Hello I've got an ammeter. Well, it's a Voltmeter ammeter watt meter. Let's take a look. it's that.

in fact, I've got a few of these things. Uh, here are three, but let's get one out of its bag. So this is a 100 volt 10 amp uh, Voltmeter ammeter. but it also displays Watts because it calculates it from those.

Oh hello, that's an interesting shunt. Well, interesting for 10 amps. Anyway, having said that, Um, this power supply I bought recently has that shunt which is even longer than this shunt and this has a maximum output of 4M. So yeah, I guess that could be 10 amps.

Let's power this up. Um, I've got a two pin jst that's actually a three pin. it is. pause to the top and then next.

So yeah, I can use that pause to the top. I've had to cut off the little Barb but pause to the top and then neg. and the ammeter looks like this. So Volts amps and calculated.

Watts There are two adjusters here. one for amps calibration and one for volts calibration. Okay, let's see if it's set up correctly and I can do that with a power supply. My Ryobi Ammeter: I've put some banana plugs onto the lead that came with this so that plugs in there.

So if I go into the Ryobi first, come out of that and go into this ammeter and then go all the way back to the power supply. Like, so we can compare these two ammeters. So I've got one, um, five volts. it won't get to 5 volts of course, because um, this is effectively a dead short.

It's just driving the two ammeters. so it's really just one amp. Let's have a look at that and that's the voltage. So yeah, we've got one amp here.

one amp here, and HHH what's one of them? Uh, well, apparently that means uh, overload. So Overload at 10 amps, let's bring the current down a bit. Oh so there we are. Nine, Seven, Eight Nine Eighty.

And this actually says 9.8 amps. So it's reading 10 times higher than it should be. This is a 10 amp ammeter and it's really 9.8 amps when only 0.98 amps is going through it. So yeah, there's something majorly wrong with this ammeter.

And in fact, if you go to the seller's sale page, you've got this review. Don't buy Unit Does Not work as advertised. The ammeter displays a value that is 10 times too high when the actual current is 0.5 amps. The meter displays 5 amps.

Both units that I've received have the same fault. So I Expect this to be a production fault. The meter is totally useless. And yeah, as it stands, the meter is totally useless because when you get a volts reading here, I've got the plug connected for that, you would have the Watts measurement would be all wrong.

That would be 10 times too high as well. So there's an adjustment. uh, potentiometer here. Can we adjust it? So uh, Nine, we want 0.978 Let's take it down.

that's gone. HHH uh oh, clockwise goes down and the lowest we can go is 7.7 amps. So no, the adjustment doesn't work either. It was nice and accurate.

Wasn't it? Nine, Seven eight. Oh, I've gone a bit over a bit too far, but Nine Seven eight, just ten times wrong now. I Gotta come clean and say that uh, the beginning of this video was all faked. I've been dealing with this problem for some time.

I contacted the seller and in fact they didn't respond and AliExpress jumped in and just said okay, we have a solution for you. Send the items back to China for a full refund. They did say that the seller would pay postage, but I'd rather spend my time rather than packing all this stuff up, sticking labels on, and going to the post office. I'd rather think about how I can fix this myself and this was my first attempt.

So I wrapped uh, tinned copper wire around the bottom part of the shunt in the hope that I could have a little bit of shunt remaining. It didn't really work because it still measured 2 amps when there was one amp going through it. So I had to sort of solder out one end of the remaining shunt and I didn't know until I looked it up what this metal is and it's not copper. it's something called manganin.

and Manganin has the property a bit like Constantan. uh, has the property that it's Uh has a very low temperature coefficient, and so for a measuring device, you don't really want it to be susceptible to changes in temperature affecting the reading that you're getting. so it has an extraordinarily low temperature coefficient. It's barely affected by temperature at all.

And of course, by putting in Copper across here, I've now got the temperature coefficient of copper as well, and that's nowhere near as good. So if we look here on the Wikipedia page for electrical resistivity and conductivity, we can see that the temperature coefficient for copper is four times ten to the minus three. Now, I presume it's resistivity per degree Kelvin I presume that's what it is. So the resistivity changes uh by a factor of 4 times 10 to the minus 3, so 0.004 for every degree Kelvin or degree Centigrade that the temperature changes.

If we go down to Manganin, which is here, it's 0.002 times 10 to the minus 3. And that's why Manganin exists because it is very unsusceptible to changes in temperature. It does have a higher resistance than copper 48 times 10 to the minus eight. uh, whatever.

these are Ohm meters, Ohms times meters whereas copper is 1.68 So Manganin was what was it? 48. So it's got a lot more resistance than copper. so I was right to put the copper across it. But of course, it's got this problem with temperature coefficient and so putting this uh, copper.

across the shunt to try and short most of it out isn't really the solution. Although having said that, of course there's copper traces running up to these pins. so there is copper in the circuit and there are a couple of wires. Of course, these uh High current wires are all copper.

But anyway, this was a mess and didn't really work, so we'll put that to one side. This ended up being the solution. So I just simply, let's get the focus back. I Just simply cut the top off the manganin wire shunt and soldered it right down.

flat against the well. as flat as I could get it against the PCB Really, just to get it as short as possible. And that ended up with something like it: measured 3 amps for the one amp that I was putting through the circuit, so it needed more than that. So shall we modify this one that's currently reading 10 times too high? Cut this shunt down and see what we end up with as an amps reading.

Okay, let's unhook all this, turn the power supply off, unhook the ammeter from this, clear my desk, and then let's cut this shunt down. So let's cut the top off this manganin shunt, leaving a little bit of return so that I can solder it back into the PCB. That should be enough, right? I'll use that bit and solder that into the PCB. So the first thing I've got to do is get these two stems out right.

Iron on hot on 360. That should do it. A little tip's a bit Mucky but let's give it a go. Okay, grab that with the pliers.

heat that up. Can I impart enough heat into this? Let's get it. Yes, I can. Let's take the other one out.

I'll just press the back button on this soldering iron. Okay, let's get some heat on the other one, getting the heat into it. That's the problem that's got a 400 degrees. by pressing the Boost button, it's getting a good physical connection between the iron and the hole.

Okay, so those are out. Let's suck these out with the solder sucker. Okay, solder sucker in you go. Let's hope.

Oh, where's my bucket of lead? Just a bit of solder on the tip because the tip shape and the whole shape are not a good match and therefore it's difficult to impart enough heat unless you've got a little bit of solder on there. Okay, let's get that hole sucked out and see if the manganine shunt will fit in those holes. So lower it down and I haven't had to remove uh yet the PCB from the plastic housing, but have I sucked these out well enough to oh yes, that has gone in? Yeah, that's fine. So I want to get it as low down as I Can that I think looks okay.

let's solder it in. get the A use the iron on the hot setting again 360. get that to flow all around which I think it has I really need to turn this around to do the other side I'm not sure what you'll get to see, but uh I need to get to see this as well as I can. it's just not flowing around that side.

Okay, that's got it right. So that's the manganin. As short as we can get it without sort of moving the hole across a bit right? let's see what that gives us. turn on the power supply.

so that's one amp. Yeah, so like I say that's now reading 2.5 amps. Oh, it's a little bit better than I thought. So that's down to about just slightly over a quarter.

and of course I can adjust that away. So I think it was positive. wasn't it clockwise to bring that down? So yeah, I can get that down to 2.5 amps. In fact, I can take it all the way down to two amps with this pot, but it'd be quite nice to have this pot roughly Central So I need to do a little bit more to bring that from Uh two and a half amps down to the one amp that I'm measuring both on my ammeter here and also here one amp on the power supply.

So what else can I do to this thing to get the amp reading down? Well, the circuit here for reading the voltage across the ammeter shunt is top of ammeter shunt goes into this potentiometer. wiper of the potentiometer runs around here through that I can't read it resistor and then it looks like it goes straight into the microcontroller or this might be a dedicated Uh Voltmeter ammeter watt meter chip and then the bottom of the pot goes through this. Now actually this resistor is a is a zero one B which from memory is a 1K and this is a zero one C which I think is 10K and then 0 1 D is 100k as I remember it I will check that. So what we appear to have is this part.

Uh now I need to take this out to have a look at the value of the pot. So four screws holding the PCB to the front panel. Let's take those out and take a look at this thing when I get the screws out. So here are the two potentiometers.

The A adjust is this one that's connected up to the shunt. so we'll have a look at the A adjust value and it's a 502 so that's a 5k. The voltage adjust pot is actually also a 502 camera's having a job because it keeps seeing all this lot so they're both 5K resistors. So the circuit here is uh, top of our meter has a small voltage on it that goes first through a 5k resistor and then a 10K resistor down to ground.

This area here looks like ground plane. So what we want to do is reduce the value of that 10K resistor to bring the whole voltage measured at the top end of the shunt down. I Mean we could reduce that resistor and increase the value of the pot. but let's just leave the pot in.

Yeah, I mean I don't have any of that kind of part of different values um and I think and I have of course already done this on other ammeters that the easiest way to modify this resistor. it's just melted off the board and blob the solder across the pads. So here we go. Let's do that.

Get some solder on the iron to get that resistor hot heat, both ends lift it off so that's it off. And now I'm just going to flood those two pads with solder and there it is blobbed across. So now we've got the 5K pot with its bottom end tied hard to ground. Let's see what we get.

So we've got this annoying 20 milliamp offset now. we'll be getting that when I first powered this up I think we were um, although I think it might have been 10 milliamps then. But anyway, let's get this hooked up to the current path. So oh, that's all still on actually.

Um, okay, let me just reposition the camera and uh yes, I've got 1.12 amps here. 1.001 amps there. 1.002 amps down here on the power supply. So what I want to do now is trim this so it'll be clockwise.

Oh, that's gone slightly too far now. Of course it's much more sensitive now because we're using the 5K to span the full range of trimming. So that's one thing we've lost. We've lost the sort of, um, soft sensitivity of this calibration pot.

and now it's all rather harsh. But there it is. 1.01 amps. Um, which it? oh, it's supposed to be 1.00 isn't it? But I'm not sure whether I'm going to be able to I want the tiniest smidge of a movement on there? Yeah, so it is more difficult to move this pot and get it calibrated now, but there we are: 1.01 or 1.00 amps.

The next thing to do I'll tidy the desk a bit. We'll check for linearity, so we'll raise it up through the amp range and see if this responds linearly. so one amp on all the devices. Okay, let's raise that up to about 2 amps.

2.030 I Have to. Just this thing moves so fast you can't control it other than individual button presses. Okay, so 2.001 2.000 and this is now saying: 1.99 I suppose I could peel this off? could I because it's not easy to read or I could bring the blinds down. Perhaps I'll do that as well.

So that's not bad, but it's a little bit out. Um, okay, let's try three amps 3.06 So 3.06 3.06 and this is reading 3.04 So where's my adjuster? Let's adjust that to 3.06 or it's very sensitive. 3.07. Okay, let's go up to four amps.

A little bit further than that. 4.09 Yes, as you can see, it's just so difficult to get that exactly right. So you end up pressing this button furiously. Okay, four amps.

Oh, that's pretty good. Four amps there. Four amps on my Ryobi DMM and 4 amps on this thing. So now I've brought it all the way down to half an amp 0.5 0.499 But this says 0.53 So yes, the linearity has suffered a bit, and in fact, if we turn that off, um, zero amps that's showing volts at the moment.

So zero amp. Zero amps. and this has got this offset of um, 20 milliamps 0.02 So it hasn't really fixed it very accurately, but at least it's now kind of working. And if you're going to use this in a non-critically important and you don't need precise accuracy application, then it might be good enough.

Now, of course, there's another problem. and that is that. Having this shunt, which I think was two and a half times the resistance that it really should be. So we've had to budge the measurement with this removal of that resistor there.

Um, we've got a higher burden voltage than is really necessary here. If we had the proper shunt, a different piece of Mangan in shorter perhaps, or certainly, uh, thicker diameter then we would have a lower burden voltage. So yeah, we've also got this additional problem that we've got a higher than necessary burden voltage now. I've got seven of these meters in total I Bought three initially from one seller that's the seller where the previous purchaser wrote: uh, don't buy this meter because it shows 10 amps when it's only one amps then I thought okay, I'll buy four more from another seller, but those are these new ones that I've opened today.

And of course they also have the piece of manganine which I think really is a one amp shunt but software in the unit which makes it measure 10 amps for what? I'm going through it. so at the moment there does seem to be a large number of these and they may be with most of the sellers you just don't know. Um, so this is really your only option is to take these ammeters that say 10 amps here, but they actually measure only up to one amp because, well, something in in the electronics. the shunt doesn't match the software.

Something's wrong. It is fixable. It's not a hundred percent accurate, and you do have that burden voltage problem, but it does kind of fix it, so maybe that's good enough. Cheerio.