SeanB's USB charger transient tests - Page 1
Forum section: electronics / testgear

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:15:21 am
content: SeanB had asked me about running some low cost AC USB chargers on the transient generator that I built to evaluate multimeters. It really has nothing to do with the meters so it gets it's own thread. Below is the jist:Quote from: joeqsmith on July 01, 2017, 05:19:47 pmQuote from: joeqsmith on July 02, 2017, 01:44:00 am

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:28:56 am
content: This was the cheapest charger from the local food store. Just two dollars... They claim UL and can supply 1A. I checked this one with no load (except for the meter) and it appears to be a nice clean 4.999 volts DC. I think I will run it at an amp.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:30:33 am
content: Looking at the charger, they show it being able to run from a 240V supply, 50/60Hz. No mention of DC. I guess the first thing is to make some sort of load.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:32:33 am
content: So for 1A at 5V we need a 5W 5 ohm resistor. A small 12V fan should be more than enough to cool it. Looks like it draws about the right current.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:34:17 am
content: Some electrical tape to hold it all together, 10 minute load... The added jacks are for the meter to monitor the voltage across the load.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:42:36 am
content: The only thing to do now is see if the unit will run from DC. Seems to work just fine.If you are really interested in looking at chargers for some strange reason, have a look at the following thread. I think SeanB's goal was just to see how much it would take to kill one.http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html

author: tautech
author_rank: Super Contributor
timestamp: July 02, 2017, 03:51:20 am
content: Quote from: joeqsmith on July 02, 2017, 03:42:36 amNot sure about that Joe.I took him to mean what transients they could withstand and if a transient damaged them what would be the consequences for the the gadget they were charging.SMPS walwarts are so common these days and it would be good to know the most robust brands for the safety of the gadgets they charge. Also there's old-school linear ones too, would they be better or worse at catching/suppressing transients ?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 04:22:05 am
content: Assuming he understood what I wrote about the generator, I doubt he would be looking for much beyond wanting to know what it would take to kill one. As I mentioned, because of the generators design it may do nothing. It was never my intent to design a generator to simulate a surge condition. With the UL rating, I assume they tested these already on a combo generator. If there were problems, they would not be approved. I am still thinking 1KV would have been the standard. Sort of like buying a handheld meter. Would you trust your $1000 cell phone on an uncertified charger? Sort of like buying a UNI-T meter and using it in a CATIII 600V environment. No thanks....As I mention as well, the half cycle generator is not made to simulate a 220 bus. I can pretty much promise that any 220V USB charger would have a major failure.In the end I see it as a pointless test because we are not using the right tool. At best, even if it lives, we give it the half cycle hit and maybe get some sparks out of the deal. Hard to say. Which is why I was trying to get SeanB to give it some thought.

author: HKJ
author_rank: Super Contributor
timestamp: July 02, 2017, 06:31:03 am
content: Quote from: joeqsmith on July 02, 2017, 03:42:36 amI have tested more than 100 usb chargers:http://lygte-info.dk/info/ChargerIndex%20UK.html(The first couple of chargers in one article, after that each gets its own article with more tests).All tests includes a few kV between mains and low volt side. There is also a tear down.

author: SeanB
author_rank: Super Contributor
timestamp: July 02, 2017, 07:35:45 am
content: Any small wall wart with an input range of 100-240VAC is going to be SMPS, and they all will work on 220VDC for sure. Only linear wall warts I have seen in the last decade were Siemens early Gigaset ones, which have a moulded transformer, and a 9VAC output, with a input voltage of 220VAC.But all from the last decade have been a SMPS, even in the cheapest nastiest nastiest emergency light, where there are some enterprising manufacturers who made a retrofit board with the same footprint as your common Chinese 9VAC 1A ( peak, on a good day, for a few minutes, with a DC resistance of around 20R on the secondary and around 10k on the primary, so ultra poor regulation figures but actually short circuit proof not by design, and with no thermal fuse in the windings either in most cases) transformer that is a SMPS, that I would not use if there is any regard you have for it actually being safe to touch the secondary side.Those are not the things to test, they pretty much are going to either fail with only minor transients, or just blow up on their own, but the better branded ones you might have lying around in a drawer that are listed and purported to pass a safety standard are the ones to see. Cheapies are only fun if you find that single example that was slipped through by accident as being great, and which will survive an actual IEC test pulse train undamaged.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 02:35:33 pm
content: Quote from: HKJ on July 02, 2017, 06:31:03 amThat's a lot of work. Saw your link that shows the tools. As your site and you mention, the kV test you are doing is for insulation. I think what SeanB is interested in was the line to line test.My generator will hardly produce enough energy to light a standard bulb. I came up with it for the specific purpose of evaluating multi-meters and it does not follow the IEC standards.https://youtu.be/1wD7Q1N1XY4?list=PLZSS2ajxhiQBI0El63arJXQwrvsvaRaDT&t=424

author: HKJ
author_rank: Super Contributor
timestamp: July 02, 2017, 02:45:37 pm
content: Quote from: joeqsmith on July 02, 2017, 02:35:33 pmYes, I test insulation and it sounds like it was line transients that SeanB wanted.My list of tools is not up to date, all tests where I specify 4242 volt I am using a real insulation tester and not a "megger".Quote from: joeqsmith on July 02, 2017, 02:35:33 pmIs that enough energy to overload the electrolytic capacitors?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:00:34 pm
content: Quote from: SeanB on July 02, 2017, 07:35:45 amI don't just have USB chargers laying around in a drawer. I would need to purchase them, like the one shown. Before we go through the trouble and wasted time, I am just trying to understand what your goals are. I can tell you that there will be no great explosions. Again, a light bulb is a very low impedance device and you see what it does to them.I can see a lot of confusion from running it. Say I turn up the generator all the way and the device survives. You will have people thinking, look, that charger survived 5KV. Really what may happen is the voltage only reaches 1KV because the energy is so low and the charger has a fairly low impedance.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:07:47 pm
content: Quote from: HKJ on July 02, 2017, 02:45:37 pmI assume you are asking about the capacitors used inside the charger? The di/dt ratings of the capacitors used in the generator are rated to handle the output of the generator connected to a short.The ones inside the charger may be protected by some sort of clamp or fuse. Hard to say without running one. Have you looked at the charger I show in the above pictures? I did not want to cut it apart just yet.

author: HKJ
author_rank: Super Contributor
timestamp: July 02, 2017, 03:14:44 pm
content: Quote from: joeqsmith on July 02, 2017, 03:07:47 pmI have not looked at that charger.Small chargers either use a fusible resistor or a real fuse (Except the cheap Chinese ones). They very seldom have MOV's.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:32:17 pm
content: Any sort of common mode choke or X caps?

author: HKJ
author_rank: Super Contributor
timestamp: July 02, 2017, 03:36:14 pm
content: Quote from: joeqsmith on July 02, 2017, 03:32:17 pmIn many larger chargers both, but they are often missing from small chargers.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 03:41:50 pm
content: Any idea for these chargers, what surge test is required for CE?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 04:25:40 pm
content: Using a knife and small hammer, I was able to crack the glue joint. Notice the locking ridge in the case design.

author: HKJ
author_rank: Super Contributor
timestamp: July 02, 2017, 04:29:15 pm
content: Quote from: joeqsmith on July 02, 2017, 03:41:50 pmSorry, but no.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 04:47:15 pm
content: Looks like 400V caps, fuse is covered, some slots to increase the clearance. Even a plastic insert for a barrier.My guess at most I would pop a fuse. I assume with the IEC standard with regards to surge testing, they are allowed to pop the fuse. The caps will surely limit the voltage seen at the inputs until the fuse opens up.Again, this was the cheapest thing I saw at the store. Basically five volts with no load and fully loaded dropping a 200mV. It's just a charger, not an HP bench supply. Two bucks, UL rated. Seems alright.One thing I did not see was any sort of step response or stability tests. Again, being a charger maybe you don't care. Maybe we could look at how stable the output is with a step on the input? The insulation tester is not going to tell you much about how it couples AC.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 05:32:32 pm
content: Here is the setup. Gave the charger several 1KV transients with this arrangement. There was no coupling from the input to the output and the fuse handled it just fine.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 06:32:49 pm
content: For CAT II, IEC would require a 12 ohm source which I have gone ahead and changed to. In the first plots you can see the 50mV is actually 5V/division and it looking across the load. The 500V/division is obviously the full rectified AC source.The second plots are looking at a 1.2KV transient. Again, I turn off the AC line when the transient is applied. This is why there is no 5V. Normally for the real IEC tests, you have to fire the surge pulse synchronous to the line. Both +/- at 0, 90, 180, 270 degrees. Again, this is a fairly light test. I can believe this part was actually tested and certified assuming they run them at 1KV.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 06:35:53 pm
content: Showing the open circuit waveform zoomed out.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 07:05:17 pm
content: 2.5, 3, 4 and 5KV. Notice the output seems fine. Again, this generator can not put out very energy.We can see the load it really having an effect on the decay time. I am sure if someone was smart enough to think I was directly coupling capacitors into the meters when I test them, someone else equally as smart is going to somehow think this has something to do with the real IEC surge test, even if I say it's not even in the ball park. Those meters you see on Fluke and Gossen's websites don't explode for lack of energy.So I'm not sure what we learned from this or even if this was SeanB's goal.About the only other thing I could do is apply a transient from the half cycle line simulator. Originally when I started working on that design, it would have been a decent setup for this test as I was targeting a typical house wiring at the junction box. But things evolve. So if you want to see it, I'll get the high speed camera out.

author: SeanB
author_rank: Super Contributor
timestamp: July 02, 2017, 08:01:26 pm
content: Thanks Joe, but not needed, I was interested to see that a device, with a UL marking, that cost $2 retail, could actually be made to survive the pulses that have killed some of the meters you tested. I guess that the meters are less dangerous though, in that they are not an item that is nearly always plugged in to the power line and expected to survive all the hash coming down.Thank you for at least entertaining the idea though, and for doing the test. I was interested in seeing that the transformer insulation was capable of handling the pulses without breakdown, which seems to be the most common failure of these chargers, demonstrated by the few examples of people being electrocuted by them during use of the attached phone during charging.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 02, 2017, 09:42:06 pm
content: Quote from: SeanB on July 02, 2017, 08:01:26 pmI would say the meters are potentially MUCH more dangerous than a USB charger than plugs into a wall outlet. First, we are talking about a CAT II environment versus who knows what. You can pretty much be sure the charger is never going to be attached to a 480 bus. Transients in CAT II may have much lower voltage, energy than CAT III. Most people don't hold the wall chargers in their hand while they are using them. Wall chargers don't have leads attached to them. The education needed to use a charger safely versus a multimeter is much less. How many people do you see post, I hooked my meter to the output of a MOT... Have you ever seen someone post the same thing for a charger? List goes on...For the insulation breakdown what HKJ is doing with the insulation tester looking between primary and secondary would be more appropriate than a surge test anyway.And again, to be clear, my generator's energy levels are much less than what you could potentially see on an AC line, even in a CAT II enviroment. You can't compare the two, although I am sure there are people out there who feel you can. It gets back to that was never a goal. If I wanted to run real line transient tests, I would have a combo generator sitting here with a blast containment setup. This is the same reason I can't look at your power strips or any other AC device like this. You think people cry foul about the testing I do now, imagine if they saw all these perfectly good meters coming apart at the seams!I know there is a lot of confusion surrounding the meter testing I do. I've shown open circuit waveforms, light bulbs, charging capacitors to the same energy levels and discharging them to a metal plate. Maybe this test will help a few more people understand about what is going on or it will just add to the confusion.Can I interest you in a slightly used AC USB charger?