How to repair the electric screwdriver battery and its faults
A cordless electric screwdriver, can always come in handy at home, but over time, its power source suddenly refuses to work. It is expensive to buy a new electric screwdriver. Its price is about 70% of the cost of the battery. And since models often change, it is quite difficult to find a new battery for this particular tool. That raises the question. what to do next. Buy an electric screwdriver or look for a similar battery? But the problem can be solved by repairing the battery itself, prolonging its life for several more years.
It is worth noting that batteries for almost all brands of screwdrivers, regardless of what country they are made in, have a similar device. But each type of battery has its own specific characteristics.
If the battery is disassembled, you can see that its device consists of individual cells connected in a common circuit in series. Many people should remember even from their school years that when charging cells are connected in series in one electrical circuit, the total capacity increases.
Types of batteries
Has a fairly high capacity, so that one full charge can be enough for 1500 cycles of operation. But at the same time, it needs constant charging. Also this type of battery is not recommended for use in low air temperatures.
Almost the cheapest batteries with a nominal voltage of 12.5 V. They have a small capacity, so the discharge occurs fairly quickly. But they cannot be recharged. Therefore, in order to prolong the life of these batteries, it is recommended that they be fully discharged before being charged. The advantage of nickel-cadmium batteries is that they charge quickly, last a long time with proper care, and work well at low temperatures.
They have a high capacity and charge quickly. Battery can be recharged freely at any time, but must not be completely discharged. Also not recommended for use at low temperatures. Cannot withstand long periods of storage without periodic discharging and recharging (after a certain period of storage, it is recommended that the battery be given a load).
On the battery case there are two pins, marked plus/minus for powering the electric screwdriver and 2 pins for charging. A thermistor is connected to one of the charging contacts, whose duty it is to protect the battery from overheating during charging. The thermistor completely shuts down or reduces the charging current when the batteries reach a temperature of 50-60 degrees. Batteries are often heated during intensive, so-called “fast” charging.
Causes of malfunction
Battery failure is possible for a variety of reasons. So before you try to repair it, you should make sure that it is worth it. It may be that the labor and costs incurred to repair it will cost more than a new purchase.
For example, a common source of problems that cause a battery to stop working is its long life. Some kinds of batteries, after a certain period of time, have a decrease in capacity and quickly lose their charge while working. Naturally, in this case, it is most likely that you will not be able to restore their performance.
There are also some other malfunctions:
Diagnosing the battery malfunction
Suspect a faulty electric screwdriver battery or have it repaired should not be done immediately, but first try replacing it with a second one from the kit, before charging it properly. If the electric screwdriver rotates poorly, it may be caused by breakdowns in its mechanics (motor or gearbox). In case of doubt you need to replace the power supply, if possible. If everything points to the battery, then you can proceed to its diagnosis and recovery.
The first thing to do is to find out the type of battery. This is written on its case and the possibility of recovery depends on this. Also the nominal voltage should be indicated. It is usually in the range of 14 19 V. Then check the battery pack without disassembling it. Two methods can be used for this:
A multimeter can be used in two modes: voltage measurement and current measurement. If there are two devices, it is even better, you do not need to do unnecessary switching.
The measuring scheme is shown below: One multimeter is switched to voltage measurement mode (voltmeter), the other to current measurement mode (ammeter). If there is only one device, then instead of an ammeter you will just have to use a wire. The wires from the battery to the voltmeter can be thin, and the wires from the power source to the battery. thicker, but you should not get too carried away, in the end for the whole circuit will be suitable wire 0.5 mm cross section.kv.
If the battery voltage is normal, but the charging current is low, much less than one amp, then for a Ni-Cd battery it may mean that one of the battery cells is defective. Electric screwdriver battery repair is out of the question here, we need to repair. For Li-ion it means that either it is normal, or also a failure of one of the cells.
Let the Ni-Cd battery have a rated voltage of 18 volts. Then it is easy to find out how many elements are inside without opening the case. Knowing the rated voltage of Ni-Cd 1.2 V, divide: 18/1.2 = 15. This means that there are 15 elements in the housing. If the voltmeter shows an idle voltage of 16.8 V, then it could also mean a short circuit of one of the banks, and just a discharge of the normal battery. Such a battery in discharged condition gives 15 V. If the charged one shows 16,8 V or so it means that one of the cells is short-circuited. It is not possible to recover either, you have to replace it.
If the battery when charging passes a current of more than one amp, and the voltage gradually increases, increasing by 0.1 V for every 5-10 minutes, and at the end of the charge the voltage is slightly higher than the nominal, then the battery is fine, restoration is not required.
This method is similar to the previous one and is probably easier. It is not necessary to disassemble the charger or use a laboratory power supply. All you need is:
Checking scheme: To do this check you first need to put the battery on a charge and charge in the usual way. Then apply the rated load. It is not difficult to find out the current, to do this, divide the power consumption by the nominal voltage. For example, if an electric screwdriver has a power consumption of 50 W (typical case), at 18 V, the current should be 50/18 = 2,77 A. To achieve such a current, or close to it, you can dial in parallel car lights from the turns.
If the battery gives out the nominal current for several minutes, the voltmeter shows a voltage slightly below the nominal, and the lights do not dim, then the battery is serviceable. It may happen, however, that for Ni-Cd soon the current starts to weaken. This is a manifestation of “memory”. If this is the case, you need to recondition it. Lithium-ion batteries have no memory effect, although in theory it exists, in practice it is believed that it simply does not exist.
This method requires disassembly of the battery case. It applies when the battery or its cell stops giving a good current, and attempts to restore are unsuccessful. One bad link is enough here, because they are connected in series. But to find such an element, you need to check the internal resistance of each of them.
Of course, we must begin with a general inspection of all the jars, check for cracks, leaks, etc.д. A faulty element will immediately give itself away.
Checking for the current output is done using Ohm’s law for a complete circuit (aka the first Kirchhoff’s law). To do this, take a resistor with a rating of 10 ohms, rated at 25 watts, and an ammeter. The tested element is shorted to the resistance included in series with the ammeter.
For example, let the Ni-Cd battery with a voltage of 1.2 V have a current of 100 mA. Write it down and measure again, but not the current but the voltage on the cell. First, let’s measure the no-load voltage, without connecting a resistor, and then connect a resistor and see how much the voltage has dropped. Let’s assume that the first time it was 1.2 V, and after connecting the resistor it was 1.05 V. Then the internal resistance of this cell: This is not too small, if all the cells are like this, then the battery will only be able to supply the electric screwdriver with half the power. The lower the internal resistance, the better the quality of the cell, but with the indispensable condition: it must give the nominal, or close to it voltage. If the voltage is too low or too close to zero, the cell is shorted, it is not good and cannot be renewed. If the internal resistance is greater than 3 ohms, then you can try to rebuild. Replace the batteries (see below) or replace.
Full or partial battery change
If the screwdriver battery can not be restored “by accident”, it is necessary to change the batteries. Any battery in a screwdriver is a chain of battery cells connected in series. With this type of connection, if one cell “drops”, the whole battery has a reduced charge and discharges quickly. The performance is only as bad as the defective battery pack itself.
How to rebuild an electric screwdriver battery: full or partial replacement of the batteries
So you can restore the battery in two ways. The first way is to find the “weakened” elements and replace them. The second way is to change “all together”. The second option is more expensive, but more “long-lasting”. With the first option, the rest, while serviceable banks, will also soon fail. You will need to repair the battery again. So it is desirable to choose the second method.
How to restore the battery of an electric screwdriver
Algorithm of restoration of direct current source for electric tool depends on the chemical composition of the sections. For example, the refilling procedure is used for nickel-cadmium products. Repair of lithium batteries requires replacing the failed sections.
In the factory the contact plates are connected by jumpers, fixed by welding. Repair at home is carried out by soldering with special flux.
Bleeding of gas from the battery
During the operation of lithium-ion cells, gases are formed that raise the pressure inside the case. If the construction does not provide for a drain valve, the wall and the cover of the case become deformed. On some products, a bloated casing opens the fuse contacts, reducing the voltage at the terminals to zero. The defective cell is detected by the test device, and then removed from the jar.
The battery is installed on a hard surface, using a suitable tool the bloated plate is pressed into place. Gas escapes from the case cavity through gaps that form, but subsequently the section fails due to leakage and evaporation of electrolyte through the hole.
The second method of restoration is devoid of such a disadvantage, the method is based on forced bleeding of gas.
Bending sideways the positive contact plate is carried out, then using a blunted awl, the safety plate is removed from its regular place on the housing. A hole is formed in the cover, through which the excess gas is bled off (a hissing sound can be heard). The bloated cover is then pressed into place and the hole is filled with solder or silicone sealant. The positive plate is attached additionally.
Restoration with water
One of the most common methods of reconditioning nickel cadmium cells is to add distilled water to the jars (using tap or boiled water is strictly forbidden).
The procedure does not require the use of special devices and is done with your own hands at home.
The user has to take apart the plastic cover of the battery and remove the cylindrical elements installed inside.
Then use a test tool to identify parts with a minimum voltage (1 V or lower).
Filling up with distilled water is done with a clean medical syringe through a hole in the housing with a diameter of no more than 1 mm. The needle is cut to a length of 1-1,5 mm, and then the tip is inserted into the cover. 0.7-1.0 cc of liquid is injected inside, with up to 0.5 cc more (data given for 18650 cell).
By replacing several cells
To restore the functionality of the can, it is possible to replace the failed batteries. A test tool is used to determine the damaged nodes, measurement is performed after removal of the protective plastic cover.
Batteries with voltage lower than 0.7 V (for NiCad) and less than 2.5 V (for Li-Ion) should be discarded. These items are replaced by batteries with identical dimensions and parameters, the jumpers are soldered with tin-lead solder (using special flux or rosin).
How to eliminate the memory effect
If not fully charged and then discharged, there is a reversible decrease in battery capacity, called the memory effect. The device remembers the lower limit of performance, which leads to a gradual deterioration in performance. The phenomenon is noticeable on nickel-cadmium type products, nickel-metal hydride batteries have a weak memory effect. Lithium-ion devices are not affected by the effect.
Makita 6270D electric drill repair and refurbishment
To restore the capacity it is necessary to perform a full discharge of the current source with the help of an incandescent lamp (designed for 12 volts) and then connect the regular charger unit. The procedure is repeated 3 to 5 times to bring the capacity to the starting value.
How to properly refill with distilled water
Sequence of actions when topping up the battery with water:
- Separate the defective cells from the common battery bank, jumpers are stored for later reassembly.
- Drill into the side of the casing at the bend in the wall. Drilling is carried out to the thickness of the casing material, drilling deep into the electrolyte is prohibited.
- Add 1 ml of distilled water into the cell cavity (using a medical syringe with a shortened needle).
- Keep the battery at room temperature for 24 hours, and then check the voltage.
- Charge the battery with a battery charger designed for nickel-cadmium power sources.
- Wait the battery for 5-7 days and then check the voltage. If the capacity drops, recharge with an additional amount of water. If the values do not fall, seal the case (using solder or silicone material).
- Join the batteries in a common jar, using contact welding or soldering. Conduct training cycles of discharging and charging the battery to increase the capacity.
The method is only suitable for nickel-cadmium type products, other batteries cannot be charged with water.
Reconditioning and recharging the battery
Electric screwdriver battery recovery with your own hands is not such a complicated process, if you understand the intricacies of electronics. The surest way is to replace the recharger with a new one. Some users take care of this in advance and buy two or three batteries.
Find out the charging time of your battery
When a problem arises, quickly replace the old one with a new one. Many people take a radical step and change the nickel cadmium batteries for lithium ion batteries. But this is not the right solution. If the device is designed for Ni-Cd, it is better to install a similar battery.
To carry out the restoration of nickel-cadmium batteries of screwdrivers will have to buy several similar batteries. There are 5 of them per set. When buying, it is important to pay attention to the size of the charges. For this purpose, it is necessary to look at the parameters of the electric screwdriver beforehand.
What is the problem with Ni─Cd batteries?
When using Ni─Cd, the voltage and discharge capacity gradually decrease. Below are the main factors that cause these processes:
- reduction of the working surface of positive and negative electrodes;
- loss of the active mass, and its redistribution among the electrodes
- occurrence of current leakage due to the formation of dendrites of metallic Cd;
- processes which result in irreversible consumption of water and oxygen;
- change in the composition and volume of the electrolyte.
similar processes occur when operating Ni-MH accumulators. The only difference is in the electrode materials used.
During the operation of Ni─Cd batteries, due to the redistribution of the active mass over the electrodes, the mechanical strength and volume of the nickel-oxide (positive) electrode change. As a result, the contact between the active mass and the electrode becomes worse. All this causes a decrease in conductivity and a drop in capacity. In the neglected case the contact between the positive and negative electrodes is simply broken. As a result, the battery ceases to show signs of life.
All these changes of the nickel-oxide electrode are caused by constant overcharging, in which oxygen is released in the space of the positive electrode. The more charge-discharge cycles the more coarsening of the active mass crystals of the positive electrode is observed. Therefore, the working surface decreases and so does the capacity of the battery.
At the cadmium electrode, the degradation process is mainly determined by the migration of the active mass. As a result, there is some loss of it. In addition, the active mass clogs the pores in the surface layer of the negative electrode. This makes it difficult for the electrolyte to reach the deeper layers. The result of active mass migration becomes the growth of dendritic bridges through the separator to the positive electrode. This leads to numerous short circuits and increases the self-discharge. The cadmium electrode also has a growth of crystals and increase in the volume of the active mass.
In addition to the processes described above, in Ni─Cd batteries there are processes of oxidation of various additives that are present in the battery. The metalloceramics of the positive electrode is gradually oxidizing with water consumption. And one more unpleasant process which leads to loss of serviceability of Ni─Cd accumulator, is a withdrawal of electrolyte from the separator. This is due to a change in the porous structure of the electrodes and increases the internal resistance of the nickel-cadmium battery. The composition of the electrolyte also changes during operation. In particular the volume of carbonates grows. The conductivity of the electrolyte decreases and all parameters of the Ni─Cd battery fall when discharged. The picture becomes particularly noticeable at low temperatures. What to do in such cases?
What is the problem when using Ni-Cd batteries
Ni-Cd batteries are designed to be installed in equipment characterized by high discharge currents. As you use it, there is a transfer of active mass between the electrode plates, which leads to a drop in strength and volume of the positive electrode. The cell is a paste consisting of nickel hydroxide and an electrically conductive material, which is applied to a steel mesh base.
Degradation occurs because the battery is overcharged, causing crystals to form from the active mass on the positive pole. Cadmium needles form on the negative electrode, passing through the thickened electrolyte to the negative plates. Crystal growth occurs with prolonged storage of charged cells or constant recharging of batteries.
An additional disadvantage of batteries is the consumption of distilled water, which is absorbed and degraded by the chemicals that make up the positive electrode. Foreign admixtures appear in the composition of electrolyte, which worsen the characteristics of the solution.
A quick check of the battery with a multimeter
Since the batteries are connected in series, it is important to know that when the batteries are in the charged condition, their voltage tested with a multimeter should be identical. In order to correctly identify the faulty link, you should switch the tester to constant current change mode, and measure each battery (bank) in the system.
If ni cd batteries are used in your case, the nominal voltage of each of the units should be approximately 1.2 V. If Li-ion batteries are used, the voltage reading should be around 3.6 V.
Repair: 12v cordless drill battery replacement
In general, in order to initialize the fault correctly, the entire battery pack is first subjected to a maximum charge for 6 hours. Then an appropriate measurement is made with a multimeter, based on the above readings for the different types of batteries. If at this stage no distortion is detected, then the battery is connected to the load in order to fully discharge it.
Having verified that the battery pack is discharged, it is necessary to measure again with a multimeter each supplying battery in the system. This will allow with a high degree of probability to locate unusable “cans”. The reading on the multimeter in such blocks will be below 0.5-0.7 V. If you have battery packs for replacement, reanimation of the entire circuit is eliminated by trivial re-soldering, removing the worn-out cells and replacing them with new ones.
Soldering is the hardest part
At the factory the batteries are spot welded. But not every home workshop has it. There are persistent opinions that the effects of high temperature on the cells disable them. Opinions are out there, but no proof. So you can connect the cells in the battery by conventional soldering. The method has been tested on Li-ion batteries as well.
For this purpose an electric soldering iron with 40. 60 W power, flux for nickel soldering or that is available and strips of not thick tin plate are taken. Tin is used to make connectors.
Before assembly it is necessary to tin all contact places of accumulators and connecting plates. Then put the plate on the contact and press it down with the soldering iron. A powerful soldering iron can quickly solder a tinned layer. All it takes is a fraction of a second.
Check the solder for physical breakage. Similarly, the following pins must be resoldered. There is nothing complicated about this process. It takes some care and skill to do it yourself. After soldering, wipe all places with alcohol to remove flux residue, assemble the battery into the case and put it on charge. After fully charging do a complete discharge to equalize the cells and the battery is ready for use.