Thoughts?

[ban-all-sheds]

This type of construction doesn't lend itself well to the flyback transformer in a SMPSU because the proximity losses are huge with that kind of winding layout.

If you're allowed to present the output from the secondary winding of such a transformer directly into the bathroom, the reason that you couldn't also use it as the input to a 5V power supply is what?

 

[endecotp]

The point about bathroom shaver transformers is that they have to present a safe 240 V output. It's the 240 V aspect that makes that difficult.

If you wanted a bathroom-safe 5 V supply it could be done easily, without the need for that sort of transformer. Just use a "medical" 5 V power supply design and encapsulate it to prevent moisture ingress.

(It would be safe in practice; not necessarily legal I suppose.)

Maybe there is a market for bathroom-rated USB outlets.

 

[ban-all-sheds]

The product is to be a combined shaver and USB outlet....

 

[Echo the husky]

Just jam an extra isolated winding on the shaver transformer, rectifier, regulator etc, though most shaver sockets are not powered unless a plug is inserted, so a switch on the sockets shutter as well.

 

[ban-all-sheds]

Just jam an extra isolated winding on the shaver transformer

There's already one - why not just a tap?

 

[Echo the husky]

That could defeat the safety if both outlets were used at the same time.

 

[aptsys]

The product is to be a combined shaver and USB outlet....

No problem with that.

 

[bernardgreen]

I am not recommending this test procedure as with some items from dubious sources it could be hazardous

To test a charger is safe.

Stand a tin can on an insulating plate. Fill with salty water. Connect an AC milli-amp meter between the tin can and an Earth (or Ground rod)

Put the charger's phone plug into the water in the tin. Plug the charge into the mains and switch on while standing away from the tin can.

Read now many milli-amps are flowing from tin can to ground.

If possible repeat the test with mains polarity reversed ( as may happen in use when the charger is a two pin device )

More than 5 milli-amps (*) and the charger should be considered potentially hazardous.

note after this test the chargers phone plug will be damaged by salt corrosion

note this method of testing may result in bent needle or fire in the milli-amp meter when a very poor quality charger is tested.

(*) the value of 5 milli-amp is considered by some to be too high for a good charger and 1 milli-amp or less should be used as the safe limit.

 

[John D v2.0]

Interesting idea, but what's the benefit of that over just measuring the current between each of the pins and the cpc using a known resistance in series?

 

[bernardgreen]

what's the benefit of that over just measuring the current between each of the pins

Probably the benefit is ease of connection of test "probes".. Getting to the pins in a USB socket is bad enough. Getting to the pins in the pico-miniature plugs used to charge phones is also impossible with ordinary test probes.

 

[John D v2.0]

True, but if it does destroy the charger in the process, you could just cut the lead and strip the wires. You could even solder/heat shrink it back together afterwards if it passes!

 

[ban-all-sheds]

I wonder what sort of person would be the sort of person who would

a) Actually own a mA meter, and
b) Not start out measuring at a high range setting if they didn't know what the magnitude of the current would be.