DIY power supply for a 12v electric screwdriver

Built-in

The undoubted advantage of built-in devices is that only a small-section power cord remains from the external parts. Not everyone can make such a power supply on their own. This requires a lot of experience, since small-sized powerful power supplies can only be made using a pulse circuit. The transformer of the required power of the classical design will not fit into the handle of an electric screwdriver, but with suitable dimensions it will have a power of several watts, which is enough only for idle operation.

cheap computer power supply for 12v cordless makita drill and grass trimmer using wire cable

Using the computer’s power supply

It is rational to assemble a power supply unit for an electric screwdriver with a 12V motor from a power supply unit from a computer with your own hands. The standard voltages of the motherboard and external devices of the computer are:

  • 3.3V;
  • 5V;
  • 12V;
  • – 12V.

Standard power supplies are capable of delivering a current of up to 10-15 A in a 12 V circuit, which is absolutely acceptable for most models of screwdrivers. At the power connectors, the required voltage is present on the black (ground) and yellow wires. The rest of the wires are not needed, and it is advisable to unsolder them directly on the power supply board so that they do not interfere and do not create a reason for closing.

In some cases, it is possible to use a computer power supply for a 14 V electric screwdriver. However, there will be a slight drop in power. But screwdrivers for 16 and 18 Volts will not work with such devices. If you have qualifications, you can make changes to the circuit of a standard power supply in order to increase the voltage, but this is usually not possible for an ordinary user.

Note! All of the above applies to outdated, but still occurring AT power supplies. modern ATX require some alterations to enable it, since it is organized on the computer’s motherboard by a special circuit.

With proper care, you can do this yourself. To do this, find a green wire on the largest connector of the device. By closing it through the button to the black ground wire, you can turn on the power supply.

Using any source, there is no need to make any changes to the tool design. To supply voltage, use the case from defective batteries, drilling holes in it for the supply wires. The conductors themselves must be carefully soldered to the output terminals without melting the plastic, strictly observing the polarity.

The assembled structure must be placed in a suitable housing and, if necessary, equipped with a carrying handle.

Power supply requirements

Regardless of what voltage the electric screwdriver is designed for, special requirements are imposed on the power supply: with a high load on the tool, for example, when screwing long screws into hard wood or in the drilling mode, the current consumption of the motor can increase up to ten amperes. If in idle mode the current consumption is no more than 1-2 A and a power supply with a power of 30-40 W is sufficient, then a power of about 200 W is required for normal operation.

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With rechargeable batteries, everything is simple. The specificity of their work is such that they are capable of delivering large currents for a short time, restoring the operating voltage during idle time. The question arises: the charger for any screwdriver is lightweight and lightweight, why not use it as a voltage source? The answer is definitely no. The charger is designed to deliver low currents for a long time, but we need high currents for a short time. Therefore, the external power supply must have a power reserve.

DIY power supply for a 12v electric screwdriver

When purchasing a cordless electric screwdriver, almost no one thinks about the service life of batteries. Depending on the manufacturer and the cost of the tool, the batteries can last up to 5 years or less. This is especially true of a tool from an unnamed manufacturer from China (and there are an overwhelming majority of them on the market). Replacing batteries with new ones is financially comparable to buying a new tool, so there is often a need to make a do-it-yourself power supply for an 18V or 12V electric screwdriver.

Impulse sources

Switching power supplies are characterized by the fact that the step-down transformer in them operates at an increased frequency, as a result of which it has minimal dimensions at the same power. The overall dimensions of the device make it possible to place the structure in a standard case instead of faulty batteries. Of the minuses. the complexity of the design for self-repetition.

Transformer devices

Power supplies on transformers have not yet lost their relevance due to their ease of manufacture and reliability. The only drawback of such products is their large dimensions and weight, but this is not essential when the device is made in the form of a separate unit and is installed permanently.

Devices on transformers are predominantly used among self-made devices, therefore they will be considered in the most detailed way.

Separate block

Due to the fact that the power supply is located outside the body of the electric screwdriver, there are no restrictions on its dimensions and weight, therefore it can be made with the desired power reserve. The only limitation is the length and cross-sectional area of ​​the connecting cords between the instrument and the power source, because, according to Ohm’s law, when the voltage decreases with the same power consumption, the current increases, therefore the low-voltage power cord must have a larger cross-section than the 220 V mains supply. See also the requirement to minimize the voltage drop across the wires. Thick cord has increased weight and rigidity, which reduces the convenience of using the tool.

Mains power supply for electric screwdriver

Impulse sources

Switching power supplies are characterized by the fact that the step-down transformer in them operates at an increased frequency, as a result of which it has a minimum size at the same power. The overall dimensions of the device make it possible to place the structure in a standard case instead of faulty batteries. Of the minuses. the complexity of the design for self-repetition.

DIY power supply for a 12v electric screwdriver

When purchasing a cordless electric screwdriver, almost no one thinks about the service life of batteries. Depending on the manufacturer and the cost of the tool, the batteries can last up to 5 years or less. This is especially true of a tool from an unnamed manufacturer from China (and there are an overwhelming majority of them on the market). Replacing batteries with new ones is financially comparable to buying a new tool, so there is often a need to make a do-it-yourself power supply for an 18V or 12V electric screwdriver.

READ  How to Use a Cordless Screwdriver

Using the computer’s power supply

It is rational to assemble a power supply unit for an electric screwdriver with a 12V motor from a power supply unit from a computer with your own hands. The standard voltages of the motherboard and external devices of the computer are:

  • 3.3V;
  • 5V;
  • 12V;
  • – 12V.

Standard power supplies are capable of delivering a current of up to 10-15 A in a 12 V circuit, which is absolutely acceptable for most models of screwdrivers. At the power connectors, the required voltage is present on the black (ground) and yellow wires. The rest of the wires are not needed, and it is advisable to unsolder them directly on the power supply board so that they do not interfere and do not create a reason for closing.

In some cases, it is possible to use a computer power supply for a 14 V electric screwdriver. However, there will be a slight drop in power. But screwdrivers for 16 and 18 Volts will not work with such devices. If you have the qualifications, you can make changes to the circuit of a standard power supply in order to increase the voltage, but this is usually not possible for an ordinary user.

How to make a power supply for the electric screwdriver

Note! All of the above applies to outdated, but still occurring AT power supplies. modern ATX require some alterations to enable it, since it is organized on the computer’s motherboard by a special circuit.

With proper care, you can do this yourself. To do this, find a green wire on the largest connector of the device. By shorting it through the button to the black ground wire, you can turn on the power supply.

Using any source, there is no need to make any changes to the tool design. To supply voltage, use the case from faulty batteries, drilling holes in it for the supply wires. The conductors themselves must be carefully soldered to the output terminals without melting the plastic, strictly observing the polarity.

The assembled structure must be placed in a suitable housing and, if necessary, equipped with a carrying handle.

Transformer devices

Power supplies on transformers have not yet lost their relevance due to their ease of manufacture and reliability. The only drawback of such products is their large dimensions and weight, but this is not essential when the device is made in the form of a separate unit and is installed permanently.

Devices on transformers are predominantly used among self-made devices, therefore they will be considered in the most detailed way.

Built-in

The undoubted advantage of built-in devices is that only a small-section power cord remains from the external parts. Not everyone can make such a power supply on their own. This requires a lot of experience, since small-sized powerful power supplies can only be made using a pulse circuit. The transformer of the required power of the classical design will not fit into the handle of an electric screwdriver, but with suitable dimensions will have a power of several watts, which is enough only for idle operation.

Transformer power supply design

This device is characterized by the presence of the following components:

  • Power transformer;
  • Rectifier:
  • Power filter;
  • Voltage regulator.

The power transformer is the largest and heaviest part of the device. It is designed to convert high input voltage to low voltage to meet the requirements of the connected load.

The rectifier’s job is to convert AC voltage to DC voltage. The most effective are rectifier bridge circuits, consisting of four diodes or a monolithic rectifier bridge.

The filter smooths out the voltage ripple after the rectifier bridge.

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Theoretically, these elements are enough for the operation of an electric screwdriver, but voltage surges in the supply network, its drawdown due to an increase in load can lead to unstable operation of the engine, and an increase in excess of the norm can lead to failure.

The task of the stabilizer is to maintain a stable output voltage, regardless of the size of the load and the voltage level of the supply network.

For self-assembly, you can recommend a simple proven stabilizer circuit, which is distinguished by a minimum of details and is available for repetition to anyone who knows how to hold a soldering iron in his hands and use measuring instruments.

In the above diagram, you can increase the capacitance of the capacitor to 1000-2000 uF, and use transistors of the types KT807, KT819 with any letter.

power, supply, electric, screwdriver

The main problem is the selection of a transformer with the required output voltage level. It should be slightly larger than what is required for the tool, since some will remain on the stabilizer elements. For normal operation of the stabilizer, it is required that the rectified voltage exceeds the stabilized one by several volts. Too much is impossible, since its excess will fall on the key transistor, heating it, and a low value in some cases will lead to a decrease in the output voltage.

Note! After the bridge rectifier and filter, the DC voltage will be about 1.4 times the input AC.

So a power supply for a 12V electric screwdriver requires a transformer with an output voltage of 12-14V AC.

Important! The transistor must be attached to the cooling radiator.

Power supply requirements

Regardless of what voltage the electric screwdriver is designed for, special requirements are imposed on the power supply: with a high load on the tool, for example, when screwing long screws into hard wood or in the drilling mode, the current consumption of the motor can increase up to ten amperes. If in idle mode the current consumption is no more than 1-2 A and a power supply with a power of 30-40 W is sufficient, then a power of about 200 W is required for normal operation.

With rechargeable batteries, everything is simple. The specificity of their work is such that they are capable of delivering large currents for a short time, restoring the operating voltage during idle time. The question arises: the charger for any screwdriver is lightweight and lightweight, why not use it as a voltage source? The answer is definitely no. The charger is designed to deliver low currents for a long time, but we need high currents for a short time. Therefore, the external power supply must have a power reserve.

Separate block

Due to the fact that the power supply is located outside the body of the electric screwdriver, there are no restrictions on its dimensions and weight, therefore it can be made with the desired power reserve. The only limitation is the length and cross-sectional area of ​​the connecting cords between the instrument and the power source, because, according to Ohm’s law, when the voltage decreases with the same power consumption, the current increases, therefore the low-voltage power cord must have a larger cross-section than the 220 V mains supply. See also the requirement to minimize the voltage drop across the wires. Thick cord has increased weight and rigidity, which reduces the convenience of using the tool.