Home Salon How to make a charger for a screwdriver. Making a charger for a screwdriver with your own hands Electronic circuit of a 14.4 V charger

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How to make a charger for a screwdriver. Making a charger for a screwdriver with your own hands Electronic circuit of a 14.4 V charger

Cordless tools use battery power to operate. Naturally, from time to time it is necessary to replenish the spent supply. This process is called charging. During the process of charging and discharging, reversible chemical reactions occur in the battery, which determine the principle of its operation.

Types of charging devices

Performing the same function, chargers have a variety of internal structure options. According to the type of voltage conversion from the household electrical network, designs for charging screwdrivers differ as follows:

Transformer;
Inverter (pulse).

Transformer devices initially appeared first because they required the simplest electronic base. The classic design of the device includes:

Transformer;
Rectifier bridge;
Filter container;
Current stabilizer;
Control circuit.

Regardless of the type of stabilizer and additional options, transformer chargers share the disadvantage of large dimensions and weight. This is due to the fact that the weight and dimensions of the transformer increase in proportion to the power of the product. Accordingly, those chargers that have acceptable weight and dimensions are capable of delivering low charging current values, and the charging process takes a long time.

Inverter-type devices that use the conversion of input voltage into high-frequency current are free from this disadvantage. This approach allows the use of small-sized transformers operating with high power values. With dimensions significantly smaller than those of transformer structures, inverter designs are capable of generating a significant charging current. The battery charging time is reduced to one hour or less.

Additional functions

The simplest charger (charger) does not monitor the condition of the battery. All this is entrusted to the user. As a result, regular undercharging, prolonged charging, and non-optimal charging process, all this leads to a sharp reduction in battery life. This type of circuitry is used only in the cheapest models of screwdrivers and cannot be recommended for purchase.

More expensive models have a built-in charge controller or shutdown timer. The battery is charged until the required capacity is reached or after a certain time. In the latter case, undercharging is possible, but long-term voltage supply is excluded. The charge level is controlled by the battery voltage level. Most types of tools in the mid-price category use just such memory models.

The most advanced models have a charge controller circuit based on the use of a microcontroller. In this case, in addition to the charge itself, a preliminary discharge of incompletely used elements is applied to a strictly defined value. This procedure eliminates the appearance of the “memory” effect characteristic of alkaline batteries and helps equalize the capacity of individual battery cells. The battery is charged according to a specific algorithm according to the manufacturer's requirements.

The charge level is controlled by battery voltage. The delta method is used. It is based on the feature of Ni-Cd and Ni-MH batteries to slightly reduce the voltage when fully charged. The controller circuit reacts to a decrease in voltage at the end of a period of time and turns off the supply of charging current.

A microcontroller-based screwdriver charger will be expensive, but it will significantly extend the life of an expensive battery and reduce the time to fully charge. This type of charge controller is included with expensive professional models of screwdrivers.

Charge voltage and form factor

Manufacturers do not have a uniform standard for tool supply voltage. On the one hand, low battery voltage reduces its cost by reducing the number of cells, on the other hand, higher voltage batteries provide a number of advantages:

Higher device power;
At the same power, current consumption is reduced;
Increases operating time between charges.

An increased number of elements increases the cost of the tool, so this approach is typical for manufacturers of high-quality and expensive equipment.

Note! If the weight of the tool is important, then preference should be given to low-voltage products. 18-volt screwdrivers have the most significant weight. The exception is lithium-ion batteries, but they can only be found in the most expensive tool models.

Since the EMF of Ni-Cd and Ni-MH batteries has a strictly defined value, namely 1.2V, then the voltage of the battery cells is reduced to a series of several values:

10 batteries – 12.0V;
11 batteries – 13.2V;
12 batteries – 14.4V;
13 batteries – 16.6V;
14 batteries – 17.8V.

You can also find other values, both decreasing and increasing, but not often.

To simplify things, many manufacturers indicate a rounded battery voltage value. For example, a battery with 14 cells is often designated 18 volts, and with 10 – 12 volts.

Screwdriver batteries differ not only in voltage, but also in the shape of the fastening devices and the location of the terminals. An important conclusion follows from this.

Important! Different batteries and devices for charging them are not compatible with each other. The exception is products from the same manufacturer, which were created with compatibility in mind.

Charger upgrades

Do-it-yourself modifications to standard chargers for a screwdriver are usually done in order to improve their characteristics. Transformer-type designs are the easiest to alter, in which only the monitoring and control circuit changes. Inverters are much more difficult to change. In most cases, modification requires a complete replacement of the internal “filling” of the device.

As a rule, charging units of the lowest price category are subject to modifications. The main options that are introduced into the redesigned structure are – This is charge level control and automatic shutdown. Alterations of this type, made using analog circuitry, are not particularly difficult and are accessible to beginner and intermediate radio amateurs.

The manufacture of more complex structures, controlled by a microcontroller, can only be done by experienced craftsmen, and also does not make much sense. As already mentioned, the simplest devices are produced for cheap tool models, and accordingly, the quality of the batteries in them is not up to par. The gain in the reliability of batteries and the extension of their life will be disproportionate to the costs of such a modification of the charger.

Repair

Just like remodeling, repairing a charger for a screwdriver requires certain knowledge in the field of radio engineering. Without experience, you can replace power cords and fuses. It is worth noting that such malfunctions occupy one of the main places in frequency. Lack of charge and power indication is usually associated with broken wires or a blown fuse. Both faults are detected by testing with an ohmmeter.

More serious repairs to charging a screwdriver, especially in expensive designs, are complicated by the lack of a circuit diagram.

Important! Do-it-yourself or unqualified repair of chargers for lithium-ion batteries can result in fire and even explosion of the battery, since batteries of this type are extremely sensitive to charging conditions.

Video

Using a power tool greatly facilitates our work and reduces assembly time. Currently, battery-powered screwdrivers have become very popular. In this article, we will consider the diagram of a typical charger for a screwdriver, as well as repair tips and options for amateur radio designs.

The power part of the screwdriver charger is a GS-1415 type power transformer designed for a power of 25 Watts.

A reduced alternating voltage with a nominal value of 18V is removed from the secondary winding of the transformer; it follows 4 diodes VD1-VD4 type 1N5408, through a fuse. Diode bridge. Each 1N5408 semiconductor element is rated for forward current up to three amperes. Electrolytic capacitance C1 smoothes out ripples appearing in the circuit after the diode bridge.

Control is implemented on a micro-assembly HCF4060BE, which combines a 14-bit counter with master oscillator components. It controls type S9012. It is loaded with relay type S3-12A. In this way, a timer is implemented in the circuitry, turning on the relay for about an hour to charge the battery. When the charger is turned on and the battery is connected, the relay contacts are in the normally open position. The HCF4060BE receives power through the 1N4742A at 12 volts, since the output of the rectifier is about 24 volts.

When the "Start" button is closed, the voltage from the rectifier begins to flow to the zener diode through resistance R6, then the stabilized voltage goes to pin 16 of U1. Transistor S9012 opens, which is controlled by the HCF4060BE. The voltage through the open junctions of transistor S9012 goes to the relay winding. The contacts of the latter close and the battery begins to charge. The protective diode VD8 (1N4007) bypasses the relay and protects VT from a reverse voltage surge that occurs when the relay winding is de-energized. VD5 prevents the battery from being discharged when the mains voltage is turned off. When the contacts of the "Start" button are opened, nothing will happen because the power goes through the diode VD7 (1N4007), the zener diode VD6 and the quenching resistor R6. Therefore, the chip will receive power even after the button is released.

Replaceable typical battery from a power tool, assembled from individual series-connected nickel-cadmium Ni-Cd batteries, each 1.2 volts, so there are 12 of them. The total voltage of such a battery will be about 14.4 volts. In addition, a temperature sensor has been added to the battery pack - SA1, it is glued to one of the Ni-Cd batteries and fits tightly to it. One of the thermostat terminals is connected to the battery negative. The second pin is connected to a separate, third connector.

When you press the "Start" button, the relay closes its contacts and the battery charging process begins. The red LED lights up. An hour later, the relay with its contacts breaks the battery charging circuit of the screwdriver. The green LED lights up and the red LED goes out.

The thermal contact monitors the battery temperature and breaks the charging circuit if the temperature is above 45°. If this happens before it works, this indicates the presence of a “memory effect”.

The basis of the design is an adjustable positive voltage stabilizer. It allows operation with a load current of up to 1.5A, which is quite enough to charge batteries.

An alternating voltage of 13V is removed from the secondary winding of the transformer and rectified by a D3SBA40 diode bridge. At its output there is a filter capacitor C1, which reduces the ripple of the rectified voltage. From the rectifier, direct voltage is supplied to the integrated stabilizer, the output voltage of which is set by the resistance of resistor R4 at 14.1V (Depends on the type of screwdriver battery). The charging current sensor is resistance R3, in parallel with which a tuning resistance R2 is connected; using this resistance, the charging current level is set, which corresponds to 0.1 of the battery capacity. At the first stage, the battery is charged with a stable current, then, when the charging current becomes less than the limiting current, the battery will be charged with a lower current to the stabilization voltage DA1.

The charging current sensor for LED HL1 is VD2. In this case, HL1 will indicate a current of up to 50 milliamps. If you use R3 as a current sensor, the LED will go out at a current of 0.6A, which would be too early. The battery would not have time to charge. This device can also be used for six-volt batteries.

Often the original charger included with the screwdriver works slowly, taking a long time to charge the battery. For those who intensively use a screwdriver, this greatly interferes with their work. Despite the fact that the kit usually includes two batteries (one installed in the tool handle and in use, and the other connected to the charger and in the process of charging), owners often cannot adapt to the operating cycle of the batteries. Then it makes sense to make a charger yourself and charging will become more convenient.

Batteries are of different types and their charging modes may be different. Nickel-cadmium (Ni-Cd) batteries are a very good source of energy and are capable of delivering high power. However, for environmental reasons their production has ceased and they will become less and less common. Now they have been replaced everywhere by lithium-ion batteries.

Sulfuric acid (Pb) lead gel batteries have good characteristics, but they make the tool heavier and therefore are not very popular, despite their relative cheapness. Since they are gel (the sulfuric acid solution is thickened with sodium silicate), there are no plugs in them, the electrolyte does not leak out of them, and they can be used in any position. (By the way, nickel-cadmium batteries for screwdrivers also belong to the gel class.)

Lithium-ion batteries (Li-ion) are now the most promising and promoted in technology and on the market. Their feature is the complete sealing of the cell. They have a very high power density, are safe to use (thanks to the built-in charge controller!), can be disposed of favorably, are the most environmentally friendly, and are lightweight. They are currently used very often in screwdrivers.

Charge modes

The nominal voltage of the Ni-Cd cell is 1.2 V. The nickel-cadmium battery is charged with a current of 0.1 to 1.0 rated capacity. This means that a battery with a capacity of 5 ampere hours can be charged with a current of 0.5 to 5 A.

The charge of sulfuric acid batteries is well known to all people who hold a screwdriver in their hands, because almost all of them are also car enthusiasts. The nominal voltage of a Pb-PbO2 cell is 2.0 V, and the charging current of a lead sulfuric acid battery is always 0.1 C (a fraction of the current of the nominal capacity, see above).

The lithium-ion cell has a nominal voltage of 3.3 V. The charging current of a lithium-ion battery is 0.1 C. At room temperature, this current can be gradually increased to 1.0 C - this is a fast charge. However, this is only suitable for batteries that have not been over-discharged. When charging lithium-ion batteries, the voltage must be strictly observed. The charge is made up to 4.2 V exactly. Exceeding it sharply reduces service life, lowering it reduces capacity. When charging, monitor the temperature. A warm battery should either be limited by current to 0.1 C, or disconnected until it cools down.

ATTENTION! If a lithium-ion battery overheats when charging above 60 degrees Celsius, it may explode and catch fire! Do not rely too much on the built-in safety electronics (charge controller).

When charging a lithium battery, the control voltage (end of charge voltage) forms an approximate series (the exact voltages depend on the specific technology and are indicated in the battery passport and on its case):

The charging voltage should be monitored with a multimeter or a circuit with a voltage comparator tuned exactly to the battery used. But for “entry-level electronics engineers,” only a simple and reliable circuit, described in the next section, can really be offered.

Charger + (Video)

The charger offered below provides the required charging current for any of the listed batteries. Screwdrivers are powered by batteries with different voltages of 12 volts or 18 volts. It doesn’t matter, the main parameter of a battery charger is the charge current. The voltage of the charger when the load is disconnected is always higher than the rated voltage; it drops to normal when the battery is connected during charging. During the charging process, it corresponds to the current state of the battery and is usually slightly higher than the nominal value at the end of charging.

The charger is a current generator using a powerful composite transistor VT2, which is powered by a rectifier bridge connected to a step-down transformer with sufficient output voltage (see table in the previous section).

This transformer must also have sufficient power to provide the required current during long-term operation without overheating the windings. Otherwise it may burn. The charge current is set by adjusting resistor R1 when the battery is connected. It remains constant during the charging process (the more constant the higher the voltage from the transformer. Note: the voltage from the transformer should not exceed 27 V).

Resistor R3 (at least 2 W 1 Ohm) limits the maximum current, and LED VD6 lights up while charging is in progress. Towards the end of the charge, the LED glow decreases and goes out. However, do not forget about precise control of lithium-ion battery voltage and temperature!

All parts in the described circuit are mounted on a printed circuit board made of foil PCB. Instead of the diodes indicated in the diagram, you can take Russian diodes KD202 or D242, they are quite available in old electronic scrap. The parts must be arranged so that there are as few intersections as possible on the board, ideally none. You should not get carried away with high installation density, because you are not assembling a smartphone. It will be much easier for you to solder the parts if there is 3-5 mm between them.

The transistor must be installed on a heat sink of sufficient area (20-50 cm2). It is best to mount all parts of the charger in a convenient homemade case. This will be the most practical solution; nothing will interfere with your work. But here there can be great difficulties with the terminals and connection to the battery. Therefore, it is better to do this: take an old or faulty charger from a friend that is suitable for your battery model, and remake it.

Open the casing of the old charger.
Remove all former filling from it.
Select the following radioelements:

Select the appropriate size for the printed circuit board that fits in the case along with the parts from the diagram above, draw its tracks using nitro paint according to the circuit diagram, etch it in copper sulfate and solder all the parts. The heatsink for the transistor must be mounted on an aluminum plate so that it does not touch any part of the circuit. The transistor itself is tightly screwed to it with a screw and an M3 nut.
Assemble the board in the case and solder the terminals according to the diagram, strictly observing the polarity. Output the wire for the transformer.
Install a transformer with a 0.5 A fuse in a small suitable housing and provide it with a separate connector for connecting a converted charging unit. It is best to take connectors from computer power supplies, install the male in a case with a transformer, and connect the female to the bridge diodes in the charger.

The assembled device will work reliably if you carefully and thoroughly

I bought a cheap Chinese screwdriver SKIL-2007, a 14.4 V battery - 1.2 A/h, in principle it can work normally, but it turned out to have two drawbacks. First - there is no adjustment of the rotation speed, I dealt with this quickly, installed a switch with a speed regulator. Secondly, there is no indicator for the end of charging. The kit includes two batteries and a simple charger, made in the form of two separate parts. In a small case, which is plugged into a socket, there is a transformer with a rectifier that produces 18 V 200 mA at the output, and a piece of wire with a connector extends from it. The second part is the charger itself with indicators, here is its diagram - Fig. 1.

The green LED indicates that the device is online. Red indicates the battery is charging and will remain on as long as the battery is connected to the charger. According to the passport, the charging time is 3-5 hours. Since it is impossible to control the end of charging using this charger, I decided to supplement it with my own. Searches on the Internet did not yield anything, I came across too abstruse ones on controllers, the program for which is sent for a separate fee, or circuits in which the charge is determined by the brightness of the LED, but this is also not the best option, since during the day in sunlight the brightness seems low, and big in the dark.

I decided to make a simple, reliable battery charging indicator from available parts. As a basis, I took a car voltage indicator (found on shelves in the garage), they are still on sale, they are a cylindrical body that plugs into the car’s cigarette lighter, at the end there are three LEDs arranged in a row, red at the edges, green in the middle . Here is its diagram (Fig. 2.) and passport details.

Controlled voltage ranges:

red LED VD3 - 12 V;
green LED VD4 - from 12.5 to 14.5 V;
red LED VD4 - more than 15 V.

Joint glow zones:

red VD3 and green VD4 - from 12.0 to 12.5 V;
red VD2 and green VD4 - from 14.5 to 15.0 V.

This circuit is suitable for a 12-volt screwdriver without modification. It does not contain scarce parts and can be easily assembled by a beginning radio amateur.

With my screwdriver, the voltage of a fully charged battery standing on charge is 16.5...16.8 V, it will not rise higher, even if it takes a day to charge. The modification of a car indicator is as follows: the case is disassembled and thrown away, leaving a 16x38 board with three LEDs. Zener diode VD1, replaced with D814G, instead of R2, install a variable resistor of 1 kOhm.

Setting: a power source with an adjustable voltage of up to 20 V is connected to the “±” input of the indicator. We set the voltage at the output of the power supply to 16.5 V and by rotating the variable resistor slider we ensure that only the green LED lights up, as soon as the red VD3 goes out, the rotation stops . This completes the setup.

I got the following charging values: Red VD3 - up to 15 V (battery is discharged). Red VD3 and green VD4 - 15...16.5V (charged 50-80%).

Green VD3 - 16.5 - 19.3 (charged 100%). Red VD2 - more than 19.3V (this indicator is practically not used).

Then, instead of a variable resistor, install a constant one, in my case it turned out to be R2 = 470 Ohms, but you can leave the construction one. The indicator is connected to the standard charger to the “±” terminals of the battery. Three holes are drilled in the case for the LEDs and the indicator is inserted into the charger case, there is a lot of space there, and it is secured. Everything original remains in its place.

When you turn on the charger without a battery, VD2 lights up. We insert the discharged battery into the charger, VD2 goes out, the VD3 indicator lights up, while charging, when the voltage reaches 15 V, the green VD4 indicator starts to light up, and the brightness of VD3 decreases and finally the red VD3 goes out, and the green VD4 lights up at full intensity, charging can be considered complete.

As a result of this addition to the charger, charging, instead of 3-5 hours according to the passport, ends much earlier. At any time, by the glow of the indicators, you can determine at what stage the battery is being charged. According to the setup method, this circuit is also suitable for other chargers for other voltages. To do this, fully charge the battery, as stated in the instructions, for 3-5 hours, then, without removing the battery from the charger, measure the voltage of the fully charged battery. This voltage is set at the output of the regulated power supply and by selecting the Zener diode VD1 and resistor R2, the indicator operates clearly, as stated above.

Often, drill buyers complain that the “native” charger for a screwdriver charges the battery too slowly. As a result, you have to repeatedly postpone work for 2-4 hours. There are 2 options to avoid this situation. In the first case, you will need to purchase a new charger, in the second, you will need to make it yourself.

Types of batteries

To figure out how to make a charger for a screwdriver, you first need to study the types of batteries and their charging modes. There are 3 types of batteries:

Nickel-cadmium

This type is referred to as Ni-Cd, it is considered a good voltage source that is capable of delivering high power. The only drawback is that such batteries are included in the list of prohibited products due to environmental considerations, so this variety will now be much less common on sale.

Nickel-cadmium batteries have an energy capacity of 1200 to 1500 mAh. The total power is provided and maintained by the number of cans inside

The maximum cell voltage is 1.2 V. The battery is charged with an electric current of 0.1-1 rated capacity. It turns out that a battery with a capacity of 5 A*h can be recharged with a current of 0.5-5 A.

VIDEO: 5 rules for charging nickel-cadmium batteries

Another name is Pb with acid gel filling. They have average characteristics and low cost. The downside is that the batteries have a large mass, which makes the device heavier. The main advantage is that it can be used in any position without the electrolyte leaking out of the container.

Their main feature is high voltage and resistance, due to which even at the end of the charge-discharge cycle there is no sharp drop in voltage

The maximum cell voltage level is 2 V, while the battery charging current always corresponds to 0.1 C.

Li-ion batteries for screwdriver

The most common type due to the complete sealing of the container. This option is characterized by increased power density, safety, environmental friendliness, low weight and ease of disposal.

Lithium-ion battery for screwdriver Li-ion 18650 Samsung 12.6V (Volt) 2400mAh

The lithium-ion cell has a maximum power of 3.3 Volts. The voltage can be gradually increased at room temperature from 0.1 to 1 C. This speeds up the charging process. But this method is only suitable for those batteries that have not been over-discharged.

It is important to remember here that the screwdriver is charged up to 4.2 Volts, exceeding it will affect the reduction in service life, and reducing it will reduce the capacity. It is very important to monitor the temperature when charging.

When developing a charger circuit for a screwdriver with your own hands, it is very important to consider which battery you plan to charge. You also need to additionally calculate its voltage - 12 Volts or 18 Volts. When operating a charger for a screwdriver, it is necessary to monitor the process using a multimeter or a system with a voltage comparator, which has been pre-configured for a specific type of battery.

VIDEO: Rules for choosing a battery for a screwdriver

How to assemble your own charger

Creating a homemade charger for a screwdriver requires compliance with safety precautions and carrying out work strictly according to a given scheme. You can use the drawing below, which is universal, since such charging equipment will be suitable for any type of battery. The only important parameter here is the charge current.

Homemade charger

When recharging, the current value fully corresponds to the existing state of the battery, and when the process is completed, the indicator becomes slightly higher.

Diagram of the simplest memory for a screwdriver

The charger for a screwdriver acts as an electric current generator using transistor VT2. It, in turn, receives power through a rectifier bridge in contact with a step-down transformer. The charge current level is adjusted by adjusting resistor R1 when the battery is turned on. It will always remain the same. R3 works as a rated current limiter. VD 6 is an LED, it acts as an indicator that determines whether charging is ongoing or has already completed.

All components from the charger circuit for a screwdriver are installed on a printed circuit board; domestic devices KD202 and D242 can be used as diodes. It is required to place the elements in such a way that there is a minimum number of intersections on the board; the ideal option would be if there are none. Leave at least 3 mm between parts.

The transistor is mounted on a heat sink 25-55 cm 2. The connection field for the charging components for screwdrivers must be covered with a housing. Here, difficulties may arise with the terminals and connection of the battery. Therefore, it is better to modify the screwdriver charger by upgrading the old one:

open the case of the outdated recharger;
remove all components and other filling from it;
install a homemade circuit into the case.

The diagram must contain the following elements:

Position name	a brief description of
	Rectifier diode 1N-4001 series
	Standard LED
	Multi-colored LED of various types
	Variable wirewound resistor 10
	Resistor element MLT0.25 series at 330 Ohm
	Resistor MLT2.1 Ohm

	K5035 or 220 1000mF over 50 Volts
	Transistor part KT 361V

	Power transformer for 220/24 V and a power rating of 100 W

Stages of work:

Select the most optimal dimensions for the circuit, which easily fit into the case with all the listed components.
Draw a thread along all its paths according to the basic drawing, etch it in a copper frame and solder all the elements.
Install the heatsink on the aluminum plate so that it does not come into contact with any part of the board.
Securely fix the transistor with an M-3 nut.
Assemble the components strictly according to the diagram and solder the terminals to all necessary parts, observing polarity. Output the electrical wire for the transformer.
Install the transformer itself, together with a 0.5 A fuse, into the housing and equip it with an adapter to enable recharging.

VIDEO: How to charge a Li-ion battery using a screwdriver

Rating of chargers for screwdrivers

For those who do not plan to do their own assembly, we suggest choosing from a range of ready-made chargers from different manufacturers.

DEWALT DCB118

The FLEXVOLT DEWALT DCB118 universal device is used to restore batteries for DEWALT screwdrivers with a voltage of 54V; you can equally successfully charge any other devices with a nominal voltage of 18 volts.

FLEXVOLT DEWALT DCB118

For convenience, there is an indicator on the body, so you can monitor the process. Type of rechargeable batteries Li-ion. Weight 850 gr. Equipment price 3500 rub.

ONE+ Ryobi RC18120

It is declared as a highly specialized device intended only for charging Ryobi ONE+ series batteries. The advantage of having only one power supply - due to this, the weight of the device is even reduced (only 460 g), while the IntelliCell™ intelligent monitoring system has been introduced, when each cell is charged to maximum within 40-50 minutes, thereby increasing battery life .

ONE+ Ryobi RC18120

The voltage is 18 volts, the battery type is nickel-cadmium and lithium-ion. There are 4 positions of the level indicator - 25…50…75…100%. The case itself can be mounted on a wall. There is a light level indication. The cost of the device is 4850 rubles.

DC10WC (10.8 V) Makita

The device is used to restore lithium-ion batteries with a nominal voltage of 10.8 volts. There is a light indication, but no automatic stop. It is advisable to control the time to prevent overfilling the container.