# What Current Does A 12v Screwdriver Consume

## What current does the screwdriver consume?

Before choosing a suitable power supply, you need to understand what current consumption you need to count on. Unfortunately, manufacturers of cordless screwdrivers do not indicate the current drawn by the motor. The capacity of the battery itself in ampere-hours, which is necessarily indicated on the battery, does not make it possible to understand what is the current consumed by the screwdriver in operating mode. The maximum that the manufacturer can indicate is the power in watts, but this is very rare, usually the power is indicated directly in the torque.

If the power in watts is still indicated, we can have an idea of ​​the current consumption and select the appropriate power supply with a small current / power margin. To calculate the current strength, it is enough to divide the power in watts by the operating voltage of the screwdriver, in this case it is 12 volts. So, if the manufacturer has indicated a power for example 200 watts. 200: 12 = 16.6 A. This current is consumed by a screwdriver in operating mode.

However, the indicated power is very rare and there is no universal figure that characterizes all 12-volt screwdrivers. You need to understand that with full braking of the motor shaft, the currents can significantly exceed the rated ones and it is very difficult to calculate this value. At the same time, analysis of various forums and their own experience showed. For the operation of a screwdriver, a current of 10 A is often sufficient, this is enough for many functions of twisting and drilling. At the same time, it is known that current surges with full shaft braking can exceed 30 A.

So what conclusion can be drawn from all this? For a screwdriver, a 12 V power supply giving 10 A of current is suitable, if it is possible to use a 20-30 A unit, this is even better. These are average figures that apply to most screwdrivers.

## Assembling the working structure

For ease of use and connection, I brought the cord from the power supply into the battery case. The cord took 3.5 meters long, which was available. I removed all battery cells from the battery and installed an LC filter. Now if I get a working battery somehow. It can always be put on a screwdriver, and the power supply can be removed in reserve. I didn’t throw out the batteries from the battery, there is an idea where to use them, but this is a topic for another review.

Since the cord connecting the unit with the screwdriver has a certain resistance and inductance, you can try to short-circuit the leads of the L1 coil. In theory, this can increase the power by a tiny amount.

With a cord, the screwdriver feels great, but to be honest, it seemed to me a little weak when braking with a hand. But the trial tightening of self-tapping screws dispelled my doubts: self-tapping screws 35 mm long quietly screw into 20 mm plywood. This means a screwdriver will meet most repair needs.

At the block, I cut off all the output wires, leaving the green start one, I soldered its end to the common conductor of the board, where all the black ones are soldered. It is best to carefully solder all the wires, but my soldering iron was too weak for that and had to be cut. To the common contact and 12 (where the yellow ones are soldered) I soldered two short, rigid copper wires and connected them through the terminal block with a cord to the shurik.

This concludes this review, which we have achieved. The screwdriver works perfectly with a computer power supply. In the future, I plan to make a solid plywood case without slots for the power supply board. Tests have shown that the heatsinks on the board do not heat up at all and there is no need to worry about overheating of elements in a closed case.

## Power Supply

We will not consider buying any blocks or transformers, if we do buy a new battery! We will consider using what is at hand. I’ll tell you right away. The charger from the same screwdriver is only suitable for drilling ripe bananas, its power is too low.

Ideally, a step-down, powerful 12 V transformer is suitable, for example, from a computer uninterruptible power supply. The power of such a transformer is usually 350-500 watts. But I did not have such a transformer available, but I had a lot of computer power supplies. I am sure that if someone has various electronic junk, computer ATX is sure to be lying around in it.

The computer ATX unit is quite suitable for a screwdriver, the load capacity on the 12 volt bus allows you to remove currents of 10-20 amperes. I would like to dispel a little myth. It will not work to cram the unit into the battery case of the screwdriver, the ATX board is too big. We’ll have to make the unit a separate case or leave it in its native metal case. Lack of native corpus. Sensitivity to dust, and even the smallest repairs. It’s a lot of dust.

## Connecting a 12 volt screwdriver to the ATX power supply

Cordless screwdrivers are very convenient to use and are widely used by both professionals and DIYers. The very first, as a rule, the battery becomes unusable. At the moment, all manufacturers of power tools have switched to lithium batteries and it is becoming more and more problematic to purchase a new nickel-cadmium battery for an old screwdriver, and the for these batteries are much higher than for lithium.

## Sample tests

Before starting the construction of a working structure, you should test everything on the “knees”, make sure that the screwdriver is stable under load and that there are no strong overheats in the power supply.

We take a computer power supply and check it: we turn it on, we find green in the output bundle of wires (they say it may be of a different color, but I always came across green ones) and short it with a jumper on any of the black ones (all black wires at the output, general output, in our case it is a minus). The unit should turn on, a voltage of 12 volts will appear between the black and yellow wires. You can check this with a multimeter or by connecting any computer cooler to the named terminals.

If everything is in order and the unit outputs about 12 volts on the yellow and black (-) terminals, continue. If there is no voltage at the output. We are looking for another block or we are repairing this one, this separate topic will be described separately.

We cut off the plug from the output of the block and take 3-4 yellow and black wires from the block and connect them in parallel. When cutting off the plug, do not forget about the green starter wire, it must be shorted to black. We got a 12 V source with a decent current carrying capacity of 10-20 A, currents depend on the model and power of the unit.

Now we need to hook up our 12V to the screwdriver terminals without a battery, we look at the polarity of the connection on the battery. Well, we check the screwdriver. Idling, then braking by hand. At this stage, I ran into a problem: when the button is fully pressed, the screwdriver works, when the button of the screwdriver is slowly, smoothly pressed, the power supply goes into protection. To reset the protection, the unit must be disconnected from the network and turned on again. It will not work at all, you need to somehow fix such instability.

In my opinion, this phenomenon may occur due to the fact that the power supply unit and the screwdriver button are controlled by PWM controllers, due to interference on the power wires, the controllers somehow interfere with each other. Trying to solve this problem using an improvised LC filter.

I assembled the filter in 5 minutes from what was at hand: 3 electrolytic capacitors of 1000 microfarads at 16 volts, a non-polar capacitor less than 1 microfarad and wound 20 turns of copper wire with a diameter of 2 mm on a ferrite ring from another block. Here is its diagram:

And this is how it looks. This is a purely trial version, in the future this design will be transferred to the screwdriver battery case and will be made more accurately.

We check the entire structure: the block does not go into defense at any button positions, great! Now you can try to tighten a few screws. All in a bunch. It feels like a screwdriver will be able to tighten larger screws.

Well, now you need to remove all the snot and heaps of wires, remove the “dead banks” from the battery case, replace them with an LC filter and already test the screwdriver in more real conditions.

To compensate for losses in the cord connecting the screwdriver to the power supply, it is useful to raise the voltage by 2-3 volts. But this is provided that you know the circuitry of computer ATX and know what to do.

If it is possible to use a powerful transformer, then its output, secondary winding should have an alternating voltage of 12 V. If the voltage is different, it is recommended to correct the secondary winding by unwinding (if the voltage is more than 12 V) or winding (if less than 12 V) several turns. It is worth noting that rectifying and filtering the 12V AC voltage results in about 14.4V no load. So do not be confused by this, this is the EMF voltage and it is natural that it is higher than the nominal.

In addition to the transformer, a rectifier is assembled, the diodes should calmly hold 30 A. It is more expedient to place the capacitor filter in the battery case, as in the version with ATX.

## AC adapter for cordless screwdriver

A friend asked me to assemble an external power supply for a screwdriver. Together with a screwdriver (fig. 1) brought a power transformer from the old Soviet burner-engraver “Ornament-1” ((See Figure 2). See if you can use it?

First, of course, we dismantled the battery compartment, looked at the “banks” (fig. 3 and fig. 4). We checked each “jar” for operability with a charger with several charge-discharge cycles. Out of 10 pieces only 1 is good and 3 are more or less normal, and the rest are completely “dead”. So, you definitely have to make an external power supply.

To assemble a power supply unit, you need to know how much current the screwdriver consumes during operation. Having connected it to a laboratory source, we find out that the motor starts rotating at 3.5 V, and at 5-6 V a decent power appears on the shaft. If you press the start button when 12 V is supplied to it, the protection at the power supply is triggered, which means that the current consumption exceeds 4 A (the protection is set to this value). If you start the screwdriver at a low voltage, and then increase it to 12 V, it works fine, the current consumption is about 2 A, but at the moment when the screw to be screwed in half enters the board, the protection at the power supply works again.

To see the full picture of the consumed currents, the screwdriver was connected to a car battery by placing a 0.1 Ohm resistor in the positive wire break (fig. 5). The voltage drop from it was applied to a computer sound card with an open input; the SpectraPLUS program was used for viewing. The resulting graph is shown in Figure 6.

The first impulse on the left is the starting pulse when turned on. It can be seen that the maximum value reaches 1.8 V and this indicates a flowing current of 18 A (I = U / R). Then, as the engine rises, the current drops to 2 A. In the middle of the second second, the head of the screwdriver is clamped by hand until the “ratchet” is triggered. The current at this time rises to about 17 A, then drops to 10-11 A. At the end of the 3rd second, the start button is released. It turns out that for the screwdriver to work, a power supply is required with the ability to deliver power of 200 W and current up to 20 A. But, given that the battery compartment says that it is 1.3 A / h (fig. 7), then, most likely, everything is not as bad as it seems at first glance.

We open the burner power supply unit, measure the output voltages. The maximum is about 8.2 V. Not enough, of course. Given the voltage drop across the rectifier diodes, the output voltage across the filtering capacitor will be about 10-11 V. But there is nowhere to go, we are trying to assemble the circuit according to Figure 8. The diodes are of the KD2998V brand (Imax = 30 A, Umax = 25 V). The VD1-VD4 diodes are mounted by hinged mounting on the petals of the burner contact sockets (fig. 9 and fig. 10). As a large-capacity capacitor, a parallel connection of 19 pieces of a smaller capacity was used. The entire “battery” is wrapped in masking tape and the capacitors are selected in such a size that the whole bundle with light effort enters the battery compartment of the screwdriver (fig. 11 and fig. 12).

The safety block is very inconvenient in the burner, so it was removed, and the fuse was soldered “directly” between one of the 220 V wires and the output of the interference suppression capacitor C1 (fig. 13). When the case is closed, the power cable is tightly crimped with a rubber ring and this does not allow the wire to dangle inside when bending it outside.

Checking the performance of the screwdriver showed that everything is working fine, the transformer, after half an hour of drilling and screwing the screws, heats up to about 50 degrees Celsius, the diodes heat up to the same temperature and do not need radiators. A screwdriver with such a power supply unit has less power compared to powering it from a car battery, but this is understandable. The voltage across the capacitors does not exceed 10.1 V, and as the load on the shaft increases, it further decreases. By the way, it is decently “lost” on a supply wire with a length of about 2 meters, even using its section of 1.77 sq. Mm. To check the drop on the wire, a circuit was assembled Figure 14, it monitored the voltage across the capacitors and the voltage drop on one conductor of the supply wire. The results in the form of graphs at different loads are shown in Figure 15. Here, in the left channel. The voltage across the capacitors, in the right. The drop on the “negative” wire going from the rectifier bridge to the capacitors. It can be seen that when the screwdriver head is stopped by hand, the supply voltage sinks to levels below 5 V. At the same time, about 2.5 V (2 times 1.25 V) drops on the power cord, the current is of a pulsed nature and is associated with the operation of the rectifier bridge (fig. 16). Replacing the power cord with another one with a cross section of about 3 sq. Mm led to an increase in the heating of the diodes and the transformer, so they returned the old wire.

We looked at the current in the circuit between the capacitors and the screwdriver itself, having assembled the circuit according to Figure 17. The resulting graph is on Figure 18, “Shaggy”. This is a ripple of 100 Hz (the same as in the previous two figures). It can be seen that the starting pulse exceeds the value of 20 A. Most likely, this is due to the lower internal resistance of the power source due to the use of parallel connection of capacitors.

At the end of the measurements, we looked at the current through the diode bridge, connecting a 0.1 Ohm resistor between it and one of the terminals of the secondary winding. Graph on fig. 19 shows that when the motor is braking, the current reaches 20 A. Fig. 20. Time-stretched section with maximum currents.

As a result, while we decided to work with a screwdriver with the described power supply, if there is “not enough power”, then we will have to look for a more powerful transformer and put diodes on radiators or change to others.

And, of course, you shouldn’t take this text as a dogma. There are absolutely no obstacles to making a power supply unit according to any other scheme. For example, a transformer can be replaced with a TC-180, TCA-270, or you can try to power a screwdriver from a computer pulsed power supply, but most likely you will need to check the possibility of returning a 12 V circuit with a current of 25-30 A.

## Power Supply

We will not consider buying any blocks or transformers, if we do buy a new battery! We will consider using what is at hand. I will say right away. The charger from the same screwdriver is only suitable for drilling ripe bananas, its power is too low.

Ideally, a step-down, powerful 12 V transformer is suitable, for example, from a computer uninterruptible power supply. The power of such a transformer is usually 350-500 watts. But I did not have such a transformer available, but I had a lot of computer power supplies. I am sure that if someone has various electronic junk, computer ATX is sure to be lying around in it.

The computer ATX unit is quite suitable for a screwdriver, the load capacity on the 12 volt bus allows you to remove currents of 10-20 amperes. I would like to dispel a small myth. It will not work to cram the unit into the battery case of a screwdriver, the ATX board is too big. We’ll have to make the unit a separate case or leave it in its native metal case. The disadvantage of a native case is sensitivity to dust, and even the smallest repairs are a lot of dust.

To compensate for losses in the cord connecting the screwdriver to the power supply, it is useful to raise the voltage by 2-3 volts. But this is provided that you know the circuitry of computer ATX and know what to do.

If it is possible to use a powerful transformer, then its output, secondary winding should have an alternating voltage of 12 V. If the voltage is different, it is recommended to correct the secondary winding by unwinding (if the voltage is more than 12 V) or winding (if less than 12 V) several turns. It is worth noting that rectifying and filtering the 12V AC voltage results in about 14.4V no load. So do not be confused by this, this is the EMF voltage and it is natural that it is higher than the nominal.

In addition to the transformer, a rectifier is assembled, the diodes should calmly hold 30 A. It is more expedient to place the capacitor filter in the battery case, as in the version with ATX.

Cordless screwdrivers are very convenient to use and are widely used by both professionals and DIYers. The very first, as a rule, the battery becomes unusable. At the moment, all manufacturers of power tools have switched to lithium batteries and it is becoming more and more problematic to purchase a new nickel-cadmium battery for an old screwdriver, and the for these batteries are much higher than for lithium.

## What current does the screwdriver consume?

Before choosing a suitable power supply, you need to understand what current consumption you need to count on. Unfortunately, manufacturers of cordless screwdrivers do not indicate the current drawn by the motor. The capacity of the battery itself in ampere-hours, which is necessarily indicated on the battery, does not make it possible to understand what is the current consumed by the screwdriver in operating mode. The maximum that the manufacturer can indicate is the power in watts, but this is very rare, usually the power is indicated directly in the torque.

If the power in watts is still indicated, we can have an idea of ​​the current consumption and select the appropriate power supply with a small current / power margin. To calculate the current strength, it is enough to divide the power in watts by the operating voltage of the screwdriver, in this case it is 12 volts. So, if the manufacturer indicated a power for example 200 watts. 200: 12 = 16.6 A. Such a current is consumed by a screwdriver in operating mode.

However, the indicated power is very rare and there is no universal figure that characterizes all 12-volt screwdrivers. You need to understand that with full braking of the motor shaft, the currents can significantly exceed the rated ones and it is very difficult to calculate this value. At the same time, the analysis of various forums and our own experience showed that a current of 10 A is often enough for a screwdriver to operate, this is enough to perform many functions of twisting and drilling. At the same time, it is known that current surges with full shaft braking can exceed 30 A.

So what conclusion can be drawn from all this? For a screwdriver, a 12 V power supply giving 10 A of current is suitable, if it is possible to use a 20-30 A unit, this is even better. These are average figures that apply to most screwdrivers.

## What current does the screwdriver consume?

Before choosing a suitable power supply, you need to understand what current consumption you need to count on. Unfortunately, manufacturers of cordless screwdrivers do not indicate the current drawn by the motor. The capacity of the battery itself in ampere-hours, which is necessarily indicated on the battery, does not make it possible to understand what is the current consumed by the screwdriver in operating mode. The maximum that the manufacturer can indicate is the power in watts, but this is very rare, usually the power is indicated directly in the torque.

If the power in watts is still indicated, we can have an idea of ​​the current consumption and select the appropriate power supply with a small current / power margin. To calculate the current strength, it is enough to divide the power in watts by the operating voltage of the screwdriver, in this case it is 12 volts. So, if the manufacturer indicated a power for example 200 watts. 200: 12 = 16.6 A. Such a current is consumed by a screwdriver in operating mode.

However, the indicated power is very rare and there is no universal figure that characterizes all 12-volt screwdrivers. You need to understand that with full braking of the motor shaft, the currents can significantly exceed the rated ones and it is very difficult to calculate this value. At the same time, the analysis of various forums and our own experience showed that a current of 10 A is often enough for a screwdriver to operate, this is enough to perform many functions of twisting and drilling. At the same time, it is known that current surges with full shaft braking can exceed 30 A.

So what conclusion can be drawn from all this? For a screwdriver, a 12 V power supply giving 10 A of current is suitable, if it is possible to use a 20-30 A unit, this is even better. These are average figures that apply to most screwdrivers.

## The current consumption of the screwdriver is 12 volts

Cordless screwdrivers are very convenient to use and are widely used by both professionals and DIYers. The very first, as a rule, the battery becomes unusable. At the moment, all manufacturers of power tools have switched to lithium batteries and it is becoming more and more problematic to purchase a new nickel-cadmium battery for an old screwdriver, and the for these batteries are much higher than for lithium.

## Assembling the working structure

For ease of use and connection, I brought the cord from the power supply into the battery case. The cord took 3.5 meters long, which was available. I removed all battery cells from the battery and installed an LC filter. Now, if I somehow have a working battery, I can always put it on a screwdriver, and put the power supply in reserve. I didn’t throw out the batteries from the battery, there is an idea where to use them, but this is a topic for another review.

Since the cord connecting the unit with the screwdriver has a certain resistance and inductance, you can try to short-circuit the leads of the L1 coil. In theory, this can increase the power by a tiny amount.

With a cord, the screwdriver feels great, but to be honest, it seemed to me a little weak when braking with a hand. But the trial tightening of self-tapping screws dispelled my doubts: self-tapping screws 35 mm long quietly screw into 20 mm plywood. This means a screwdriver will meet most repair needs.

At the block, I cut off all the output wires, leaving the green start one, I soldered its end to the common conductor of the board, where all the black ones are soldered. It is best to carefully solder all the wires, but my soldering iron was too weak for that and had to be cut. To the common contact and 12 (where the yellow ones are soldered) I soldered two short, rigid copper wires and connected them through the terminal block with a cord to the shurik.

This concludes this review, we have achieved what we want. The screwdriver works fine from a computer power supply. In the future, I plan to make a solid plywood case without slots for the power supply board. Tests have shown that the radiators on the board do not heat up at all and you don’t have to worry about overheating of the elements in a closed case.