How to check the battery of an electric screwdriver

How to check the battery of an electric screwdriver

In order to properly charge an electric screwdriver battery, a certain ambient temperature must be provided. The optimum temperature is 10 to 40 degrees Celsius. An undesirable point is the possible overheating of the battery pack during the accumulation of charge. To avoid the possible negative consequences of such a phenomenon, it is necessary to disconnect the battery for cooling from the charger.

It is not advisable to leave the batteries in the charger after they have reached full capacity or to insert them into an electric screwdriver which is then not to be used, but rather to put them in the tool case.

Recommended charging time varies from 30 minutes to 7 hours, depending upon battery type. Consult the battery manual for specific power tool models. These instructions must be followed precisely in order to ensure a long service life of the product. Most battery chargers have indicators that tell you where you are in the charging process. In such cases, it is easy to tell by the illumination of a certain color LED how much to charge the batteries precisely. Stop the process immediately after reaching full capacity.

Basic battery types

The most common type of battery used in screwdrivers is the nickel-cadmium battery. The main advantages of such elements are recognized high capacity with small size and weight, as well as a fairly long service life (up to 3500 cycles). The electromotive force of the element is up to 1.37 V and the specific electrical energy is up to 65 Wh/kg. Restricts the use of such elements (especially in imported tools) harmful production.

Nickel-metal hydride batteries for electric screwdriver become the main competitor of nickel-cadmium copies. The main advantage of such elements is safety and environmental friendliness. It is recommended that cells be stored in a charged condition, since if left unused for a month they may be discharged to the point where they cannot be recharged.

In the latest models of screwdrivers modern advanced types of batteries are used: lithium-ion and lithium-polymer. They have a very high capacity in a small size, but their cost is still quite high.

Checking the battery with a multimeter

First, check the parameters several times during charging:

The current change mode is uniform. it increases in the first hour after turning on. If the value is higher than 1 A after an hour, the device is fine, and there is no need to take it apart. Otherwise it should be done by soldering the connections with a soldering iron.

To quickly test the battery with the tester, follow these steps:

• by multiplying the number of cells and 1.2 V, obtain the value for idle;
• conduct a test of the battery of an electric screwdriver with the help of probes on the contacts;
• compare these readings with the no-load voltage.

You can compare the result of the measurement to the data in the manual. For nickel-cadmium batteries the corresponding value is 1.2-1.4 volts, for lithium ones it is 3.6-3.8. Inconsistent results indicate a malfunction in some part of the unit. Remove them from the battery case for testing. Carefully examine the power supplies for any signs of rust, electrolyte leakage, or shock marks.

Characteristics of electric screwdriver batteries

Measuring the voltage of the battery jars

A battery consists of 10 or 12 cells, 1.2 volts each. First check the quality of their connection with each other. Sometimes some of them break off, causing problems with the tool.

Electric screwdriver battery diagram

If there are no problems with the contacts, measure the voltage of each part of the accumulator, which should not be less than 1.2. Solder the pins with the soldering iron. Power cells should not be connected to the probes. Connect probes to poles. If the voltage is less than normal, replace them with new ones.

It may happen that the test does not find any defective components. Then repeat the process under load. Connect a 12 volt bulb through a 10 ohm resistor of 25 watts. Calculate the internal resistance level by dividing the voltage by the amperage, minus the load resistance. Turn on the light bulb for 2 minutes. The brightness should not change. If it quickly goes out, the storage capacity is insufficient.

When carrying out actions aimed at checking the battery cells, you should not forget the influence of such a factor as “memory effect”. The phenomenon itself is that due to frequent charging of the drive, the battery cells can change their capacity. Happens because of the charges remaining from the previous charge. Nickel-cadmium “banks” are more susceptible to this phenomenon than other batteries.

The battery of an electric screwdriver is checked when fully charged. The full test takes place in several stages.

Inspection Tools

You can check the electric drive by using:

The first step of the test

The voltage and current are measured while charging the electric storage battery. Readings are taken periodically after a certain amount of time. With increasing time the voltage rise decreases.

For example, after ½ hour of charging the voltage will be 13 Volts. If measured after another half hour, the voltage will be 13.5 В. After 2 hours of charging the voltage will be about 14 V. This indicates that the maximum has been reached. A fully charged battery has a voltage of 17 V.

The quality of a battery can be evaluated by measuring the current during the charging process. If the battery is in good condition, it is characterized by a steady increase in current of 1 hour during the charging process. When the current passes the 1A mark the drive is functioning normally.

The battery installed in an electric screwdriver can be checked with a tester or voltmeter by measuring the voltage between the poles. Without load, the voltage will correspond to the no-load voltage. So, if the 12 “cans” with a rating of 1.2 V operating voltage will be 14.4 V, the no-load voltage will increase to 17 V. A decrease in this value indicates that some cells in the battery are not working or that the drive has not fully recharged.

From the results of the first check you can get an initial impression of the performance of the battery cells. This will help determine the need to disassemble the battery.

Testing under load

To determine how long it will take for the battery to discharge, the battery pack should be tested under load. The load should be selected according to the capacity of the battery pack. If this is not known, it is assumed that the load capacity is equal to half the product of the current delivered by the battery during operation and the storage voltage. This is generally accepted to be 35-40 watts. You can use a car headlight as a load (35W) or use a 12W spot lamp with the same power.

To measure the battery, the battery is connected to the load through an ammeter. Readings are taken with a voltmeter. “Banks” are connected for 2-3 minutes. Measured voltage must be greater than 12.4 В. If the reading is between 12 and 12.4 V, it means that there is a defective cell in the battery. The presence of faulty cells can be indicated by a decrease in brightness of the lamp used as a load. If the lamp goes out within the allotted time period, it means that the accumulator discharges very quickly. it has a very small capacity.

Checking the Battery

So, let it turn out that with the help of preliminary tests it was found that there are defective cells in the battery. Then you must disassemble the battery and remove the batteries “banks” connected in series. As mentioned above, the battery consists of 10-12 such cells with a voltage of 1.2 В.

First, a visual inspection of the connections of the cells is made for irregularities. They may cause a reduction in the performance of the battery as a whole.

After the inspection, the voltage of each “bank” should be measured. The voltage of one cell should not be less than 1.2 В. When carrying out measurements, the battery cells should be disconnected from all connections to sensors of any kind. The measuring instrument should be connected to the terminals of the battery. Low-voltage “banks” should be replaced. If no faulty cells are found during the measurement, the cells should be tested under load.

Checking for Resistance Values

The ability of each battery to function normally can be checked by comparing the internal resistance of the “banks. This is determined by dividing the operating parameters of the voltage by the amperage and subtracting the load resistance.

Operating voltage must be measured under load. A resistor of 10 ohms and 25 watts should be used as the load. Each battery is checked. Measure the operating current and voltage.

For a better understanding here are some approximate calculations. Let’s assume that in the course of measurement under load the data is obtained for one “bank”: working voltage. 1.19 V and a working current of 112 mA. Before you do the calculation, remember to convert the current value from mA to A. 0.112 А. Let’s perform the corresponding operations (1.19/0.112). 10 = 0.63 Ohm. Recall that the subtracted value in our expression is the load resistance of the resistor (10 Ohm).

Checking the other parameters

Each type of battery has a certain amount of self-discharge.

Control the self-discharge by measuring the voltage every day for a month.

Checking the cells of the power supply for the “memory effect” is carried out by fully charging the battery and fully discharging it. Carry out several charge-discharge cycles (3 or 4). The battery can be discharged by means of a 12 V lamp. In the course of the test perform measurements of the residual operating voltage and the no-load voltage. After repeating the cycles repeatedly, the “memory effect” will disappear.

Measuring under load

If the battery shows a relatively normal result in no-load operation, you can proceed to the test under load. A resistor can be used as a motor equivalent. Its resistance is chosen with reference to the nominal load current of a household electric screwdriver, which at no-load operation is not more than 2 amperes (most likely 1.1,5 A), at an average load of about 5 A, at maximum. up to 10 A. Therefore, it is appropriate to choose a resistor so that the current is 5 A for the test.10 А. The value is calculated according to Ohm’s law: R=U/I. So, for an electric screwdriver for 12 volts, the resistance of the resistor should lie in the range of 1.2.2.4 ohms. The power should be between 60 and 120 watts. Such a resistor is hard to find, so you can connect in parallel, for example, 6 10 W resistors of 10 ohms each and get a load of 60 W and a resistance of 1.6 ohms.

Load a charged battery onto this equivalent and measure the voltage under load.

Check the battery for an equivalent load consisting of incandescent bulbs (if you have a second multimeter, it is desirable to monitor the current in the circuit).

Another option is to make an equivalent of incandescent bulbs, connecting them in parallel if necessary, until the desired power is reached. But keep in mind that the resistance of the lamp filament depends on the current flowing through it. LED fixtures are free of this disadvantage, but their power consumption is much lower than that of traditional light sources. To get at least 60 watts of power (input power, not equivalent!), a sufficient number of LED elements will be required.

Under load, the voltage will slightly decrease relative to the no-load level. The degree of reduction depends on the condition of the battery. There are no clear criteria for the acceptable level of voltage drop, but you can roughly estimate the condition of the battery by comparing it with a new battery.

It should be noted that regardless of the brand of an electric screwdriver and the country of manufacture, batteries have an identical structure. The assembled battery pack looks like this.

If we take it apart, we can see that it is assembled from small cells that are assembled in series. And we know from the school physics course that elements having a series connection make up their potentials.

Note. The sum of each cell gives us the final voltage at the battery terminals.

The set pieces or “banks” are usually of standard size and voltage, differing only in capacity. The capacity of the battery is measured in A/h and is indicated on the cell (pictured below).

The following types of cells are used for screwdriver battery layout:

• Nickel-cadmium (Ni. Cd) batteries, with a nominal voltage of 1.2V at the “banks”;
• Nickel-metal hydride (Ni-MH), cell voltage. 1,2V;
• Lithium-ion (Li-Ion), with a voltage of. 3.6V.

Let’s consider in detail the advantages and disadvantages of each type.

• The most common type due to low cost;
• Not afraid of low temperatures, such as Li-Ion batteries;
• Stored in a discharged state, while retaining its characteristics.
• Produced only in the “third world” countries, because of the toxicity of production;
• Memory effect;
• self-discharge;
• Small capacity;
• Low number of charge/discharge cycles, so they do not “live” for a long time under intensive use.
• Ecologically clean production, it is possible to buy a high-quality branded battery;
• Low memory effect;
• Low self-discharge;
• The higher capacity compared to Ni. Cd;
• charge/discharge cycles.
• No memory effect;
• Almost no self-discharge;
• High capacity of the battery;
• The number of charge/discharge cycles is many times greater than in previous types of batteries;
• To gain the necessary voltage it is necessary to have fewer “banks”, which significantly reduces the weight and size of the battery.

We have got acquainted with the elements, let’s move on to the other elements of the battery pack of an electric screwdriver. Disassembly of the unit, for example, to repair the battery of an electric Hitachi screwdriver (shown below), is very simple. unscrew the screws around the perimeter and disconnect the housing.

• Two power, “” and “-“. for charge/discharge;
• The upper controlling one, it is connected with the temperature sensor (thermistor). The thermistor is necessary to protect the batteries by shutting off or limiting the charging current when the cells exceed a certain temperature (usually in the range of 50°C to 600°C). Heating occurs because of the high currents during forced charging, the so-called “fast” charging;
• The so called “service” contact, which is connected with a 9Kohm resistor. It is used for complex charging stations, which equalize the charge on all cells of the battery. In the home such stations are useless because of their high cost.

This is actually the whole construction of the battery. Below is a video on how to disassemble the block.

Testing with load

This method involves the use of several bulbs or small electric motors that are connected to each feeding element in the battery system of an electric screwdriver.

First the whole battery is fully recharged. Then to each “bank” is connected one bulb at 3-4 V or a low-power “motor. This method allows you to identify without measuring instruments non-functional elements in the system, which first of all will lose their charge under load. Units that have lost capacity will certainly reveal themselves.

What additional methods are available for screwdriver battery recovery?

It is worth noting right away that not all batteries are subject to the possibility of recovery. In particular, with the best success can be reanimated “banks” with the type marking ni cd. Most typical screwdriver models are now equipped with this type of battery. Of course, in the market of tools you can find Makita or hitachi or Bosch screwdrivers, the power element of which is built on a lithium basis, but these models are not so much.

In general, if we talk about the serviceability of the battery pack and methods of restoration, in any case you should pay attention not only to the batteries themselves inside the case, but also make sure that the charger is working properly. It is likely that the power supply unit has lost its ability to provide the required charging current.

Many masters, faced in practice with the repair of nickel cadmium power elements, restore them by adding electrolyte. While working, the battery begins to lose the electrolyte, as it evaporates.

Physical impact on the battery “bank” with a drill helps to remedy the situation. Make a small hole in the body of the battery (diameter 0.8-1mm). Using a syringe with a needle inside the battery inject a couple of drops of distilled water. The hole is then securely filled with epoxy. This cycle of measures will prolong the operation of the power cell for a few more charge/discharge operations.

Of course, the easiest and most obvious way to resuscitate the battery pack for an electric screwdriver is to physically replace the faulty unit with a workable one. Here even the help of a specialist can be inappropriate, because the operation can easily be done even by someone who has at least once used a soldering iron and held a screwdriver in his hands. The main thing here is to show a little skill so as not to allow the overheating of the batteries at the time of soldering / unsoldering.

Of course, there are quite a lot of ways to reanimate batteries, but not every one of them is available to the average user. If you can not prolong the life of your screwdriver with a regular battery yourself, then ask for help from qualified professionals. They will make an error-free diagnosis and “figure out” how to restore a tool battery with minimal labor.

(15 ratings, average: 3.53 out of 5)