Test of a PSU like the one that went on fire.

a while back I made a short video about one of these power supplies just basically saying that he had sent me a picture that someone else had sent him and it showed that the whole plastic front of the power supply had gone too far so I immediately ordered one the power supplies because that sort of stuff is interesting noticing this little metal inside the Seleucid to know about that I'll try not to drop that in the live circuit board because it is live at the moment and before I start this on to show you a little quirk this power supply has I've connected an LED to it using it on the more initially constant voltage but the current is not too high for this LED but watch what happens when I start regulating the current down the current limiting jakirah and it was really unstable it flickers visibly it's pulsing the current regulation and again a lot of noise from an inductor and Runa fits this you know Putin doctor or the switch mode air transformer but say I'm making that noise so let's turn the power off again noting that the circuit in here is still live so the first thing we'll take a look at the circuit rafters but the first thing to note is that the leads that come with it are not really worth keeping I'm just going to unplug this before I stick around in there I'm gonna top this over here I will take a look at the lead because this is a leader came for UK use and it's got the dreaded sleeved earth pin know the reason sleep that pins are normally sleeved in these plugs it's normally just the live and neutral pins and it's soon as you put the plug in you can't touch the pins until they're fully you know that they don't make connection till they're freely inserted the earth pin should be solid metal and I'll show you why if we get a material on continuity and I measure from the earth connection in the socket to the earth in the plug you get continuity that's good this is our classic plug air socket and one of the things that that's notable is that the earth has to make connection first for safety so the earth connection is rate up the terminal rate of the frontier so if I plug this in it's making connection with a earth no and I can demonstrate that that the plug isn't fillion so I can basically just stop to lead in here stick it in our terminal and you're getting continuity as soon as I push that plug in soon as I push it in new earth cannot continue to anymore so though there is an earthen this cable they've defeated it by sleeving that pin so if you have products of bypassed quality control by coming directly from China via eBay check if you're in the UK that you've not got want anything with these plugs with the sleeved earth pin if you have discard them and replace them next thing it falls down quite badly on is the test leads let's pull the test leads off and a few of you mentioned when I put that video up in the first place that the leads are supplied with are pretty bad and they are the very thin but it's not just because they're thin if you unscrew a I'll just screw that bit back in where's our screwdriver there we go if you're on the screw the grub screw that holds the wire in position it's just it's not beard as symbol it is beard but it's not beard and folded it's not even a thick conductor it's a modest it's not bad but it's not great but all they've done is they've stripped it fold it over and then grip that with the screw and that doesn't be a very good connection and it's notable and I'll show you the thermal images of this that this connector that particularly the negative connector was getting very hot because I did put this under a test the original picture was of a post by it have been loaded up to eight amps so I put an eternal or donor I used 250 watt 12 volt halogen lamps just connected and pile across the open quite a high voltage drop across this lead I just basically turned the voltage up until I got to the eat amps I required and then I let it bake for a while and the results were that everything inside the power supply was phone but the negative lead here on the front of the power supply where these are the leads plugged into the connectors on the front it was at forty three point four degrees Celsius and you know I suppose it's random how good a connection you're going to get you know it depends how which way the strands ended up pointing in the factory so that could have been a factor of someone else mentioned that the connections on the back of the power supply that go onto that there's wear loose and that could also have caused us a burning issue particular that that's and what is the head current and you can see the heat transferring through this is the front panel this is the heat coming through from that hot connector coming on through the socket but inside the unit itself is fine the hottest component here was let's say bring this round again they're the hottest component was this resistor down here which i think is a in line with the main transformer think it's a current sense transistor for the switch one power supply secretary for feedback and it was modestly warm the components in this side where you know the transistors that drive i'm guessing that these are the transistors that drive the switch would a transformer but they weren't particularly hot i see the temperatures the resistor was at 82 degrees celsius in a ambient temperature of 20 the hot components down here are supposed to get hot there the NTC thermistors down here there the inrush limiting thermistors they limit the current and everything else was just acceptable the transistors were about 46 the diode in the back a and the mosfet that's in the back was 40 and you know nothing really major it seemed to be handling the power quite well so let's take a look at the circuit in this i'll just pull this we don't completely know since i don't need to pair this up for this probably good things i'll be poking my fingers inside so what do we have but it means come in and the earth gostrey on to the chassis here and the chassis is used for air continuity over to the front we've got two blue class-wide pastors down here at which connect from the live in neutral to the ground we've got there to NTC and rush limited limiting resistors basically they start with a fairly high resistance that basically limits the inrush discharging these big capacitors and then as they become flaws in the heat up and the resistance drops down laura till he reaches out of equilibrium point and it just takes the sharpness off that in russia we've a common word suppression choke down here which is two opposing windings that counteract each other magnetically when there's common noise coming here at the power supply it doesn't really have much of an impedance of means going in but it does have a limiting effect and the noise going back out again a little yellow capacitor down here which is ex2 suppression capacitor and then we've got a fairly chunky bridge rectifier and we've got two 250 volt capacitors which are most likely in series will they will be in this supply and i see some resistors down there which are probably bouncing resistors one at 0 0 300k and then interestingly the there's another complete power supply section we've got a bridge rectifier here capacitor here and we've got a DK 1 1 2 which is an interesting little switch wooden ship last philip associated with this transformer here and it's a is a quite an unusual chip because I printed something out I've completely forgotten to bring it over it's a very very simple chip it's got a very low component count there's not even a bootstrap circuit there's not even such a feedback I mean there's a little small capacitor for the control circuitry but it's really just to provide stable feedback through an opto isolator down here and and what's interesting about this is that instead of being MOSFET based it's actually based on a standard uni Junction transistor like a typical silicon NPN stout transistor which is odd err but it seems a very popular chip and there this transformer is not skimping this is a big chunky transformer for such a power supply and this first ply is purely for powering the displays in the front and the feedback circuitry and this chip here which is a ke7 500 beats which will power supply driver chip and it appears to be driving through what may be an each bridge down here this transformer here which then probably drives the MOSFETs in this side so it's basically galvanically isolated from the main switching supply not sure why it would have to be galvanic Li oh yes I do actually know why I would have to be galvanic class leader because that's all their output control circuitry yeah that would be a really good idea galvanic Li isolating that we've got quite a lot of support components around here ah and what says m3 to form guessing that's kind of an LM three to four quad op amp we've got two little trimmers which I'm guessing when you adjust just the display in the front you get coarse and fine controller voltage coarse and fine control over current that's a reason enough way to do it my first power supply did that and it means that you just get you typically you start off by getting the same knob and you turn it to a roughly middle position and then you tweak this to roughly the board you want then you faint unit with this one it's a good system and these knobs affect directly what the the feedback from the switch will power supply is doing but the displays are basically just dumb displays they're measuring the current across a shunt and the measuring the voltage across the output and you can just fine-tune those I'm guessing with these two trimmers here noting that by sheer coincidence and this isn't this maintenance friendly the two trimmers are right next to an exposed live means connection keep that in mind if you ever have a we poke around that area definitely a sharp screwdriver and was another plastic handle and keep in mind that all the secretary in this area should be class you should treat it as being at mains voltage well from here this heatsink potentially which i think is the components are isolated from it but you know just regard everything after the eye and just regard the whole thing as live that's the best bet if you want to play safe the spiritual power supply's coupling through this big transformer that's all just looks really well built I thought these were going to be 2 diodes this one is a nice off colorless site it was recently color because I I used for the first time successfully I used that heat sink compound trick air from eevblog for you just wait for that heatsink combat across because I can lead read the laser engraving and it works really well it really just getting a dab of the weight compound rubbing it on and buffing it fills all those air laser engrave slots and you can read it so this is a diode package but this is a MOSFET I'm not sure if the MOSFET might be part of the current-limiting I'm not sure if it's gating the switch would power supply completely for that or actually pulse width modulator output which is a possibility is that just the way it sounded it was a bit hard we've got a bank of a capacitor or some maybe they're in parallel perhaps just to hide up a decent value this massive choke which is not really glued down as Q or tied down and some more capacitors and output and fundamentally that set the current sensing is done via if you can't really see it's under this that let Troy torque or there's a little wire loop there just that a standard meter shunt just poking up and back down again to the circuit board and it looks like a proper calibrated shunt then the front is just the display drivers fundamentally and all they're doing is just displaying what's set in these knobs and by the current measured and the voltage measured it's very simple so then it's a to the power supply is okay it doesn't get too hot it's got another hard quark if you set it a little level it just the fan just keeps just jittering just backwards and forwards like it's just being pulsed and so I've not given this a fool I've not given an isolation test it would have been interested to your completed bits I can't do that right now just a time constraints but maybe in the future I'll tear this complete of it that would be quite interesting get the circuit board out it but so far yeah it looks like it's built like a really good quality switch with power supply and it's let down badly by those really crappy leads or another thing about these leads and this is another common thing with these the crocodile clip end as is so often the case all they've done is fold the wire under the crimp round again so again it's not a soldered connection one of the first things I do when I get a set of leads like this is take that open the crimp up and solder those connections on to the crimp so it is a proper electrical connection likewise with this one I'd strip this and a but possibly operate the cable actually or get a decent cell leads and then properly terminate it so at this screw is pinching on to twisted and folded cable so it really filled that tunnel up so that's my guess as to what happened I don't see if it was a similar power supply to the so do I see much really to go on far here the circuit board should be fr4 sometimes and things go wrong it can burn and smolder and track but the most combustible bit has been this but the only really combustible bit is this front panel here and it is very possible that one of these connectors that just wasn't capable of taking that e amps or something down maybe a the screw down here just wasn't tight and debts a caused that problem whereby it's just are heated up to the point the flash detonated so if you've got one of these power supplies make sure your leads good make sure you either solder these or change them out for better ones that you've opened up and checked out see if they're good enough for you but other than that you know it seems reasonable enough for a basic general purpose power supply this is where being able to do a flash test would be quite interesting this to actually give a real high voltage test other things were they've not they've got another I was going to say class white pastors north of class wire or not but their little blue capacitors they've got them between the output and ground that's me partly for a noise reduction and partly it's going to protect us from a if you connect this high frequency plasma power supplies to with a lots of high frequency voltage RF energy fed back from the power supply looking for a way to earth those are capacitors may actually provide it and limit the risk of you know exceeding the voltage then solution of voltage of the transformer so it looks you know it looks a chunky robust well bill power supply to all intents and purposes bit quirky with the current feedback BAM other than that for the price it represents modest value for money that you know it's a quite usable but just a upgrade your leads bonus extra footage let's test the keyboard so I'm going to lock the faulty plug off that inherent design fault plug you chopped quite a nice little cable I'm going to strip it and we'll do the flame test and see if it's copper or if it's a copper coated aluminium and ice or tune how thick it was it's supposed to 0.75 it says feels spongy okay doesn't feel right hmm okay let's do a flim test this is a non-key ball which is copper let's say zoom up and we'll do the flume test and what should happen if it's real copper is that as it heats up it shoots of glue red heart but it shouldn't malformed in any way so that's how pass it's getting very hot that kid was getting hot but nothing's mal forming it goes are black and discolored let's try this one now it's copper coated aluminium it's all just flopped okay so where that cables going the bin

Channel: bigclivedotcom

Views: 126,024

Rating: 4.9492731 out of 5

Keywords: YouTube Editor, PSU, cheap, ebay, power, supply, fire, cable, overheating, thermal, crimped, bent, strands, improperly, terminated, cca, copper, coated, aluminium, switchmode, switch, mode, 30V, 10A, halogen, test, voltage, current, limiting, Ave

Id: 70d6LBXw3o0

Length: 16min 42sec (1002 seconds)

Published: Fri Jul 14 2017