SeanB's USB charger transient tests

[joeqsmith]

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:

Joe, just for a lark, can you put a few USB wall warts ( not the cheap ones, but ones from reputable manufacturers, because we all know how the cheap ones will fail anyhow) across your line simulator and see what it takes to kill them. My guess is that almost all of them will fail 2kV, but just how badly they do this, and how much they smoke doing so. Most will probably work fine with your test voltage, being universal input devices. You will just need a sacrificial USB voltage monitor and a resistor to draw 100mA to 500mA out of them during the test. Pretty much how they behave in transient conditions, and what a simple mains transient like a motor disconnect on the same branch circuit will affect them.

I would guess they fall under the generic case and are only required to be tested at 1KV line-to-line.   

Again, that sub 20J I test with is basically nothing.  I don't see it ever causing a meter or other device to explode or put out much for smoke.   Really what you would want to do is run these on a real combo generator if you wanted to see something more like the Fluke multimeter videos where they show the cases coming apart.  This is nothing close to what I have setup.

True, but you do have a good audience, and it will be a good thing to show that cheap and nasty really is that, even with limited energy. I think the saving grace for most products these days is the thin wire they use, which acts as an impromptu fuse when the thing fails short circuit. As the fuse is often the thing "designed" out by the cost cutters, and the wire is also "value optimised" to be as thin as possible and as low grade copper as possible this probably is the only thing keeping the fire rate down.

The transient generator will not put out the transient superimposed on the AC line.  Actually, I can't generate an AC wave with it, only the full rectified 220V.   Assuming you understood this, I am not following your thoughts of having a load and monitoring their outputs.   Could you explain this?     

I had attempted recently to try and understand a trolls comment about me applying a set of capacitors directly across the meters when I test them.  I found the comment very strange as I have shown the open circuit waveforms MANY times.  Anyone with some basic skill would understand that something is causing that decay and it's obviously not the meters.   The meters have a very high input impedance so normally all that energy is actually dissipated internal to the generators output network.  So as long as the meter does not breakdown, there will be very little that happens.   It could be a 10KJ supply and it would make no difference.  This is why you never see me run the half cycle generator unless a meter breaks down with the new generator.  Nothing will happen unless something does breakdown, then we get a little punch.  I had made a video about that generator, basically I was trying to simulate a half cycle of the CAT III 600V environment. 

The chargers on the other hand are not going to be designed for industrial use.  Not that all meters are.  I like Gossen's several comments about me running an industrial meter at 10V/m which is pretty much the industrial standard.  They test at 3 which is what my toaster is rated for.       Anyway, these chargers would not handle a hit from that half cycle generator because again, this is trying to simulate a much higher levels than the chargers are designed for.    Also, the chargers by nature are a low impedance device.  After all we are trying to charge something with them.   So the generator may not put out enough energy to do anything.   It's like this people who post, I connected my Fluke to a 40KV supply and it lived.  Then you try to get them to explain the sources output impedance....    It's an endless supply of humor.

Point of going over all that again is that I am trying to see how you would propose that we actually run these USB supplies using this setup.  I have no problems running a few but want you to think about what it is you are asking.

Load them with 100mA or less, just basically to get some of the less regulated ones not actually providing a 5v output, as I have seen many that will be 6V with no load and then drop with load. You DC source of 220V will be enough hopefully to provide this 0.1W of power to the DUT, and then the single pulse will easily show how they fail at providing creepage and spike resistance. Load could be basically a LED and a series resistor, and then a 68R resistor to get to around that 100mA, though I would hesitate to connect any meter you like to the secondary side, unless it will survive the full test voltage itself, or you have a big supply of those HF free meters to sacrifice on the secondary.

Interesting.  You think these would all run off DC?  Or have you actually tried this with a few of them?   I was thinking some of the lower end ones would not have a transformer in them.    The generator is programmable for the amount of current it can supply. 

I would have no concerns about hooking most of the remaining meters to the output to monitor.  It won't be any worse than what I have put them through!     We could use the 121GW now, well maybe..  That poor meter just does not seem to get treated with the respect it deserves around here and I wonder if Dave understood what his meter was in for when he sent it.   

[joeqsmith]

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.

[joeqsmith]

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.

[joeqsmith]

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. 

[joeqsmith]

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.   

[tautech]

 

[joeqsmith]

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

[tautech]

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

Not 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 ?

[joeqsmith]

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.   

[HKJ]

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

I 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.

[SeanB]

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.

[joeqsmith]

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

I 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.

That'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

[HKJ]

That'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. 

Yes, 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".

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

Is that enough energy to overload the electrolytic capacitors?

[joeqsmith]

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.

I 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.   

[joeqsmith]

Is that enough energy to overload the electrolytic capacitors?

I 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.   

[HKJ]

Is that enough energy to overload the electrolytic capacitors?

I 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.

I 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.

[joeqsmith]

Any sort of common mode choke or X caps? 

[HKJ]

Any sort of common mode choke or X caps?

In many larger chargers both, but they are often missing from small chargers.

[joeqsmith]

Any idea for these chargers, what surge test is required for CE?

[joeqsmith]

Using a knife and small hammer, I was able to crack the glue joint.  Notice the locking ridge in the case design.

[HKJ]

Any idea for these chargers, what surge test is required for CE?

Sorry, but no.

[joeqsmith]

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. 

[joeqsmith]

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.

[joeqsmith]

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.

[joeqsmith]

Showing the open circuit waveform zoomed out.