There comes a time in the life of every “radio killer” when you need to weld together several lithium batteries- either when repairing a laptop battery that has died from age, or when assembling power for another craft project. Soldering "lithium" with a 60-watt soldering iron is inconvenient and scary - you will overheat a little - and you have a smoke grenade in your hands, which is useless to extinguish with water.
Collective experience offers two options - either go to the trash heap in search of an old microwave, tear it apart and get a transformer, or spend a lot of money.
For the sake of several welds a year, I didn’t want to look for a transformer, saw it and rewind it. I wanted to find an ultra-cheap and ultra-simple way to weld batteries using electric current.
Powerful low voltage source direct current, accessible to everyone - this is an ordinary used one. Car battery. I'm willing to bet that you already have it somewhere in your pantry or that your neighbor has it.
I'll give you a hint - The best way getting an old battery for free is
wait for frost. Approach the poor guy whose car won’t start - he will soon run to the store for a fresh new battery, and give the old one to you for nothing. In the cold, an old lead battery may not work well, but after charging the house in a warm place it will reach its full capacity.
To weld batteries with current from the battery, we will need to supply current in short pulses in a matter of milliseconds - otherwise we will not get welding, but burning holes in the metal. The cheapest and affordable way switch the current of a 12-volt battery - an electromechanical relay (solenoid).
The problem is that conventional 12-volt automotive relays are rated for a maximum of 100 amperes, and short-circuit currents during welding are many times higher. There is a risk that the relay armature will simply weld. And then, in the vastness of Aliexpress, I came across motorcycle starter relays. I thought that if these relays can withstand the starter current, many thousands of times, then they will be suitable for my purposes. What finally convinced me was this video, where the author tests a similar relay:
My relay was purchased for 253 rubles and reached Moscow in less than 20 days. Relay characteristics from the seller's website:
- Designed for motorcycles with 110 or 125 cc engine
- Rated current - 100 amperes for up to 30 seconds
- Winding excitation current - 3 amperes
- Rated for 50 thousand cycles
- Weight - 156 grams
I was pleased with the quality of the unit - two copper-plated contacts were installed threaded connections, all wires are filled with compound for water resistance.
On a quick fix I assembled a “test stand” and closed the relay contacts manually. The wire was single-core, with a cross-section of 4 squares, and the stripped ends were fixed with a terminal block. To be on the safe side, I equipped one of the terminals to the battery with a “safety loop” - if the relay armature decided to burn out and cause short circuit, I would have time to pull off the terminal from the battery using this rope:
Tests have shown that the machine performs well. The anchor knocks very loudly, and the electrodes give clear flashes; the relay does not burn out. In order not to waste a nickel strip and not to practice on dangerous lithium, I tormented the blade of a stationery knife. In the photo you see several high-quality points and several overexposed ones:
Overexposed dots are also visible on the underside of the blade:
First he piled up simple diagram on a powerful transistor, but quickly remembered that the solenoid in the relay wants to consume as much as 3 amperes. I rummaged around in the box and found a replacement transistor MOSFET IRF3205 and sketched out a simple circuit with it:
The circuit is quite simple - actually, a MOSFET, two resistors - 1K and 10K, and a diode that protects the circuit from the current induced by the solenoid at the moment the relay is de-energized.
First, we try the circuit on foil (with joyful clicks it burns holes right through several layers), then we take out nickel tape from the stash for connection battery assemblies. We briefly press the button, we get a loud flash, and examine the burnt hole. The notebook was also damaged - not only the nickel was burned, but also a couple of sheets underneath it :)
Even a tape welded at two points cannot be separated by hand.
Obviously, the scheme works, it’s a matter of fine-tuning the “shutter speed and exposure”. If you believe the experiments with the oscilloscope of the same friend from YouTube, from whom I spied the idea with the starter relay, then it takes about 21ms to break the armature - from this time we will dance.
YouTube user AvE tests the firing rate of the starter relay in comparison with the SSR Fotek on an oscilloscope
Let’s supplement the circuit - instead of manually pressing a button, we’ll entrust the counting of milliseconds to Arduino. We will need:
- Arduino itself - Nano, ProMini or Pro Micro will do,
- Sharp PC817 optocoupler with a 220 Ohm current-limiting resistor - to galvanically isolate the Arduino and the relay,
- Voltage step-down module, for example XM1584, to turn 12 volts from the battery into Arduino-safe 5 volts
- We will also need 1K and 10K resistors, a 10K potentiometer, some kind of diode and any buzzer.
- And finally, we will need nickel tape, which is used to weld batteries.
We upload some simple code to Arduino:
Const int buttonPin = 11; // Shutter button const int ledPin = 12; // Pin with signal LED const int triggerPin = 10; // MOSFET with relay const int buzzerPin = 9; // Tweeter const int analogPin = A3; // Variable resistor 10K to set the pulse length // Declare variables: int WeldingNow = LOW; int buttonState; int lastButtonState = LOW; unsigned long lastDebounceTime = 0; unsigned long debounceDelay = 50; // minimum time in ms that must be waited before triggering. Made to prevent false alarms when the release button contacts bounce int sensorValue = 0; // read the value set on the potentiometer into this variable... int weldingTime = 0; // ...and based on it we set the delay void setup() ( pinMode(analogPin, INPUT); pinMode(buttonPin, INPUT); pinMode(ledPin, OUTPUT); pinMode(triggerPin, OUTPUT); pinMode(buzzerPin, OUTPUT) ; digitalWrite(ledPin, LOW); digitalWrite(triggerPin, LOW); digitalWrite(buzzerPin, LOW); Serial.begin(9600); ) void loop() ( sensorValue = analogRead(analogPin); // read the value set on the potentiometer weldingTime = map(sensorValue, 0, 1023, 15, 255); // convert it to milliseconds in the range from 15 to 255 Serial.print("Analog pot reads = "); Serial.print(sensorValue); Serial.print( "\t so we will weld for = "); Serial.print(weldingTime); Serial.println("ms. "); // To prevent false positives of the button, first make sure that it is pressed for at least 50ms before starting welding: int reading = digitalRead(buttonPin); if (reading != lastButtonState) ( lastDebounceTime = millis(); ) if ((millis() - lastDebounceTime) > debounceDelay) ( if (reading != buttonState) ( buttonState = reading; if (buttonState == HIGH) ( WeldingNow = !WeldingNow; ) ) ) // If the command is received, then we start: if (WeldingNow == HIGH) ( Serial.println("== Welding starts now! =="); delay (1000); // We issue three short and one long squeak to the speaker: int cnt = 1; while (cnt<= 3) {
playTone(1915, 150); // другие ноты на выбор: 1915, 1700, 1519, 1432, 1275, 1136, 1014, 956
delay(500);
cnt++;
}
playTone(956, 300);
delay(1);
// И сразу после последнего писка приоткрываем MOSFET на нужное количество миллисекунд:
digitalWrite(ledPin, HIGH);
digitalWrite(triggerPin, HIGH);
delay(weldingTime);
digitalWrite(triggerPin, LOW);
digitalWrite(ledPin, LOW);
Serial.println("== Welding ended! ==");
delay(1000);
// И всё по-новой:
WeldingNow = LOW;
} else {
digitalWrite(ledPin, LOW);
digitalWrite(triggerPin, LOW);
digitalWrite(buzzerPin, LOW);
}
lastButtonState = reading;
}
// В эту функцию вынесен код, обслуживающий пищалку:
void playTone(int tone, int duration) {
digitalWrite(ledPin, HIGH);
for (long i = 0; i < duration * 1000L; i += tone * 2) {
digitalWrite(buzzerPin, HIGH);
delayMicroseconds(tone);
digitalWrite(buzzerPin, LOW);
delayMicroseconds(tone);
}
digitalWrite(ledPin, LOW);
}
Then we connect to Arduino using the Serial monitor and turn the potentiometer to set the length of the welding pulse. I empirically selected a length of 25 milliseconds, but in your case the delay may be different.
When you press the release button, the Arduino will beep several times and then turn on the relay for a moment. You will need to lime a small amount of tape before you select the optimal pulse length - so that it both welds and does not burn holes through.
As a result, we have a simple, unsophisticated welding installation that is easy to disassemble:
A few important words about safety precautions:
- When welding, microscopic splashes of metal may fly to the sides. Don’t show off, wear safety glasses, they cost three kopecks.
- Despite the power, the relay can theoretically “burn out” - the relay armature will melt to the point of contact and will not be able to return back. You will get a short circuit and rapid heating of the wires. Think in advance about how you will pull off the terminal from the battery in such a situation.
- You can get different degrees of welding depending on the battery charge. To avoid surprises, set the welding pulse length on a fully charged battery.
- Think in advance what you will do if you make a hole in the 18650 lithium battery - how you will grab the hot element and where you will throw it to burn out. Most likely, this will not happen to you, but with video It is better to familiarize yourself with the consequences of spontaneous combustion 18650 in advance. At a minimum, have a metal bucket with a lid ready.
- Monitor the charge of your car battery, do not allow it to be severely discharged (below 11 volts). This is not good for the battery, and it won’t help your neighbor who urgently needs to “light up” his car in winter.
When it comes to converting a battery to 18650 (for a screwdriver with Ni-Cd/Ni-MH or for a home emergency DIY power supply like a Tesla Powerwall), many manuals and instructions are silent about how to connect the batteries. Not all of them are suitable for durability and even safety.
Is it possible to solder 18650 batteries?
When assembling several cells for a laptop or as part of a large battery (for various purposes of ensuring autonomy, including vehicles), the task is to connect 18650 batteries. And many lovers of DIY crafts consider soldering as one of the options.
Remember, lithium-ion batteries (18650 and any other Li-Ion) when heated from a soldering station (or even a low-power soldering iron) are destroyed in their structure and irreversibly lose part of their capacity!
That is solder 18650 batteries should not be done unless absolutely necessary. Or you will have to put up with a change in chemical composition and deterioration in performance. In addition, the solder connection is unreliable if the battery overheats. The metal is also impractical for compact assembly due to the random shapes of the solder and vulnerability to external influences.
The installers themselves rightly note in the comments that when the lithium-ion battery is exposed to temperature, you also expose it to the risk of deformation. safety valve. This key safety element of the 18650 battery is located under the positive terminal and is made of a polymer that can withstand maximum operating temperatures no more than 120°C.
What do professionals use to properly connect 18650?
You can achieve reliability and safety in assembling a battery from several batteries using professional methods, or at least those that have proven their practicality and safety.
How to properly connect 18650 batteries:
contact welding (spot);
using factory holders (holders);
neodymium magnets (powerful eternal magnets);
gluing;
liquid plastic.
Professionals use the spot welding method - this method is also recommended for industrial assembly of products with 18650 batteries. An example of budget spot welding for the home was discussed in detail not long ago on Geektimes.
Popular in the DIY community are rare earth neodymium magnets that hold pins tightly and allow you to quickly construct temporary or small household items. For long-term, compact projects, liquid plastic or even glue is best.
To quickly assemble a configuration of several 18650 batteries, you can buy holders with a plastic case and factory contacts for manual soldering without fear of overheating of the lithium-ion batteries.
Only in certain cases, when other options are not suitable or impractical (depending on the conditions), soldering should be performed by professionals. Their responsibility falls on the choice of low-temperature solder, as well as guaranteeing the performance and safety of the battery during further operation.
Everyone knows that a lithium polymer battery cannot be overheated or soldered with a regular soldering iron. But what to do if you still need to connect two batteries. This will be discussed in the article.
When I was building the Cessna, site users advised me to buy at least two batteries so that I wouldn’t have to go out into the field to fly for a few minutes.
We ordered two of these batteries .jpg)
Battery Turnigy 1300mAh 3S 20C Lipo Pack
Product http://www.site/product/9272/
One of them categorically did not want to take the charger. Sometimes it immediately gave a burst error, sometimes during charging. I soon discovered that the contacts inside it were shorting. So I started flying with just one battery.
Now I got around to taking it apart. After removing the outer wrapper, it was discovered that the iron plate between the first and second cans was torn and contact was ensured only due to the “tightness” in this place.
When I started poking around and completely broke away. 
But everyone knows that LiPo batteries cannot be overheated above 60 degrees Celsius. Regular solder melts at about 200 degrees Celsius. Moreover, the solder practically does not stick to these plates due to the sticky layer, which means you will have to tin for a long time. As luck would have it, only a couple of millimeters of this plate remained on one can.
Then I remembered about Rose’s alloy. Its melting point is only 95 degrees Celsius. Those. it can even be melted in boiling water. 
I didn’t have an adjustable soldering iron at hand, so I had to solder with a regular one. The temperature was regulated by “undocking” the soldering iron from the socket. Rosin melts at about 70 degrees, so ten seconds after heating until the rosin melts, you can safely turn off the soldering iron.
I first clamped all three “antennae” with steel wire that needed to be soldered together (two from adjacent stickers, the third with a white wire for the balancing connector) and started soldering. This wire later helped me very well - as I wrote earlier, the native plates very diligently repel the alloy, at first the solder stuck just to this wire, and then slowly transferred to the plates. 
The rest of the wires can be clamped with a rubber band, otherwise they interfere very much with this “jewelry work”. 
After soldering, I cut off the excess steel wire, took care of the insulation, and reassembled everything. At the end I wrapped everything with regular electrical tape. Now I have it white. 
I ran 5 charge/discharge cycles. The charge shows normal.
Tomorrow I'm going to test it on a Cessna.
I would also like to add that disassembling and soldering LiPo batteries is associated with a great health risk and this article is in no way a guide to action!
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When working with mobile household devices or special tools with a built-in power source, there is often a need to solder a wire to the battery.
Before you begin this seemingly simple procedure, you should carefully prepare, which will guarantee that you will receive a reliable and high-quality connection at the end of the work.
Both the alkaline or lithium battery itself and the connecting conductor soldered to it need preparation.
These procedures also include the preparation of the necessary consumables, including such important components as solder, rosin and flux mixture.
The most difficult and crucial moment of the upcoming work is stripping the battery terminal to which the connecting wire is supposed to be soldered. This procedure may seem simple only to those who have never tried to do this.
The problem in this case is that the aluminum contacts of power supplies (finger or other type - it doesn’t matter) are susceptible to oxidation and are constantly covered with a coating that interferes with soldering.
To clean them and subsequently isolate them from air you will need:
- sandpaper;
- medical scalpel or well-sharpened knife;
- low-melting solder and neutral flux additive;
- not a very “powerful” soldering iron (no more than 25 watts).
After all the specified components are prepared, the following operations must be performed. First, you need to carefully clean the area of the intended soldering, using first a scalpel or knife, and then fine emery cloth (this will ensure better removal of the oxide film from the contact area).
At the same time, the bare part of the soldered wire should undergo the same stripping.
Immediately after preparation, you should proceed to protective treatment of the terminals of a finger-type or any other battery.
Flux treatment
To prevent subsequent oxidation of the contact, the surface of the battery, cleared of plaque, should be immediately treated with a flux mixture made from ordinary rosin.
If, for example, there are no greasy stains from oils on the phone battery contacts, simply wipe them with a soft flannel soaked in ammonia.
After this, you will need to warm up the soldering iron well and solder the contact area with a few quick touches. At this point, preparation for soldering can be considered complete.
Soldering process
After each of the connected parts has been cleaned and treated with flux, they proceed to directly soldering the wires to the contact area of the battery.
To carry out this final procedure, you can use the same 25-watt soldering iron that was used to prepare the battery terminals from NI or CD.
As a solder, you should choose a low-melting composition, and for good spreading, use a rosin-based flux.
The final soldering procedure should take no more than 3 seconds. This applies to any type of battery (both NI and CD).
The most important thing is to prevent overheating of the terminal part of the element, as a result of which it can be seriously damaged. The possibility of its complete destruction (rupture) during the soldering process cannot be ruled out.
When considering how to solder a wire and a battery, it should be noted that this situation occurs much more often than it seems. First of all, this applies to special construction tools (if it is necessary to solder screwdriver batteries, for example).
There are often cases when the built-in power supply of the tool used is completely destroyed for some reason, and there is nothing to replace this screwdriver with. In this situation, the conductors powering the device are soldered to a spare battery designed for the same voltage.
The considered technique can be used when you just need to solder two batteries together.
It should be noted that instead of soldering, spot welding is used in production for batteries. But not everyone has a device for this type of connection, while a soldering iron is a more common device. That’s why soldering comes to the rescue at home.
Batteries and accumulators
When powering radio equipment from batteries and accumulators, it is useful to know the common connection diagrams for batteries and accumulators. The fact is that each type of battery has a permissible discharge current.
Discharge current is the most optimal value of the current consumed from the battery. If you consume a current from a battery that exceeds the discharge current, then this battery will not last long, it will not be able to fully deliver its calculated power.
You probably noticed that electromechanical watches use “finger” (AA format) or “little finger” (AAA format) batteries, and for a portable lamp flashlight larger batteries (format R14 or R20), which are capable of delivering significant current and have a large capacity. Battery size matters!
Sometimes it is necessary to provide battery power to a device that consumes significant current, but standard batteries (for example R20, R14) cannot provide the required current; for them it is higher than the discharge current. What to do in this case?
The answer is simple!
You need to take several batteries of the same type and combine them into a battery.
So, for example, if it is necessary to provide a significant current for the device, parallel connection of batteries is used. In this case, the total voltage of the composite battery will be equal to the voltage of one battery, and the discharge current will be as many times greater as the number of batteries used.
The figure shows a composite battery of three 1.5 volt batteries G1, G2, G3. If we take into account that the average value of the discharge current for 1 AA battery is 7-7.5 mA (with a load resistance of 200 Ohms), then the discharge current of a composite battery will be 3 * 7.5 = 22.5 mA. So, you have to take in quantity.
It happens that it is necessary to provide a voltage of 4.5 - 6 volts using 1.5 volt batteries. In this case, you need to connect the batteries in series, as in the figure.
The discharge current of such a composite battery will be the value for one cell, and the total voltage will be equal to the sum of the voltages of the three batteries. For three AA format (“finger”) elements, the discharge current will be 7-7.5 mA (with a load resistance of 200 Ohms), and the total voltage will be 4.5 Volts.
