How To Make An Electric Screwdriver From A Screwdriver

How to check the battery of a screwdriver with a multimeter? How to check the battery of a screwdriver with a multimeter? General advice before testing different batteries. How to check the charger, the voltage of the battery cells, the screwdriver without the battery.


The malfunction may lie not only in the battery, but also in the charger itself. Therefore, you first need to check the charger for the screwdriver with a multimeter.

On it, the mode of measuring direct current is turned on and, using probes, it is connected to the charger. The value of the current on the meter should be as close as possible to that indicated on the case. If this is not the case, then it is better to replace the device with a new one.

Battery voltage

After the first stage of verification, it will become clear whether the device is working properly or not. If the testing indicated a discrepancy in the parameters, then it is logical to proceed with the repair, accompanied by the replacement of faulty cans.

You need to open the battery case and identify the malfunction. For this, a multimeter is also used, which is connected to each element separately. The voltage of each can must be at least 1.2 V. All discrepancies indicate a breakdown of the element. Defective cans must be removed from the common chain and replaced with new ones.

If such a check does not reveal a breakdown, then you need to resort to stress testing again. And here the level of resistance is of fundamental importance, which is directly related to voltage and current strength. Each element is tested separately and resistances are calculated as well. In the event of a malfunction, this indicator will clearly deviate from the norm and quickly identify the broken element.

General recommendations before testing the battery

Immediately before checking the battery, it is necessary to clearly determine what type of battery the battery belongs to. Depending on this type, the approach may be different. For example, the most common nickel-cadmium batteries are highly sensitive to operating conditions. Infrequent or irregular full recharges will drastically reduce battery capacity and the battery will not fully utilize its resources. We will consider the types of batteries in more detail below.

It is also recommended to fully charge the battery before checking. This will allow you to make more accurate conclusions about the performance of the device. It has been proven that the most accurate readings are taken under load. And a full charge is a very suitable type of load.

Before testing, it is necessary to minimize the influence of the “memory effect” on the device. Since this effect appears with batteries in case of improper use, in order to eliminate it, it is necessary to use the battery several times in accordance with all the rules.

It is enough to carry out charge / discharge cycles 3 times to significantly reduce the effect of the effect. For a faster discharge, it is best to use an incandescent lamp, which, together with a multimeter, will need to be connected to the battery.

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If everything is done correctly, then after a few full cycles the battery will be able to restore its capacity and can again be used in a screwdriver. If the operation did not help, then the problem was different.

Screwdriver battery: design and types

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

how to make an electric screwdriver from a screwdriver

If we disassemble it, we will see that it is assembled from small elements that are assembled sequentially. And from the school physics course, we know that elements that have a serial connection harmonize their potentials.

Typesetting parts or “cans”, as a rule, have a standard size and voltage, they differ only in capacity. Battery capacity is measured in Ah and is indicated on the cell (pictured below).

For the arrangement of screwdriver batteries, the following types of elements are used:

  • Nickel. Cadmium (Ni. Cd) batteries, with a nominal voltage on the “banks” of 1.2v;
  • Nickel-metal hydride (Ni-MH), voltage across elements. 1.2v;
  • Lithium-ion (Li-Ion), with a voltage of 3.6v.

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

  • The most common type due to its low cost;
  • Low temperatures, such as Li-Ion batteries, are not scary;
  • It is stored in a discharged state, while maintaining its characteristics.
  • Produced only in third world countries due to toxicity during production;
  • Memory effect;
  • Self-discharge;
  • Small capacity;
  • A small number of charge / discharge cycles, which means that they do not “live” long with intensive use.
  • Environmentally friendly production, it is possible to purchase a high-quality branded battery;
  • Low memory effect;
  • Low self-discharge;
  • High capacity compared to Ni. Cd;
  • Charge / discharge cycles.
  • Price;
  • Loses some of its characteristics during long-term storage in a discharged state;
  • It does not “live” for a long time at low temperatures.
  • No memory effect;
  • Self-discharge is almost absent;
  • High battery capacity;
  • The number of charge / discharge cycles is several times greater than that of previous types of batteries;
  • To set the required voltage, fewer “cans” are required, which significantly reduces the weight and dimensions of the battery.
  • High price, almost 3 times in comparison with nickel. Cadmium;
  • After three years, there is a significant loss of capacity, because Li decomposes.

We got acquainted with the elements, let’s move on to the rest of the elements of the screwdriver battery pack. Disassembling the unit, for example, for repairing the battery of a Hitachi screwdriver (shown below), is very simple. We unscrew the screws around the perimeter and disconnect the case.

The housing has four contacts:

  • Two power ones, “” and “-“, for charge / discharge;
  • Upper control, it is switched on through a thermal sensor (thermistor). A thermistor is necessary to protect batteries, it cuts off or limits the charge current when a certain temperature of the cells is exceeded (usually in the range of 50. 600c) Heating occurs due to high currents during forced charging, the so-called “fast” charging;
  • The so-called “service” contact, which is connected through a 9K ohm resistance. It is used for complex charging stations that equalize the charge on all battery cells. In everyday life, such stations are useless, due to their high cost.
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That’s actually the whole design of the battery. Below is how to parse a block.

Fault definition

We figured out the purpose of the battery structure elements, now let’s look at how to determine the malfunction, this is part 2 of the screwdriver battery repair. Immediately, we note that all the elements cannot fail at once, and since our circuit is sequential, when one element fails, the whole circuit does not work. So, our task is to determine where we have the weakest link in the chain.

To do 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 volt. The procedure is as follows:

Thus, we found candidates for “resuscitation” or “amputation” and replacement with new elements.

If your screwdriver operates on a voltage of 12 or 13 V, you can search with a simpler method. We disassemble the fully charged battery and connect a 12 volt lamp to the contacts “” and “-“. The lamp will be a load and will drain the battery. Next, we take measurements on the battery cells, where the voltage drop is strongest, there is also a weak link.

There are other ways, instead of a lamp, you can choose a resistance, but for this you already need the basics of electrical engineering, and it is doubtful that a resistor with the necessary resistance would be at hand.

Other faults are very rare. For example, loss of contact at the soldering points of the batteries or the power contacts of the unit, failure of the thermistor. This problem is more inherent in fakes. In view of the rarity, we will not focus on the battery elements.

With the “problem” elements sorted out, it is necessary to repair. How to repair a screwdriver battery? In general, there are 2 methods available for repair, so to speak. This is the restoration and replacement of elements that have become unusable.


The cost of a new screwdriver is approximately 70% of the cost of the battery for it. Therefore, it is not surprising when, faced with a battery failure, we ask ourselves the question. What’s next? To buy a new battery or screwdriver, or maybe it is possible to repair the screwdriver battery with your own hands and continue working with an already familiar tool?

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In this article, which we conventionally divide into three parts, we will consider: the types of batteries that are used in screwdrivers (part 1), their possible causes of failure (part 2) and available repair methods (part 3).

Making a homemade power supply

If you are familiar with the principles of building electrical circuits, you can make your own power supply. A diagram giving general concepts is shown in the illustration.

The transformer can be picked up from an old tube TV, or other household appliances. Power 220 volts 250-350W. The main thing is the power supply. The donor should not be pulsed.

The voltage on the secondary winding is 24-30 volts. The secondary winding is made from a wire of the corresponding section.

However, if the output winding current is at least 15 amperes (see transformer specification), there is nothing to worry about.

After the losses on the diode bridge (1-1.5 V on the diode), you will get the required output value.

If you have an electrical engineering education, make the calculation yourself. Or in a practical way: by connecting a 220 volt 100W incandescent lamp as a load, measure the output voltage. E

If it exceeds the needs of the screwdriver, reduce the number of turns of the secondary winding of the transformer.

Ac adapter for screwdriver in battery housing

If your tool is not too powerful, you can place the power supply in a handle or case from damaged batteries.

Battery case power supply

Mobility remains, you are limited only by the length of the network cable. The only problem is how to squeeze a sufficiently powerful transformer into a small case.

We recall Ohm’s law again, and understand that a powerful 220 volt electric motor can be compact.

How to do it yourself from a wireless screwdriver wired and why you need it

In recent years, cordless tools have become so firmly established in our lives that now, if a screwdriver breaks, we simply cannot imagine how we can do without it, especially when there is a solid amount of construction work ahead.

Such a misfortune happened to me once. In the midst of work, due to the failure of the battery, my screwdriver fell silent, and immediately everything stopped.

It’s good that one of my colleagues arrived at the site on a scooter, which was equipped with a small 12-volt battery. There was nothing to do but try to connect the tool to the terminals of the battery removed from the scooter. Much to my surprise, everything worked out great. Although the screwdriver was designed to operate from 18 V, when connected to a 12-volt battery, it began to twist the screws even better than with a standard battery!

If it was not difficult to connect the wires to the battery terminals, then with the ends going to the screwdriver contacts, I had to work a little.