Save $500/day when you DIY your own batteries!!!

Hi everyone, I just finished building this DIY battery and the capacity test worked amazing. Stick around if you want to see exactly how I built it and tested it. Hi, I'm David and welcome to my channel where I like to build DIY projects. renewable energy and energy efficiency for this build we are going to use this empty battery box which has the same dimensions as some of the popular brands you can buy. It has a very nice form factor. Now it's a completely empty box and we're going to fill it up using some of these lithium iron phosphate cells.

Now these are new cells from the battery connection and they are 3.2 volts nominal because they are lithium iron phosphate. At the end of the project we will do a capacity test and review all the numbers and see what the final cost is. Hopefully we'll be able to build it less expensive and more affordable than you could buy it off the market and it should be a lot more fun to build it ourselves. here we go, okay everyone, let's take a closer look at these cells that we're going to use. These are new battery connection cells of 3.2 volts nominal and 5000 milliamp hours and they were manufactured just a few months ago and if we put these, side by side, we can see that the new lithium ion phosphate battery is in actually a little bit higher, which surprised me because it says 65 and this one is also 65 18 and this one is 32, but this one turned out to be longer. so it might be more like 32 by 700 65 millimeters, so it's right on point with the seven centimeters, which will be 70 millimeters, so I really wish they would label this as a 32 32-700 plan that would fit them into something really tight and that might make a difference for you the five millimeters, okay, let's put this away, we have about an inch or three centimeters of extra space left, as far as how many of these cells we can fit in here, I bought a bunch. of these two cell holders and three cell holders and they will fit in this orientation, so we have four on the bottom and five tall, so we have a little bit of play, but not enough to go with the five wide, so this works fine.

We're going to get 20p or 20 cells in parallel and 4s, since these are 5000 milliamp hour cells based on that number, this will turn out to be exactly a 100 amp hour pack now that there's a little bit of room. here the cap is taller than the top of this lip and that extra height will help

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we add the bms now the cells and cell holders that I bought from Battery Hooking and this case I bought on aliexpress and I will leave links to everything in the description below if you are going to buy some battery connection you can use the coupon code davidpaws and that will give you 10 off so we will take four of these cells and put them in series which will create a nominal 12 pack ,8 volts which will work very well, it will have a good voltage range for typical 12 volt applications, well the eight cell holders are now ready.

I noticed a little quirk where I have two cell holders joined together which caused this weird little bug where some of the dovetails come out on the wrong side right where I have all three and they both line up with each other. Now it won't cause any functional difference, but that could have been eliminated, say if you only had the three cell holders. Just and then I cut the last of the three cells. I ordered a box of 100 of these cells because I wasn't sure exactly how many I could fit. Turns out 80 fit very well with plenty of room for the BMS. so you can order as many as you want, you don't have to order a box of 100.

Now, something to note: the box got a little damaged during shipping, which I'm a little disappointed with. You know, I wish it wasn't like that. the case but

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I opened it the cell itself doesn't look like it has any damage it doesn't look like it has any dents but I'm still not going to use the cells in the four corners and with all the cells in one of the trays we'll take the next one and put it in here and we will give you some. Oh, it went in easily enough. Sometimes you have to shake it a little to get the cells to fit.

The covers could come off and it could fall apart if I'm not careful, so I'm going to hang this over the edge a little bit and I have some of this cap ton tape and this is a high temperature tape before I tack weld them, they'll be parallel to the cells I want to double check that all the cells are within one tenth of a volt of each other 3.29 3.28 excellent each cell is between 3.2 and 3.3, so we are within one tenth. I didn't see anything below 3.24 and yesterday I didn't see anything above 3.29. I've been spending quite a bit of time simulating different scenarios.

I have different types of nickel strips of different thicknesses. Here's a coil of nickel-plated copper strip, so I've been simulating different scenarios and testing. To find the best solution for how I can do this, when planning

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serial connection, there are several things that need to come into play. Part of it is how does this all fold up or go into the cabinet, how are we going to do that? connections, but also how many amps are we going to carry. This cell group has 20 cells. This can easily put out 100 amps and this bms that I have is a 100 amp bms but you don't really want to charge them with more than 50 amps which would be a half c rate and that's because when you start charging a cell with a rate of more than half a c, you will start to accumulate excess heat and when these are packed together in a small enclosure that can start to become a problem now not necessarily but potentially and that is why even other companies like Battleborn Battery, Kilovault and Victron Energy when they have these modules that are already built as a 100 amp hour lithium iron phosphate, they recommend in the user manual not to use.

Beyond half a C it should not exceed a load of 50 amps and that is due to heat buildup. Now when all of these factors are taken into account, I have decided to limit the amperage capacity of this pack to 50 amps, so I have a midnight solar here. 50 amp brand circuit breaker, so that will be the weakest link. Now I want to make sure that all my series connections are capable of generating 50 amps continuous without overheating. Now, for example, this nickel strip measures 0.15 millimeters by 8 millimeters. This is good. for about 5 amps now, this is a double width nickel strip made for 32 millimeter cells, which is what we have here now, if you look at just this part, just a stretch, this is about what it was, 15 millimeters per 0.2 millimeters so this is good for 12 amps so if I use five of these strips that's a continuous 60 amp capacity and I know the series connections won't be the limiting factor I won't overheat them now that I I have made fun of how I am.

I'm going to fold these accordion style here just with tape here in the middle, we've put a nickel strip on and it's not spot welded yet and I just put a piece of cap on the tape to keep it in place and a ruler to make sure. which we're aligned so I have a temperature sensor here and it's just stuck on this xt90 connector and I want to stop when we start to overheat we're going to change the joules and we're going to go to 50 joules now 50 joules is about right for 0.2 millimeters of nickel that's what we're using here so we're at 50 joules now we press this once I'm going to go down to calibrate we're going to press calibrate it's going to tell me open i click to say yes I'm open now it says short, so I'm literally going to hold these two probes very tight together and press and hold.

You saw the wires jump because it actually sent some electricity through there and then we can let go when it said okay. Now I'm going to press this again, I'm going to go up to Enter and Auto mode, if you can hear that click now, we just finished that row and they all look good. 50 jewels, let's see what our temperature is, 84.4 degrees. Celsius and that probe is there on that xt connector if I take off a glove and check yes, yes, that's hot, so I'm going to remove the tape and reposition this and that will give the xt90 a chance to cool down. a little bit, I see it drops pretty quickly, but that's a lot, 50 joules, it's not that important when you're using thin material because you can lower the power setting now that this is done spot welding and I put a layer on. of Kapton tape, I want one more layer because they are going to bend and touch each other.

Now this is a paper with adhesive on one side and I looked for battery paper and this is what came up. I think I already heard someone call it barley paper before it felt like a thick construction paper adhesive on one side, remove the backing now I'm going to stick this on the negative battery up to the seam, this is the exciting part when folding it . This is there, so yeah, so I think it's going to work fine. Here you can see the nickel right there and I'm just pressing these two sides together to make sure the nickel has a nice crease right at the intersection.

Well, here we go. Here is the positive side. I set this up yesterday where I oriented all the nickel strips on a piece of plywood, then soldered them to four layers of copper strips so I could get the amp carrying capacity I want, and then just soldered on a couple of 10 gauge wires Now I used a pair of 10 gauge wires because they are the same gauge wires that the BMS has. I still have more spot welding to do here, but I have to wait until the spot welder cools down and these positive wires are I'm going to go out and go up the side and I still have to do the negative on that one.

Okay, all the solder points are done on the top, so now let's fold this over. This is the wiring harness for the bms. Now the main positive wire is this one. The red needs to go here to this positive bus bar and then each one needs to be connected subsequently. Now I'm letting that normally I would like to put this in first, but I'm letting the spot welder cool down right now. So I'm going to go ahead and solder them while I can and then we'll spot weld the last main bus bar later okay so if I open this up I can see there's a few in here so let's go ahead and try to solder that okay , so this worked fine now.

Sorry, I just couldn't get a good camera angle to show you while I was doing it, but I just peeled off some tape and put it on there. I'm going to tape this back up. There is now a small gap in the plastic. Look, there's a high spot in the plastic here and here and there's a gap where the cable comes out. Well, I put some duct tape on there and now I'll do it. close this again and you can see there's a lot of space that's not going to short out the next cell like it's not going to rub off doing that, so it's in place, this one is in place next, I'll go right here. to that. because it's nice and convenient so I'm going to grab the plug and the first two wires are ready so I'm going to grab the third wire and now I'm going to run my fingers through it so I don't mess it up and this is the one that's going to be soldered here is a little bit of flux, so the first thing is to put a little bit of solder there, okay, now we have the bms and it comes. over here and I want to connect it right at this point, so what I did was I just took a little strip of nickel and I jumped it over these two wires and I spot welded them together and that's going to help keep them down and in place to get something. solder from the back, so now we have the bms attached to this, which I prepared in the correct orientation.

All of these nickel strips need to be spot welded here on the battery, but I'm going to go ahead and solder the last one. cable for the bms voltage sensor, which is this black one, so it's soldered well, there we go good, so now I have all the voltage sensing cables. I have not finished. I still have more spot soldering to do, but this is overheating. so I'm going to let it cool here we have the voltage sense wires so what I like to do before I plug this into the bms we need to make sure that I haven't crossed any wires I haven't jumped any the wrong location so To do that, let's take a multimeter and we'll set it to DC 3.2 volts.

You must be careful not to touch the two multimeter probes. Now this should increase another 3.2 and it increased another 3.2. Yes. The last and final 13 are perfect, it's easy to follow the wires when there are only 4 of them, but when I'm making my big 14 or 16 battery packs, sometimes you can cross them, but we have them all in the right location. now if you cross them and connect it to the bms, you'll probably blow up the bms, burn one of those little chips now that I've glued this top end and we have the bms attached, which is back here. so let's go ahead and put some more paper in this set.

Okay, this looks great now that it's a solid package. Well, here we go. I have to put spacers so the cables on this side don't get crushed. then here and probably on this side as well, I'll just add some block or something, so I want to use this half inch cutting board as a spacer on this side and I want to keep all these wires and stuff from hitting the side of the box, so now I'm going to route this part right here for this cable, probably if I did it again I shouldI've put the positive wires up here, but I thought you know, diagonally because that helps even out the flow. but I don't know, it's probably not necessary anyway let me get this right.

I took out the board and I'm going to put it here like this. I need to cut this tape because the tape is in my way as much as I am. It's like having that tape down here, you can see it coming in, so I'm just reaching with my finger and pushing it into that slot and then I can push it against there and now I'm going to tape this in place. I have a half inch cutting board on each end. I also have a half inch piece of cutting board down here and it's on track for that. positive wire, okay, let's tilt it up, I think it's going to work, yeah, it should work, uh-oh, sticking in a little bit, okay, snug fit, when I plug this in, I'm going to put a bluetooth dongle here, now this .

It may or may not work with Android, but I'm going to try it now. This bluetooth dongle is a separate part that you can buy. It does not come with the bms. I was able to download the app from the battery connect website. I opened the app on my phone and I was able to discover the bms, but I couldn't actually open the bms within the app, instead an error message appeared on the screen saying that it doesn't work with the version of Android I have. this phone is a google pixel 3 so whatever version comes with it now this is my wife's apple phone and it looks like it has figured out the bms so let's go ahead and see if we can get information from the bms it says waiting for data and it looks like it opened hey that's cool so here's the bms bluetooth dongle we have a blue light and it looks like it's connected to the apple so in this case we're looking at 21 13.13 that's cool let's see what the settings. the factory, let's see here if we set the write parameters in bms it costs more money hmm uh, I guess the free version of the app will let you see the cells, look at maybe the watts going in and out, what it says power there, but it will not.

They won't let me set the parameters, so what voltage to overload, what voltage to balance that kind of thing. We have the circuit breaker rated for 150 volts DC and 50 amps and I'm going to put it as close to this positive terminal as possible so that the rest of this room won't interfere with the bms, so if I put it like this you'll see that I'm just going to open the cover here and I want that the breaker and the bms be on different sides so they don't interfere, i start by cutting this close to the inside because i can always make it wider.

You see, I need two holes for the two screws. It's going to be a little displaced, but I think it will fit like this. I do not do it. Sure, still, if they're going to reach, they're pretty short, but let's try it, so here's the screw and I use this thread tester and I found out that it's 6 by 32 5 16 right now, let's see if we can get it. a half inch one going through my pile of random screws. I was able to find a couple of 6x32's but they are too long so let's go ahead and put them in and then we'll measure how much we need to cut so now we have the circuit breaker in place and if I turn it over we can see how much the screws stick out.

Now I have the screws bottoming out inside the breaker, so now I can measure this distance and that's what we need to cut and it shows. like we would have to cut three tenths of an inch if I cut them just using a hacksaw, which would leave a rough edge that would then have to be cleaned up, so there is an easier way to cut them, this is just a pair of wire strippers, no I know of a generic one that I've had for as long as I can remember, but it has 632 printed on it right there, so what you can do is open it up and screw it into the 632 hole. and there are threads on this top piece of metal and then the bottom hole is just open, so he's going to cut it with scissors, he's just going to cut it for us.

You can see it going through there now, if I apply pressure it will cut it. but I haven't measured it yet, so we know we want to cut three tenths of an inch, so we'll come here towards the back. Now remember that it's going to cut it right in the middle between the two, so I'm going to go like this now, that would cut too much, so I'm going to back it off a little bit, so now I'm just going to tighten this like this, there's the piece that came off and we're going to unscrew it and while we do.

I have to unscrew it with a screwdriver because that will come out of there we go, so it should screw in nicely, now those screws are shorter. We were able to screw the circuit breaker into place. I teased what I needed with this piece of nickel. and now I'm putting it on this piece of copper that I've drilled these holes in and what this is going to end up doing is making the connection between the circuit breaker, it's going to continue like this and then it's going to bend and go away. there let's see if this double layer can fit here yeah it fits over that stud it looks like it's a little out of place I just think it's the curve let me try to bend it back now one layer could probably handle the amps no there is a tooth problem. flange bolt thread locker, there we go to the circuit breaker, great, okay, both are tightened nice and tight.

I threw some paper between the battery cells and the bms, just one more layer of protection. I marked here the distance that this edge of the plastic comes out so that they don't interfere and I'm going to tape this bms and place it like this very close to this edge so that I have enough room for the slack of this cable, all that I need. this edge is enough space for the edge of the lid, there are two layers of the lid here, so this can get very close to that side, the temperature sensor is underneath, the voltage wires come here, so let's tape this up adhesive for the next one. what to do, we're going to cut this out, we're going to put some ring terminals in here with the hydraulic crimper that's going to be on both sides and finally we can connect it to the cap section now each one.

One of these wires is a 10 gauge fine strand wire with silicone insulation, so it is high temperature insulation. They are good cables. I think I can fit them on an 8 gauge ring terminal, so I have some eight gauge ring terminals. Here we are friendly. both wires can go in at the same time now we can crimp it. I'm going to try a number 10 die, see if it works. I pull each wire individually and I don't get any movement, so we're good. Okay, now these three have loctite, I put just a little bit of electrical tape over those terminals, so now we have a lot of slack there, now we just need to crimp the ring terminal for this one, this is the ring terminal that I had and I I drilled to accept the larger bolt for the brass terminal.

Now I'm not happy with it, so I'm not going to put any loctite in it. I already went online and ordered a new crimp ring for this. So I'll fix this as soon as it arrives, but I want to finish testing this battery and show you the video. I don't have Loctite because I'm going to replace this ring terminal, that red wire that I have. I miss the bms so I'm going to reach in with my fingers and pull it to the side a little and we should be fine. I'm going to put a layer of electrical tape here right now because I have to get it.

Here in a few days, when the new ring terminals arrive, the battery will be complete, but we still have to test it, so give me a minute and I'll clean the work table because I have four days of tools accumulated here. Me four days to build this will probably take you a lot less if you do it

your

self because you won't have the camera and the lighting and you'll be trying to get all that, so I have these cables that I built earlier. a whole collection of different adapter cables that i have had to build for different projects, this one here has ring terminals on a 10 gauge wire to an xt60 connection breaker, so now it is charging, this is about 100 watts, so I set it to 6.5. amps just because I want to see the balance function and we had two for a second there and then one went off let's see if we can move the cells a little bit closer now we're at 43 millivolts so it looks like it stopped before the cells actually they reached 100 percent it says over voltage protection it looks like cell group number two must have overshot and is not rocking right now the bms turned it off but i wasn't sure it was absolutely one hundred percent so i turned it back on just in a ampere, that's the i.

I programmed it to one amp and the purpose is to allow balancing to take place. It looks like cell group number two has a bit higher voltage so it's balancing out, but the bms probably closed it. probably before we hit 100 percent because this probably went into overvoltage protection, so the more times I cycle the battery, the more chance it will balance. Now it looks like it's not balancing when it's just in storage mode, it's only balancing while charging, so it will eventually allow for more capacity, but if I were to do a capacity test right now, it would be a little low, so probably I'll cycle this a few times and then try to do a chamber capacity test so that cell group two is definitely at a higher state of charge than the other three groups of cells and right there we hit excess voltage. and it turned off and i heard this beep and it turned off but the internal bms is what turned it off this guy didn't. it reaches the pac voltage so it's good that the bms is working when you hit a surge so the bms is doing its job and the more times you cycle it the more it can bring you back together.

I have had this inverter for a long time. I only use it in my car if I need something, but otherwise I don't have many 12 volt things. I prefer larger inverters, so here's the bypass for the meter, so we'll go ahead and turn this on now. a 300 watt inverter and I think this was a 250 watt heater and we'll do a little charge and then we'll try to charge it again a little bit more, okay, so the heater turned on, we're done. 300 watts on the DC side which could cause this to overheat. We will see. I have actually never done a capacity test on this inverter to see where it actually overloads.

It shows 21.46 amps, 21.2 amps, so they're close, this shows 286 watts and 281 watts, so if anything this reading is a little bit lower and as you can see the differential of the cells fell very close to each other as soon as you put a charge on them because this is on that voltage curve plateau if you're not sure what I'm talking about, these are lithium iron phosphate cells and they have a voltage curve that it's very steep at the beginning and then drops off very steep at the end, so when you're in this mid range here between about 3 volts. and 3.4 volts, it's all a plateau and you just see it go very high right at the top end and at the bottom end, so we generally recommend top balance or bottom balance.

Now I didn't top or bottom balance these cells or the cell groups specifically because I wanted to see this bms do its balancing function. Sorry, I'm holding the cell phone. The cell phone is just my monitor with the app for the bms, but I really wanted to see it do its balance. make sure that has happened and that's it, if you had the top balance of these groups of cells, the bms would not have seen a differential and would not have done any balancing and would not have been able to check if that worked or not, we have not started balancing however, that means the differential is not big enough, yes, so it is at 15 millivolts that it starts to balance out.

You can see it jumping between 14 and 15 millivolts as soon as it hits 15 it starts to balance out. Now the balance is just tiny little resistors that are built into this thing, we're almost ready to overvoltage here 3.65 there we go and it made it so the bms went off and that means it made such a fantastic beep that we caught it on camera, it's okay, we're ready to start the discharge capacity test, so let me turn this off here and I'll unplug it so we don't have anything else on that side here on the meter, we have an extra 17 watt hours, so we want to get rid of that, here Come on, zero turn. on the inverter turn on the heater now we're going to ramp up okay great let's check what time it is 11 16.

We're discharging great so we'll let this run and see what our capacity is so this will take four or five hours to discharge and then We can go back and find out what our capacity is. At this point we're probably about two hours into the test, everything is still working, so this shows that we've used. 40 amp hours, let's see boom, we're still rocking, let's look at the numbers, we're over 1.2 kilowatt hours, that's incredible, we're almost done as far as this is concerned, we're almost at 100 amps. hours but we still have room in the cells, so I'm very excited to see what this actually turns out.

I hope the bms doesn't turn off when the bms thinks it's at zero. I hope it continues to work. I'm still not sure if it's going to stop. I haven't programmed it.I haven't configured it at all. I'm just assuming it's a 100 amp hour battery. We are almost done. The beeping just started in the inverter, so the inverter tells us. that we are at low voltage, we are at 10.67 volts, one of the interesting things is how the voltage just drops off a cliff after three volts per cell, there really isn't much power in a lithium iron phosphate cell below 3 volts the limit is 2.5 volts per cell so we're going to go until the inverter shuts down or we get to 2.5 volts per cell which would be 10 volts okay it just shut down at two points , uh, 10.3 volts, let's take a look now our cells are going to recover a little bit here, they were a little bit lower, but we got 1478 watt hours 1478 watt hours ah, that's just amazing.

These cells in the battery connection are rated as 5000 milliamp hour cells, but I got an extra 15 percent more than I should have. we've come out of these things which is just amazing I love it when a company can deliver more than I mean that's really fantastic I love having a circuit breaker built into the battery and the temperature uh let's check what the temperature is we get there at 27.3 degrees Celsius, 33.2 pounds, a friend of mine has a vinyl cutting machine, so I'm going to put a logo here and this will be my 12 volt battery here we go there we go there we go amazing I'm proud of put my name on this battery I like to have the switch circuit built in, you know it's in a neat package.

Thank you all so much for watching, if you enjoy the videos please like and subscribe to the channel in the description below. There will be a parts list and please leave a comment below if I can think of a better way to do this or something I should include in a future video. Thank you so much.