The cost of a new screwdriver approximately 70% consists of the cost of the battery to it. Therefore, it is not surprising when faced with a battery failure, we ask ourselves the question. what next? Buy a new battery or a screwdriver, or maybe it is possible to repair the battery of a screwdriver with your own hands and continue working with a familiar tool?
In this article, which we will conditionally divide into three parts, we will consider: types of batteries that are used in screwdrivers (part 1), their possible causes of failure (part 2) and available repair methods (part 3).
Screwdriver battery: design and types
It should be noted that, regardless of the brand of the screwdriver and the country of manufacture, the batteries have an identical structure. The assembled battery pack has this form.
If we take it apart, we will see that it is assembled from small elements that are assembled in series. And from the school course of physics, we know that elements that have a serial connection unite their potentials.
Note. The sum of each battery also gives us the total voltage at the contacts of the battery.
Stacked parts or "banks", as a rule, have a standard size and voltage, they differ only in capacity. The battery capacity is measured in Ah / h and is indicated on the element (shown below).
The following types of elements are used to build screwdriver batteries:
- nickel. cadmium (Ni. Cd) batteries, with a nominal voltage on the "banks" of 1.2V;
- nickel-metal hydride (Ni-MH), the voltage on the elements is 1.2V;
- lithium-ion (Li-Ion), with a voltage of 3.6V.
Let us consider in more detail the advantages and disadvantages of each type.
- The most common type due to low cost;
- Low temperatures are not scary, such as Li-Ion batteries;
- It is stored in a discharged state, while retaining its characteristics.
- It is made only in the countries of the "third world", due to toxicity in production;
- Memory effect;
- Small capacity;
- A small number of charge / discharge cycles, which means that they do not “live” for a long time with intensive use.
- Environmentally friendly production, it is possible to purchase a high-quality branded battery;
- Low memory effect;
- Low self-discharge;
- Big capacity, in comparison with Ni. Cd;
- charge / discharge cycles.
- Loses some of the characteristics during prolonged storage in a discharged state;
- At low temperatures, it does not “live” for a long time.
- No memory effect;
- Self-discharge is almost absent;
- High battery capacity;
- The number of charge / discharge cycles is many times greater than that of previous types of batteries;
- To set the required voltage, fewer “cans” are needed, which significantly reduces the weight and dimensions of the battery.
- High price, almost 3 times in comparison with nickel. cadmium;
- Three years later, a significant loss of capacity occurs, because Li decomposes.
We got acquainted with the elements, let’s move on to the remaining elements of the battery pack of the screwdriver. Dismantling the unit, for example, to repair the battery of a Hitachi screwdriver (shown below), is very simple. we unscrew the screws along the perimeter and disconnect the case.
The housing has four contacts:
- Two power, "" and "-", for charge / discharge;
- The top manager, it is connected through a temperature sensor (thermistor). A thermistor is needed to protect the batteries, it turns off or limits the charge current when a certain temperature of the elements is exceeded (usually in the range of 50. 600C). Heating occurs due to high currents during a forced charge, the so-called “fast” charging;
- The so-called "service" contact, which is connected through a 9K resistance. It is used for complex charging stations that equalize the charge on all elements of the battery. In everyday life, such stations are useless, due to their high cost.
That’s the whole battery design. Below is a video on how to parse a block.
Video: How To Disassemble A Bosch 14 Screwdriver Battery
We figured out the purpose of the battery structural elements, now we will consider how to determine the malfunction, this is part 2 of the repair of the screwdriver’s battery. Immediately, we note that all elements cannot fail at once, and since we have a consistent circuit, when one element fails, the entire circuit does not work. So, our task is to determine where we have the weakest link in the chain.
For this, we will need a multimeter, and for the second method of troubleshooting a 12V lamp, if your battery for a screwdriver is also 12 volts. The procedure is as follows:
Note. The difference between the elements in the battery of 0.5. 0.7V is considered significant, this means that the element is becoming unusable.
Thus, we found candidates for “resuscitation” or “amputation” and replacement with new elements.
If your screwdriver is powered by 12 or 13V, you can search by a simpler method. We disassemble a fully charged battery and connect a 12 volt lamp to the contacts "" and "-". The lamp will be a load and will discharge the battery. Next, we take measurements on the battery cells, where the voltage drop is the strongest, there is also a weak link.
There are other ways, instead of a lamp, you can pick up resistance, but for this, the basics of electrical engineering are already necessary, and it is doubtful if a resistor with the necessary resistance was at hand.
Other faults are very rare. For example, loss of contact at the places of soldering batteries or power contacts of the unit, failure of the thermistor. This problemma is more inherent in fakes. In view of rarity, we will not focus on it, we will confine ourselves to battery elements.
With the "problem" elements sorted out, it is necessary to repair. How to repair a screwdriver battery? In general, 2 methods are available for repair, if I may say so. This is the restoration and replacement of elements that have become unusable.
Is it possible to “reanimate” elements and how?
We proceed to part 3 of the repair of the screwdriver’s battery and immediately make a reservation that the concept of “resuscitation” for lithium-ion batteries is not applicable. There is no memory effect in them; most likely, lithium decomposed, and nothing can be done about it. In such batteries, it is necessary to find out what the cause of the malfunction is: the element itself or the control circuit. There are two options:
- we change the control circuit from another, but similar to ours, battery, if it helps, we find a replacement and change it;
- apply 4V to an element with a current of approximately 200mA, for this you need an adjustable charger. If the voltage on the element rises to 3.6V. the element is serviceable, the problem is in other elements, or in the control circuit.
Repairing the battery of a screwdriver is mainly available for Ni-Cd batteries, but they are usually the most common in household screwdrivers.
So how to reanimate a screwdriver battery? There are two types of “resuscitation” for these types of batteries:
- Compaction or compression method (it will work in cases where the electrolyte is still in stock but the volume is lost);
- "Firmware" voltage and current greater than the nominal. This method allows you to eliminate the memory effect, and although not completely, but to restore the lost capacity.
This method is shown below in the video.
Note. As a rule, in a nickel-cadmium battery, the main reason for the loss of capacity is the boiling of the electrolyte, and if it is critically small, no “firmware” will help.
This method, if its result is positive, will not solve the problem of failure of the elements. Rather, he will only delay the replacement of those that have become unusable and in the future, still need to repair the battery of a Makita screwdriver or any other.
Repair and replacement of screwdriver battery cells
A more effective way to repair batteries for a screwdriver is to replace the elements that we have identified as faulty.
Note. When purchasing a new element, make sure that its capacity and dimensions coincide with the native elements.
We also need a soldering iron, low-corrosion flux (preferably alcohol rosin flux) and tin. We are not talking about spot welding, since there is hardly a need to purchase or assemble it for a one-time battery repair.
There is nothing complicated in the replacement itself, especially if at least some. then there is experience in soldering. In the photographs everything is shown in sufficient detail, we cut off the defective element, instead of it we solder a new one.
It should be noted several nuances:
- When soldering with a soldering iron, try to solder quickly, so that the battery does not heat up, because risk ruining it;
- if possible, implement the connection using your own plates, or use copper of the same size, this is important because the charging currents are large and, if the connecting wires are incorrectly cross-section, they will heat up, respectively, the thermistor protection will work;
- in no case confuse the plus of the battery with a minus. the connection is serial, which means that the minus of the previous bank goes to the plus of the new bank, and the minus to the new one. plus the next one.
After the new elements are soldered, it is necessary to equalize the potentials on the “banks”, since they are different. We carry out a charge / discharge cycle: set to charge for the whole night, give a day to cool and measure the voltage on the elements. If we did everything right, the picture will be something like this: on all elements the same indicator of the multimeter, within 1.3V.
Next, we begin to discharge the battery, insert the battery into the screwdriver and load it “to the fullest”. The main thing is to spare the screwdriver himself, otherwise you will have to repair it too. Bring to full discharge. We repeat this procedure two more times, i.e. charge and completely discharge.
It should be noted that the process of erasing the "memory effect" should be carried out every three months. It is carried out by analogy to the training described above.
Such a not-so-cunning procedure will extend the work of your screwdriver, at least until you have to change it yourself to a new one.