Hum on speaker and mic when charging on the USB cable.

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jimbob79

673 posts

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#208537 16-Feb-2017 10:11

I got a new changer for my iPhone and I noticed a hum/popping sound when the phone is being changed.

I think that 'noise' was being regenerated by the charger. Would put a 10~100uF smoothing capacitor help reduce this problem?

ubergeeknz

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#1721080 16-Feb-2017 11:01

Probably not a very good charger. Best fix is to use a better charger...

richms

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#1721113 16-Feb-2017 11:35

Firstly check that the charger is actually an approved type, excessive leakage and ripple is usually the result of a crap one that might be highly dangerous.

http://www.businessinsider.com.au/apple-fake-chargers-study-2016-12

If you know someone with a portable appliance tester for doing test and tag, put it on the isolation setting between the input mains pins and the output of it - both the shield of the socket as well as the negative of the USB lead since many do not connect to both, and watch it fail on the 1000v range if its a knock off.

There are some that do pass which just because of the size of them need a really large interference capacitor, and that means lots of leakage current, so really they should be an earthed design but that means needing a more expensive 3 pin cable which they decide not to. I have a 6 port that is like that - passed the 1000v test fine but still has about 500 microamps of leakage thru it.

Richard rich.ms

ubergeeknz

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#1721127 16-Feb-2017 11:50

Yeah, some of those cheapie chargers are dodgy af. I took one apart where the 5v feed was protected from the mains pins ONLY by the insulation of the wires themselves, they were literally pressed against the live mains pins internally when I took it apart. Only a matter of time before one or other side of the 5v feed became live. Scary.

richms

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#1721154 16-Feb-2017 12:15

Its more in the transformer that is the real issue. Bigclivedotcom on youtube has done many teardown on cheap ones that are quite horrifying.

Those wires have actual pvc insulation that is rated to a voltage. Inside the transformer the wires are enamel coated, and they are suposed to not cross when leaving it and have insulating layers between the 2 windings on the mains side and the one on the low voltage side. They often do not. So the only thing stopping you frying is a couple of layers of pretty crap paint that has being flexed around when winding it so will have tiny cracks waiting to open up over time.

Then there is the lack of PCB seperation, hes looked at many where there is sub mm between the sides of the power supply. Ripe for a flashover there. Thing is the flashover doesnt have to start on the mains side. If you are all statically charged up and touch the phone, it can discharge to earth thru the phone, usb cable, across the tiny gaps in the power supply to mains and then earth. Once it does that it may keep arcing with mains coming back over the already established arc into you, holding the metal phone connected to the charger. Will ususally go un noticed since you are clearly not earthed since you had a static charge.

Richard rich.ms

ubergeeknz

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#1721240 16-Feb-2017 13:26

yeah I wish I'd gone deeper on this one, after seeing that I just broke the power pins out and binned it.