Hello! Some more detail on these battery testers or cell testers. The Bt168 with its Uh meter with a needle and the Bt168d which has the digital display. Now there is a Bt168 Pro of which I've bought eight. I'll come back to the reason why later on, all that seems to be is a digital one which has a slightly longer body.

Because the annoying thing on here is you can't quite get an 18650 in there. So I Think the idea of the pro is it's a bit longer. This slides out a bit further and you can get 18650s in there. Okay, the schematic of the electrical one, the non-electronic one is this.

So this one loads the battery up with a fairly low resistance. For the 1.5 volt cell which goes across there, it's 3.9 ohms. For the 9 volt cell which goes across there, it's 220 ohms. So there's a current path down there.

You can work out the current quite easily from these two values. There's another current path that goes through the 560 ohms and down through the meter. and there's actually another current path which goes down here. And of course, when you put a 9 volt battery on here, it all works in the other direction.

You've got that current path, that current path, and that current path. The maths is quite complex, but it doesn't really matter too much. What this effectively does is load down the cell with a low resistance and then pass a current through this meter. And if this meter is a fixed resistor, and of course you can just say puts a potential across this meter.

But it doesn't actually measure anything because it doesn't show you volts or amps, it just shows you good, average or bad. Now The bt168d Works In really a totally different way. Rather than load the battery down and then have a meter show you whether it's good or bad, the emphasis here is on voltage. So you put your cell in here and it gives you a voltage quite accurately to two decimal places, but it really doesn't load the cell down much.

This cell I've marked with a double X It is profoundly flat. I Have a rubber band here as well. Actually, let me set that up. so I'll put the cell in with the rubber band so that it holds it in place and you can see that a profoundly flat cell which will drift right down to almost no voltage at all.

or at least to the voltage where this thing cuts out. Because this has a circuit which has two really very different inputs. The input from the 1.5 volt cell goes into a boost converter because it has to boost up the voltage of this cell high enough that it can drive this electronics. And my guess is that this is 3.3 volt Electronics or three volt Maybe with the nine volt, it just seems to go into an Ldo regulator, a linear low Dropout regulator and that powers up the electronics for this.

Now talking about loading the cell down, this doesn't do much of it. All it does is draw enough current to power up the microcontroller and the display, so the loading is quite gentle. The emphasis here is much more on getting an accurate voltage reading. Now I can show you the difference really between the loading on these cells.

this cell in here, you've seen it drop from about 1.36 to 1.30 but it's quite slow If I Now put that in this battery tester. you can see that it says that it's in the replace section red, but see how quickly that's going down that's loaded up with the three R9 resistor and so the voltage across this cell is dropping really quite quickly If I put it back in here. now you can see that it's it's actually climbing now because the loading has been taken off it. So that's a very good representation of the fact that this really isn't loading the cell very heavily.

So what I wanted to do with this unit was see how at what voltage this cell needs to get down to for the Boost converter into in this thing to fail to boost to enough voltage to power the microcontroller and display. So I'll try and load this down with the other tester. So I need to hold it in here for a while and get that needle really right down quite low. The voltage on this cell will then recover up a bit and then The small amount of loading on the 168 d will gradually pull the cell's voltage down to the point where the Boost converter no longer functions.

This could take a while, so I might have to film this and do some speeded up sections. but I just want to get this drained down as well as I can so that I can get this test started. Let's try that. Okay, that's down at 0.79 but it is actually going up at the moment 0.8 So what I'll do is I'll just leave this for a bit, wait till it starts falling again and then I'll film it to catch the point where the Boost converter in here can no longer Drive the electronics from this cell, right? it's down to 0.5 volts.

That's got a little way to go yet. Um, I Done this before and I seem to remember it dropping out at 0.43 So let me just speed this section up. and uh, we'll bring it down to the point where the microcontroller. well actually what seems to happen is the the microcontroller still seems to be alive and the LCD driver still seems to function, but the microcontroller is unable to take a measurement and this just goes to zero.

But I'll just speed this up until we get to that point. Okay, that's interesting. that's at a different voltage to what it was doing before. it was going down to 0.43 That went down to 0.47 Um, but it's somewhere below half a volt.

Now you can see that the microcontroller is reboot booting furiously and the LCD driver is barely working. So I think we can say that the lowest voltage that this input the 1.5 volt input can measure is about half a volt. What I want to know now is what's the highest voltage it can measure. So let's get some Cr203 twos out of this packet and stack them up in here and see what we measure.

Oh wow, this is double layer plastic. They don't just fall out the back. I'm gonna have to cut them out. Okay I Was just wondering whether these are double sealed to stop kids.

Um, getting them out easily because kids swallowing these is a really bad thing. Okay, let's check. Um Now where's positive? it's red I suppose, isn't it? Oh, that's that end, isn't it? Uh, so it's perfectly happy with 3.04 volts. Let's try two cells.

Yes, happy with 6.0 Ooh, that fell a bit there, didn't it? Let's try three cells, right? That's interesting. That's saying. 8.00 volts now clearly isn't that? It's going to be 9 volts or thereabouts. So it looks like the 1.5 volt input the the Boost converter input tops out at 8 volts.

which is interesting because the 9 volt input clearly won't do that. But yeah, half a volt minimum for this and this is the input I'm going to use because the reason I've bought eight of the pro version the slightly longer digital version is that I intend to put one of these voltmeters on each of eight cells in a Lithium-Ion phosphate pack. So the fact that this input can go down to half a volt and up to 8 volts covers completely the Lithium voltage range. so that's fine.

But now let's check the nine volt input range. Okay, I think these are all charged I'll use this orange one. So a single cell, we get 8.96 volts. How am I going to get more volts than that? Okay, a 9 volt with two 1.5 volt alkalines? Assuming I get a connection? Yes, I have and that's it.

Oh, it's not a very good connection, but I'm getting 11. let me just get this to work: 11.98 volts. So almost 12 volts. Let's go a little bit higher, right? A 9 volt, an alkaline, and a 3.2 volt Lithium that makes about 14 volts.

I think and we're getting oh, okay, we're getting a one in the left hand position and a V now. I assume that's over volt. So I'm just wondering actually whether the top voltage of this one is around that 12 volt mark. And if you're interested I'm not, particularly because I'm not planning to use the nine volt input, but I'll just try this with a 3.2 volt cell on the nine point volt input.

And yes, that works down to 3.3 volts now. I've got a feeling there's a three volt regulator that sits just inside these nine volt connections. So my guess is if I use a 1.5 volt Alkaline, let's get this hooked up. I'm guessing yeah, it just doesn't power up because it cannot generate the three volts or whatever the microcontroller needs.

it's going to be three or three point three, uh, to power up the display circuitry. Uh, Interestingly, when I put this 3.3 volt battery on the 9 volt input, we get oh, we get 3.31 or 3.32 When I put it on the 1.5 volt input, we get 3.33 So they're fairly similar, but slightly different because if they follow completely different paths into the display circuit now, I've just drawn a little diagram mimicking this one, but it's this is a block diagram because the schematic doesn't make any sense. The 9 volt input goes through a three volt Ldo. I'll take a look inside in a moment that drives the microcontroller and the display, and there's obviously some sort of input to the microcontroller directly from the nine volt input so that you can measure its voltage.

On the 1.5 volt side, there's a boost converter, which is typically an inductor, and oh uh, is that correct? Yes. And then there's a switch in that midpoint down to ground, so you pull that down. When you release it, the voltage on the output of the inductor flies up, flies through the diode and charges a cap to give you your higher voltage. so you can boost anything from half a volt up to enough for voltage to drive the microcontroller.

and we saw that you can put up to eight volts on the input here before the display stops increasing. So yeah, the 1.5 volt input and the 9 volt input go in through these different routes. So the issue? really? If I'm going to use this as a self-powered voltage indicator for eight cells in a Lithium-Ion phosphate battery pack. When I get my eight of these: I Want to take a cell with a very stable voltage Lithium-ion phosphate.

This cell is perfect for that, and just check that they all read the same voltage. In other words, what is the consistency in voltage reading accuracy between eight random select selected digital battery testers? Okay, let's finish this video off with a quick look inside each of these battery testers. and this one. For some reason, the connector comes away with the bottom and also this one and that's what's inside.

Let's have a closer look. So inside the Bt168 with the analog meter, there's the four resistors on a little tiny PCB We've got the analog meter here which is just sort of sitting in the shell like so you've got the nine volt input there, the 1.5 volt input there, and ground which goes onto this common piece of metal which does both the nine volt cell and the 1.5 volt cell. That is the schematic. Those four resistance values.

There are some other schematics of the Bt168 on the Internet with different values up the top here, but these values are these actual resistors here. I've checked them and on the 168d, the digital one. Um, yes, you've got the microcontroller and the display. I Don't know whether you'll see this, but along this bottom Edge you can just see a bit of pink.

possibly I don't know whether you can see that as pink, but that's the zebra strip that. um, there are a few pads on the back of this. PCB zebra strip down to the LCD LCD which is there. Here's the Boost converter circuit.

There's a chip here. It's got a number on it, but when I looked it up, it looked like a 3.3 volt regulator. but I don't think it is I Think that must be the Boost chip. There's the inductor capacitor.

It's got to be a diode here somewhere. Well, there's a diode there, so that could be it the chip itself which does the measurement. Here's the nine volt input. It seems to go through a little MILF 4148 type diode that's an Ht-30 which looks like a three volt Ldo near regulator.

And then there's a few resistors on there too. Um, so that's it for this video. Just looking at the differences between the old analog one and the digital version. These two backs look like the same molding I can't actually tell which one came off which.

Um, one says battery size and the other says batter size. but I don't suppose it matters which one goes on the back of which unit. Anyway, that's it for this video. Cheerio!.