How to test an electric screwdriver without a battery
How to repair an electric screwdriver battery at home
The cordless electric screwdriver is a handy mechanism that allows you to quickly deal with repairs. Instead of a heavy drill on a wire, it is better to take a lightweight screwdriver that can handle the same tasks without being tied to one place.
They have one problem. batteries fail. There are many reasons for this:
- Long downtime. Modern lithium-ion batteries require periodic charging and discharging. They drastically lose capacity if they are idle for a long time.
- Temperature drops. Li-ion does not tolerate high temperatures well. Therefore, there are recommendations for storing these batteries in the refrigerator. But they cannot work in such conditions.
- Overdischarge. The protection system can cause the batteries to discharge to zero and a large current must be applied to the input to resurrect them.
General repair recommendations
How to restore the battery of an electric screwdriver? You need to have an elementary understanding of electrical engineering. The battery circuit is idle. Ordinary serial circuit (plus connects to minus).
When repairing Ni-Kd, the following recommendations should be taken into account:
- They have a memory effect. The classic scheme for commissioning such batteries is 3 full charges and 3 discharges to zero. The new element must go through the same buildup.
- A similar item. So that it does not get knocked out of the chain and does not break the battery at all, the new element must fully correspond to the previous rating.
The lithium battery of an electric screwdriver can be repaired at home if you consider the following:
- They cannot be soldered. Intolerance to high temperatures will lead to a non-repairable condition. To do this, you need to use contact welding (it heats the electrode for a short time without harming the battery). If there is no access to CS: GO, soldering with a very powerful soldering iron from 100 watts is allowed. Movement must be fast and accurate.
- Identical models. Now there are several main manufacturers of lithium batteries, which are used in popular foreign models of screwdrivers, such as Hitachi, Makita and domestic ones: Interskol, Zubr.
Replacing cans in the battery
How to repair the battery for an electric screwdriver? The easiest way to revive the battery is to replace one of the cans.
It is necessary to find a defective element with a low voltage. To do this, you need to use a tester.
Instructions on how to check the battery of an electric screwdriver with a multimeter:
- A conventional multimeter has two test leads. a red and a black one. There are two contacts (plus and minus) from opposite ends of the can.
- The tester selection lever is set to “constant voltage” mode. If the multimeter has an automatic selection of values, this is enough. If it is not there, you need to put the lever in position “20”.
- Probes are applied to the contact pads and the voltage is measured. The real voltage is shown on the screen. If there is a “-” sign in front of the numbers, then the probes need to be changed with each other.
- Each bank is checked using this algorithm.
When a broken element has been found, it is simply soldered off and replaced. You need to use a powerful soldering iron so as not to overheat the jar.
Topping up with distilled water
Rebuilding the battery of an electric screwdriver with topping up should take place with a completely discharged battery. Ni-Kd batteries are covered with paper. If there was evaporation, then there will be noticeable traces on the surface.
After measuring the voltage, you need to completely discharge all the banks using a 12 volt bulb. After that, the voltage is measured again. Those elements where it dropped to 0.7 are faulty.
To fill in distilled water, you need to make a hole in the side of the can. A groove is made with a very thin drill (0.5-0.7 mm). You need to make sure that it does not go inside and damage the plates.
A small amount of water is poured with a syringe with a fine needle. After that, the breakdown must be closed with epoxy resin or sealant.
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The battery can now be rocked. Each unit must be discharged to zero again by attaching 1.5 volt bulbs to them. When the procedure is over, the battery is collected and it is necessary to carry out 5 charge and discharge cycles.
The most common cause of failure is the failure of only one element. They are connected in series, which means that even a drop in capacity on one battery will lead to a complete malfunction of the entire battery. In this case, we need:
- Screwdriver. Usually the body is connected with Phillips screws. Some models have foolproof protection and there may be vandal-resistant sprockets, triangles or even spanners.
- Multimeter. Any model is enough, even the cheapest DT-830. Since measurements are taken in millivolts, Soviet dial voltmeters will not work.
- The battery is disconnected from the screwdriver. It must be fully charged.
- The case is disassembled.
- Now you need to remove all the jars. There are more of them in Ni-Kd, since the nominal voltage of one section is less.
- Voltage is measured on each bank. For nickel-cadmium, 1.2 volts is nominal. For lithium. the normal voltage is in the range of 3.6-3.8 volts.
- After measuring, you need to look at which banks the voltage is reduced. For example, if the voltage is 3.8 on two lithium batteries, and 3.5 on one, it means that it is defective.
- The battery is assembled and installed in the instrument. Now she needs to be set to zero.
- The battery is disassembled and the voltage is measured again. If the voltage on the alleged element is much lower than on the others, then it is being replaced or repaired.
Repair and replacement of battery cells
Do-it-yourself electric screwdriver battery repair can be more extensive. For example, conversion of Ni-Kd to lithium ones. To do this, you need to purchase several Li-ion batteries and a charging board. The number of batteries must correspond to the original voltage rating.
As practice shows, most screwdrivers can be easily converted from one type of battery to another, without any problems. With increased exposure, resistance to constant use and higher capacity, your old electric screwdriver will last much longer.
Checking by resistance value
Finally, you need to check the element showing normal voltage for current output. There can be only one such element in the battery, but due to the serial connection, this is enough for the current to be interrupted in the entire battery. To check, you need to take a known resistance, let’s call it R, indicated by a value of several ohms with an error of at least 1% and a power of 5 W or more. In no case is it a light bulb, in which the resistance is highly dependent on the flowing current. Then the following is performed (it is desirable to record the result of each measurement):
- Measuring the current I flowing through R with an ammeter;
- Measurement of open-circuit voltage U1 on the element;
- Connecting R to the element and measuring the voltage U2;
- Internal resistance calculation.
The internal resistance of the can is calculated from the known current I and the voltage difference: U1. U2.
Elements with an internal resistance less than 0.5 ohms can be considered good. If it is larger, then it is better to replace such an element with a serviceable one.
Checking other parameters
Each type of battery has a certain self-discharge rate.
- Nickel-cadmium battery can be discharged by 20%;
- nickel metal hydride. 30%;
- lithium-ion storage. up to 8%.
Self-discharge is monitored by measuring the voltage every day for a month.
Checking the power supply elements for the presence of the “memory effect” is carried out by fully charging the battery and completely discharging it. Several charge-discharge cycles (3 or 4) are performed. The battery can be discharged using a 12V lamp. During the operation, the residual operating voltage and the open circuit voltage are measured. After repeated cycles, the “memory effect” will disappear.
Checking under load
It makes sense to do such a check on a fully charged battery. There are few devices at home, so you have to do some calculations. The best way to check is to load the power that the electric screwdriver itself has. Of course, using an electric screwdriver itself for this is hardly convenient. But first you need to know its power.
Sometimes the power is written on the nameplate or in the instrument manual. But it so happens that only the torque and the number of revolutions are indicated. Together with the known battery voltage, this gives enough data to calculate the wattage using the formula:
where the moment M is expressed in Newtons per meter and the angular velocity ω is expressed in radians per second. It is easier to calculate after converting newtons to kg and radians to revolutions, rounding off the corrections for losses:
For example, suppose the rotational speed of an electric screwdriver is 1500 rpm and the torque is 2 Nm. Then P = 35 W. From the known nominal voltage of the battery, for example 14 V, you can find the current by dividing the power by the voltage: 35/14 = 2.5 Amperes. We also find the load resistance by dividing the voltage by the current: 14 / 2.5 = 5.6 Ohm.
On batteries, they also write the capacity in Ampere / hour or Watt / hour. Now, knowing all the data, we can estimate the expected discharge time. Let the capacity of the jar be 1200 mA / h = 1.2 A / h. Dividing the capacitance by the current, we get the expected time (t1 according to the graph above): 1.2 / 2.5 = 0.48 hours, or 29 minutes. In general, half an hour of work for a charged, serviceable battery, the quality of which we will take as 100%.
- Multimeter or voltmeter;
- Wire as above;
- 12V headlight bulbs;
The result of the check is a graph similar to the one shown above, but built from real readings and superimposed on the calculated graph. It will clearly show the quality of the tested battery.
Replacing “cans” in the battery of an electric screwdriver
The task itself is simple. It is good if you have experience in soldering. In the connection of the elements, the faulty battery is cut off, a good one is put in its place, then soldering is performed. As you can see, nothing complicated.
However, in this case, several important nuances should be taken into account:
- you need to solder quickly so that the “banks” do not heat up. this may affect their performance;
- to connect the elements, it is better to use native plates, or copper, but of the same dimensions;
- when attaching a new element to an old one, do not confuse plus and minus. When connected in series, the minus from the previous battery goes to the plus of the new battery.
After soldering, you should carry out a charge-discharge cycle, and then measure the voltage on the “banks”. It should be around 1.3V.
Checking batteries for an electric screwdriver is not very simple, but quite feasible for tool owners. If you suspect a malfunction, you need to start by measuring the battery voltage. After that, you need to measure the current that can be obtained from the battery. If this current is insufficient, the test can be continued at the level of individual elements. This is due to the need to disassemble the battery.
The most expensive and important part of an electric screwdriver is its battery. Therefore, when the electrical storage fails, you do not want to buy a new tool. How to check the battery and make repairs in the event of a battery malfunction can be read below.
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The design of the battery of an electric screwdriver and the types of “cans
Regardless of the country of manufacture of the electric screwdriver, all batteries have the same structure. Inside the accumulator there are rows of batteries connected in series. batteries or “cans”. The resulting battery voltage is created by summing the voltage of each battery. “Banks” have the same parameters. size and voltage. Batteries differ only in power.
The battery of an electric screwdriver itself has four contacts:
- two power contacts are used for charging and discharging batteries;
- the third contact (control) is connected to a temperature sensor built into the battery. It serves to protect the charger from overheating;
- the fourth contact (service) equalizes the charges in all batteries.
Electric screwdriver batteries are composed of the following types of storage cells, which have their own advantages and disadvantages.
Ni-Cd. nickel-cadmium batteries, voltage. 1.2 V.
- low cost;
- are not afraid of low temperatures;
- can be stored discharged.
- the manufacture of these batteries is considered harmful, so they are manufactured in “third” countries;
- have a “memory effect”;
- have a small capacity;
- have a small number of cycles (charge / discharge). do not “live” long with constant use.
Ni-MH. nickel-metal hydride batteries, voltage. 1.2 V;
- are made in an environmentally friendly production, high quality branded products;
- has a low “memory effect”;
- low self-discharge ability;
- have a large capacity and a large number of cycles.
- high price;
- during long-term storage in a discharged state, some of the characteristics are lost;
- do not function for a long time at low temperatures.
Li-Ion. lithium-ion batteries, voltage. 3.7 V.
- there is no “memory effect”;
- there is no self-discharge;
- have a high capacity;
- there are a large number of charge-discharge cycles;
- a small number of batteries are required to generate enough voltage in the battery, which reduces the weight and size of the battery.
- very high price (almost 3 times more than other types of batteries);
- after 3 years capacity is lost due to decomposition of lithium.
At its core, a battery is a constant current source. By converting a chemical reaction into electrical energy, it can release stored electricity into a circuit. When charging, the current flows in the opposite direction, thereby charging the drive.
The main parameter of any battery is the capacity of the stored energy. It indicates how much current the unit can deliver during an hour and is measured in A / h.
Any battery operates on the principle of electrolysis. This means that its design includes two mandatory elements. the anode and the cathode, which are in the electrolyte. As a result of a chemical reaction, an electric charge is created at the poles. The battery voltage is determined by the potential difference across the poles.
Checking by resistance value
The normal functioning of each battery can be verified by comparing the internal resistance of the “banks”. The value is determined by dividing the operating parameters voltage by current and deducting the load resistance.
The operating voltage is measured necessarily under load. As a load, you should take a resistor with a resistance of 10 ohms and a power of 25 watts. Each battery is tested. Measure the working amperage and voltage.
For a better understanding, here are some approximate calculations. Let’s say, during the measurement under load, data were obtained for one “can”: operating voltage. 1.19 V and operating current. 112 mA. Before making the calculation, do not forget to convert the current value from mA to A. 0.112 A. We perform the appropriate actions (1.19 / 0.112). 10 = 0.63 Ohm. Recall that the subtracted in our expression is the load resistance of the resistor (10 Ohm).
Checking under load
The procedure allows you to determine the discharge time of the battery. When choosing a load, the power of the latter is taken into account. If there is no data on the characteristic, then it is equal to ½ of the current strength. To check it is enough to take a 12-volt car or halogen lamp with a power of 40 W.
- connect the lamp to the negative terminal of the battery;
- the second wire is connected to the “plus”;
- register values on a multimeter;
- for 2-3 minutes. connect the battery.
If during this period the brightness of the lamp does not decrease, then the battery is working normally. Voltage reading must be greater than 12.4V. A drop in voltage from 12V to 12.4V indicates the presence of a faulty cell. If the lamp goes out quickly during the test, then the storage capacity is very low.
To restore 80% of the capacity of nickel-cadmium batteries, it helps to carry out charge / discharge cycles for 4-5 times. If you work with a disassembled battery, then a shock effect with a large current helps to restore the weakened batteries.
All types of “cans” (lithium, metal hydride), except for nickel-cadmium, cannot be restored.
To test an electric screwdriver, you will need the following set of tools:
- multimeter, replaces voltmeter and ammeter;
- pliers or clamps;
- several 12V car lamps;
- mounting wires with a cross section of 0.5 mm2 and a length of 1.5-2 m;
- original or compatible charger (suitable from the car if it is equipped with built-in elements for measuring current and voltage).
In some models, the design of the battery pack does not allow connecting devices without disassembling the case. therefore it is recommended to have a soldering iron in stock.
What does an electric screwdriver or tool design consist of?
Externally, models with different power supplies are almost identical. The difference lies in the presence of a cable for the former and a battery, which is a power source, for the latter.
The main structural elements include:
- Housing. Made of impact-resistant plastic with rubberized inserts. Includes electrical, mechanical components.
- Reducer. It can be classic or planetary. The second option is more common, as it is mainly designed for 2 speeds. The second mode is suitable for using the device as a drill.
- Spindle. A hex or keyless chuck is screwed onto this element. rigging.
- Electric motor. Consists of a rotor. which is an anchor, and a stator. A brushless motor is considered better than a brushed motor in terms of technical characteristics, but its price is higher. Battery models are designed for the installation of any motor, and when assembling the network only the second option is used.
- Button or trigger “Start”. Provides start-up or shutdown of the electric screwdriver.
- Spindle speed controller.
- Clutch designed to adjust the torque. Allows you to limit the strength of the tool. Made in the form of a ring with a scale.
- Switch for the direction of movement of the executive body. The reverse provides the opportunity.
There are mainly used 2 types of rechargeable batteries. nickel-cadmium or lithium-ion. The latter are considered more durable, their price is 3-4 times higher. In addition to the power parts, a thermistor (responsible for the temperature of the “cans”), a thermal switch (opens the circuit when the battery overheats), a control board (Li-ion models) are usually located in the unit box.
Some models have a backlight lamp, LED display, screw depth limiter, slots for replaceable bits. They increase the comfort of using the electric screwdriver.
General recommendations before testing the battery
It does not matter which brand the model belongs to. Bosch, DeWALT, Interskol or others. Before checking the battery of an electric screwdriver, you need to determine the type of power source. It is indicated on the housing of the unit. Many models have nickel-based batteries with a “memory effect”. The capacity of “cans” in such batteries is rapidly decreasing.
Experts also recommend charging the battery pack as usual. which will ensure that the readings taken by the tester are clear. Load test provides the most accurate information on instrument performance.
The suitability of the battery is checked by observing the current strength during charging. A steady rise in performance indicates a malfunction.
To eliminate the presence of a problem with the charger, perform a number of actions:
- on the multimeter, set the constant voltage recording mode to 20V (if the battery voltage is 24V, then the nominal 200V is displayed on the tester);
- the charging plug is inserted into an outlet;
- the output voltage is recorded at the terminals of the charging block.
The result should be 2V higher than the battery rating. If it is lower, then the problem lies in the charger of the electric screwdriver.
When checking an electric screwdriver, disassemble the case
Checking the storage batteries
Let us assume that faulty parts are identified during preparatory checks. A person needs to disassemble the battery in order to remove the batteries (“banks”) one by one. Batteries installed on screwdrivers include 10-12 of these parts. Each has a voltage of 1.2 V.
Deterioration of the battery performance may result in damage to the battery connections of the drive. therefore, it is preliminarily recommended to check such areas for violations by visual inspection.
Then the voltage of each “jar” is measured. In the first element, the value should not fall below 1.2V. The device is connected to the “pluses” of the battery. If no deviations are found during the procedure, then a load test is carried out. Low voltage elements need to be replaced.
Checking other parameters
Each type of battery is characterized by its own percentage of self-discharge per month:
- nickel-cadmium. 20%;
- lithium-ion. up to 8%;
- nickel metal hydride. 30%.
To find out the level of self-discharge, daily monitoring of the voltage value helps. Measurements are carried out for 1 month. It can see how quickly the battery is draining.
The “memory effect” in parts of the power supply is determined during 3-4 charge / discharge cycles. To discharge the battery, use a 12V lamp. In this case, the open-circuit voltage and the residual operating voltage are measured.