). Switch, if any, needs to be beefy as hell. Sockets can more easily handle such loads - they are rated to ~10-20A continuous (and much more momentarily).

author: Gyro
author_rank: Super Contributor
timestamp: January 06, 2022, 09:37:29 pm
content: QuoteThe thing about mains switches is that the have proper Silver alloy contacts. They handle surges rather better than bits of brass.

author: mark03
author_rank: Frequent Contributor
timestamp: January 08, 2022, 02:28:24 am
content: Quote from: TheMG on January 06, 2022, 07:23:05 pmI'm currently renting an apartment in a house which dates to the early 1900s. It has these snap-action switches which are very satisfying to operate. I don't know how old the switches are. They look old, and I have never encountered snap-action switches anywhere else in my life (I'm almost 50 years old). Are they still available today? Pretty sure it's not the sort of thing you could find at Home Depot.

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 08, 2022, 03:08:42 am
content: Quote from: mark03 on January 08, 2022, 02:28:24 amTry the commercial/industrial grade parts, you can buy them at Home Depot type places, they just cost more. Not super clicky/snappy but they definitely toggle with a bit more authority and tolerate more abuse than the cheap stuff. Same goes for outlets, buy commercial or better and they stay tight.Sometimes you find an even better light switch in old buildings, they're totally smooth and silent, because there's a big mercury tilt switch inside.

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: January 08, 2022, 03:50:30 pm
content: Quote from: mark03 on January 08, 2022, 02:28:24 amFrom your description, it sounds like they may be the original "Tumbler" light switches designed to cope with 120v DC supplies. Modern light switches, designed to interrupt 120 and 240 volt ac supplies, take advantage of the 120/100 zero crossing current/voltage events to reduce the contact separation distance requirements of switches designed to cope with DC supply voltage.The same consideration applies to mains voltage fuses where the modern 30mm cartridge fuse used on ac supplies can do the job of those bulky porcelain rewirable fuse holders with some 4 to 6 inches of fuse wire required to allow the arc length to grow to the quenching point.Those tumbler switches have a louder, more pronounced 'snap action' simply because of the need to rapidly separate the contacts by some 20mm or so versus the rather petite 3 to 5 mm separation distance requirement of a modern (and cheaper) 5 or 10 A rated 120 or 240 volt ac light switch.