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All right, this video is a user manual for our new 4s lithium-ion phosphate pcb battery board right. This is a pcb printed circuit board that is designed to put four cells in series to make 12 volts and which type of cells the 26 650s look like this they're very popular they're, usually lithium-ion, phosphate and 4s at 3.3. Volts right, 4s, 4 in series will make 12 volts, which is very usable for all kinds of applications, including automotive, uh and all kinds of other stuff right. So that's what these boards are made.

You can buy them like this and what allows you to do is make a battery pack without soldering and without having to buy extra expensive. You know special tools to to put a battery pack together right, so this is very easy uh you can put these batteries and these boards, just sort of like you - would load batteries into your remote control uh to operate your your tv right. So that's what this is so this is how easy it is to put it together, but before that, let's talk about the batteries, so these are uh. Lithium-Ion, phosphate batteries.

26. 650.. When you get your batteries, if they're brand new, then they're likely all at the same voltage and they're all likely they're all going to be around the same capacity right, because that's what new means so they're new, you probably don't - have to check every single one of The cells you can do this and load them up like this and then just build your battery pack without having uh scrutinize your batteries too much. But if you're using older batteries or use batteries, if you're like recovering cells from some other packs and uh, you don't know the the state of charge or you don't know, the condition of your batteries, where you're gon na have to make sure it's very important.

When you load them into these boards here that they're all the same voltage right, so how do you check for the same voltage? Well, you just used a multimeter there. We go that's 3.3. We have backwards there, but that's not important if you check it. 3.333.

3.334. Okay, that's like very close. 3.335. Okay, so you know three decimals in if there's difference, that's very, very minimal! It's it's fine! So you have to do that to all your batteries and once they all match, then you can safely put them in here.

Things will work better if you do this right, if you don't, if you put batteries in there that are all different state of charges, then you could kill some batteries. The bms system will eventually balance them, but it will take a while, if they're drastically out of uh out of sync with each other right, if they're in balance, so the better balance they are. The faster you'll be able to use your battery pack and the just a better experience that you will have now you can, if you have a huge system that you're going to build, there's probably easier ways to check your batteries like, for example, you can get one Of these things, this is a state of charge, meter right, it's called the ist bg-8s and then this is a cable that i'll have link on the bottom of this video. What you do is you have the negative and then there are holes in the back of the board here and that's the negative.

This is the negative, so you just put it on here right and then it requires two batteries to turn on. So here we go. This is battery number one, the closest to this uh connector and then battery number two. So there we go see how um it turned off.

So now you get to see graphically here the state of charge. Three point three, one. Four three point: three: two: oh there's a six millivolt difference. That's very that's not much! So that's! Okay! I'd, say anything like below 50 millivolts.

I guess it's! It's okay! You can consider them somewhat balanced anything below 50 millivolts. The bms will take care of it. But if it's more than that, you will want to uh change those batteries and uh and and balance them before you put them in here. Let's see if we can get another one, okay, so here's something like 24 millivolts and you could totally tell oh yeah there.

We go see how it looks like there, okay, so if you're doing large groups, what you can do is you know you keep the lower voltage batteries and then you can populate the boards right likely you're going to have more batteries that are at the same voltage As this and then you can build boards with them, if there is a difference in here as long as it's not super drastic, it's not like close to a bolt just half of all the difference. Whatever you can safely build a battery pack with slight differences. The you know, the higher voltage pack will send energy to the lower voltage pack and it's going to do it at a rate. Uh slow enough for these boards to handle it and nothing's gon na melt - and you know it's gon na - be fine right.

But if it's like really drastically, you can't put one: that's like you know, uh three volts and then one that is going to be like at 3.6 volts. You know more than half of all, then that's that's too much and then the the energy flows might be really high. The rate of energy transfer is going to be too high and then you're going to run into problems. So so that's those are the two steps same voltage same capacity and same voltage between the boards.

They could vary a little bit like half a volt, it's okay, but anything more than half a volt between boards uh. Then you shouldn't do it now. So here's how the next step is you put them together? Let me show you how to do that all right, so you can buy these in many different forms. You can buy a single board and it's going to come with four 30 millimeter long standoffs, but then you could also buy kits of like five 10 25 of these boards and when you buy multiples like that, you're gon na get also the four stand.

Standoffs per board, but then you're also going to get um. You know nuts and you're gon na get some plastic standoffs and those are the feet. Those are isolators, you use them on the first board. So here's how you do it you put them through here and then you attach that there right, then you do it on the other feet here, the ones in the back.

Sorry about my nails. I was doing uh cleaning transmission parts this morning, so they're all full of grease. Okay. So that's what you do you put them like that and those are made out of plastic and the reason why they're made of plastic is so that this is isolated, because these are electrically charged.

This is how you transfer the energy from one board to the next, and so they are electrified. If you put a metallic one in here and you set it a metallic space or a surface, it's going to short out so keep in mind. These are electrified. So what you do is you load up your second board in here whoa? I made a mistake.

These are loaded backwards, all right after you put the standoffs there. Now you can load up your next board and keep in mind. These are electrified, so be careful if you made a mistake and in any of these boards and you loaded a cell backwards or all of them backwards or something when you go here and you set it down, it's gon na spark and it's gon na burn uh. It's gon na blow one of these fuses.

These are all fused, so they're very safe. Even if you make a mistake, it's just going to be a little spark and then and then that's it, but you're going to if you see sparks while you're doing this, then you're doing something wrong you! Some of these. You have to check every board that they're right positive goes on this side. Negative goes on this side.

These batteries look almost the same. You could have one backwards and completely just miss it right. So if you start seeing sparks, don't just keep going make sure that you figure out why that is, if you see sparks if these are way too different right. If this one's like at 80 or 90 state of charge and this one's at 10 uh state of charge, then also when you put them together, there's gon na the rate of current that is going to transfer from the higher battery to the to the lower is Going to be high enough to maybe surpass five amps and one of these fuses will blow.

So if you get blown fuses, it's because your uh, the batteries are not all the same. Uh voltage, uh uh and the the boards are not the same voltage between them. Right so there we go, you do that. If you don't see no sparks, then uh yeah, you did everything right.

So again you use four more standoffs, you hand tighten these uh. These standoffs don't over, tighten them because you can mess up the threads. You could crush crush the boards here, just hand, tighten them right. Here's the third board there we go comes the final part, some of the kids.

You might have to buy this separately, you can buy it separately or you can buy it with the kit. This is a bms system. The battery management system is basically a switch that this is disconnected from here when it's off, but when it turns on it, connects it, and then you get power on this side. You get 12 volts here.

So the way to can turn this on is through these cables. It checks the voltage of each individual group. There's four groups of batteries here number group number one group number two three and four: they all have to be matching if they're too far apart, because you didn't do a good job, uh assembling this the correct way, then this bms will not turn on and when You put it in there. You won't have 12 volts here right and so that's what you have to do when you put it in there, you got to check that you have the correct voltages and all the groups also here fuses trace uses.

If you make a mistake and the the voltage difference is too drastic from one cell to the other or one group of cells to the other, what's gon na happen is that these trace fuses each board has them. You see them they're right. There they're tiny little traces and they're designed to blow around five amps, and so they will also blow, and so, if you have trouble waking this up once you put your whole thing together, then you have to double check that that all of these are intact. All these fuses are intact, and then you get you have good voltage in between here uh and they're, all uh matching, and then this thing should turn on right.

So right now, when you put it here, nothing's gon na happen, because the bms doesn't know what voltage these are. It's it's not until you connect the ribbon cable to all these boards that this uh gets the voltage signals in here. So the the very top uh board here you just use the nuts okay last step is the ribbon cable? So if you did everything right, you shouldn't see any sparks or any smoke or anything when you're connecting this, these connectors have a keyway. You see that keyway there and the connectors also have a keyway here.

This is a key. This is a keyway, so you have to match them towards the outside, and all you do. Is you connect them in there? There we go first one. Second, one again: if you did everything right, there should be, no sparks should be, no heat should be no smoke.

So here's the last one now you're connecting all of those boards into the bms, so the bms is off right now it should turn on when you do that there we go. How do you test to see if it's on? Well there we go 13.8 volts. If you see anything different like nine or eight, that usually means the the bms is off right and what you're seeing there is like a a ghost voltage. It's just leakage from the from the transistors here, they're off, but they're, not 100 off.

There's eight bolts in here, but when you connect anything in there they don't it doesn't have the power to power anything so any voltage that is less than like 12 volts or the aggregate of all the cells right. So here's the aggregate. This is how you find out what the batteries are at 13.38. This is before the bms and the connectors after the bms, so the power, the electricity comes from here, uh and then it goes through the bms, and then it comes out this connector here.

So they have to match when it's on it'll match perfectly 13.38 and then the one after the thing 13.38. So if it's less than that, if you see a difference, it usually means this is off. Another way to check to see if the bms is on is to check continuity to check. If this is connected to this, remember this, this is a switch, so there are mosfets in here that when they turn on, they connect this to that, but when they're off then there's no connection between there and that's it.

That's your battery here, uh! You can use this battery to power all kinds of things that are 12 volts. Now this right here, it's the throttle, there's the bottleneck of the current right, this handles uh. So this is a 50 amp continuous bms, so this handles 50 amps, anything more than that it'll start heating up too much and it'll just turn itself off right now the batteries can do about 1c and they're about the batteries are 3.7 amp hours. So these boards can handle five amps total because anything above five amps these uh, these fuses are gon na melt right, they're gon na blow.

So, in order to do 50 amps uh, you need at least 10 of these boards right, but you could put more than 10 like you could have an unlimited amount of these boards right. If you don't need more than 50 amps, then you can use a single bms, but if you need more than 50 amps, let's say you need a 100 amps. Then you can get two of these bms boards and then stack them either right next to each other or put a long stack and separate them right and different uh places in the stack. And then you combine the two outputs and then that's going to give you a hundred amps.

But of course you need enough of these boards at five amps to give you that, so you need a minimum of 20 boards right. So each one gives you 5 amps. 20 boards will give you 200 amps, so you size your battery according to your needs. Your power needs to your load right.

So if your load only uses a hundred watts right or maybe like 10 amps or whatever, but you want a battery that lasts you a long time like a week or something you can build a bunch of these boards and put them together and then a single Bms will be good enough to handle anything below 50 amps, so you don't need to buy more bms's or x amount of bms's per x amount of boards. That's not how you size it! You size it according to your needs to your load needs. If you need a hundred amps, you need two boards. If you need 150 amps, then you need three of these bms's to be able to power your battery pack.

So that's it. This is a super easy way to make lithium iron phosphate batteries. This is 4s. 12 volts, which is useful for all kinds of things, and these boards you can find them on, and this system is highly highly modular.

I will show you guys how to build different, bigger packs, uh of different voltages too, using other boards that are designed to make it really easy for you to do it, and this is in the in in future videos. So thank you for watching this. Video we'll see you next time, bye.

11 thoughts on “Build 12v LiFePO4 battery Packs the Easy Way”
  1. Avataaar/Circle Created with python_avatars jerry davis says:

    I build the," Build 12v LiFePO4 battery Packs "' , I am not sure on how to charge the unit. I was going to use it to power my 12v boom box build. I think I know how to charge it I just would like to be sure. Can you explain?

  2. Avataaar/Circle Created with python_avatars Mind Meet Maker says:

    There must be a limit to how many pcb to one BMS as each level the cells are parallel i.e. cell 1 of all levels are parallel to the BMS and the balance resistors are normally very small so if you stack to many boards it will never balance quick enough and a single cell could over charge or trigger Over voltage or am I missing somthing here?

  3. Avataaar/Circle Created with python_avatars Alexandre Lollini says:

    You can't stack like crazy : the brass standoffs are a limiting factor : I think a maximum of 8 boards, or 8 boards on each side of the bms can be safely used. 8 below and 8 on top. and that will be heavy enough for an unit to manipulate. With the li-ion 18650 7S I do stacks of 14 with the bms in the middle. I have tried more but measures from the top and middle do not match, so this means that voltage sag can tax more the middle than the bottom or top and then you do not use each cells the same amount, making then age differently. Better limit the max stack for the brass standoffs.

  4. Avataaar/Circle Created with python_avatars eddiekytia says:

    So the link for new batteries are for 3200mah so if I made 4 stacks with a bms how many true amp hours would that make of a 12v pack. Hope I don't sound stupid I'm just learning about batteries. I'm guessing 3200mah x 4= 12.8 ah with 20amp max output?

  5. Avataaar/Circle Created with python_avatars Mitch Martin says:

    @jehugarcia, you should look at putting that fuse horizontal in the next board revision. would make it much easier to replace in the future. What material are those standoffs? Have you measured the resistance of them? Have you thought about going to a mating connector instead of electrically connecting the boards via the standoffs? Without loctite, I've had those type of standoffs loosen up pretty quick with any sort of vibration.

  6. Avataaar/Circle Created with python_avatars AJBtheSuede says:

    I can't remember the last time I clicked on a video from this channel and found that it tried to do ANYTHING else than sell something. Educate, entertain, ramble, test…. Nope. Only sales pitches. I miss the VW van, that was huge fun 🙂

  7. Avataaar/Circle Created with python_avatars Kevin x says:

    Please please please remember to talk about or show an example of the chargers we should use for those batteries.


    If we can charge phosphate batteries with regular lithium battery chargers.

  8. Avataaar/Circle Created with python_avatars Dan Williams - Shake, Rattle, and Roll says:

    Does it come in 24v?
    Do they work with an active charge system like solar panels? (I have an mppt charge controller, 40A, getting up to 35v; currently on 12v, but that struggles to keep my laptop powered while editing video or gaming, so I'm thinking about upgrading to 24v)

  9. Avataaar/Circle Created with python_avatars Peder Bjørndal says:

    The problem with this kind of cell is that voltage does not tell state of charge. You can saturate an cell at 3,45v to 100% and its full even if not charged to 3,65v. So an BMS has a really hard time balancing them. A cell can be absorbtion charged at a lower than max charging voltage all the way to their design capacity – it just takes a long time.

  10. Avataaar/Circle Created with python_avatars Jason Broom says:

    So, what you are demonstrating here is a 4s-4p pack. That would give you around 190wh with a max discharge rate of around 20 amps? Is that correct?

  11. Avataaar/Circle Created with python_avatars Paul Curtis says:

    Dream come true, I'd love to see a 48V pack. I'm going to eventually need 12Kw storage in 48Volts, but I will need to add packs over time so I can pace the growth.

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