EEVblog Electronics Community Forum
EEVblog => EEVblog Specific => Topic started by: EEVblog on November 03, 2017, 12:44:56 am
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Smoke in the EEVblog Lab!
What component failed and caught alight in the RD Tech DPS5020 Power Supply Module?
This was supposed to be a build video and review until it caught on fire!
https://www.aliexpress.com/store/product/RD-DP-and-DPS-Power-Supply-communiaction-housing-Constant-Voltage-current-casing-digital-control-buck-converter/923042_1000004752402.html (https://www.aliexpress.com/store/product/RD-DP-and-DPS-Power-Supply-communiaction-housing-Constant-Voltage-current-casing-digital-control-buck-converter/923042_1000004752402.html)
https://www.aliexpress.com/store/product/RD-DPS5015-Constant-Voltage-current-Step-down-Programmable-digital-Power-Supply-buck-Voltage-converter-color-LCD/923042_32702714880.html (https://www.aliexpress.com/store/product/RD-DPS5015-Constant-Voltage-current-Step-down-Programmable-digital-Power-Supply-buck-Voltage-converter-color-LCD/923042_32702714880.html)
https://www.youtube.com/watch?v=Q2rvAoO-MIA (https://www.youtube.com/watch?v=Q2rvAoO-MIA)
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(https://www.eevblog.com/forum/blog/eevblog-1035-flaming-diy-power-supply/?action=dlattach;attach=366721;image)
I think I would like to see some follow up from the producer before I jump in.
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The way that cap was soldered in between of 2 terminals, means a lot of mechanical stress. Even more stress happened when wires were screwed to those terminals. MLCCs are very susceptible to mechanical stress and microcracks may happen causing leakage and shorts. As of lower voltage specified part, MLCCs are very tolerant to overvoltage and usually survive even 5x times above their spec. So this unlikely to be an issue.
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I actually as example can say about one MLCC on Raspberry pi 2 and 3 failing short or heavily leaking. It always the same C97 cap nearby to mounting hole even though there are multiple of the same type capacitors on the same power rail.
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This big issue aside, these units are interesting, especially the slightly cheaper lower current ones. But once you add the case, plus a powerful enough power supply input, you can probably get some entry level complete power supply units for the cost.
Of course, if you already have a powerful input supply and possibly a case, and just need a converter, it's probably a good deal. Well, if it's more reliable than this unit in the video.
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The way that cap was soldered in between of 2 terminals, means a lot of mechanical stress. Even more stress happened when wires were screwed to those terminals. MLCCs are very susceptible to mechanical stress and microcracks may happen causing leakage and shorts. As of lower voltage specified part, MLCCs are very tolerant to overvoltage and usually survive even 5x times above their spec. So this unlikely to be an issue.
I'm not sure I'd agree with MLCCs being tolerant of sustained over voltage, they handle transients and high peak voltages for short periods (minutes etc) but the reliability of them plummets at higher voltage. In this example with Dave's power supply thats probably not coming into it as the device wasn't running for significant periods of time and your suggestion of mechanical stress is a strong contender for the failure mode. There are some good manufacturer application notes on how to align and stress relieve parts on PCBs using slots or other parts to control where the strain occurs.
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The way that cap was soldered in between of 2 terminals, means a lot of mechanical stress. Even more stress happened when wires were screwed to those terminals. MLCCs are very susceptible to mechanical stress and microcracks may happen causing leakage and shorts. As of lower voltage specified part, MLCCs are very tolerant to overvoltage and usually survive even 5x times above their spec. So this unlikely to be an issue.
I'm with you on that. On the previous company I worked for, they take great pains about mechanically stressing MLCC parts. Then for high reliability power lines, we always used two in series.
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Anyone else notice this bodge. At least i hope it's an intentional bodge.
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Anyone else notice this bodge. At least i hope it's an intentional bodge.
Good catch. Bodge or contamination?
It is concerning as to what else failed. Any half decent bench type power supply should happily survive direct shorts on it's output. Dave said there was a burning smell again, the thermal camera would have come in useful. Is the charred FR4 conducting 11W of power? Still the CPU should not be rebooting, unless the input PSU was current limiting.
Dave do you still have your 'PSU Killer', it would be interesting to see a working example being out to the test.
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I guess it went from "interesting, only 20 bucks" to "not recommended" then.
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I'm not sure I'd agree with MLCCs being tolerant of sustained over voltage, they handle transients and high peak voltages for short periods (minutes etc) but the reliability of them plummets at higher voltage.
Type 2 and 3 ceramic MLCCs extremely drop their capacitance at high voltage, so voltage ratings may take it into consideration. I haven't done extensive testing. But I've done some experiments, as running 16V X5R capacitors on 120V for like for 10 minutes. I don't say they remain reliable at this voltage, just that generally it should not catch fire, especially that fast.
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Anyone else notice this bodge. At least i hope it's an intentional bodge.
I don't see it on the other parts of the video like 10:25, so likely it's a piece of something which got there during video filming.
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The way that cap was soldered in between of 2 terminals, means a lot of mechanical stress. Even more stress happened when wires were screwed to those terminals. MLCCs are very susceptible to mechanical stress and microcracks may happen causing leakage and shorts.
Totally agree, the orientation of this cap is a no-go. If there is absolutely no other place for this capacitor then I would have rotate it 90 degrees, so the capacitor terminals are in parallel to the connectors.
Bram
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Greetings:
1. Now that you have cleaned up the damaged area, I would check to see the voltage at the front output binding posts now that the USB monitoring is non-functional.
2. I notice that there are 3 major traces in the area of the damage:
a: output +
b: output -
c: the circuit that would have been connected to C33 if the cap was fitted (no info on what that signal is)
3. Do not discount the possibility that that last circuit could have been damaged as a result of the cap failure.
Why was it necessary to use the ceramic type of cap used?
Also, I think that some output hardware fuse is needed there. The failure seemed to last too long.
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Anyone else notice this bodge. At least i hope it's an intentional bodge.
The "bodge" wasn't there from beginning of the video
https://snag.gy/4HFhAc.jpg
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Anyone else notice this bodge. At least i hope it's an intentional bodge.
Those are tin whiskers and it's a normal process while tin ages. ;)
j/k
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Dave, that's been a very instructive video!
In automotive applications, there were several design rules on MLCCs, for safety reasons, that the whole xx k$ car does no burn.
These rules were violated in this application:
- Don't place MLCCs at the edge of a PCB (biggest mechanical stress during PCB assembly / further manufacturing bending situations)
- Never place single MLCCs directly on the battery input (automotive clamps 15 & 30)
- Use relaxed PCN layout and handling on MLCCs, like enough space to connectors, not too much solder mass, smaller case size, (1206 gives higher mechanical stress, due to mismatch PCB vs. MLCC ceramic), no manual soldering, etc.
- Use enough headroom in voltage rating, for sufficient voltage compliance and ESD resistance, especially on capacitors, which have direct access to connectors to the outside of the application.
- use 100V types when the board supply system (or the application itself) might introduce inductive spikes on the supply line
If MLCCs are used at the battery input, there were several safety measures to be implemented:
- use two MLCCS in series, each from different supplier. If one fails fatally (shorting), the other will avoid complete short
- use safety types, with 'soft' or 'flexible' termination. These fail open, but do no short
- Use small case sizes (1206 not preferred), and avoid "on-the-edge" values, that's the highest capacitance / voltage type of a case size.
- Don't use too small case size, as these are more susceptible to ESD damage... 0603 and 0805 preferred.
- Generally, use MLCCs of known-good suppliers only (which also have a QA system). These also implement additional surge testing in their production line, for example.
Frank
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The 5015 version does not appear to have that cap
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I'm not sure I'd agree with MLCCs being tolerant of sustained over voltage, they handle transients and high peak voltages for short periods (minutes etc) but the reliability of them plummets at higher voltage.
Type 2 and 3 ceramic MLCCs extremely drop their capacitance at high voltage, so voltage ratings may take it into consideration. I haven't done extensive testing. But I've done some experiments, as running 16V X5R capacitors on 120V for like for 10 minutes. I don't say they remain reliable at this voltage, just that generally it should not catch fire, especially that fast.
I've plenty of data from products I've worked on, and failure near to or slightly above the rated voltage of an MLCC is greatly elevated above the estimates from HALT experiments, there is a short reference to the same within this comprehensive document:
https://nepp.nasa.gov/files/25843/2013-Teverovsky-pres-MLCCsBME-n263.pdf
Immediate failures on first power on are typically from damage by mechanical stress, but the failures into the lifespan of the product are strongly affected by operating voltage and many companies will have mandatory derating factors based on their extensive historical data.
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When I first started reading up on this kind of DC-DC converter, I found something that made me drop the idea. Some race condition or potentially destructive circuit thing could happen suddenly and unexpectedly.
Something like that.
But, I don't remember the specifics, just that something I saw made me say "No" to myself and just drop the idea.
It was in a thread here. I don't remember the title of the post. I doubt if I bookmarked it. I just made a mental note to myself not to buy one.
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Is this the kind of supply that seems to always need a small load for stability?
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At around 15:00 Dave says that it's set to 10V, but it looks like 18V to me. The 8s and 0s are almost indistinguishable in that font.
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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.
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That failed power supply board is still pulling juice with no load - so that leaves the possibility that the output cap might have been the victim, not the perp here. No matter however many design mistakes were made. Obviously this is a cheap power supply board, with not a lot of design regard for reliability - but it is still interesting to dig deeper to find the -real- cause and use that as another good example of what can go wrong on a board design.
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!
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"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...
@Dave
Have ben any response from the manufacturer?
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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?
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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).
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"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.
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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.
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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".
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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.
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FWIW, and IMHO, the photoshopped click-bait previews that have been showing up lately are unbecoming of a serious channel.
Carry on.
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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.
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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
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its like loose wheel nuts on a Chinese car. your supposed to check them before use. :-DD
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! :-/O your an electronics engineer. :-+
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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. 8)
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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.. 8)
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I imagine that such flames as depicted in the video thumb are not outside the realm of possibility, given the subject failure.
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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.
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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.. 8)
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.
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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.
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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?
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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.
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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.
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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.
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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 :-+
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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?
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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' :o 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.............. :popcorn:
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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.
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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! :palm: and yes I have considered buying the same power supply module my self when all the bug's r out.
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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.
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I have a PS built on an earlier DPS5015 (non communicating) model fed from a 750VA torroid. It is working perfect.
I have measured with my scope the output of the PS (attached is a screenshot). CH1 is connected to DPS5015 negative, CH2 probe to +. Crocodile clips are attached to the scope earth (same potential as the metal case of the PS as Dave earlier showed in his video about scope safety).
What I see is when PS power is on (DC output of DPS5015 is still off) on both channels there is a sine wave: Pk-Pk=278V, Max=142V, Min=-138V, RMS=94V, f=49.85Hz absolutely overlaping. So, there is no potential difference between the thwo output leads.
When I turn the DC output on and crank the voltage up, the two waves are separating as you can see on the sreenshot. Mesurment is on for CH1, MATH is calculating CH1-CH2.
Readings of CH1 and CH2 (not visible on the picture) at 50VDC output with no load: CH1/CH2, Pk-Pk=278/278V, Max=166/116V, Min=-112/-166V, Ampl=280/280V, RMS=98.9/96.8V.
MATH: Pk-Pk=4V, Max=52V, Min=48V, Ampl=4V, Mean=50V. This is the white line. So, there you have the 50VDC output.
Question: DPS5015 is said to be a buck converter, but it seems to (me) operate different.
Could someone more experienced put some light on basic operating principle, please or direct me to a site describing it.
If it is unic, we may ask Dave to do a review sometimes.
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I have a PS built on an earlier DPS5015 (non communicating) model fed from a 750VA torroid. It is working perfect.
I have measured with my scope the output of the PS (attached is a screenshot). CH1 is connected to DPS5015 negative, CH2 probe to +. Crocodile clips are attached to the scope earth (same potential as the metal case of the PS as Dave earlier showed in his video about scope safety).
What I see is when PS power is on (DC output of DPS5015 is still off) on both channels there is a sine wave: Pk-Pk=278V, Max=142V, Min=-138V, RMS=94V, f=49.85Hz absolutely overlaping. So, there is no potential difference between the thwo output leads.
When I turn the DC output on and crank the voltage up, the two waves are separating as you can see on the sreenshot. Mesurment is on for CH1, MATH is calculating CH1-CH2.
Readings of CH1 and CH2 (not visible on the picture) at 50VDC output with no load: CH1/CH2, Pk-Pk=278/278V, Max=166/116V, Min=-112/-166V, Ampl=280/280V, RMS=98.9/96.8V.
MATH: Pk-Pk=4V, Max=52V, Min=48V, Ampl=4V, Mean=50V. This is the white line. So, there you have the 50VDC output.
Question: DPS5015 is said to be a buck converter, but it seems to (me) operate different.
Could someone more experienced put some light on basic operating principle, please or direct me to a site describing it.
If it is unic, we may ask Dave to do a review sometimes.
Looks strange. How did you rectify the toroid output?
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Have full wave rectifier and a big electrolite cap. On primary installed a soft starter circuit. Otput is 60.5VDC. Just at the max. input for DPS5015.
The measured voltages look really stange. The freq is equal to the mains. As soon it was a used transformer now I suspect it leaking mains voltage to the ground (metal case of the unit). Maybe caused by insufficient insulation resistance of the transformer or other short. I think this is a possible fault. If there is not enough current flowing to blow the fuse, it may continue working, but if so it is life dangerous. So, I plan to open up, disconnect sensitive parts, make an insulation resistance test of the toroid.
Do you think I am on the right track? Many thanks for you help.
Sorry, that it is out of topic here, because I am moving from DPS5015 to troubleshooting the PSU supplying the input to it.
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Have full wave rectifier and a big electrolite cap. On primary installed a soft starter circuit. Otput is 60.5VDC. Just at the max. input for DPS5015.
The measured voltages look really stange. The freq is equal to the mains. As soon it was a used transformer now I suspect it leaking mains voltage to the ground (metal case of the unit). Maybe caused by insufficient insulation resistance of the transformer or other short. I think this is a possible fault. If there is not enough current flowing to blow the fuse, it may continue working, but if so it is life dangerous. So, I plan to open up, disconnect sensitive parts, make an insulation resistance test of the toroid.
If you have everything floating on the TX secondary side it could be just normal mains leakage across the transformer.
You could try a 10k between the scope probe's signal and GND clip to see if there's any current behind it.
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If you have everything floating on the TX secondary side it could be just normal mains leakage across the transformer.
Exactly.
I have measured with my scope the output of the PS (attached is a screenshot). CH1 is connected to DPS5015 negative, CH2 probe to +. Crocodile clips are attached to the scope earth (same potential as the metal case of the PS as Dave earlier showed in his video about scope safety).
You misenterpreted scope safety video. In short - you are measuring isolation leakage using scope. Usually you will find some, especially using 1:10 probe, but this is not how it shall be measured. Better check isolation of your supply (transformer) using just multimeter in AC current mode.
To see output ripple of isolated ([edit] with both "+" and "-" terminals floating against scope ground ) supply, you just use single channel of the scope, AC coupling, 1:1 probe. Tip to "+" and ground crocodile/clip to "-".
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Made some checks as directed.
Everything is floating on the secondary, it is sure.
Mesurments taken at unit power on, DC output off:
No current flows from any of the DC outputs to the ground.
Voltmeter still mesures 101VAC between both, - and + DC leads and ground (=PSU metal case=earth).
So, is that correct I am seeing on the scope CH1 and CH2 (picture in the first post) normal mains leakage across the transformer going through the full wave rectifier, elco cap, DPS5015 and so to both, + and - DC output leads?
Leak of mains through the failing isolation of the transformer to the ground is excluded?
If that is correct the unit is working perfect and we should not repair what never went wrong? :-)
Made a a ripple test far all interested in DPS5015 performance. Load is a 12V, 10W halogen bulb.
Screenshot of the scope is attached with maths on. Ripple=around 400mV
Thank you all helping.
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Frequency is similar to what I saw (67KHz) but ripple is more than 10x what I get @ 31mV
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Frequency is similar to what I saw (67KHz) but ripple is more than 10x what I get @ 31mV
Maybe the probe setting is wrong 1x vs. 10x.
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Quote from: plazma on Today at 07:02:59 AM (https://www.eevblog.com/forum/index.php?topic=97960.msg1354188#msg1354188)>Quote from: ChrisLX200 on Today at 06:49:14 AM (https://www.eevblog.com/forum/index.php?topic=97960.msg1354169#msg1354169)
Frequency is similar to what I saw (67KHz) but ripple is more than 10x what I get @ 31mV
Maybe the probe setting is wrong 1x vs. 10x.
My Tek TDS3014B scope automatically detects if I'm using 1x or 10x probes, can't make that mistake..
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Voltmeter still mesures 101VAC between both, - and + DC leads and ground (=PSU metal case=earth).
Voltage measurement does not tell much. You have to measure AC current. Shall not exceed 210 micro amperes: https://en.wikipedia.org/wiki/Electrical_safety_testing (https://en.wikipedia.org/wiki/Electrical_safety_testing)
Regarding supply noise cannot comment - because do not have such (kind).
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Quote from: plazma on Today at 07:02:59 AM (https://www.eevblog.com/forum/index.php?topic=97960.msg1354188#msg1354188)>Quote from: ChrisLX200 on Today at 06:49:14 AM (https://www.eevblog.com/forum/index.php?topic=97960.msg1354169#msg1354169)Frequency is similar to what I saw (67KHz) but ripple is more than 10x what I get @ 31mV
Maybe the probe setting is wrong 1x vs. 10x.
My Tek TDS3014B scope automatically detects if I'm using 1x or 10x probes, can't make that mistake..
I mean you and I got the ripple about the same and Valley got the probe settings wrong.
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Probe is set to 1x (on the probe and the scope), but it is perhaps picking noise from all around.
You can see here in Dave's video, how much stuff is influencing this kind of mesurement and how to do it properly:
https://www.youtube.com/watch?v=Edel3eduRj4 (https://www.youtube.com/watch?v=Edel3eduRj4)
Excellent work.
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Made some checks as directed.
Everything is floating on the secondary, it is sure.
Mesurments taken at unit power on, DC output off:
No current flows from any of the DC outputs to the ground.
Voltmeter still mesures 101VAC between both, - and + DC leads and ground (=PSU metal case=earth).
So, is that correct I am seeing on the scope CH1 and CH2 (picture in the first post) normal mains leakage across the transformer going through the full wave rectifier, elco cap, DPS5015 and so to both, + and - DC output leads?
Leak of mains through the failing isolation of the transformer to the ground is excluded?
If that is correct the unit is working perfect and we should not repair what never went wrong? :-)
Made a a ripple test far all interested in DPS5015 performance. Load is a 12V, 10W halogen bulb.
Screenshot of the scope is attached with maths on. Ripple=around 400mV
Thank you all helping.
Voltmeter still mesures 101VAC between both, - and + DC leads and ground (=PSU metal case=earth).
Voltage measurement does not tell much. You have to measure AC current. Shall not exceed 210 micro amperes: https://en.wikipedia.org/wiki/Electrical_safety_testing (https://en.wikipedia.org/wiki/Electrical_safety_testing)
Regarding supply noise cannot comment - because do not have such (kind).
I have done some more mesurements according to helping friends here in order to be on the safe side.
PSU power is on, voltmeter, AC current set to the smallest 2mA range gives on both leads 0.04mA. This is about five times less then 210microA, mentioned by ogden. If we divide the 101VAC RMS by this, we get 2.5MOhm. This is an acceptable velue for insulation resistance as well, I believe.
Also, I have done an insulation resistance test on the primary between the ground and the pins of the plug (mains switch on, of course) at 500VDC with Voltcraft ET-200 tester. It gives me resistance above range, 500MOhm, which is excellent.
If we would open it up one more insulation resistance test could be performed between primary and secondary windings, but for now I skip this. Do not want to dig into it, othervise testing could damage the converter.
Based on the above information perhaps we can conclude that the unit is not dangerous.
Thank you all again.