Hello! Another item from my recent post bag video. uh I've been playing with this and I understand it now in a bit more depth. I'm keeping it in a food container because well, if you look at my desk, I'll show you my desk. That's what my desk looks like and there are things just sort of lying about.

Well, if I did that with this device which has voltage on it from these cells and also considerable amounts of potential current on the bottom. you know between that connection and that connection for example, then yeah, things could get a bit hot. Okay, so what is this device? In essence, Well, in essence, it is a single cell. Uh, Lithium Nickel, Manganese, Cobalt charger and discharger.

Let's switch it on and it's got a screen with lots of information on it including the voltage of this cell. You can see that one is fully charged current watts, milliamp hours, milliwatt hours, a resistance check. Oh, I'm not quite sure how it does that. a timer and now it goes dim after a while and I think I know how it does that I Think this transistor here is pulse width modulated by the microcontroller and so after a while to save power, the display just goes dim.

Now you can see that it's actually very dim at the moment. and that's because this cell is really not very well charged at all, right? It was at three volts and it's probably a little bit less now. So if it can only charge and discharge the right hand cell, what's the left hand cell for? Well, it's to power this unit, but it only Powers the microcontroller and the display. It can't actually charge the right hand cell for a couple of reasons.

One, there's no Step Up circuitry. The voltage of this is going to be less than the voltage of the cell being charged when it's nearly full, that is. And also, of course, if these cells are the same capacity, by the time this one becomes fully charged, this will have become empty. so that doesn't really work in practice.

So the only way to get this unit to charge the right hand cell is to plug USB into this type C socket here. So that's what I've done I've plugged uh USB It's actually a type A to type C cable and I'm using this USB outlet very specifically because it's got a feature which you really need. is this on or off? Okay, so that's when it's off if I now turn this on. Um, this is a very useful thing if you want to know whether this cell is a bit low because there's no real way of telling other than putting a DMM across it when you plug in the external USB type C.

If when you switch it on and off, the display changes in brightness. and of course, if you go to the bright mode it also changes in brightness, then you know that this cell is a bit low. So what I'm going to do now is I'm going to switch the cells over so that we know that this one is got a good charge in it and this is pretty hard to do. These sockets are extremely tight I'm using half a lolly stick to lever the cells out.

but yeah, they're really tight and every time you put them in and take them out, you do a little bit of extra damage to the plastic coating on your cell. so it's not something you really want to do that often. which makes the whole purpose of this unit a little bit impractical. Oh, which was that? That was the low cell, right? I'll put that one in here, make sure I get positive at the bottom and then this one can go in there.

And that means now that when I switch this on, it will have a good brightness to it. You can see that this cell is very low. It's 3.13 volts. so you really do need to use a USB power bank that doesn't shut itself off in the absence of a heavy load or even a light load for that matter.

Because if you're particularly if you're doing looping on this thing when you're charging the cell on the right. Yes, it pulls one amp of current. Uh, it is one amp, isn't it? because that's a linear charger. But when you're discharging the cell on the right, the current from it is going into these resistors.

so it pulls almost nothing from this. And then what will happen is if you've got a power bank that shuts off, it's a little shutoff and then the whole thing will just cease to function. So yeah, pick a power bank and this happens to be on this Ryobi USB battery topper thing be one that just stays on all the time until you manually switch it off. Okay, a little bit about the operating system.

Uh, any button brings the display back up to full brightness. The left hand button toggles the Highlight between the mode, the discharge stop voltage, and the number of Loops. So I want to change the mode from charge. This changes the mode, you've got discharge Auto and charge.

So I'm going to go to discharge to 3 volts which won't take very long because it's a 3.13 and the right hand button starts the discharge. So there it is, discharging, it goes down to three volts, dips a little bit below that and the microcontroller eventually works out that that's the end and it puts up end on the display. If you start the discharge and then stop it again, it puts stop on the display. Okay, let's try a charge.

so I'll change the mode to charge and we'll start that and I've already told you that you can't charge the right hand cell from the left hand cell. It doesn't work. The microcontroller takes a few seconds to work that out and then just says end. So what we need to do now is: plug in the USB Type-c Now you won't notice any brightness change I don't actually know whether that's on or off.

That's interesting I Have to work that out. Okay, my USB is on. Now if I set this to charge, it is set to charge I'll start that it's charging and now it does charge and it charges courtesy of this TP Or in fact it's a TC 4056 which is a Uh. We all know it's a generic uh Single Cell lithium cell charger And this is where when you charge, you can only do it on Lithium Nickel manganese.

Cobalt Although you could conceivably discharge an 18650 lithium-ion phosphate because you can set this stop voltage down I think to a minimum of 2.5 volts. Um, you can't charge it because this charger is specifically for Lithium ternary Nickel manganese. Cobalt Uh, let's see what happens if I just pull the USB type C out. it now can't charge.

How quickly will it realize that it can't charge? Yes! So it's gone immediately to end. Now you can discharge something plugged into the right hand USB type C socket and you can see immediately that my Uh USB outputting device is showing 4.7 volts. I can't charge it because it doesn't make any sense if you try that. I Think it will just say end because like I say you can't force charge back out of a USB type C.

Well, not unless you sort of have PD spec or something like that. so that just ends. But you can discharge it. So let's change the mode to discharge and we'll start that running and it will discharge my power bank.

Now this will take ages because it's got a 4 amp hour uh, power power Tool battery on it and I have to say that I can't quite see the purpose of this because let's say you discharge a power bank. So let's say I want to discharge this power bank and measure its capacity now I know from the rear that its capacity is what's this one? 15 000 milliamp hour. So 15 amp hours I mean at one amp, that's going to take quite a while anyway. But also, you're measuring the amp hour capacity at 5 volts.

so you're going to get a number far less than this. And of course, you've also got conversion inefficiency in the Boost converter where this device boosts up to 5 volts to put that out of the output socket. so you're not going to get a useful number measuring the capacity in amp hours of an external device. The only way I could see this being useful is if you could get some sort of module which takes an 18650 and perhaps has a USB type-c socket Outlet on it which would be pretty non-standard and then you feed the 3.7 volts round to this unit on the USB type C.

I Can't quite see the purpose of measuring 5 volt devices. we're just going to get nonsense numbers that don't tie up. It's going to be really disappointing because you'll get a far lower amp hour rating than the one actually on the power bank. Can't really see the point of that.

Okay, so this device charges the right hand cell using a Tp4056. And of course it takes a long time because the Tp4056 takes this up to 4.2 volts actually. As measured on here, it's ever so slightly higher. And then of course it winds the current down until it gets down to about a tenth of the nominal current, which is set to one amp.

That's done by a resistor selection one of these two resistors next to the Tp4056, and so the very last part of the charge takes ages. Now there is a facility on here to Loop charge and discharge to do multiple. Cycles Well, the rate at which this charges the cell um, discharging is fairly consistent. Well, Actually, it's not consistent because it's constant resistance.

It's 2 8 ohm resistors in parallel, which is four ohms. Now, these cells start at about 4 volts, so initially you get one amp, but of course as the voltage Falls when this gets to three volts, I equals V over R. So that would be three over four. So that's three quarters so it'd be 0.75 of an amp by the time that this gets down to three volts and the discharge process stops.

so it's not constant current discharge. Okay, let's look at some of the circuitry. So as you saw two eight Ohm resistors in parallel four ohms. Now they're pulled Low by this n-channel mosfet.

It's an uh, what's it called 8250 Yes, A250 A Um, but there's another 8250a and I Thought maybe they're just in parallel or one does each resistor, but it doesn't work like that. This one pulls the resistors to ground. I Mean it's only passing one amp so it's not under any stress. This one pulls the negative of the cell under charge and discharge to ground.

So of course, if you're discharging, the microcontroller will turn on this mosfet that pulling the negative side of the cell to ground and also turn on this mosfet, putting the negative side of the resistors to ground and then the resistors are across the cell and it will discharge. But I Was wondering what happens if you plug in the USB type C with 5 volts on? It hasn't got five volts on at the moment. Um, wouldn't it charge this cell because all you've got here next to the socket is a diode through which current from the USB flows into the circuit. Well, there's a really intriguing little bit of circuitry here.

When there's any voltage on here, probably more than about 0.6 volts, it drives this transistor. it goes into the base of this transistors through a suitable resistor. this then pulls its collector low and that pulls the Gate of this mosfet low so that this mosfet is turned off and that takes this cell effectively out of circuit. The microcontroller doesn't really know this is happening because it's a it's an electrical connection where if this is plugged in with any voltage on it, it just disconnects this cell.

So yes, it prevents um plugging in USB here and it just forcing current into that cell. But it's a curious setup. I Mean it's the only way it could have been done. but um, like I say I Don't really see the point of this external test socket anyway.

Um, so like I say charging is done with the TP 4056. Um, two little diodes down here. What they do is they there's one coming from this cell into the microcontroller and there's one coming from the USB type-c into the microcontroller. That way, with two diodes here, you can't charge this cell from USB type C and you can't have this sales voltage going back through USB type C.

So those sort that out. There's another diode here and when I did the thermal imaging of this thing, you saw that dog get hot when this cell was charging and so the path is USB Type C through that diode and into the TP 4056 And that needs to be a fairly uh, large diode because it's got a constant one amp flowing through it and you can see that that thing gets quite warm. There is only one diode there though, because of course you can't charge the right hand cell from the left hand cell, so there's no path between the two cells. You can only charge this cell through USB type C.

so that explains that diode. This is a 3.3 volt regulator and that explains why when this cell is down at 3 volts, you see a little pickup in brightness on the display because when you plug in USB of course the voltage on the microcontroller rises from about 3 volts minus the volt drop of this to 3.3 volts. so it all lifts up in brightness. and I Think this is just a little transistor and I'm pretty sure it's connected to the backlight so that this half brightness business, which can be rather annoying.

I'm pretty sure what happens is the microcontroller after a while, just pulse width modulates that transistor and therefore, pulse width modulates the backlight. LED So that's it really? That explains everything. There's nothing on the back I've been through all the components and most of the features of the software. I Mean there's a few other bits and pieces like it does.

Milliamp hours, Milliwatt hours I Don't know how it does this resistance measurement, but it does. I Can't give any indication of how accurate that is. Yeah, it's just a single cell charger and discharger with so many quirks it takes a long time to explain them. like the fact that you can't charge this cell.

Well, the the left hand cell holder is literally just to power the unit if you don't have USB type-c plugged in here. but you can't charge this cell from the left cell so you have to have it externally powered. If you want to do charging, you can do discharging. So assuming all your cells were fully charged, you could put them all in here.

Not that you'd want to because these sockets are really hard to get cells in and out of. But yeah, you could go through a whole bunch of cells and discharge them and Mark on their capacities, you can see I've done that. I mean in fact, this was something like 1280 five or something and I thought, what's the point in writing the very precise number on there I'll just round it up. Um, yes, it's just full of quirks like The Quirk of having it be able to measure, um, something externally and do a discharge test on that and this extra circuitry to disable the cell if you do that and this business that this would only be really of any logical usefulness if this came directly from just a cell without a power bank boost converter.

So it's a quirky, and quite frankly, rather useless device. There are other variants of this. Actually, it's so quirky that I quite fancy collecting the other variants. there's one with a monochrome LCD quite a large LCD in the middle, not this lovely color one.

and there's another one actually I've seen with a seven segment display which is probably utterly horrible. And look, there is another one where you can put four cells in as and as I Understand it and it's got a little heatsink with a fan so it doesn't use resistors. it probably uses a constant current electronic DC load. But then, of course you're getting to the point where this just behaves a bit like a four Channel lithium cell charger a commercial one rather than just a bare PCB variant.

But yes, it's a very interesting Vice And as I say I may possibly buy the other variants just for fun Factor Not for any other reason. Oh, I need to mention the auto feature. There we are Auto What this does is it charges the right hand cell fully, which as I say takes a long time, then it discharges it fully and puts a milliamp hour and presumably Millie what our reading on here and then it charges it fully again so that you end up with a fully charged cell and as I say you can set the loop counter anything between one and nine I think so you can do that nine times, which would take an entire day. So I'll put a link to this device that I got on AliExpress in the description below.

Oh yeah, don't forget to press press the like button. subscribe all that kind of stuff. Um, but for this video, That's it. Cheerio!.