How to check the battery banks of an electric screwdriver

How to check the battery banks of an electric screwdriver

Technically you can determine the closed battery by measuring the voltage of each bank separately, with a voltmeter. To measure the voltage at each bank, you need to use a load fork. Under load, the voltage of the bank below 1.7 V says about its defect.

The most reliable way to test is with a fully discharged battery. The battery should give out 12 V. The value less by a multiple of 2 will determine how many banks are defective. Further you need to determine why the bank is short-circuited. If the battery is expensive and new, having worked less than 3 years, it can be resuscitated. But for this you need to have locksmith skills, tools and follow the safety precautions.

The first step of the test

Voltage and current measurements are made while charging the electric drive.Monitor the drive periodically after a certain time interval. As the time increases the voltage increase decreases.

So, after half an hour of charging the voltage will be 13 V. If the measurement is taken after another half hour, the voltage will be 13.5 В. After 2 hours of charging, the voltage will be approximately 14 V. This indicates that the maximum has been reached. A fully charged battery has a voltage of 17 V.

You can verify the quality of a battery by measuring the current during the charging process.If the battery is in good condition, it will show a steady increase in current for 1 hour during the charging process. When the current passes the 1A mark the drive is functioning correctly.

The battery installed in an electric screwdriver can be tested with a tester or voltmeter to determine the voltage between the poles. no load, the voltage will be the same as the no-load voltage. So, if for 12 “cans” with a rating of 1.2 V operating voltage is 14.4 V, the no-load voltage will increase to 17 V. A decrease of this value means that some cells in the battery are not working or the battery is not fully charged.

Initial measurement

Before the initial measurement should try to conduct the procedure of charging to the nominal voltage. Then wait about an hour for the self-discharge to stabilize and measure the battery voltage. It should be equal to the voltage indicated on the case, but you should not trust this figure for 100%. it often has a marketing character and may be somewhat overstated. Therefore it is better to determine the voltage so: take the voltage of a single cell (it depends on the type of battery) and multiply it by the number of cells in the battery. If the quantity is not known, then take the multiplicity so that the final voltage does not exceed that indicated on the housing.

Battery type No-load voltage, voltsVoltage limits for good cell, V
Lithium-ion 3,7 2,7. 4,2
Nickel-cadmium 1,2 1.1,4
Nickel-metal hydride 1,2 1,1-1,25

So, if your electric screwdriver has a lithium-ion battery labeled 20 volts, this probably means that a fully charged battery will actually have 3.75=18.5 volts.

If the voltage is lower, it means that the battery has lagging cells. Another possibility is that one or more of the cells is open and when connected in series, does not allow the remaining cells to charge (charging current flow circuit interrupted).

If the voltage of a battery that has undergone the charging procedure is lower than expected by a multiple of one or more of the single cell voltages, there is reason to believe that there are fully defective cells. So, if the NiMH battery is rated at 14 volts (expected 1.211=13.2 volts ) at idle 12.0 volts, then there is reason to believe that one bank is faulty, and if 10.8, then two.

check, battery, banks, electric, screwdriver

Checking the battery of an electric screwdriver for performance

Every owner of an electric screwdriver sooner or later encounters malfunctions in its operation. But you should not rush to throw out a problematic device and go to the store for a new one, or carry it to a repair shop. With a minimum of knowledge you can independently determine the cause of the problem, buy and replace the right element.

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Checking the battery of an electric screwdriver

The main rule of battery testing is to fully precharge the battery. The most accurate measurement will be that held under load. To do this, connect a light bulb of the appropriate voltage to the battery components in turn.

Before testing the battery for performance, it is advisable to find out whether the malfunction is due to a poorly functioning charger unit.

Test the charger in the following order:

  • The unit is plugged in.
  • Set the multimeter to DC measuring mode.
  • Connect the appropriate probes to the plus and minus sides of the battery charger.
  • If the voltage deviates from the values indicated on the battery pack, it must be replaced or repaired.

Testing the battery capacity of an electric screwdriver with a multimeter

The battery capacity of an electric screwdriver is checked with a multimeter in the following sequence:

  • The battery pack is fully charged.
  • The output current at the battery terminals is measured with the meter probes.
  • If the readings do not match the parameters specified in the tool’s instruction manual, the battery pack is disassembled and the batteries are removed for further testing.

It is important to remember that this varies between 1.2 and 1.4 volts for nickel cadmium batteries, and between 3.6 and 3.8 volts for lithium batteries. Deviations from the normal range indicate a battery failure.

If preliminary testing by the tool indicates that the banks are faulty, proceed to disassemble the battery case. Banks are cells which are connected in series and placed inside the battery. This is the battery that holds the electrical charge and powers the tool. As a rule, any battery consists of 10-12 cells of 1.2 volts.

Initially you should visually check the integrity of the connections between the banks. It often happens that several individual cells drop out of the circuit due to a breakage, which leads to the deterioration of the battery as a whole.

If all connections are correct, measure the voltage of each bank individually. The voltage must be at least 1.2 volts. Measurements are made with a multimeter, the probes of which are connected to the poles of the can. If the instrument does not show voltage, such banks should be replaced. If the defective parts are not identified, you need to repeat the test under load.

This is important: the test of the cans with the meter should be carried out when the individual elements are disconnected from any sensors, for this purpose it is necessary to solder the circuit.

To fix the battery, a minimum of electrical knowledge is required. even a novice homeowner can handle it. Self-repair of an electric screwdriver battery will save the family budget and give your tool a second life.

Causes of shorted battery cells

The main problem lies in non-compliance with the instructions for use of the car battery. Tightly spaced plates, the active putty on the grids, precisely designed to work under flooding, with the voltage, within the permissible. Crumbled mass, sulfation, sharp bump on the case is a prerequisite for contact of the plates with opposite charges. If one bank works with overload, it discharges faster, sulfates, and the first will fail.

What to do to avoid short circuiting the battery bank and make the battery work for a long time? Keep the battery clean to prevent excessive self-discharge currents. Do not leave a discharged battery uncharged for a long time. A discharged battery will over freeze in the cold, since it has a weak electrolyte. Often the entire battery must be discarded because of 1 can. There are several reasons why it can short-circuit:

  • Factory defect. warranty case.
  • Severe impact on the case.
  • Chronic undercharging and overdischarging are the most common causes of malfunction.

Checking the Battery of an Electric Screwdriver

To determine the actual basic parameters of the battery, check.

battery cells may change their capacity

Check the battery of an electric screwdriver when fully charged. The complete test requires several steps.

Test tools

You can test the electrical storage device by

The first step of the test

After about a half hour of charging the voltage will be 13 volts. If the current is measured after ½ hour, the voltage will be 13.5 В. After 2 hours of charging the voltage will already be about 14 V. This indicates that the maximum is reached. A fully charged battery will have a voltage of 17 V.

You can verify the quality of the battery by measuring the current during the charging process. If the battery is in good condition, it will exhibit a steady increase in current of 1 hour during the charging process. If the current passes the 1 A mark, the battery is functioning normally.

Some elements in the battery are not working

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By the results of the first check you can get an initial impression of the performance of the battery cells. This will help determine if the battery needs to be disassembled.

Load test

To determine how long it will take for the battery to discharge, you must do a load test of the drive. The load should be chosen according to the capacity of the battery. If it is not known, assume that the load capacity is half the product of the current delivered by the battery during operation and the drive voltage. This value is usually taken as 35-40 watts. So you can use a car headlight as a load (35W) or use a 12v spot lamp with the same power.

The battery has a defective cell

Checking the batteries in the drive

So let’s assume that you have determined with the preliminary tests that there are defective elements in the drive. Then it is necessary to disassemble the battery and remove the cells (banks) connected in series. As mentioned above, a battery consists of 10 to 12 such cells with a voltage of 1.2 В.

After inspection, the voltage of each “jar” 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 sensor connections. The meter should be connected to the battery terminals. “Under-voltage banks to be replaced. If no faulty cell is found, the jar should be tested under load.

Resistance test

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

A resistor of 10 ohms should be used as a load

Small Cordless Screwdriver Shootout

For better understanding we give approximate calculations. Let’s suppose that in the course of measurement under load the data for one “bank” is obtained: working voltage is 1.19 V and a working current of 112 mA. Before performing the calculation, remember to convert the current value from mA to A. 0.112 А. Proceed accordingly (1.19/0.112). 10 = 0.63 Ohm. Recall that the subtracted value in our expression is the load resistance of the resistor (10 ohms).

Checking the other parameters

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

Check the power supply elements for the “memory effect” by fully charging the battery and fully discharging it. Several charge-discharge cycles (3 or 4) are carried out. The battery can be discharged with a 12 V bulb. In the course of the action, measure the residual operating voltage and the no-load voltage. After repeating the cycles many times the “memory effect” will disappear.

Instructions for action

Before you declare a battery unusable, you must test it to see if it works.

The tools for the test

To test the battery you will need a voltmeter, ammeter, connecting wires, and tools for grasping contacts: clips like alligator clips or clamps. Sometimes the design of the battery block contacts does not allow the devices to be connected without disassembling the enclosure. It is very possible that you will have to deal with soldering. Here is a list of things you will need:

  • Charger (original or compatible);
  • Multimeter (or better two);
  • Resistance of 4.7 10 ohms for a power of 5 W or more;
  • 12-volt car bulbs, a few of them;
  • Installation wires, cross section 0.5 mm.A kv, 1.5-2 meters;
  • Screwdriver;
  • Sharp knife;
  • adhesive tape;
  • A soldering iron with solder and flux.

Instead of a native battery charger, a laboratory power supply, with a voltmeter and ammeter for a current of a few amperes and a voltage of a few volts above the rating of the battery being tested, would be very suitable. For example, a car switchgear, if it has good integrated current and voltage meters.

To test the battery of an electric screwdriver a multimeter is most often used, but is also suitable for measuring the battery capacity.

In addition to everything else, you need to prepare a comfortable workplace with good lighting, put away flammable liquids and objects.

First step

First you need to set the type of battery. It is written on its housing. There must also be a nominal voltage and capacity in Ampere Hours or sometimes Watt Hours. The voltages used may be of the following ranges: 9.6, 10.8, 12, 14.4, 18, 24, 36 V. The type of battery and the voltage rating give you the opportunity to determine the number of banks inside the unit:

Electrochemical system Maximum voltage, V Nominal voltage, V Minimum voltage, V
Ni. Cd 1,37 1,2 1,0
Ni. MH 1,25 1,2 1,1
Li. ion 4,2 3,7 2,7

A typical battery discharge schedule will also be helpful:

A corrected battery after a charge shows the maximum voltage Umax. After a period of time it falls to the nominal Unom. Then the battery gives off current for a long time, at the interval t t1. During this period, as a rule, the nominal voltage slowly decreases to the minimum Umin. At the end of discharge, the battery begins to give off no current at all, and the voltage begins to drop rapidly.

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An unloaded voltmeter on a normal battery should give a voltage close to the nominal. If the voltage is a multiple of the nominal value of the batteries used, then one or more have shorted. It could also mean a deep discharge or even a broken circuit. The real test, therefore, is to check under load. Before such a test, you should first fully charge the battery in normal mode, as this is done before prolonged battery operation.

Initial Measurement

Before the initial measurement, an attempt should be made to conduct a charging procedure to the nominal voltage of. After that, wait about an hour to stabilize the self-discharge processes and measure the battery voltage. It should be equal to the voltage stated on the case, but you should not trust this figure 100%. it is often of a marketing nature and may be somewhat overstated. Therefore it is better to determine the voltage as follows: take the voltage of a single cell (it depends on the type of battery) and multiply it by the number of cells in the battery. If the number is not known, take a multiple so that the final voltage does not exceed the voltage indicated on the housing.

Battery type No-load voltage, V Voltage limits of the good cell, V
Li-ion 3,7 2,7. 4,2
Nickel-cadmium 1,2 1.1,4
Nickel-metal hydride 1,2 1,1-1,25

So, if it is marked on the case of an electric screwdriver that the lithium-ion battery has a voltage of 20 volts, it probably means that in reality on a fully charged battery will be 3.75=18.5 volts.

If the voltage is lower, it means that the battery is lagging behind. Another possibility is that one or more cells are open and when connected in series, they do not allow the rest to charge (charging current flow circuit is interrupted).

If the voltage of a battery that has undergone the charging procedure is lower than expected by a multiple of one or more of the single cell voltages, there is reason to believe that there are completely defective cells. So, if the NiMH battery at 14 volts nominal (expected 1.211 = 13.2 volts) in fact at idle 12.0 volts, then there is reason to believe the fault of one bank, and if 10.8. then two.

What does the battery consist of

The internal structure of the battery of any electric screwdriver, regardless of the country of manufacture, is absolutely identical. If you disassemble the plastic block, inside there are always “banks” assembled in a certain sequence. The battery’s voltage rating as a whole is added up based on the U level that each battery has individually. The battery also has four contacts, two of which provide charge-discharge cycles, the third is connected to the temperature sensor, and the fourth, which has a service purpose, is responsible for equalizing the charge potential in all cells.

1997 NiCd Cordless Screwdriver Teardown (It still works after 20 years!)

check, battery, banks, electric, screwdriver

So, the connected “banks” of the battery of the power tool are nothing but source of current with a constant value, in which the conversion of chemical reactions into electrical energy takes place constantly. This is how the battery releases stored energy into the circuit. And when it’s being charged, the process is reversed: the battery simply draws energy from the mains.

How to charge the battery properly

To keep your battery working longer, you need to be careful about charging it, especially right after you buy it. Because of violations of the rules most often appear “memory effect” and other problems. These are the basic requirements:

  • Different models have separate requirements.
  • The battery should be disconnected immediately after a full charge.
  • Ni-Cd batteries must be left discharged for a long period of time.
  • Ni-MH batteries should be left fully charged.
  • Li-Ion batteries should not be stored fully discharged.

Run the battery through several complete charge-discharge cycles for the first time or after long periods of storage. Before prolonged use, you should at least conduct an initial check of the battery, because even one faulty “bank” will disrupt the operation of the entire device.