This article will discuss car tourism, recreation, camping, and the power supply for all of the above, as well as how to build a portable 12V LiFePo4 battery, what it can be used for, and where the declared power of car USB chargers is hiding.
I'll start from afar
I have been into car tourism for a long time. These are trips by car with overnight stays and day stops far from civilization. The duration of such trips can be up to two weeks, during which we set up camp in the most beautiful and hard-to-reach places.
While the car is running, it naturally takes care of all electricity needs. Everything that needs to work and charge does. But when it's turned off, the power consumption required by the camp drains the under-hood battery quite quickly.
Why not lead-acid
Using a starter battery for long-term power supply to electrical appliances is a bad idea. Starter batteries are already under constant stress, often not in the best shape, and with a voltage above 12 volts, they only give up half their capacity, and the second half is already below 12 volts. In addition, their starting current drops significantly with discharge. A battery discharged to 50% of its nominal capacity can't even come close to delivering the declared starting current. In short, after lighting the camp at night, the risk of not starting the car in the morning is quite high. And besides lighting, there are many other consumers, and the stop can last more than one day. Moreover, charging a lead-acid battery is a special kind of art. It doesn't charge quickly: first, the alternator quickly raises the voltage on the battery with a high current, and then it slowly charges with a small current in 'top-up mode,' as it's called on modern chargers. But that's only half the problem. The other half is that when you're in the forest or on a lake shore, the people around you, and you yourself, will not be thrilled with a car rattling in the camp.
You can use deep-cycle lead-acid batteries, but they also charge slowly, are heavy, and suffer from low voltage after giving up half their capacity.
What needs electricity and how much?
Charging all devices, from flashlights to phones, including IQOS, e-cigarettes, and walkie-talkies
In a crew of 2-3 people, they will definitely bring 3 flashlights and 1-2 phones to charge. And neighboring crews will bring another half a dozen different devices. This is because in most cars, power is not supplied to the USB chargers without the ignition or ACC mode, which themselves consume 3-7 amps depending on the car.
Camp lighting
Average lighting usually requires 10-20 watts. It can look different: on a mast, on an expedition roof rack, on a tree, or on a rope stretched between trees. In winter, the lighting works 7-10 hours a day.
I use an eight-watt diffused light floodlight on a mast and, if necessary, two ten-watt COBs on a wire to attach to the ceiling of a tent, under an awning, or on any branch.
Lighting the camp area Beautiful lighting of the camp area
And sometimes the lighting can be this beautiful and festive. New Year 2025, Lake Khurla-Kyol, KChR. Heating
I used to carry a two-kilowatt gasoline generator and electric heaters. Thank progress, that time is over! Now everyone uses diesel autonomous heaters, or simply 'dry heaters.' We won't consider exotic dry Webastos, Eberspächers, or Binars. I'll talk about the Chinese ones; there are two varieties: 2 and 5 kW. There's also an 8, but it's a re-flashed 5. Structurally, it's a boiler inside which diesel fuel burns, a turbine blows into the combustion chamber, and the outside is designed like a radiator, blown by air from an impeller at one end.
Diagram of an autonomous heater 2 kW heaters are mainly integrated into cars. And 5 kW heaters are used to heat tents and shelters. The heaters do not have their own battery and are connected to an external one.
Starting the heater begins with igniting the glow plug, which consumes 10A for several minutes. During operation, consumption varies from 0.5A at minimum for 2 kW to 2.5A at maximum for 5 kW. And before turning off, the heater also burns the plug for about a minute with a current of 10A. Overnight, this amounts to 5 to 25 Ah. And during a long stop in winter, heating in both cars and tents runs continuously for several days in a row. Primarily for those who have properly set up their power supply system.
These heaters are quite capricious, especially those that often operate at high altitudes — in the mountains. They get clogged with soot and in particularly sad cases can take hours to start (a reminder about the 10A at startup). Partly because of this, you don't want to turn them off :D
I have a 2 kW heater installed in the car, and sometimes I connect a second one separately for the tents.
Cooling food and drinks
Yes, this is my favorite car refrigerator. As we found out in the last article, its minimum consumption is 15 Ah per day. This is achieved by storing pre-chilled products at +2-4 degrees Celsius. If you need to freeze something or quickly cool a lot of beer, the consumption immediately doubles. This is true for a small refrigerator of 15-30 liters.
Sometimes at night I connect two refrigerators: mine and a friend's — because his dry heater is already running off the under-hood battery, and if you add a refrigerator to it, you might not be able to start the car in the morning.
Occasionally, you can cheat a little: the refrigerator is on during the day, and at night it gets cold, and it's turned off. But this is only if there's nothing in it that can defrost or spoil, because when it gets down to +2°C at night, nobody brings a refrigerator with them anymore.
Heating food
Do you know what to do with yesterday's frozen shashlik from the table on a cold winter morning? Of course, put it in the multi-cooker! We have a whole day of driving ahead, and we can enjoy hot food at every stop! I use a 12V multi-cooker that handles this task perfectly. It doesn't matter if you're stopped or driving: the food is always hot.
I also sometimes use an electric thermal mug — you can reheat cooled mulled wine. It's 120 watts.
The total consumption of all appliances, of course, varies greatly depending on the surrounding conditions, but on average it is in the range of 20 to 40 Ah per day — if we're talking about a full day of camping, not just an overnight stay.
The issue of camp power supply has several solutions:
Gasoline generator.You take it far away from the camp, but you can still hear it. It rattles, sometimes the smell of exhaust wafts into the camp, it stinks of gasoline when transported in the car, requires jerry cans, consumes a lot of fuel, and takes up a lot of space, especially with the cans. And a generator of two kW, which can be used to heat a tent with an electric heater, takes up even more space and consumes even more gasoline, and also requires waking up 1-2 times a night to refuel it. I tried traveling with it, and I didn't like it.
Solar panels.The camp is usually set up not in direct sunlight, but in the shade, and the panels have to be moved to where there is direct sun. They take up space, are easy to break, crush, or damage, and you still need a battery with them.
Do nothing, leave everything as it is and choose to get help from a friend. He'll light up the camp, chill the cognac, charge your phone. What else do you need? Oh right, heat the tent. You can come with your own air duct, set up your tent next to his, and run heating from your neighbor.
A separate lithium battery, charged from the car.This is my choice, which has been working flawlessly for 5 years and tens of thousands of kilometers.
Examples of air heating distribution in a tent camp
I'll tell you more about it
From 2020 to the present day, I have been using a 12V 55Ah LiFePo4 battery that I once assembled from prismatic cells in a plywood case. It doesn't even have a BMS, but it has an active balancer and a heating system, implemented with a seat heating mat and a simple thermostat without a display, set to a range of 0-5 degrees Celsius.
A few photos of it
This battery is in the trunk. I made a spot for it there with a mount and an XT60 connector, and I install it before trips.
It is connected as follows:
Under the hood, a solid-state power relay is connected to the positive terminal of the main battery, paired with a 12V 250A automatic circuit breaker. This relay is connected to and controlled by a Pandora DX90 alarm system. The logic is simple: if the voltage in the car's electrical system rises to 13.5V, the relay turns ON. After the engine is turned off, the relay turns OFF after 5 minutes. Why not turn it on immediately after starting? Well, what if I started the car with my last bit of power, barely turning the starter, or even got a jump from another car? I need to charge the starter battery first, and then distribute the electricity.
In addition to the Pandora controlling the external battery charging in automatic mode, it can also be turned on and off from the alarm fob and forcibly disconnected with a button on the automatic circuit breaker under the hood. It shuts down the entire system.
From the relay and the circuit breaker, the positive wire goes to the back. As far as I remember, it's 7 AWG copper.
Behind the rear seats, on the wall of the organizer, a 30A 14.2V DC-DC charger and a Bluetooth coulomb meter with a 150A external shunt are mounted.
Photo of the charger with the coulomb meter installed in the car
On the other side of this organizer wall, in a box, is the lithium battery, connected with an XT60 connector. For convenience, I call it the 'reserve' battery.
When the battery is connected, you can monitor its charge, discharge, see the currents, voltage, and remaining capacity from your phone.
In the trunk, there is a cigarette lighter socket, a built-in USB charger module, and an XT60 connector for a reliable connection of lighting and an extension cord. When the car is running, all these units are powered by the vehicle's electrical system and do not load either the lithium battery or the DC charger, allowing the battery to charge fully, even if powerful devices are connected. But as soon as the car is turned off, the relay powered by the vehicle's electrical system opens, and they all switch to power from the reserve battery. The switch is instantaneous, and consumers don't notice it.
Also powered from this line, but bypassing the battery, is the built-in compressor. And the autonomous heater, but it has two power sources: from the reserve and from the main battery, the desired one is selected at startup.
Thus, it turns out that while driving, we store energy that we can calmly spend during a long stop. One of the advantages of LiFePo4 batteries is that they charge very quickly. They can be charged with a current equal to their capacity. I don't have that much current, but 30A is also a lot. For comparison, the power of 1 sq.m. of solar panel is 150 watts at a right angle to sunlight at noon. We, on the other hand, have 400 watts at any time. My 55 Ah battery charged fully in about 1.5 hours after two days of use.
This system has been working properly for 5 years, but then a new consumer suddenly appeared — a boat electric motor. A small motor that attaches under the bottom of a SUP or kayak and allows you to relax a bit.
My battery was not ready for this, as it's made of plywood and only 55 Ah, while the motor consumes 25A. Before going out on the water, I would wrap it in film to keep it from getting wet. It helped, but then I just got tired of it. This is what prompted me to build a new battery that can be used in a boat, in a car, and in any conditions.
Choosing components
One of the main criteria is size. I need the battery to fit in its place in the car. I wanted to make a 150 Ah battery, but after writing down the dimensions of different cases and different battery cells, I realized that only 100 Ah cells fit my size, and in the absolute smallest case you could possibly stick them in.
A study of the range of cells showed that at the moment the best option is EVE LF105AH cells with a nominal capacity of 105 Ah, and an actual capacity of 110 to 115, depending on the batch.
I bought 4 of these cells manufactured in March 2025, along with 3 textolite plates and 3 busbars for connecting the batteries. Including delivery, it cost me 11,000 rubles.
My approach is to first buy the maximum amount of everything necessary, then carefully arrange it, and then start the assembly work. This minimizes failures when something suddenly doesn't fit or doesn't go in, and some irreversible steps have already been taken.
The next thing to buy is the case. I decided to build it not in a classic rectangular battery case, but in a suitcase with a handle, as it should be more durable and convenient to use.
Suitcases are like matryoshka dolls — they look the same, but are different sizes.
I chose this one:
Measurements showed that everything should fit inside, and it will fit in the place of the old battery in the car.
So, the suitcase was bought, and it turned out to be of quite good quality.
Next, I need a BMS. I looked at photos, read reviews, and liked the Daly BMS. Many people use them in such builds.
I want to talk about the BMS in detail, many will find it interesting.
BMS (Battery Management System)
The main purpose of the BMS board in a battery:
Preventing overcharge by limiting the charging voltage.
Preventing over-discharge by disconnecting the battery from the consumer when the lower voltage threshold is reached.
Protection against overload with a large discharge current, also known as short-circuit protection. It also disconnects the battery from consumers when the current threshold is exceeded.
Eliminating cell imbalance through balancing. When the voltage on one cell becomes higher than on others, the balancer starts to discharge it to the neighboring cells.
But a modern BMS is a whole computer. Its capabilities far exceed the basic functionality. It has ports for interacting with external devices via CAN, RS485, UART, as well as DIO, outputs for external temperature sensors (up to 4 for small BMSs), Bluetooth, and Wi-Fi. The number of settings is unimaginably huge. The board can be controlled from a phone by installing an app and connecting via BT, or from a computer via Wi-Fi or a UART or RS485 cable.
Previously, to know the consumption currents, charge, and remaining capacity, you had to install a separate coulomb meter (like I have). But now all this is available on your phone from the BMS itself.
The BMS always knows all the battery parameters. If you find it inconvenient to use your phone and want to have the data always visible, there are about 5 different displays that connect to the BMS via the UART interface and show all the parameters. There are small information displays, and large ones with a touchscreen and configuration options. In addition to them, there are also various external indicators with a digital display or a diode scale, GPS modules, heating modules, etc.
On the previous battery, I made the heating with third-party means: it had a thermal relay configured with DIP switches, and a disconnect button. But now you can connect a heating module to the BMS and configure the battery temperature control from your phone (which I will do next).
Daly has two series of BMS: red and blue. For some reason, almost everyone builds with the red one. I started to study the differences, and it turned out that the red one lacks cell balancing! An external active balancer is installed separately with it. But in the blue one, it's built-in, and it also has built-in Bluetooth, while the red one comes with it as an additional device that plugs into a connector. The blue one is slightly more expensive, by 300-500 rubles. But that's 10-15% of the total BMS price, so we immediately discard the red one.
I plan to install the board across the suitcase, at the bottom of the cells. I need a current with a margin, 100-150A.
We look at the board sizes and see that the 100-150A boards fit snugly in our suitcase in terms of length. But for some reason, the 100A board is a few millimeters wider. So, I'll take the 150A one, such a margin might be useful if I use a powerful inverter or start the engine.
I managed to buy a blue Daly 150A 4-8S BMS for 3300 rubles on the gas marketplace.
So, we already have the cells, the suitcase, and the BMS. Let's move on to making a wish list.
I often used the previous battery outside the car as well: I connected a cigarette lighter socket to the XT60 and plugged in the refrigerator and USB chargers. Therefore, the cigarette lighter socket and USB must be permanently installed in the case. An XT60 is a must, and it would be good to have an XT90 as well. The BMS is rated for 150A, but the XT60 is for a maximum of 60A.
So, we need:
XT60;
XT90;
a cigarette lighter socket;
USB-A and Type-C.
I decided to place all this on the side wall. But during detailed planning, the XT connectors moved to the front wall, while the cigarette lighter and USB remained on the side. A bidirectional charging module based on the IP2368 chip was also added to the USB. Its feature is that it can charge both the battery from a mains (phone) charger and any devices from this battery through a single Type-C port. So, it turns out there will be two Type-C connectors in the case.
Car USB chargers — where's the power?
What could be simpler, right? Built-in car USB chargers — surely there can't be any problems with them! But it turned out to be the opposite.
First, I took two built-in chargers in cylindrical cases with a display and a button, which I had bought a couple of years ago, out of the closet. I connected them to a power supply, plugged in my phone... and saw 15 watts on the power supply display. I tried another phone, and again — both chargers were 15 watts!
This was strange, as it seemed such weak chargers hadn't been around for a long time.
Then I ordered a similar module, but a little longer, in an aluminum case and with a declared power of 65 watts. I connected it and saw voltage spikes, inadequate operation, and a maximum power of 18 watts. I returned it and went to 'browse' AliExpress. There, various USB charger boards with power from 60 to 140 watts were offered one after another. And I ordered 3 different ones: a small 60-watt board, a medium 60-watt board, and a larger board with a heatsink, for 140 watts.
Fortunately, everything arrives quickly from there now, and soon I returned to testing. But the results plunged me into despair: all the modules showed the same 15-18 watts. I tried different cables, different phones, but consistently got the same result.
Then I decided to re-read all the descriptions of these modules. And in the process, I began to suspect that all the declared power is hidden in a high input voltage, unattainable in a car's electrical system.
All 6 different chargers had a declared input voltage range of 6(8)-30V. But they can't boost... Then it turned out that they can't even output a voltage equal to the input. From a 12V car power supply, they can't output 12V according to PD and QC standards. Not to mention the 20V specified in these standards. And for some reason, they can't even do 9V.
I should clarify that when I talk about a 12V input voltage, I mean 12V as a standard. In fact, on the power supply, I always set it to 13.5+-0.5V, simulating the voltage on the battery or in the vehicle's electrical system.
And there it is — the power!
Then I raised the voltage on the power supply to 24V. And the chargers came to life. I had a 140-watt module connected, and it immediately delivered 110. I tried the others, the 60-watt ones, and they immediately delivered all 60. It was a great feeling to find what I had been looking for for so long.
I realized that there was no other option but to install a step-up converter in the battery case as well.
There are several varieties of compact DC-DC step-up converter boards available for sale. Their specifications, as stated in different product listings on marketplaces, varied greatly. So I bought two boards that were more or less suitable in size.
I received two boards, let's call them 'small' and 'large'. Initially, it seemed that the small one wouldn't be powerful enough, and I would have to use the large one. But when I saw them in person, I realized that the large one wouldn't fit in the case, so I started testing with the small one.
Each board has two adjustments: output voltage and current limiting. The principle is simple, like a water tap: clockwise to close, cutting off the supply, counter-clockwise to open, increasing the 'pressure'. This is the easiest way to remember.
I set the output to 24V and turned the current to maximum. I first connected the most powerful charger and plugged the cord into my phone. The charging started to accelerate, and my eyes widened. The numbers on the power supply stopped at 142 W. I looked at my phone, and the thought flashed through my mind: 'Is it still alive in there?' The next step was to try to limit the current on the converter to make the charger behave a bit more modestly) But it didn't lead to anything good. You can't limit the current for these chargers. When they hit the limit, they reboot and start accelerating from the beginning.
Then I connected two 60-watt chargers to the converter one by one, and they both delivered 60. But they got very hot, and they don't have heatsinks, and there's no place to put them. So I decided to stick with the 140-watt charger (it has a heatsink), and later I added more heatsinks to it. The board cost 600 rubles. And since the small converter board showed such good results, I decided to use it. It cost 350 rubles. Both of these boards have an aluminum base designed to be mounted on a heatsink with its entire surface, which is very convenient.
I also got excited about the idea of bidirectional charging, as it allows you to charge the battery with any mains phone charger. And it should also be a powerful charger for USB devices itself.
They are highly configurable: you can set from 2 to 6 cells, choose the assembly type: lithium-ion or lithium-polymer — you can limit the current, voltage, and even select the battery capacity the boards will work with — the correctness of the LED charge indicator depends on this. However, the maximum you can set, I think, is 30 Ah. Well, the indicator is definitely not important to me.
I tested two such modules, one of which was less stable and didn't provide much power, while also being bulky. So I settled on the purple module, adding heatsinks to it. It cost 700 rubles.
Some readers may have a question: so you have boards with connectors soldered on them, and you have a suitcase-style case. How do you make it so that you can plug cords into these connectors from the outside of the suitcase?
This is where sealed, panel-mount connectors with a short pigtail sticking out the back come to the rescue. They are inserted into a hole in the case and secured from the back with a nut. I need three of these: two Type-C and one USB-A. With delivery, they cost 2300 rubles. It seems unreasonably expensive. We order and receive these connectors, as well as a panel-mount cigarette lighter socket and XT90 and 60 connectors for mounting on the case. About 300 rubles each.
In addition to all of the above, you need to organize a power on/off button for the battery. This is where a smart BMS comes in handy. It has this capability and a corresponding socket. You just need to buy a connector with a wire. Actually, it comes with a button, but it's no good, you can just throw it away and buy a decent one.
Are you warm, maiden?
How to find out how much vertical space we have left under the closed lid?
Very simple. Take the suitcase, put the battery cells in it, orienting them as they will be positioned later. Place a piece of tape on them sticky side up, a ball of plasticine on it, and another piece of tape on top of that sticky side down. Close the lid and open it. And measure the height of the flattened ball. I got 11 mm. And at that moment I realized that I was installing a heater. 11 mm is quite enough for this: a sheet of polystyrene foam — 3mm, the thickness of the heating mat — 1 mm, the thickness of the self-adhesive carpet — 2 mm.
The heating mat is still not enough to wrap all the walls of the battery, so the top wall can do without it. One sheet of polystyrene foam on the top and bottom, and I'll line the inside of the case with carpet. The heating will be glued to the bottom, side walls, and the back wall of the assembly. In total, we get 11 mm in height and a tight fit of the assembly in the suitcase.
So, we need a heating controller. The native controller from Daly is 600-900 rubles.
Why does a battery need heating at all?
The fact is that most LiFePo4 batteries cannot be charged at sub-zero temperatures. There are special 'winter' batteries that are filled with the appropriate electrolyte, and they allow it. But all others must be charged at temperatures above 0°C.
If I understand the physics of the process correctly, the reason is as follows: when the battery temperature drops below 0°C, its voltage drops and it becomes possible to top it up, even if it is fully charged. The battery starts to accept a charge. At the same time, if you just thaw it, the voltage and capacity will return to their maximum. And it turns out that in a frozen battery, we are pushing the capacity and voltage to the top. And then it thaws and raises the voltage even higher. The amount of energy in it begins to exceed its nominal capacity. Very roughly speaking, a 100 Ah battery suddenly has, for example, 140 Ah. And it degrades quickly. I don't claim to be an expert here, I'm just saying how I understand it. If I'm wrong, I'd be glad if someone could describe the process more accurately.
Assembly
So, for the battery assembly, we have the following list of parts:
Case — a plastic suitcase with a handle. Marketed as waterproof.
The battery cells themselves, LiFePo4 EVE LF105AH — 4 pieces.
Daly 150A 4-8s blue BMS.
0.5 mm textolite plates, matching the size of the cell's side wall — 3 pcs.
Busbars — 3 pcs. They are sold ready-made, for specific cells.
XT90 and XT60 connectors for case mounting — 1 pc each.
140-watt USB charging module — 1 pc.
140-watt bidirectional charging module — 1 pc.
DC-DC step-up converter — 1 pc.
Cigarette lighter socket for mounting in a wall/partition (with thread and nut) — 1 pc.
USB Type-C connectors for mounting in a wall/partition (with thread and nut) — 2 pcs.
USB-A connector for mounting in a wall/partition (with thread and nut) — 1 pc.
Silicone power wires — 6, 7, 8 AWG.
Round button with backlight.
Button with wire and connector for BMS.
Various wires with cross-sections from 0.1 to 4 mm2.
2 mm textolite — several pieces of 20*30 cm.
Self-adhesive carpet (car carpet) — a piece large enough for the entire inside of the case.
3 mm polystyrene foam — 1 sheet.
Seat heating mat with carbon fiber inside — 1 pc.
Daly heating controller — 1 pc.
Reinforced tape — 1 roll, 3 cm wide and 15–20 m long.
Double-sided tape — 1 roll, 5 cm wide, on a film or reinforced base.
Stainless steel screws, nuts, washers, lock washers M3, M2, M2.5 — various lengths, countersunk and regular heads.
Lots of different heat shrink tubing. Adhesive-lined is a must.
Terminals for M6 bolts, for wires with cross-sections of 10, 16, 2.5, 4, 1.5 mm.
Terminals for M3 bolts for wires with cross-sections of 1.5, 2.5, and 4 mm.
Corrugated cardboard for mock-ups.
For tools, we will need (don't kick me):
A 20-30 watt soldering iron for small connections.
An 80+ watt soldering iron for soldering XT60 and 90 connectors.
Soldering supplies: solder, flux, etc.
Hydraulic crimping tool.
Angle grinder with a 115-125 mm cutting disc.
Rotary tool with milling bits (manicure ones will do) and diamond discs ⌀ from 2 to 4 cm.
Cordless drill with drill bits and a countersink.
Fine marker, rulers, vernier caliper.
1 mm textolite, a sheet of 20*20 cm or so.
Step cone drill bit up to 32 mm.
Scissors that cut well.
Utility knife.
Vise.
Pliers, round-nose pliers.
Small, carbide-tipped cutters.
Large cutters or good metal shears for a clean cut on thick wires.
A lot of patience and accuracy.
I don't have everything either, I borrowed some things (the crimping tool).
Let's begin
First, I took the cells, placed 0.5 mm textolite between them, secured them well, and wrapped them with reinforced tape.
Don't forget to determine which side will be positive and which will be negative before assembly.
But the BMS turned out to be a bit too long, and it needed to be trimmed a little. One terminal had to be shortened by 2 mm and rounded, and the other just shortened.
After cutting with an angle grinder, everything fit perfectly.
Around this point, I realized that I needed a frame on which all the modules and the BMS would be located. They can't just lie in the case or hang there on wires.
It was decided to make the frame from 2 mm textolite, and to first make a mock-up of it from cardboard.
I made it so that this plate fits snugly against all the walls as much as possible. Then we trace and cut it out of textolite with an angle grinder. Don't forget to finish the edges.
Now we have some dimensions, we can see what's what, and we can estimate the placement of all the connectors on the case.
The cigarette lighter socket and all the USB connectors fit snugly on the side wall. But there's no room for the XT connectors there, so they will be located on the front wall.
The XT60 fits perfectly under the suitcase latch, and the XT90 looks harmonious inside the handle.
Just in case, I want to warn you: do not place connectors in the lid of the suitcase! You won't be able to arrange the wires when you close it.
We mark with a caliper and a marker and cut with a micro-milling cutter. It doesn't go through the entire thickness of the plastic, so after it, I finished cutting the holes with a utility knife.
Before continuing to arrange the case, let's assemble the battery pack itself so that it gets closer to its final size, and then we'll test fit everything else.
We need to start with the heating. I laid out the heating mat, placed the assembly on it, and marked where I could and should cut off the excess. The heating mat can be cut across, and you can cut off the empty 'fields' where there is nothing. I pre-cut two layers of thermal insulation from polystyrene foam and placed them under the busbars. I could have used one 5 mm layer, but I didn't have it, so I used two layers of the 3 mm I had.
I tucked the BMS temperature sensor 3 cm under the polystyrene foam. I taped its wire along the middle of the back wall (back relative to its position in the suitcase).
After that, I cover the assembly with double-sided tape and stick the mat to it.
Important! In the photo above, you can see the thermal fuse (near the scissors). It is sewn into the mat at the factory and is an emergency temperature limiter that turns off the heating when it reaches 60 degrees. The mat should be positioned so that it is located near the front wall, near the suitcase handle. The back wall of the assembly will be pressed tightly against the suitcase, and it will get in the way there, but there is room for it at the front.
On the bottom of the battery (which will be on the right in the box), I folded the mat like an envelope and glued it. In the center of this pocket, in the upper half of the battery, I placed the second temperature sensor. There is no heating in this spot, it didn't reach there, so it's a great place to install the sensor. Then I wrapped it all with tape.
I decided not to install the top layer of thermal insulation yet, it will get damaged if I do all the further test fittings with it. So let's start the test fitting without it.
We need to prepare the textolite plate and, if possible, install everything on it.
We place the BMS on it, mark the holes with a marker, drill with a 3 mm bit, and countersink from the back.
If you haven't figured out why there's a rectangular cutout in it, it's very simple — the connectors attached to the suitcase case will pass through it.
Now let's turn the plate over and estimate the placement of the USB charging modules and the step-up converter.
The plastic on the USB and Type-C plugs that go into one board had to be trimmed a bit with a knife, otherwise they wouldn't fit into the closely spaced connectors.
I'll jump ahead a bit and say that the two upper boards are positioned well, but the bottom one is just terrible. It's impossible to plug a connector into it, and you can't lower the plate into the suitcase with the connector already plugged in either.
But for now, we continue to think that everything is fine and drill the plate.
The heating module is perfectly located above the BMS. It will play another important role there — it will become a hub for connecting all the low-current devices located on the board, because it has convenient screw terminals.
Now it's time to solder the wires to the XT 60 and 90 connectors.
The soldering points on these connectors are made in the form of half-tubes. At first glance, they seem to be fixed there, but that's not the case — they rotate. By grabbing this half-tube with thin pliers, you can turn it. And this can be done both for convenience of soldering and for convenience of routing the wires.
I will have to solder the wires to these connectors at a 90-degree angle, otherwise I won't be able to install them, as there are only a few millimeters between the connector and the assembly.
We measure the length of the wires so that we have enough, and add 1-1.5 cm. If we leave the wires long, everything won't fit.
Then we cut and crimp the ends. There was a problem with the crimping: the crimping tool I borrowed didn't work, the hydraulics were leaking somewhere inside, and it wasn't developing any force. So I took its dies, unscrewed the guide pins from them, and put the dies in a hydraulic press.
Now let's work with the case again. We need to mark and make 4 round holes in the side wall: 30 mm, 18 mm, 18 mm, and 24 mm. For this, I bought a step cone drill bit.
When marking the holes, you must remember that the front panel of each connector is larger than its threaded part, and there must also be a nut on the thread at the back that will rotate. This must be taken into account when calculating the distance between the centers of the holes! Because it's very easy to make a hole into which it will be impossible to install the connector later. And it will be difficult to fix (but possible).
After the holes were ready, I asked my wife to line the inside of the case with carpet. I can't glue straight myself: it always comes out 100% crooked. And here we have a very complex shape, you need to make a development of an oblique parallelepiped with rounded corners. In short, my clumsy hands would have had a field day with this task.
One wall was intentionally left unlined. The reason is simple: there is catastrophically little space there, and I'm afraid the heatsinks on the boards will catch on the carpet.
Now let's insert the connectors and see how it looks.
Pay attention to the bent terminals. This was done in a vise, with a small hammer. It may require a little heating with a torch. These two negative terminals are attached to the BMS with one screw, and they fit perfectly one inside the other. This must be done so that it can be assembled and screwed together.
Next, I cut four rectangles from a 3 mm sheet of polystyrene foam, matching the dimensions of the assembly's walls, stuck them on with double-sided tape, and then went over the edges with reinforced tape.
The situation with the left wall of the assembly is as follows:
On it are the cell contact pads, connecting busbars, balance wire terminals, as well as the main wires that power the connectors and modules of the battery. All together, this can be quite bulky, and usually is.
I can't afford that, everything I planned simply won't fit.
So I tried to make everything as flat as possible. To do this, I had to use screws with a head height of 1 mm and a thread length of 6 and 8 mm.
I screwed the 8 mm ones into the cells themselves, and the 6 mm ones into the positive terminal T-connector, which is 3 mm thick.
A little about the wires...
With the negative wire, it's as simple as can be. Only one comes to the assembly, from the power input of the BMS — 6 AWG. And a thin balance wire also goes to this terminal.
But with the positive, it's more complicated. Too many wires have to go to it:
7 AWG wire from the XT90.
8 AWG wire from the XT60.
Balance wire.
BMS power wire (yes, it's separate).
Heating module power.
Power for the DC-DC Step-UP and 140-watt USB charger tandem.
Power for the 140-watt bidirectional charging module.
Cigarette lighter socket power.
It's impossible to place so many wires on one terminal properly.
I had to think about this thoroughly.
The solution was as follows:
I'm making a 'T-connector' from a 3 mm plate. It has three holes: a central 6 mm one, and two outer ones with M6 threads. In the center, one terminal with the BMS power and balance will be attached. On the sides, two wires, 7 and 8 AWG, will be attached. Since the box widens slightly towards the top, there is more space at the top, and the thicker wire will be the upper one. Along with it, another wire will be clamped — 4 mm2. It will go to the heating module and will be clamped there under an M3 bolt. And under this same bolt, the wires of all the other devices located on the plate will also be clamped.
I did the same with the negative contact on the heating module. All the negatives from the devices on the plate went to it. If you remember, the negative from the BMS comes to the heating module with a small double terminal, i.e., without any wire at all.
Thus:
I don't need to run a bunch of wires across the entire battery.
I disconnect the + and - of all devices on the plate with two screws.
I don't have any additional wire connectors (terminal blocks, WAGO, etc.).
The left side of the assembly remains as flat as possible.
The left wall is ready and fully assembled. Now we need to deal with the right one.
We make the first trial push and encounter a failure.
You can see that it's impossible to assemble this structure in this form. It's a logical dead end.
It seemed like a fiasco. I was so upset that I went to bed.
The next day I returned to work and decided to remove this board, assemble without it, and then try to find a new place for it.
It also turned out that it's impossible to put the terminals on the cigarette lighter socket. They are bent outwards so as not to rest against the assembly. And it's simply impossible to put the mating parts on them inside — there's no room for them.
Without the purple board, everything fell into place nicely.
It was decided to cut the terminals on the cigarette lighter socket flush, solder 5 cm of wire to the stubs, and install an XT30 connector on the end.
After a test installation of the plate, it was discovered that there is a good spot for the purple board on top of the textolite plate. True, it will be held there not by screws, but by two plastic zip ties. But this is not critical and is quite acceptable.
A wire with an XT30 was also soldered to it.
And from the heating module, I ran a wire with a double XT30 connector on the end. I just took two connectors, sanded off all the markings with sandpaper to make the adjacent walls flat, and glued them together with superglue. I made jumpers on the contacts and ran one 2*1.5 mm wire2.
I applied sealant to all the parts on the boards that could vibrate and fall off — chokes, trimming resistors, heatsinks, capacitors. All of this is glued and dampened to the board with sealant.
In the photo above, you can see that the step-up converter's back wall does not touch the textolite plate. I left a gap for cooling, the distance there is 2.7 mm.
Later I will stick a copper heatsink from an M.2 SSD onto its wall. They are 20*70 mm in size, and come in thicknesses from 1.5 to 6 mm with a 0.5 step.
I ordered two 1.5 mm ones.
I didn't mention the on/off button — I had to trim its contacts because they were hitting the assembly.
A perfect spot was found for it right in the center of the front wall. I removed the pressure relief valve from there, it's not needed anyway, and drilled the hole out to 12 mm.
I soldered a wire with a connector for the BMS and a wire for the light indicator to the button. On the latter, I soldered terminals for an M3 screw and then screwed it under the bolts on the heating module.
Next, you need to cut a rectangle from 1 mm textolite, the height of the assembly and 2/3 of its width, and insert it between the front wall of the suitcase (which has the power connectors and button) and the assembly. This is a safeguard in case of impact, fall, or other mechanical damage, to prevent the exposed parts of the connectors at the soldering points from piercing the cells. If this happens, there will most likely be a fire. LiFePo4 batteries themselves do not burn, but in the event of a short circuit, the temperature will be so high that everything around them will catch fire.
The button's operating algorithm needs to be configured, and this is only possible from a computer. There are no such settings on the phone.
We will need a cable with a USB-UART or USB-RS485 converter. Buy only the official one, it comes with the right connector. But official ones also vary, be sure to check with the seller if it will fit your BMS.
You need to install the UART or RS485 driver and the BMS-Tool V1.14.59 program. There are several suitable programs, but this one is the most understandable.
We open the port, connect, go to the Manufacturing section, in the right column we see the Key logic setting. This is the power button. There are the following options: disable charging, disable discharging, and put the BMS to sleep. These options can be combined. I chose, as you can see in the photo, to disable discharging and put it to sleep. And I decided not to disable charging. Let it be possible to charge a turned-off battery. It's safer and seems more practical.
The heating algorithm can also be configured from the phone. I set it to turn on at 0 and turn off at +5 degrees Celsius.
The battery is assembled!
Now let's test the charging.
Everything works.
The function of limiting the maximum battery voltage, configurable in the BMS, is very useful for extending the battery's life. We set it to 14.2 volts and can charge it with any charger, even a 15-volt one. When it reaches 14.2, it will stop charging, and the charger will show that it's complete. The standard finishing voltage for charging a LiFePo4 battery is 14.6V, but it's better to set it to 14.2. It will charge 1% less, but this will significantly extend its lifespan.
I hope my experience will be useful to someone. Portable batteries are quite in demand now, but there are no assembly instructions in Russian, and everyone builds to the best of their understanding. I tried to show how you can build a battery for yourself, what options in it can be useful, and what is needed to integrate each of them.
The end
