Hello there,

(See attachment first then video second)

There are rules set for making wall warts that force them to adhere to certain safety standards. Apparently some companies do not follow the rules and make seriously dangerous wall warts that are used for various things including charging cell phones.

One of the main requirements is physical isolation of the primary and secondary coils. In the older simple non regulated wall warts this had to be two coils separated on the core not one coil wrapped on top of the other even if there was tape between the layers. This would mean more or less wrapping one coil on one side of the core and the other coil on the other side of the core. See the example in the attachment.

Now that we have progressed into the regulated type wall warts i wonder if this has changed or something because of the high frequency transformer where a regular line frequency transformer used to be used.


Dangerous USB phone chargers 14 (a 4-port 3A charger with a switch) - YouTube

 

From a 2020 article in the Bangkok Herald:


https://bangkokherald.com/thailand/...oi-et-girl-10th-thai-electrocuted-since-2019/

 

From a 2020 article in the Bangkok Herald:
View attachment 282313

https://bangkokherald.com/thailand/...oi-et-girl-10th-thai-electrocuted-since-2019/

Hi,

Yes i have heard of that before too it's very sad that they can let something like this happen in the modern age we think we are in.
It's cave man era all over again if they dont live up to the safety standards.

I posted a couple problems i have come across earlier but there are others too such as not fusing the input at all.

 

This discussion brings to mind a BBC programme.

 

This is why authentic UL markings and listings are so important on a device.

 

...if you can really count on the marking being real licensed markings. I have seen cheap products made in a certain Asian country with every safety mark I have every seen - on one product! Printing is cheap.

 

This discussion brings to mind a BBC programme.

Hi,

Nice sunglasses

Yeah i am starting to think (see post after yours too) that the only way to be absolutely sure is to buy two and do a complete tear-down and complete analysis. I never thought about this too much before seeing that video i posted. I knew a lot about the safety standards i used to work in that industry, but didnt realize that companies could cheat too and without realizing it make the product prone to isolation failure.

Now i wonder if any of mine are dangerous. What we need is a non destructive test but that may not be possible. I have too many too it would take a year to take every one of them apart and analyze the construction in detail like he did in that video i posted.

 

...if you can really count on the marking being real licensed markings. I have seen cheap products made in a certain Asian country with every safety mark I have every seen - on one product! Printing is cheap.

Hi,

Yes so true, but what can we do about it. We cant take every one apart. I know of no non destructive test either.

Maybe what we need is an isolation transformer to plug all our wall warts into that way we get isolation for sure.

 

I use some of those cheap 5V wall warts with USB connectors and I often test the AC ground leakage current between one of the output pins and earth by connecting a 1k resistor from the output to earth by noting the AC voltage across the resistor, and if I get more than a couple milliamps (hasn't happened on these yet) the wall wart goes into the trash.

 

I use some of those cheap 5V wall warts with USB connectors and I often test the AC ground leakage current between one of the output pins and earth by connecting a 1k resistor from the output to earth by noting the AC voltage across the resistor, and if I get more than a couple milliamps (hasn't happened on these yet) the wall wart goes into the trash.

Hi,

That sounds like a good idea, but after that video i may start looking for a reasonably priced isolation transformer. It doesnt have to be very high power for a few wall warts or the regular size and output.

 

Travel transformers, like you might plug an electric razor into are pretty inexpensive, but I wonder how many have their windings isolated from one-another.

 

I use some of those cheap 5V wall warts with USB connectors and I often test the AC ground leakage current between one of the output pins and earth by connecting a 1k resistor from the output to earth by noting the AC voltage across the resistor, and if I get more than a couple milliamps (hasn't happened on these yet) the wall wart goes into the trash.

You inspire me to come up with a simplified test rig for a tester. An outlet to plug the power supply into and a USB cable to plug into the supply. It would be easy to check mains isolation but are there some other tests worth doing? If I incorporate a megger into it, I could check HV isolation as will, I suppose. It doesn’t have to be laboratory-accurate, just thresholdy…

It‘s an interesting project to ponder.

 

Travel transformers, like you might plug an electric razor into are pretty inexpensive, but I wonder how many have their windings isolated from one-another.

Yes i wondered that too, plus the ones i see are not just isolation anyway they either step up 120 to 230 or 230 down to 120 and some that go 120 to 100 or 100 to 120v. So not sure i could use one of those anyway.

 

You inspire me to come up with a simplified test rig for a tester. An outlet to plug the power supply into and a USB cable to plug into the supply. It would be easy to check mains isolation but are there some other tests worth doing? If I incorporate a megger into it, I could check HV isolation as will, I suppose. It doesn’t have to be laboratory-accurate, just thresholdy…

It‘s an interesting project to ponder.

Hello there,

I considered an electrical test too and came to the conclusion that it would be hard to test or something like two traces that were risky being too close together for the voltage they are supposed to keep apart and also for some slight unnoticeable damage.
To me that spells physical inspection. Inspection of the circuit board at least and might be hard to tell how well the transformer achieves the required isolation too. Maybe a megger would work but not sure if it would damage the circuit components.

 

Hello there,

I considered an electrical test too and came to the conclusion that it would be hard to test or something like two traces that were risky being too close together for the voltage they are supposed to keep apart and also for some slight unnoticeable damage.
To me that spells physical inspection. Inspection of the circuit board at least and might be hard to tell how well the transformer achieves the required isolation too. Maybe a megger would work but not sure if it would damage the circuit components.

Actually that’s that the megger part is for. Put a few thousand volts through it and if there‘s a problem you will know.

 

Actually that’s that the megger part is for. Put a few thousand volts through it and if there‘s a problem you will know.

Hi,

That wont damage any parts? If not it could work, but will it detect traces 1mm apart instead of 1.5mm apart.

 

But if it fails the test you probably don’t want to use the charger anyway.

 

Hi,

That wont damage any parts? If not it could work, but will it detect traces 1mm apart instead of 1.5mm apart.

A Megger (megohm meter) or it's fancy cousin an insulation tester uses high voltage at low current to check for insulation breakdown. This would include tracking between traces. There are automatic testers for mains isolation as well.

 

Hello there,

(See attachment first then video second)

There are rules set for making wall warts that force them to adhere to certain safety standards. Apparently some companies do not follow the rules and make seriously dangerous wall warts that are used for various things including charging cell phones.

One of the main requirements is physical isolation of the primary and secondary coils. In the older simple non regulated wall warts this had to be two coils separated on the core not one coil wrapped on top of the other even if there was tape between the layers. This would mean more or less wrapping one coil on one side of the core and the other coil on the other side of the core. See the example in the attachment.

Now that we have progressed into the regulated type wall warts i wonder if this has changed or something because of the high frequency transformer where a regular line frequency transformer used to be used.


Dangerous USB phone chargers 14 (a 4-port 3A charger with a switch) - YouTube

Just adding this for general edification for the curious- not a comment on what you stated (which is correct).

Some companies don't want to pay the fees require by places like UL Labs (for USA products, 'CE' for European, etc), for testing- because they don't understand the value of what UL Labs does- UL Labs, and companies like them, for a fee, test a product in as many ways as possible to break them, and once they put their lable/seal on the product as 'SAFE' it means _they_ assume liability for the product- because it is considered 'SAFE' in terms of insurance liability, and hopefully actually safe to consumers.

 

A Megger (megohm meter) or it's fancy cousin an insulation tester uses high voltage at low current to check for insulation breakdown. This would include tracking between traces. There are automatic testers for mains isolation as well.

Hello again,

Well my understanding is that it is not really just about testing the unit *as is* it is also testing to see if when it is damaged in certain ways would it still pass the tests. The only way to get that info is to examine the physical build of the unit under test, or to be the one that designed it in the first place.

The best practice used to be to put two coils on the same core but have them physically isolated from each other, not wound on top of each other with just tape. Im not sure we could detect that from an electrical test from an external connection to the unit under test. I would think a tear down is the only way.
For example, there could be two traces that are separated by 1/4 inch, one a low voltage 5v output, and the other a 230vac input. No problem there until we look at the mounting of a metal bracket right over top of the two traces 1/2 inch above. If the unit under test is compressed it may cause a short, or if the bracket is mounted with just glue or some cheap rivets we would not be able to detect that from the outside of the unit under test.

Certainly a hi pot test is better than nothing of course

My vote is for a separate isolation transformer to plug the wall warts into, but that would have to be well specified and possibly tested too