EEVblog #1035 - Flaming DIY Power Supply

[Kleinstein]

...
I suggest it's time Dave pull out his FLIR camera, power up that failed supply board briefly (maybe outside to avoid the stench?) and really see what's getting hot... and perhaps that will lead to more clues as to the real failure cause.  There might be something that failed FIRST upstream of that cap?  Or maybe the failed cap caused a second failure??  Let's take a look!

It is hard to imagine a failure mode of a buck converter, that can damage the ceramic cap at the output. The more likely sequence is the damaged cap causing secondary faults.

With the cap failing in a kind or arc, there is a chance to cause damage from high AC amplitude. Also the input supply going into current limit and dropping in voltage might not be that kind to some circuit parts. Finally it could be just the high power / current at the output causing trouble (the problem with exaggerated current rating).

[Fungus]

"Nice", and i was planning on getting one from them. After this i think i wait with the purchase until Dave finds out what the hack is happened...

Seems simple enough: A bad capacitor.

The lower power versions apparently don't have a capacitor there.

[bitwelder]

Have ben any response from the manufacturer?

Look at the Youtube comments by 'RD Tech'. They seem to have reacted rather quickly, admitting the design problem and working on a solution.

[MisterDiodes]

...
I suggest it's time Dave pull out his FLIR camera, power up that failed supply board briefly (maybe outside to avoid the stench?) and really see what's getting hot... and perhaps that will lead to more clues as to the real failure cause.  There might be something that failed FIRST upstream of that cap?  Or maybe the failed cap caused a second failure??  Let's take a look!

It is hard to imagine a failure mode of a buck converter, that can damage the ceramic cap at the output. The more likely sequence is the damaged cap causing secondary faults.

Quite likely but it never hurts to verify the failure cause and not just assume it was the cap failing first.  I've seen this happen before with un-expected causes, especially on these apparently very efficient smps converters.  Depending on the exact design, sometimes if they are using active mode flybacks that are under-rated, then at higher input voltages the thing starts outputting higher current / high voltage spike AC when an active mode flyback switch fails partially shorted - and it starts taking out even properly de-rated caps downstream.   Or other failures where the board assembly house accidentally installs series 1k resistors on the switch gate drive circuits instead of 10 ohm (That gets exciting when the whole board goes up in smoke at power up), etc.   Ask me how I know these real world failures can and do happen. 

Or it's just the cap, (I agree is likely), but now you still want to know exactly why the second (or more failures) happened.  Yes, Dave didn't really clean the charcoal resistor from the output, but the power supply was drawing too much current even with the output switched off (I think).  So that's not it.

In any case: since that cap is sitting right on the output, then the exact failure should be investigated to confirm it was the cap that failed first, and then what caused other failure/s?.  Dave's got the toys to play with, right?  That flaming cap could just as easily have been on the user's circuit side, and you'd try to design the product so that's it's not prone to cascading failure events.  In other words you'd like the power supply board not to die every time someone tries to power up some maybe mis-wired prototype circuit.  Maybe the user's under-rated cap blows up but you don't want the power supply to die with the cap.  That's what we're aiming for, at least in spirit.

Besides, it's fun to see the FLiR in action!  This would be a good excuse to drag it out and have some fun, that's all   Every failure is a teaching moment.

Otherwise this power supply seems to be just another example of "you get what you pay for". 

[Cerebus]

Yes, Dave didn't really clean the charcoal resistor from the output, but the power supply was drawing too much current even with the output switched off (I think).  So that's not it.

Just went back to the video to check. It was showing all zeroes with the output off, and drawing 1.9W quiescent power. All depends if, like some supplies, it monitors the output V & I even when it is nominally off, or whether it just always zeroes the display when the outputs are off.

One of the advantages of old supplies with analogue meters is that many of them still tell you the truth about the voltage at the terminals even when the supply is off and unplugged from the wall. Score one for old school.

[John Coloccia]

FWIW, and IMHO, the photoshopped click-bait previews that have been showing up lately are unbecoming of a serious channel.

Carry on.

[Cerebus]

FWIW, and IMHO, the photoshopped click-bait previews that have been showing up lately are unbecoming of a serious channel.

I suspect that Dave will just say it's a cost of doing business on YouTube, you have to stand out enough to get the initial attention. It's YouTube, not Electronics Weekly, The Journal of the Institute of Physics or The Economist. I can't say that I like it, but I understand why Dave might feel he needs to do it.

[innkeeper]

I'm betting on that PCB being charred enough between the output terminals that it's now looking more like a smallish resistor than the highly insulating FR-4 that it once was.

in my experience that is exactly what happens on severely chard boards i'm sure dave would ahve thought of that if it wasn't so late in the evening.
Maybe dave will do a quick resistance check between and posts the result.

i recently repaired a power supply on a peace of audio gear and had this exact  issue with the chard area being only a few ohms even after diligent cleaning / scraping.  I  had to wire around that part of the board isolating it. thankfully it didn't short between layers or id probably needed to cut that part of the board out

[jonovid]

its like loose wheel nuts on a Chinese car. your supposed to check them before use. 
its the old find the fault, hidden in plain sight game. 
Dave needs a Laff box on the show. you know  Canned laughter- audience in a box, lots of FX bottons LOL!
you know make one!  your an electronics engineer. 

[Cerebus]

I'm betting on that PCB being charred enough between the output terminals that it's now looking more like a smallish resistor than the highly insulating FR-4 that it once was.

That was my first thought, as well... 

Dave, why didn't you check the resistance between those terminals in the charred area before you powered it up?  I would expect that area to have issues after the cap blew up.  Alternatively, if you did check and it seemed to be OK, why didn't you mention that in the video?

Well, Dave's done a follow-up video and indeed there was a low resistance (~50R) between the output terminals via the charred board.

So, I called it right! My reward is going to be sitting here for the next five minutes looking as smug as a cat, and that's pretty smug.

[Freelander]

FWIW, and IMHO, the photoshopped click-bait previews that have been showing up lately are unbecoming of a serious channel.

I suspect that Dave will just say it's a cost of doing business on YouTube, you have to stand out enough to get the initial attention. It's YouTube, not Electronics Weekly, The Journal of the Institute of Physics or The Economist. I can't say that I like it, but I understand why Dave might feel he needs to do it.

I actually think it is quite sad IF 'Dave feels he needs to do it'
It's his channel at the end of the day. However, channels with an order of magnitude more subscribers do not feel the need to resort to such  actions in any way. Hell, A bit of tongue in cheek is one thing, but creating a completely false image and impression of a product from a fair , honest and respected manufacturer is not really appropriate imho. If a product has a problem by all means it has to be reported fairly. If it is cr&p then absolutely say it is cr&p, but fake images ?  IMHO they are uncalled for and derogatory and are certainly not the best way to promote anything.
Meanwhile ... back at the ranch... life continues..

[metrologist]

I imagine that such flames as depicted in the video thumb are not outside the realm of possibility, given the subject failure.

[Kleinstein]

The MLCCs don't have much flammable material inside. The smoke an charring is more from electric heat and the FR4 board. So with a less powerful supply the damage would be much smaller.

To get nice flames an old tantalum cap or Li based battery are more suitable. Some film caps can also cause quite a firework at sufficient voltage.

[Mr. Scram]

I actually think it is quite sad IF 'Dave feels he needs to do it'
It's his channel at the end of the day. However, channels with an order of magnitude more subscribers do not feel the need to resort to such  actions in any way. Hell, A bit of tongue in cheek is one thing, but creating a completely false image and impression of a product from a fair , honest and respected manufacturer is not really appropriate imho. If a product has a problem by all means it has to be reported fairly. If it is cr&p then absolutely say it is cr&p, but fake images ?  IMHO they are uncalled for and derogatory and are certainly not the best way to promote anything.
Meanwhile ... back at the ranch... life continues..

Linustechtips had this exact discussion a few months ago. Apparently, these thumbnails do make a significant difference in regards to popularity. Whether we like or not, unfortunately.

I can imagine it may be perceived as disingenuous or unfair towards the manufacturer.

[Brumby]

I imagine that such flames as depicted in the video thumb are not outside the realm of possibility, given the subject failure.

My thoughts follow on a similar line.

If Dave were to have portrayed destruction like the Great Chicago Fire, then it certainly would have been out of bounds.  However, by adding some fire to a thumbnail, the worst I could criticise him for is being melodramatic.

I will admit I was a little disappointed when we didn't get to see real flame in the video, but then the case wasn't open at the critical moment.  When the damaged PCB was shown, I was well and truly forgiving of the thumbnail image.  There was some serious heat created - and actual flame involvement did not seem too far fetched at all.

[NivagSwerdna]

I'm going to ask a dumb question...

Why would you want a power supply that needs a power supply to work?  Where are you meant to get the 55V DC required to smoke it if you don't have a PSU to start with?

Aso... Isn't Isolation important?  Otherwise you can fry yourself and your stuff with Ground Loops?

[ChrisLX200]

For myself I have a few (more than a few..) wall warts lying around, some quite decent @ 24V/4A. These units make it easy to produce a CC/CV output with a neat interface. Slight problem that the output is a bit noisy but it does free up a channel on the main bench PSU.

[Fungus]

Why would you want a power supply that needs a power supply to work?

Because you can use a cheapo, leftover, fixed voltage supply. eg. an old laptop power brick.

[Cerebus]

I'm going to ask a dumb question...

Why would you want a power supply that needs a power supply to work?  Where are you meant to get the 55V DC required to smoke it if you don't have a PSU to start with?

There are lots of very cheap new off-line switch mode power bricks available. There are also a lot of surplus 48V nominal telecom power supplies available on the second user market, often the real output is higher than the nominal 48V. Plus one might just have something salvaged lying about - if I see a big industrial DC power supply in a dumpster I am so taking it home with me even if I don't yet have a use for it  ("Yes, dear it is large, but so is your shoe collection and, it's a bargain, it's free.").

Aso... Isn't Isolation important?  Otherwise you can fry yourself and your stuff with Ground Loops?

Naturally you're relying on the primary, off-line, supply to provide isolation and to be floating.

[jonovid]

i have considered buying the same power supply module my self. as I like cool color panel displays with lots of graphics in a kit.
however i do not believe it rated at 50 volts IMO that's way too high for cheap chinese Silicon!
also if they say its 4 amps I do not believe it! as the probability its more like 2 amps max.
take a good look at its cooling! do you believe its wattage. do the thermal test.
derate, derate if its cheap & chinese.
a suggestion, if you can have lights ,& camera rolling whan ever you plug somthing in, or power somthing up,
particularly if its old, or cheap & chinese. getting it all on camera, is priceless 

[NivagSwerdna]

Because you can use a cheapo, leftover, fixed voltage supply. eg. an old laptop power brick.

Hm.  I can see people doing that but isn't that really far from ideal from a bench PSU... maybe cheapo bench supplies aren't isolated?

[Freelander]

Linustechtips had this exact discussion a few months ago. Apparently, these thumbnails do make a significant difference in regards to popularity. Whether we like or not, unfortunately.

I can imagine it may be perceived as disingenuous or unfair towards the manufacturer.

Fair point but I think Linus's original objectors to his new leader image format was more of the fact that it had changed to a more 'colourful' format that some saw as a bit 'gimmicky'. I actually like the new LTT format I Must confess. The difference is though, as you allude to also, is that I have never seen an LTT leader image that distorts the issue in such a definite way. All I see with linus are some jaunty images and a lot of 'XYZ' headers with question marks at the end. Very tame.
Oh, I must add - re LTT, Max the camera girl is fit as &^%$    .. great viewing but mostly behind the camera - sob sob..............

[Cerebus]

i have considered buying the same power supply module my self. as I like cool color panel displays with lots of graphics in a kit.
however i do not believe it rated at 50 volts IMO that's way too high for cheap chinese Silicon!
also if they say its 4 amps I do not believe it! as the probability its more like 2 amps max.
take a good look at its cooling! do you believe its wattage. do the thermal test.
derate, derate if its cheap & chinese.
a suggestion, if you can have lights ,& camera rolling whan ever you plug somthing in, or power somthing up,
particularly if its old, or cheap & chinese. getting it all on camera, is priceless 

Have you not watched Dave's Vid on the smaller modules from the same supplier? They also have what seem like overinflated specs but when Dave characterised one it actually met the specs with very respectable dissipation and efficiency.

[jonovid]

i have considered buying the same power supply module my self. as I like cool color panel displays with lots of graphics in a kit.
however i do not believe it rated at 50 volts IMO that's way too high for cheap chinese Silicon!
also if they say its 4 amps I do not believe it! as the probability its more like 2 amps max.
take a good look at its cooling! do you believe its wattage. do the thermal test.
derate, derate if its cheap & chinese.
a suggestion, if you can have lights ,& camera rolling whan ever you plug somthing in, or power somthing up,
particularly if its old, or cheap & chinese. getting it all on camera, is priceless 

Have you not watched Dave's Vid on the smaller modules from the same supplier? They also have what seem like overinflated specs but when Dave characterised one it actually met the specs with very respectable dissipation and efficiency.

I must take the time to read all text before posting!  and yes I have considered buying the same power supply module my self when all the bug's r out.

[Clear as mud]

FWIW, and IMHO, the photoshopped click-bait previews that have been showing up lately are unbecoming of a serious channel.

I agree.  I see that sort of stuff on videos like "Biggest Airplane in the World!" and the preview shows some fake aircraft with about 24 engines, which is not to be found anywhere in the video.  It makes me mad and I am not likely to click on anything from that channel again, if I remember who it was.

I didn't mind the fake gold coins on the April Fool's joke video, partly because it was obviously fake - I even thought it was just big french fries at first, and didn't realize it was supposed to be gold until after I watched the video - but actual flames coming from a device with the title "Flaming Power Supply" is the sort of stuff that makes me not want to watch the channel anymore, if that picture is not an actual excerpt from the video.  I'll keep watching, because it's EEVblog and I know Dave has good content, but if that was the first video I had ever watched from EEVblog, I probably would be put off from watching the channel again.