Hello Today This it's my 4S battery. Uh, 4s2p Lithium-ion phosphate battery and it's been mounted to this wooden Contraption and it now has four of these little LCD volt meters permanently attached so that I can see the voltage of each cell at all times. What I want to do today is charge this battery and I'm going to use my little desktop bench top power supply I need a couple of wires to go into the battery, so is this going to spark? It's going to back feed this battery into the output capacitor so shouldn't be too bad. No, not too bad.

Okay, that's my power supply connected to the battery now. I Think what I'm going to do is charge these cells to three and a half volts each. So what I want on here is 14 volts Because that will mean half of 14 is seven, half of seven is three and a half. So three and a half volts per cell and then we can watch how the cell voltages increase once.

I Switch on the power supply. 14 volts, one amp. that'll do. Let's switch on so it's currently at 13.3 volts.

it's going up one amp. Let's take a look at the voltage meters. Are they going up? Yes! I think so 335-336-336-336 I'll come back in a minute Now up to 13 and a half volts and we have three, three nine three three nine, three three eight and three point Four zero volts now. I've got no BMS on here yet.

no balancing, no anything really, just the voltmeters. So I am going to have to keep an eye on this. but even if the cells are out of balance by going to 14 volts on my power supply, then even if one of the cells is a bit higher looks like that last one is uh I shouldn't hopefully get Beyond 3.65 which is really the maximum. You should take Lithium-ion phosphate um on any one of the cells.

So let's wait till the power supply gets up to uh. 14 volts goes into voltage limiting. You can see it's constant current at the moment which is the yellow LED the constant voltage LED is the top one that's a green LED When that's on, we'll be at 14 volts and we can see what the cell voltages are now up to 13.75 volts on the power supply. and there's been a bit of a Switcheroo on the voltmeters.

It looks like cell 2 is now in the lead. they do Dart about batteries are strange things. Just got to the point where the power supply has switched from constant current to constant voltage at 14 volts 13.97 and the cells are a little bit out of balance. Yeah, we've got 3.55 on Cell 2 and 3.46 on Cell three.

so I think we need to balance them. So here's a four cell active capacitor balancer which I got uh I showed in a recent Uh post bag video. I've put banana plugs onto the five leads so let's plug them in cidentally now that the Uh battery as a whole has reached 14 volts, the current required to keep it at that voltage just Falls continuously and I'm not sure what that will eventually fall to, but presumably almost nothing to keep this battery at 14 volts. Okay attaching balancer.

So I'll start with most negative, which is black that can go into the most negative on my battery. Next is white, so that will go to the next most positive point on the battery. Um, the little green light comes on, but it's very dim. so I don't think it's doing much on the balancer.

Next is yellow that goes into that point I Don't think the lights got any brighter there has it. Oops, that was erroneous. It's not yellow. Next, it's actually green.

So let's put Green in the next most positive hope I Haven't blown up the balancer, then it's yellow. I've only got one hand here so it's a bit tricky. So yellow goes into next most positive and then red is the most positive of the balancer and that goes into the most positive point on the battery. What's happening to the cells? Well, probably not much at the moment, but let's give it a bit of time and they should balance up well.

there's not much to see here. What would be nice to know is what are the currents going through all of these wires on the balancer? In other words, is it actually shoveling current between cells and will this actually end up being balanced? I think I'm going to get all my Dmms I've got three Dmms I'll put them in circuit with say let's say the three middle connectors there, the three yellow ones and we'll look at the currents. Here are the three Dmms all set to current. So let's start by looking at the current say in this middle balance lead I Hope the balancer doesn't mind having random plugs being removed.

uh I think I want that in common and then I will put no I want the balance Uh, if it's forcing current I think I wanted in the 10 amps and then the common can go up to the Battery Point There, let's do that. and that shows me that it's shoveling a negative current of 111 milliamps. Um on the green wire which is the center point here. Now you can see that's on this board here.

so it's between cells two and three and cell 2 is higher than cell three. so it should be shoveling current from cell to to cell three. So let me think about what this means just for a minute. Yes, I Think what this means is that um, the balancer is pulling current because if the current must be flowing from Common to the 10 amp socket, it's pulling current out of this node this point between cells two and three.

And if you pull current out from that node, your discharging cell 2 because you're pulling current out and your charging cell three. I Think that's what it means. All right, let's have a look at another one. We'll do the node between cells one and two.

Now, they're both at the same voltage, so there shouldn't be any current there. So that's the white wire. Let's pull that out and put it into the 10 Amp socket on the first meter. I'll just get another banana lead and certainly that seems to be the case.

There's only 18 milliamps being transferred. Again, it's negative. So I think it's transferring from cell one to cell two. Now we can't see any voltage difference there.

Um, 90 milliamps being transferred I Believe from cell 2 to cell three and let's see what's being transferred. Well, now these ones. it should be transferring from cell 4 back to cell three. So according to this, we should see a positive current on the third meter.

And yes, that is indeed what we're seeing. Sorry, it's not very easy to see, but that's plus 75 milliamps and the second meter is minus 75 milliamps. And if you look at cells two, three, and four, we're shoveling current from cell 2 to cell three, and also from cell 4 to cell three. So certainly currents are there.

Currents are flowing. and I Think you can see from these four meters that they are balancing out. What's my power supply doing? Now it's 14 volts. But what about the current? Okay, that's dropped down to 70 milliamps and I wonder if that's supporting the difference in these three currents? It's very complicated, so let's just have a think about this: if you're forcing current into a node and it looks like the balancer which is dangling down there at the moment, is forcing current, uh, forwards into the node.

this one between cells, uh, three and four. That one is. And so let's so we're forcing current into here. Now, if you force current into there, you force current into this cell.

So you're charging this cell and you force current forward through that cell. And to my mind, that's discharging that cell. So yes, discharging cell four and charging cell three. And that's that.

Of course, is what we want because cell 4 is at a higher voltage than cell three. Anyway, multimeters don't lie. Um, so not much current going between the first two cells. Not surprising they're at the same voltage.

60 milliamps negative current between cells two and three. So that's transferring current from cell two to cell three, and 60 milliamps of or 64 of positive current between cells three and four. And so to my mind, that's transferring current from cell four to cell three. Now, of course, the balancer is trying is transferring currents everywhere.

It's taking Uh current from all the cells and flattening all the voltages out so they're the same and then writing it back. It's doing a kind of read and write, writing it back to the four cells such that uh, I mean it's unintelligent. This thing is just a completely unintelligent capacitor. Switcher And it is just shoveling energy between the cells until there isn't any voltage difference between them.

So I'll leave this whole Contraption here for a few more minutes and we'll see if the currents all reduce and the voltage is on. The four cells all equalize. Now, down to 30 milliamps on the third meter. 23 milliamps Nine milliamps.

Uh, three five two three five one three five one three five three on the power supply. It's now only requiring 36 milliamps to hold this whole system in equilibrium. I'm just going to cheat a bit here actually if I can do this with my only two hands I just want to bring that cell fall down a bit and I've got this car headlamp bulb. so I'm just going to put across cell four.

Let's see if that oh yes, that's pulled it down, hasn't. It will allow the balancer to push that back up now. and actually you can see that having done that, it's immediately sent the third ammeter into a negative current. which I believe means that it's uh, sucking current out of this node.

which I think means it's discharging cell three and charging cell four, which would be what would be required now that I've pulled the voltage of cell 4 down a bit. Anyway, that's fun with a 4S life Pro 4 battery and what you can do. and you can see what's going on with four voltmeters and three ammeters, and even knowing how much currents being put in by the power supply. Yeah, that's it for this video.

Cheerio! It's been about half an hour now. I've been editing the video and now we're down to some quite small currents: 20 milliamps on the power supply to maintain the battery at 14 volts. The current's on the meters and are very low. three milliamps, one milliamp, and four milliamps.

and you can see that the four meters are all basically in alignment. Now, remember when I tested those Um battery testers, they all read slightly different voltages, so it's quite possible. In fact, the currents tell the story, don't they? When these currents are all zero, then the battery voltages are all the same. So actually, those first two meters are reading slightly low.

Ironic that they're slightly mounted low on that piece of wood. That was absolutely pure coincidence. but there we are. All the cells are in.

Balance Cheerio Again.