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USB charger problem - live cable

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Lee697:
G'day

I bought my son a 240V USB charger at Officeworks yesterday - branded 'comsol'. Model no WCN34BK

Last night he complained he was getting tingling off of the metallic shielding of the USB cord - it is one of the ones from Jaycar with a metallic armour around the cable (childproof!). It was late, so I unplugged it and told him to leave it.

This morning - I plugged it in and measured the voltage from earth (household socket pin) to the shielding - 100V AC.
I did the same with an Apple branded charger we have - earth to shielding - 0V.

Can anyone suggest what is going on?? Cheers....
Lee

sleemanj:
Leakage through the noise suppression capacitor to mains earth.

There should be no current behind it.

Apple supply may have the sheilding connected to earth directly.

Read the first answer here
https://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do

Whales:
EDIT: "Y capacitor" == "noise suppression capacitor" in most power-supply contexts

Two-pin wall plug on it I presume?

Half of mains suggests it could just be Y capacitor tingle.  Can you safely add a 10K resistor between your two DMM probes as you measure that voltage (eg via alligator-leads)?

If that collapses the voltage down to something more sensible: it's a double-insulated design with class Y caps leaking a bit of mains.  Standard design practice, I hate it but it's how they do it.  Lots of topics on this forum about it if you search.

If the voltage doesn't collapse to something more reasonable under the load resistor: suspect it's faulty charger, indeed treat it as unsafe until you know otherwise.

The apple charger may use different size Y caps, a fully-isolated design (EDIT: wrong way around?) or be a 3-pin wall plug.  There are many ways to reduce or eliminate the tingles in such devices, but they all cost more money.

Lee697:
Thanks chaps.... indeed there is no current behind it, else my tongue test might have turned out differently! :O

I'll try the resistor now.....

Lee697:

--- Quote from: Whales on February 01, 2020, 10:27:27 pm ---Two-pin wall plug on it I presume?

Can you safely add a 10K resistor between your two DMM probes as you measure that voltage (eg via alligator-leads)?

If that collapses the voltage down to something more sensible: it's a double-insulated design with class Y caps leaking a bit of mains.  Standard design practice, I hate it but it's how they do it.  Lots of topics on this forum about it if you search.

If the voltage doesn't collapse to something more reasonable under the load resistor: suspect it's faulty charger, indeed treat it as unsafe until you know otherwise.

The apple charger may use different size Y caps, a fully-isolated design (EDIT: wrong way around?) or be a 3-pin wall plug.  There are many ways to reduce or eliminate the tingles in such devices, but they all cost more money.

--- End quote ---

I paralleled a 10K resistor across - voltage dropped from 99V AC to 2V AC.... sounds OK....
Both of these chargers are 2 pin units.....

In any case I might relegate the metallic sleeved cords to the car for the kids..... :)


and thanks again!

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