High frequency sound from switching supply, any danger?

[sairfan1]

Some of my power supplies (Chinese wifi socket, Dell laptop charger, Sony Headphone charger) are 24 hours plugged in to main power and gives continuous high frequency sound but these items are working good.
I'm afraid if this is sign of upcoming problem that can cause any danger like fire etc. or should i ignore it, as i often listen this kind of sound from switching power supplies.

thanks,

[HB9EVI]

I already had a cheapy chinese SMPS with suspicious noises which went PUFF with smoke and fire; fortunately I sat right there when it happened. I have some wallwarts steadly plugged for routers/modems, but they are from reliable sources so I don't worry too much.

[No.Mad]

Hey sairfan1,

question: was the high pitch/frequency noise present from a moment you bought it and plugged first time? Or it happened to show itself after some time?

If it's first case: bad design causing resonance in switching circuitry. Somebody f*ked up as a designer.

If it's the latter: one of the components was compromised, busted and shifted all specs into resonance. Imminent fail will occur.

Regards

[LateLesley]

It's one of the common problems with switchers, sometimes the switching frequency, or a harmonic of it falls into the high audio range, and can be heard by some people. (And Pets). If the noise has been there from new, it's probably nothing to worry about, but if it is a new noise, it could be a sign that some components are wearing (due to temp, stress etc), and could fail in the future.

It's probably not a good idea to leave these supplies running 24/7, unless absolutely necessary, and I'd go as far to say not to leave them unattended either. These things do wear out, especially ones with modern cheap caps. Some caps are only rated for ~2000Hr use, or about 84 days of 24/7 operation. It doesn't mean they fail after that, just that they are not guaranteed to not fail after this time. Though it gets longer, the cooler they run. (you helped me learn something today! ) http://www.rubycon.co.jp/en/products/alumi/pdf/Life.pdf

[mcinque]

If it's first case: bad design causing resonance in switching circuitry. Somebody f*ked up as a designer.
If it's the latter: one of the components was compromised, busted and shifted all specs into resonance. Imminent fail will occur.

THIS^

[David Hess]

Pulse frequency modulation (constant off-time) switching can cause a hiss or whine in the audible range.  Current mode control results in sub-harmonic oscillation in continuous conduction mode unless slope compensation is used.  Neither is destructive or a problem other than being annoying.

[GromBeestje]

The sound a switching power supply makes may depend on the load. I have a phone charger which makes noise when there is no load, but is silent when there is a load. This means I can hear when my phone is fully charged.

So, if your chargers make sound after the charging is finished, but not during charging, I suppose it's okay.

[sairfan1]

I opened the socket and could not find any damaged components, that means its safe and there is nothing going wrong with it?

Wifi sockets are more important for me as they are connected 24/7 i can remove rest of the things when I'm not around.  I bought 5 Wifi sockets for my lab as I often forget to switch off things or sometime not at home but worried if i properly switched off my gadgets, looks like wifi switches are itself danger, does any different solution comes to your mind to monitor connected devices?

I'm attaching image of wifi switch i opened so that we can evaluate if they are designed reasonable.

[No.Mad]

Is it me seeing things or there are rusted screws?

[HB9EVI]

Doesn't look that bad, but seems to miss at least proper filtering for the SMPS.
Knowing what devices are on the market, I'd be careful what to let run unobserved after all.

I don't know the brand and the store you bought it; personally I'd go for a well known brand from a reliable source to be on the safe side. There was too much in the media about flimsy mains devices which went up in fire or otherwise caused harm

[HB9EVI]

yea, the one on the right bottom looks strange; hard to say what's up there

[sairfan1]

Yes it was rusty screw.
I bought from ebay for $18 each, later i saw at some local stores and surprised that they are selling at almost same price, not sure if they are good quality.

[No.Mad]

I don't know the brand and the store you bought it; personally I'd go for a well known brand from a reliable source to be on the safe side. There was too much in the media about flimsy mains devices which went up in fire or otherwise caused harm

+1

You don't want your precious test equipment to go with a magic smoke. Trust me. There is a saying: those who want to save money by buying cheap tools and services will be doomed to spend more time and money on rectifying flaws of bespoken.

TLDR: Cheap chargers and mains PSUs is bad.