TNP #14 - Teardown & Analysis of a Somewhat Dangerous LiPo-Based Mini Spot Welder

[Music] hi welcome to the noise pack just a very quick video on one of these fairly popular now spot welders based on lipo batteries now these things used to be made with either super capacitors or with very high performance transformers that's because you need a very high amount of current in order to weld anything but these puzzles are fairly short and a couple of developments for instance the availability of mosfets with extremely small turn on resistance and lipo batteries that are capable of delivering extremely high current for at least very short process have made these things really popular now at the same time because there are so many of them now they're being mass manufactured in china sometimes they have a bit of shady manufacturing and i wanted to open one and take a look and see how it is i just picked one randomly from amazon nothing in particular didn't even really do too much research so the principal operation of all these is exactly the same they give you some vote these probes essentially they put a small voltage on these probes so when you short them it detects that you have connected it and then after a small delay it shorts those mosfets in and applies the battery directly across these you get a huge amount of current for a short amount of time and you can adjust that delay and you can also adjust how long those pulses are that's how you weld very simple and straightforward and no wonder these things have become so popular so let's take a look inside of it first and make sure it is in good shape and then we'll do a couple of tests so let's see what we have inside of this unit now the principal operation of all these circuits are exactly the same what you have is a big battery with a lot of current driving capability just a lithium polymer battery and then you're going to need a couple of mosfets with extremely small turn on resistance so that you can put the battery directly across the terminals so that you can create a pulse and that pulse is enough to to melt whatever material you're trying to weld into each other that's it the rest is just additional fancy things like controlling the duration of that pulse as well as you know usb charger which is a gimmick in my view so if you look at the other side you see there are three mosfets here and there are three mosfets underneath this i think i should be able to take this off actually there we go that's just a display a little i squared c all that screen and there it is there's a little microprocessor down there and like i said the rest is nothing fancy and the mosfet this one uses is from on semiconductors and they have a turn on resistance of 5 million but only when they reach 10 volt vgs so that's not the condition they're running in because the highest voltage they have access to is this one unless there is a dc-dc converter in particular to bring the gate voltage way way higher either way there are six of them so they should give you fairly small on resistance now some of these traces have a few thicker wires soldered on top of them this is to again reduce their own resistance any any resistance that you have between this and your device is going to reduce the amount of current you can drop into your weld point so they're trying to reduce it as much as they can now one thing i don't like at all is the fact that look how long these fins are look how much they stick out now this is the bottom of the case this is where these fins are and the case is metallic so if these two touch the bottom of the case or inside of the chassis they can short this out that would be a disaster most likely this will vaporize but as soon as these vaporize they will create a kind of a gas of ion metallized particles and they can continue that short circuit inside a confined space and create a big fire this can be a very dangerous situation i don't know why don't you just cut this out it will make things a lot better there's also you know little solder points left here there's a little one left there it's not good i'm not quite happy with the way this is put together but this is by far in my view the most dangerous part of this so i'm going to touch this up a little bit clean it a little bit and make it safer so that we can do a couple of weld points with it okay i went ahead and retouched everything i also added a bunch of solder to all the wires to make the resistance even smaller and i shortened those so that they're a little bit better i may put even some glue on them so make sure they don't touch anything but i think i'm fairly convinced that this is now okay in terms of safety so let's put it back together all right now that it is somewhat safer let's go and turn it on see what it gives us there you go so it gives you the battery i already fully charged it and you can adjust the delay at the top you can see it says one second power 20 that's the essentially means the large longest pulse you can have it also gives you the input current and the output current through the usb ports i guess that's kind of a nice feature so you can see how much it charges it only charges at two amp maximum so these things because they're using the battery voltage directly across the terminals the maximum current you can get from them is going to be a function of how well they are charged so you should really keep them fully charged if you want to get the absolute maximum out of them let's do a tiny little test with that but i'm actually more interested in measuring the absolute maximum current that i can get from this at its largest or should say longest pulse because the longest pulse and the highest current that gives you the total amount of energy that this thing can dump into your welding point and that's essentially the best you can do with this so let's do a quick welding and then we'll measure the current all right here's the end of a battery and a piece of a nickel strip let's just put that on top let's take an electrode and see what we can do with it here we go hey not bad that's pretty fun actually oh look at that that's pretty good wow that is really good i have to say i'm a bit surprised i cannot remove this wow that's impressive this is the highest power you can do but i gotta say it did a really good job wow right let's measure the maximum current now to measure the maximum pulse of current that comes from something like this can be somewhat challenging because the current could be more than a thousand amps and the pulses are fairly narrow so you have to capture it somehow if you don't have the appropriate current probe you may not be able to do it but of course here we have the fluke 345 pq clamp meter which i repaired in one of the previous videos and this thing goes up to 2000 amps and it has an inrush function where it can trigger itself arm itself and then measure a small pulse of current going in now if you don't have this it's not a problem you can just make your own little loop calibrate your loop with some known value of current and do a relative measurement assuming everything remains roughly linear which is also completely acceptable essentially that's exactly what this is there's a loop in here and it's using that measurement so let's go ahead and see what happens i'm going to just pass this through our loop over here and i'm just going to short it together because when you shorted together you have the absolute maximum current it takes all the resistance of this into account let's see how much current we can get okay everything is armed and ready here we go okay i think we caught it all right here's a result let's see what's the maximum current so here's our pulse i'm going to scroll through it 960 amps wow that's what happens when the pulse begins now you can see a tiny little slope and it goes down that's the battery that's the best it can do so if you go forward you can see them it reaches a value as low as 904 amps so it drops by about you know 54 or 56 amps during the tiny period it has now this is a very short pulse you can see it starts from about 100 millisecond and it goes to about 150 milliseconds or so yeah so it's about 50 millisecond maximum pause this is the longest pause it provides but it's also the one where it's going to have the largest drop across time overall i think it's pretty good yeah so there you have it a quick video again this is not an endorsement for this particular brand this is just the one i randomly picked but i do suggest that you take a look inside no matter which one you end up buying if you do end up buying one of these because you want to make sure that it is really safe there is a huge amount of energy stored in this and can easily ruin your day and set things on fire if you're not very careful anyway as always talk to you in the comment section [Music]

Channel: The Signal Path

Views: 44,024

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Id: mt0229lU9sU

Length: 7min 45sec (465 seconds)

Published: Mon Mar 14 2022