iPhone chargers. To test or not to test?

[timhoward]

I may owe the OP an apology as I've just observed that an iPhone charger actually appears to have a metallic earth pin (and a class II symbol). Without pulling one apart I don't know the value of IR testing it that end. I like the comment about testing the USB output side.

 

[Lucien Nunes]

Our first positive result for an insulation breakdown between input and output was on a laboratory power supply in a school in the 1990s. The Radford Labpack was a multi-output bench PSU of the 1960s/70s which, although generally well made, had a flaw in the wiring loom construction. Amongst the outputs was a 6.3V 8A floating (not earthed) supply for valve heaters and optical ray lamps, which unlike the other outputs was not separately fused, relying on the mains fuse to protect the transformer. Unfortunately the wiring in the loom was the wrong gauge and could not withstand the short-circuit current for long if this output was shorted by the user, resulting in general insulation damage to the loom. One possible result was the 6.3V wiring melting into contact with the mains line to the fuseholder, making the 6.3V sockets live with mains. As the secondary was floating, it continued working, with the experimental apparatus that students used to connect with bare 4mm plugs all being live with mains on one side and mains +6.3V on the other.

We sent out a warning to all organisations using our testing service, to send all units in for inspection and modification (the manufacturers were no longer in existence.) Dozens of units had insulation damage, although I can't remember how many actually had the output live with mains. I remember the head of the PAT department who might have been the first to discover the problem, having a rather heated conversation with one of the teams whom he suspected of not always testing insulation to PSU outputs. 'Why wouldn't you ******* test them?' was his question.

 

[DPG]

Our first positive result for an insulation breakdown between input and output was on a laboratory power supply in a school in the 1990s. The Radford Labpack was a multi-output bench PSU of the 1960s/70s which, although generally well made, had a flaw in the wiring loom construction. Amongst the outputs was a 6.3V 8A floating (not earthed) supply for valve heaters and optical ray lamps, which unlike the other outputs was not separately fused, relying on the mains fuse to protect the transformer. Unfortunately the wiring in the loom was the wrong gauge and could not withstand the short-circuit current for long if this output was shorted by the user, resulting in general insulation damage to the loom. One possible result was the 6.3V wiring melting into contact with the mains line to the fuseholder, making the 6.3V sockets live with mains. As the secondary was floating, it continued working, with the experimental apparatus that students used to connect with bare 4mm plugs all being live with mains on one side and mains +6.3V on the other.

We sent out a warning to all organisations using our testing service, to send all units in for inspection and modification (the manufacturers were no longer in existence.) Dozens of units had insulation damage, although I can't remember how many actually had the output live with mains. I remember the head of the PAT department who might have been the first to discover the problem, having a rather heated conversation with one of the teams whom he suspected of not always testing insulation to PSU outputs. 'Why wouldn't you ******* test them?' was his question.

I remember the Labpack power supplies well from the physics labs at my secondary school. Lots of different outputs, but absolutely no regulation.

I also remember melting a line right across the bench I was working at once. I had connected a length of wire across one of the outputs ready to create an electromagnet. Teacher not impressed!

 

[marcuswareham]

A few people on YouTube have some videos of them tearing down cheap usb chargers and the like

Alot of the cheaper ones have very poor seperation between mains input and low voltage output, and there have been quite a few reports of the seperation failing and mains voltage being present on the usb, this presents a shock risk & I would thinking the device plugged into it wouldn't be to happy also

So I would say testing that isolation is a good idea, likewise spending a little bit more on chargers

 

[chrisdungan]

I’ve just spent the day testing about 40 iPhone chargers. Sticking 500v through them and they all pass. Does everybody agree that they have to be tested?

What are you ACTUALLY testing with a PAT tester and a charger? like what is there to test??
these types of switched mode powerpacks only have accessible 230v on the inlet pins. All the rest is either inaccessible or ELV output. Yes I've had issues with induced 230v but when you test the output with a low Z voltmeter the 230 disappears. I reckon if you want to be safe ( like in a school for example) have the supply sockets protected with a 10mA RCD.

 

[Lucien Nunes]

What are you ACTUALLY testing with a PAT tester and a charger?

As per @marcuswareham, the rather important insulation between input and output. Some low-cost non-OEM chargers have design and/or construction flaws leading to only the barest minimum of basic insulation. E.g. we have seen units with 1mm PCB track separation, which is an unacceptable creepage distance but it works so they do it. Others rely only on enamelled winding wire on the transformer to achieve separation, the inter-winding taping or ELV secondary over-sleeving having been omitted. Even where the design is sound, in cheap units with poor manufacturing QC there could be any kind of assembly error such as the input pin flylead trapped against an ELV solder joint, or the secondary transformer leadout snagged around a live component.

Genuine OEM chargers are in a different league of quality when new, but can still have drinks poured over them, or get dropped down the stairs...