Hello! This video is a post bag related specifically to building my big battery. So I think I'll start by going and having a look at my big battery. So here's the uh big battery. I've had to put it in the kitchen today because I'm running out of space and I can't really go outside today.

Yeah, it's really horrible, wet and rainy. so I can't even really get to the shed today. Anyway, back to the battery. So this is the 8S 8 cells in series.

You can see the8 cells on the top there. uh, 5p. five cells in parallel. So I got two sets of these boards.

Uh, the top boards are linked to the bottom boards now with these high current cables. The angle brackets on the top mean that I can get to all of the intermediate Uh cell points for things like the balancer. Well, also the Voltmeters and you can see the eight Voltmeters. I've hooked up the first and last just to show what they'll look like.

eight Voltmeters and you'll notice they're in a slight Arc and I've done that intentionally because these voltmeters in the middle read: slightly high, Uh, well, slightly higher than these other voltmeters. So when this battery is fully balanced, there will be an arc of voltages because of the fact that these Uh battery testers aren't all exact in agreement. So that's the state of play of the 768 W battery as it is at the moment. Let's go and look at some post um containing things to, uh, continue this build and the first one really is this.

So let's move everything out the way and take a look at what's in here. and it's this. So let's tear open the pack and get this out. It is An8 cell.

uh, active battery balancer. Now you've probably seen that I already have a four cell version of this which appeared to work very well. So I've gone and got the 8 cell version. Uh, these are the cables that come with it.

Now when I opened the four cell, uh version I said oh, these are oh there. Go there. Go all the plastic feet. Um, these are very optimistically thick.

another plastic foot. the fourth one shot across the room. thick wires. but actually I've seen currents of up to uh I think about 500 milliamps with this thing.

Get rid of all the rubbish. Um, so yeah. I mean these wires are probably good for about uh, probably 10 amps or so. but um, yeah.

I think they're commensurate with the sort of currents. I think the maximum current this says it could do is 3 amps. but I very much doubt you'd see three amps unless one cell was fully charged and another one was fully depleted. Uh, the color sequence is slightly interesting.

in here. it goes: black, white, green, yellow, green, yellow, white, what's that one there? Oh, green and red and so on the battery. I'm going to sort of follow this color sequence now in terminal posts. you don't get white, you get blue, but I can go red, green, blue for white, yellow, green, yellow, green, white, and then black just so that it will cause probably slightly fewer slip.

UPS um with connecting the banana plugs. Here's the four cell version of this balancer, which I put through its Paces in a recent video. uh about voltages and currents when using an active balancer on a battery. but let's take a look at these uh balancers on AliExpress So here's the item on AliExpress Press uh, it's a whole group active balancer, Lithium, Lithium, or Life Po 4 battery equalizer.

You can see here that they do the four cell version. They do a 6S version and this is the 8S version. The 4S is 531, 6s is 828, and this 8s version $25 There's also $418 uh for shipping and a of course that will be added when you buy it a DIY box. Electronics Mal Okay, next up these four and I'm going to open all four of them together.

Um, I Know there are wires in here, so I've got to be careful with my cutting. Perhaps I'll cut them off camera, right? They're all open. so let's pull out the content. So we got that.

We've got that. We've got this. this one and this one. Okay, let's take a look at them and they are these things.

Uh, Bms's now. Three of these would appear to be uh 4S Bms's These two look identical actually, apart from the color coding, this one's got a lot of orange and yellow in it and this one's more primary colors. Uh, this one's bigger and is an 8s. BMS Uh, this one is a 4S BMS Very different looking this one.

Uh, it's got a little metal plate sitting over the mosfets, but they all essentially work the same way. You've got a row of mosfets in parallel, Youve got a set of charge mosfets, a set of discharge mosfets. Um, you've got a controller I See, this one's got two for whatever reason, and you've got some balancing circuits now. these all balance at very low currents, and so that's why I use the active balancers cuz I Just don't think these achieve anything, particularly with lithium ion phosphate, because very quickly it falls to its middle area where all the cells are pretty much the same voltage anyway, and a balancer has negligible effect.

It only really does anything when the cells are pushed up to their top where top balances or pulled I suppose down to their bottom voltages where the balancer bottom balances all the cells. Uh, I've actually got another one sitting on my desk here, which I opened a little while back cuz I Was just intrigued to see it. It's got a sort of black plastic cover over the Uh circuitry on the bottom of the PCB and a metal heat sink which sits on top of all the mosfets. but it's essentially the same layout.

You got your charging and your discharge mosfets all in parallel uh, so the more of those in a row there are, the more current it can handle Uh, and you've got balancing circuitry and a microcontroller or a control chip to measure all the voltages and look for any one of the four or eight cells going below its minimum voltage. where whereupon it cuts off the charge mosfets. or if any one of the four or eight cells goes above its maximum voltage, it cuts off the sorry, cuts off the charge mosfets there. If if a cell goes below its minimum, it cuts off the discharge mosfets.

Now I Think most of these are what they call common Port Um, where you just must have a P minus that's pack negative and a B minus. So B minus goes to the most negative point of the battery array. and then P minus is what you use as your outside connection, but you both charge and discharge from that P minus. Now this one's slightly different because this is a separate Port uh BMS So you've got a B minus, a P minus, and a C minus.

So this is pack negative and all the switching is done in the negative of course. Uh, this goes to the negative of the battery cells. This is your pack negative for discharge and this is your pack negative for charge. So you would charge and discharge through different ports on the BMS Uh, Okay, let's well.

I'm not going to look at all these on AliExpress but let's just pick one. Let's pick this one and look at it on Ali right? This is one of those Ms's Uh on AliExpress They're very cheap I mean 297? Okay, yeah, there's shipping of 313 but I mean the total price is something like $6 C going to add on vat? Um, but yeah, these things are manufactured in vast quantities. so they are very cheap. So here you can see.

oh, that's got. yeah, this is the one that had the aluminium cover over it. the very tiny one. It is an 8s.

You can see the eight or the nine way uh connector there. These are the Balan circuits with the 101 resistor which is one Zer that's 100 ohms and these presumably mosfets. And then these are the mosfets which are the charge and discharge um, switches. It's common Port So it's got a P minus up here and a B minus down here.

There's no C minus. There's no separate charge port. Um, this one came from Lyp Z ux store but all these things are a similar price. They're all pretty good value now.

I Will put links to all of the ones I bought uh in the description below the video so that you can, uh, have a look at all of them. but I Think the common factor between all of these I mean yes, they are all very low priced. They're all pretty small as well, aren't they? and they all are all obviously very cheaply made. Uh, the sort of BMS you might use in a electric scooter you know, the type that catches fire overnight.

No, that's not true. Those electric scooter fires are largely down to people. uh, replacing the uh uh, the AC power block with the wrong type and then of course it Cooks the batteries. Anyway, enough of that I want to open that box now? Yeah, this one because this was me.

sort of saying I don't know about all of these. They're all a bit small and cheap looking, so this is kind of a step up. This is the next Uh level up in terms of BS Bms's It's not a smart BMS It's not programmable, it is all fixed voltages, but it's just the sort of Next Level So this is the BMS It's just a heavier. in fact I Got a feeling yes it is.

The PCB is actually aluminium. so all the surface mount components are uh, stuck down on on to what is essentially a metal. PCB Then there's another aluminium sheet across the top. We've got nice um contact points which are these little threaded mounts and they supply all the Uh screws and the ring terminals.

for that. it's an 8s BMS There's the cable that came with it and the manual is also in there. So this is um Yun I think it was uh BMS It's a slightly different price bracket. It's probably more like about 15, but you can see there are a lot of mosfets in there.

Uh, 3, four, five, 6, 7, 8. There's probably about 10 in parallel and you can see on the end here I'll get in a bit closer. Yeah, you can see on the end here. Uh, the mosfets sitting under this sort of conductive heat foam which is pressing down on all of them as I I Say there are a lot.

Oh, maybe these end ones are dodes. Oh actually no, no, no, they're mosfets. The middle legs been cut off because of course it's the same connection Point as the tab. So yeah, they've all got their middle legs cut off.

But uh yeah, this is I Think this is rated for well. Yes, it says everything here. it's an 8s nominal 24 volt. Actually, it's 25.6 isn't it life? Po 4 BMS 3.2 volts per cell.

That's the model number. common port for charge and discharge. so it's a common Port BMS 80 amps. which is why they've given you these big chunky terminals.

They've paralleled up 2 B minuses and two P minuses. Um, so P minus connect to charge and discharge NE negative pole B minus connect to the actual negative pole of the the cell array. So yes, I just felt that this was a slightly more up Market Uh, more EXP Expensive but much better made. Oh, there's some more stuff on the back.

oh it's all in Chinese uh BMS So let's go and take a look at that on alley. So this is the item. It is a Yunu star BMS Uh yeah. now this one will work with 5S 6s, 7s or 8s Life Po 4 Lithium ion is a different one.

You have to select that in these down here. So I specifically bought a Life Po 4 Uh, not sure what those voltages are. 8 amps with balancer so this also has a balancer in it. It's probably not a high current B balancer.

We'll look at that in a moment. So yeah, $13.85 Free shipping, but you got to add Vats that's probably around 15. That sort of ballpark common Port 4 s28 Uh, free assembly cable, free wiring ring Terminals and free screws on here. Now the choices are SI Oh H Oh, that's the price for the 6s.

sorry uh, let's go to the 8S Life Po 4 Yeah, it's not a massive amount more. I mean that's 47. Still free shipping. They do 7s lithium ion 7s, Life Po 4 6s lithium ion 6s LIF Po 4 So this came direct from the Yunar BMS Factory Store Uh, they only do Bms's I think or related products.

Let's just scroll down a bit and have look at some of the description. Uh yeah, can be used for 4S to 8s, 12v to 24v battery pack. They do lithium iron versions and Life Pro four make sure you buy the right one. Uh, lots of details here.

uh including all of the set points: Overcharge protection voltage is triggered at 3.75 for life Po 4 overcharge protection delay time uh, what's that 1 second uh for life po for oh much shorter times for lithium iron Not sure why that is uh, overcharge protection recovery voltage is 3.60 for life Po 4 So all the detail is here and it just seems like a a bit more of a serious BMS Um, applying these to my build the balancer I did think that and I got be careful not to drop this. that could sit there under the center volt meters and you can see the connector for that. I can drop the wires down into this sort of void on top of the cells and then bring the wires up and the banana plugs will go into these banana sockets. So yeah, that could go there I Think there's a little LED on here somewhere? Is that it there? Yeah, there's an LED Oh yeah, it's up on that left hand side so there'll be a nice little led to see there.

So I'd quite like to have that visible on the front I mean I was thinking that could go around the back, but I would like that to be visible now. I've noticed that the BMS has no mounting points on it. These Corner rivets are actually screwed in with screws. On The Backs There's no actual mounting for this.

However, what has just occurred to me is that it could sit there, couldn't it? Because this point here is B minus. So that goes to the Nega most negative point of the cells. If I brought another couple of these sort of Link pieces across onto these screw points that would just sit on the side and then the cable come out of the top there and go into what I was thinking of doing. with that was using Fork terminals under these.

um, these tightened down thing. So Banana plugs in the top for the balancer Fork terminals in there and then actually these uh, Voltmeter. these wires from the voltmeters will go actually onto the threads underneath because I've put little 4 mil uh lugs on those. So yeah, I'm quite liking the idea of hanging the balancer off the side there simply because it's got no way of mounting it other than mounting it using these.

um, these screw terminals here. And so these are today's post bag items. Now if you've liked this video, press the like button, Press the like button and a big thanks as always to my Patreon patrons. I Mean let's be clear about this.

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