What determines the power of the cordless screwdriver

Household or professional

As you know, professional screwdrivers are more expensive, but this is not accidental. They are made with a large margin of safety, for which higher quality and more expensive materials are used. In addition, they have more power, which makes it possible to screw in longer screws and / or work with tougher materials.

determines, power, cordless, screwdriver

The difference between a professional and a household screwdriver in a resource

To decide a household or professional screwdriver you need, estimate the amount of work that will need to be done. If you are starting a construction or major renovation, you probably need a professional or semi-professional model. If the tool is needed periodically. to twist / twist something from time to time, everyday life is more than enough. With such work, the resource of a professional tool will simply not be in demand. So choosing a screwdriver according to this criterion is not very difficult.

Rotational speed and torque

The torque with which the screwdriver can turn the screw is determined by the torque. It can be quite small for household models. 10-15 Nm, and it can reach 130-140 Nm for professional ones. Therefore, pro screwdrivers can easily and quickly tighten large self-tapping screws and work with hard materials.

But a large torque is not always necessary and not with all materials; therefore, screwdrivers provide the ability to adjust the applied force. There is a limiter for this. It is designed as a movable ring, which is located behind the chuck.

The higher the RPM, the stronger the torque

There is a mark on the ring, by placing it opposite a certain number, you set the maximum force that the tool can develop. Upon reaching this value, the chuck will scroll to idle. the screw will no longer be tightened. The achievement of this value can be clearly tracked. the ratchet turns on.

Many models of screwdrivers can work in two modes: the actual tightening of the fasteners and drilling. Such models are called a screwdriver-drill, but now there are most of them. To switch to drill mode, the switch is set to the extreme position (having previously replaced the nozzle). At the same time, the maximum speed is turned on, which allows you to drill even rather hard materials.

The main parameters of the battery and the tool itself

The main parameter that characterizes the operation of a screwdriver is the voltage of the battery, which, in turn, determines the power of the electric motor and the torque. For household models, the difference in voltage between screwdrivers is small. on average, it is in the range of 10.8-14.4 V. productive options designed for constant use can be equipped with batteries of 24-36 volts.

The battery voltage of the screwdriver depends on the type of battery. you can answer what the difference is, knowing what metals were used to make it. For nickel-cadmium batteries, larger in size with a similar capacity, the value of the indicator is a multiple of 1.2 V (this is exactly the voltage for one cell of which the battery pack is composed), for lithium-ion batteries. 3.6 V.

Other equally important characteristics include:

  • the power of the screwdriver, by which you can also determine the speed of tightening screws and self-tapping screws. To carry out repairs on our own, models with a capacity of 500-700 W are quite enough. A professional repairman will need more powerful equipment. 800–850 W;
  • the number of revolutions of the rotating part of the device per unit of time. This parameter determines whether the screwdriver will be able to perform the task assigned to it. for example, tighten the required type of fastener. So, for a bolt, self-tapping screw and a screw, 500 rpm is enough, for drilling it will take 1200 rpm;
  • torque, the value of which can become one of the main answers to the question of what the voltage of the screwdriver’s battery affects. According to this characteristic, it is possible to determine both the diameter and the length of the screw to be screwed or self-tapping screw. Large fasteners, as well as drilling deep and wide holes and hard materials, require a serious torque value. The maximum value of the indicator is 10-60 Nm.

There are two types of screwdriver torque. starting (larger in magnitude and required to start the device into operation) and constant, that is, working. The parameter value for modern equipment models can be adjusted. to find out how many modes can be selected for a particular device, you can find out in the documentation available for it. over, tools with a pulsed mode of operation (turning on the rotating part by jerks) have more screwing capabilities. allowing you to periodically increase the torque, they can screw in a larger screw.

The given value of torque from electric motors is not constant and depends, first of all, on the speed of the motor, the higher the speed, the lower the torque on the shaft.

In addition to the voltage of the screwdriver and its power, the capacity of the battery should also be evaluated. The characteristic is measured in ampere-hours or milliampere-hours. The higher the indicator, the longer the screwdriver can work without recharging.

The average battery capacity of the household model is 1300 mAh, which is enough for 2-3 hours of operation. Professional equipment requires more time to complete the work. and a master who uses a screwdriver for a whole working day should purchase a model with 1.5-2.0 Ah batteries.

Technical specifications

After you have decided on the type of screwdriver and power supply, you need to focus on the technical specifications. They determine which screws and in which material you can screw.

An example of the technical characteristics of a screwdriver

Chuck type

The screwdriver chuck is of two types: key and keyless. The quick-release (usually has three petals) allows you to change the nozzles in a matter of seconds. the cartridge is turned a little by hand, the nozzle is changed, after which it is turned a little in the opposite direction again. In addition, there is one more positive point: in such a holder it is fashionable to install a nozzle of any thickness. The main thing is that the shank fits into the holder.

Types of chuck for screwdriver

The same operation with a key chuck requires a special key. It is inserted into a special socket, rotated until the nozzle is free. After replacement, the key turns in the opposite direction. The disadvantage is obvious: you must have this key at hand.

Let’s see what’s inside Cordless Screwdriver

By their structure, keyless chucks can have one or two couplings. If there are two couplings, one of them fixes the chuck, the second. the shaft. If there is only one coupling, then there is a shaft locking button on the body.

It is not difficult to choose a screwdriver according to this parameter. usually everyone converges on quick-clamping ones. They allow you to fix nozzles of large sizes, although they are a little more expensive, all other things being equal.

Summarizing

Summing up the article, it is worth noting that the power of the screwdriver battery, although it is an important parameter when choosing a suitable model, is much more important than the voltage and capacity indicators. And it is often worth paying attention to the torque only if it will be used not only for screwing in, but also for drilling. You should also know that the maximum power of a cordless screwdriver of all commercially available models has a device with a voltage of 36 V, a torque of 60 Nm and a capacity of 3000 mAh. Such equipment is rather difficult and not very convenient to use without professional experience. And, therefore, you should opt for less productive options produced by well-known and reliable brands such as Bosch, Hitachi, Makita, AEG, Dewalt and Metabo.

Hello.
How many amperes does a 14 volt screwdriver consume? I want to attach a power supply to it.
I thought maybe a power supply from a laptop would fit (16V 5A), if it’s weak, then I think you can buy a more powerful power supply.

It consumes differently, from 5-7A in a lightly loaded mode, up to 10-15 and even up to 20-25A in dir. tightening on vehn. ratchet level. PSU is not convenient, now there is a sea of ​​modern batteries: lithium-iron-phosphate (LiFePO4), lithium-ion (Li-Ion) and lithium-polymer (Li-Pol), i.e. there is something to replace the old junk. In general, the problem is discussed on many forums, take a look here, for example, there is something to read on this issue:
http://electrotransport.ru/ussr/index.php/topic,3117.0.html?PH PSESS

How many amperes does a 14 volt screwdriver consume? I want to attach a power supply to it.
And what is the capacity (in A / h) of the battery of the screwdriver you have?

PSU is not convenient, now there is a sea of ​​modern batteries. those. there is something to replace the old junk.
Yes, there is a replacement, but separately purchased batteries are very, very.
ZY I have a set “MAKITA” with two Ni-Cd batteries of 12 V, 1.3 A / h each, after being fully charged with a standard charger, unused batteries, alas, lose their charge in 2.3 days, i.e. there is a significant loss of capacity. The set of tools was purchased in 2007, was used infrequently.

Yes, there is a replacement, but separately purchased batteries are very, very.
ZY The “MAKITA” kit with two Ni-Cd batteries of 12 V, 1.3 A / h is in stock. After full charging with the standard charger, the unexploited batteries, alas, lose their charge in 2.3 days, i.e. there is a significant loss of capacity. The set of tools was purchased in 2007, was used infrequently.

There is one good way to revive accom. This occurs in acc. NI-CD crystallization, and they do not hold the charge well. To destroy it, you need to apply eg. with high current. from welding KEMPI. Minus to minus acc., plus wire several times to read on the positive terminal, smoothly. And you will be happy for another 200 charges, approx. discharges. Or a couple of acc. It is possible to connect in the afterbirth from the car. For Ni-Cd acc., it is necessary for long-term storage, do it once a month. two full discharge and charge. I have a screwdriver about 10 years old and works like a clock. But first try 3-4 cycles times. Try heating, and let’s cool down for half an hour, each time. I revived mine like this for the last time. But when it’s completely stuck, then the above should be done. I rewind the start button with a wire until it stops. But look not to stand long when stopping. These acc. They do not like deep discharge. Otherwise, there will definitely be a kirdyk. And every time you lose power, when you work, do not be lazy, always discharge the battery to the end. This greatly affects the durability. I personally always do this, and it works for years.

For some work, you have to tighten a lot of self-tapping screws. You can, of course, do this manually with a screwdriver, but this requires considerable effort and takes a long time. To speed up the process, you need to choose a screwdriver. There are quite inexpensive models. household ones. which, nevertheless, greatly facilitate the installation and dismantling of screws. And some can work in drill mode.

Screwdriver power

Model Tool type Chuck type / diameter Maximum idling speed Maximum torque Number of speeds Maximum drilling diameter wood / metal Battery type, charging time Battery capacity / voltage Battery capacity Attachment capacity Weight Package contents Price
Bosch GSR 1800-LI 1.5Ah x2 Case hammerless drill quick-clamping 0.8-10 mm 1300 rpm 34 Nm 2 29 mm / 10 mm Li-ion 1.5 Ah / 18 V reverse, spindle lock, electronic speed control power button lock 1.4 kg case, two batteries, charger RUB 6.7. RUB 7.5.
Bosch GSR 18-2-LI Plus 2.0Ah x2 Case hammerless drill quick-clamping 1.5-13 mm 1900 rpm 63 Nm 2 38 mm / 13 mm Li-ion 2 Ah / 18 V reverse, spindle lock, electronic overload protection, electronic speed control bit socket, spot light, power button lock 1.49 kg case, two batteries, charger 11 thousand rubles. 13.5 thousand rubles.
Makita 6347DWDE hammerless drill quick-release / 1.5. 13 mm 1300 rpm 80 Nm 2 38 mm / 13 mm Ni-Cd 2.3 Ah / 18 V reverse, electronic speed control bit socket, power button lock 1.5KG two batteries, charger, bit, case 13 tr.
Makita 6347DWAE hammerless drill quick-release / 1.5. 13 mm 1300 rpm 80 Nm 2 38 mm / 13 mm Ni-Cd 2 Ah / 18 V reverse, electronic reverse, electronic speed control bit socket, power button lock 1.5KG two batteries, charger, bit, case 11.3 tr. 12 tr.
Hitachi DS18DVF3 hammerless drill quick-release / 13 mm 1200 rpm 45 Nm 2 21 mm / 12 mm Ni-Cd 1.4 Ah / 18 V reverse, electronic speed control bit socket, additional handle 2 Kg case, flashlight, set of attachments 7.6 tr. 9.5 tr
Hitachi DS18DSFL hammerless drill quick-release 2mm / 13mm 1250 rpm 41 Nm 2 38 mm / 13 mm Li-ion 1.5 Ah / 18 V reverse, electronic speed control power button lock 1.7 kg two batteries, charger, case RUB 8.7. 11.6 tr
Metabo BS 18 10mm 1.3Ah x2 Case hammerless drill quick-clamping / 1-10 mm 1600 rpm 48 Nm 2 20 mm / 10 mm Li-ion 1.3 Ah / 18 V reverse, spindle lock, electronic speed control bit socket, spot light, power button lock 1.3KG two batteries, charger, case 7.7 tr. 8.1 tr.
Metabo BS 18 Li 2012 13mm 2.0Ah x2 Case hammerless drill quick-release / 1.5-13 mm 1600 rpm 48 Nm 2 20 mm / 10 mm Li-ion 2 Ah / 18 V reverse, spindle lock, electronic speed control bit socket, spot light, power button lock 1.5KG two batteries, charger, case RUB 10.3. 10.9 tr.
RYOBI RCD18021L hammerless drill quick-release / 1.5-13 mm 1600 rpm 45 Nm 2 38mm / 13mm Li-Ion 1.4 Ah / 18 V reverse, spindle lock, electronic speed control socket for fastening bits, magnetic holder on the body, spotlight, power button lock 1.2KG one battery, charger, bit, bag 7.1 tr. 7.8t.r.
RYOBI R18DDP-0 hammerless drill quick-release / 13 mm 1600 rpm 45 Nm 2 32 mm / 13 mm 18 in reverse, electronic reverse, spindle lock, electronic speed control socket for fastening bits, magnetic holder on the case, locking of the power button 1.81 kg bit (without battery and charger) 2.7 tr. 2.9 tr.

It is worth saying a few more words about the number of work speeds. Not to be confused with the number of rotation speeds. These are two modes of operation that are used when working with different sizes of screws or drills. When working with small screws / drills, you can select a higher speed, when screwing in large screws or drilling large holes, a lower speed.

Screwdriver power

In most instructions for using a screwdriver, such an indicator as power is not indicated. However, for those who choose a tool, it is perhaps the most important. And it is not indicated because the concept is, one might say, combined. So what determines the power of a screwdriver? This is, first of all, battery power and torque. In order to assess the power of the screwdriver as a whole, you need to take into account all these indicators.

Let’s consider the power components separately:
– Battery voltage. It determines the power of the engine and the amount of torque, as well as the operating time of the screwdriver. The average power of household screwdrivers is 10.8-14.4 volts (V). However, there are models with batteries up to 36 volts.
– In addition to voltage, it is worth evaluating its capacity, which determines the operating time and is measured in ampere hours. The average battery capacity of a screwdriver is 1.2-1.5 Ah.
– The torque, that is, the rotational force that the tool develops, determines the length and diameter of the screw that the screwdriver is able to tighten. The higher it is, the more power the screwdriver has. The torque rating differs depending on the material to be drilled. The technical data sheet of the tool usually indicates the size of the maximum possible drilling diameter for various materials. In addition, a distinction is made between hard torque (starting power) and working, that is, constant. A hard moment is always higher than a constant one. It should also be noted that the torque in modern screwdrivers. the value is adjustable, in the technical data sheets, again, it is indicated how many installations the screwdriver has and the maximum possible torque. Provides a maximum torque of approximately 10 to 60 Newton meters (Nm). It is worth noting that, all other things being equal, the power of the screwdriver increases significantly if it has the function of working in a pulsed mode (jerks). Power is increased due to the fact that periodically hard torque is triggered.

Don’t try to get the most powerful tool. With excess power, you will screw in the screws too hard, the head will be deeper than the surface, which spoils the appearance and makes it difficult to unscrew the screws if necessary.

Let’s summarize. Before choosing which power of the screwdriver is right for you, you should decide for what purpose the tool will be used. For rare use in a home workshop, a simple low-power tool is suitable, with a voltage of 12V, a capacity of 1.2Ah and a maximum torque of 10Nm. Such a tool can be used when assembling furniture and screwing in small self-tapping screws for attaching home furnishings (curtains, paintings, etc.). The greatest power is achieved with indicators of 36 V, 3 Ah and 60 Nm. Such screwdrivers are considered professional, working with them requires certain skills, the price for them is quite high. In any case, before buying a screwdriver, you should carefully study the technical data sheet and compare all the values ​​given in order to represent what final power is available to your chosen tool.

Operating rules

The use of an impact screwdriver will be safe and as effective as possible only if it is done correctly. Obviously, the first tip is to read the instructions before use, but there are other reasonable tips for use.

For example, if possible, do not set the equipment to maximum torque, because many fragile materials with a treated surface can simply be torn from this, and you will ruin the workpiece. In addition, working at maximum speeds up tool wear, not to mention the fact that in this mode you need to hold it tighter, otherwise it may even be possible to get injured.

The modes of operation, by the way, are described in the instructions for a reason. each of them assumes optimal settings for performing this particular task, and for another it may not be suitable. So, drilling is needed to make holes, and the screwdriver mode is to screw in fasteners, when used, on the contrary, efficiency decreases, but the risk of injury increases.

It is completely unacceptable to change the settings on the fly, with a rotating chuck. this can break the unit.

Always wear protective goggles and gloves, especially with fragile materials. When drilling walls, make sure there are no electrical wires in advance. Remember that the continuous operation of the device is limited. if the nozzle or any other unit is noticeably warm, let it cool.

By the way, if the drilling mode is not provided for in a specific model of a screwdriver, then it is better not to try to drill anything with it. such experiments often end with a burnt out engine.

When using a cordless screwdriver in cold weather, be prepared for the fact that a battery of any type, especially a lithium-ion battery, will discharge much faster, therefore you need to charge it more often.

What is it and what is it for?

An impact screwdriver is a special power tool that allows you to most effectively drill walls in order to drive screws and install other fasteners. Unlike bumpless models, this relative novelty in the domestic market makes a hole not only due to the actual rotation, but also with the help of directional blows. The latter usually do not have a permanent character. the corresponding mode is turned on at the request of the operator or automatically if the drill runs into an obstacle of particular hardness. In a sense, it’s a little jackhammer.

Impact screwdriver. the device itself is more complex and “smart”, therefore, a certain versatility should not be surprising. This means that the tool, as a rule, is fully compatible with various attachments, due to which the scope of its potential application significantly expands. instead of a drill, you can attach, for example, a hole saw or a mixing attachment.

A distinction should be made between an impact driver and a similar drill. The latter, being focused on making holes, assumes a longitudinal direction of impacts, while a screwdriver strikes as if longitudinally, due to which it significantly increases the torque.

It is logical that such a tool is somewhat more expensive than non-impact models, but its purchase is often justified even at home. the external, load-bearing walls of multi-storey buildings are usually distinguished by the highest strength, which only an impact screwdriver can overcome.

The device is also appreciated by professionals who drill walls or various parts every day. according to them, for all its assertiveness, the drill of an impact driver usually does not cause significant damage to the fasteners, increasing their durability. This characteristic is especially valuable in the context that the same tool is often used to assemble furniture.

The classification of impact screwdrivers is not so extensive, but it can still drive many inexperienced consumers into a dead end. Most of all, the logic in dividing tools into drills, screwdrivers and screwdrivers confuses, but in fact everything is extremely simple here: the mechanism is generally the same for everyone, and the exact name depends on the nozzle.

So, a drill is usually equipped with a drill for making holes, and a screwdriver and a screwdriver at the same time know how to screw in fasteners. Some models imply a simple replacement of nozzles, therefore they can have complex compound names like “screwdriver-drill”, but if such multifunctionality is not provided, the unit is called the most accurate term.

Often, when choosing, beginners are also confused by the fact that the device is supposedly electric and pneumatic. Electric models are the most common, especially at home, but pneumatic ones are perhaps very rare models that will definitely not be in demand at home, the main places of their use are various service stations and tire fitting enterprises.

Since the screwdriver is powered by electricity, it is impossible not to clarify that it can be both mains and battery. The first is good for minor home repairs or daily work in a well-equipped workshop, because it is lighter, and the master does not need to constantly remember to charge the battery.

However, it is the battery version that is the uncontested solution during the construction process or for outdoor use when the working site does not imply the presence of functioning outlets.

How to choose?

When choosing a specific model of impact screwdriver, pay attention to the smallest details. The first thing that people usually pay attention to is the type of food. Pneumatic models will definitely not be needed at home, but electric ones are network and battery models, as mentioned above.

The network option is good for working in an equipped room, it is most appreciated for its almost unlimited power. Having given preference to just such a device, evaluate its cable. it must have a considerable length and thickness, have good insulation and not raise doubts about the strength of the place where it enters the unit.

In the case of the battery model, there are more selection criteria. First of all, you need to find a balance between a large battery capacity, which extends the battery life, and the weight of the device, because a capacious battery always weighs quite a lot.

Another point is the choice of the type of battery: today the most common lithium ion models, but nickel-cadmium are also found. The first ones are good with a small mass with a significant capacity, they allow charging at any time, but they are more expensive than the main competitor and can wear out quickly at low temperatures. The advantages of the nickel-cadmium solution completely eliminate the disadvantages of the lithium-ion version. such a battery is cheaper and not afraid of frost, but it is heavy and environmentally hazardous, and most importantly, it must be completely discharged and then fully charged, otherwise the “memory effect” will provoke rapid wear of the carrier.

Batteries can produce different voltages, but for periodic household work, you can choose models with a value in the range of 12-18 V.

At high voltage, the engine power also increases, but for home use, sky-high rates are not needed: 500-700 W is enough, otherwise the tool will be heavy and unreasonably expensive.

Screwdriver chucks, in which replaceable nozzles are attached, are quick-clamping and key. The first can be organized in different ways, but its advantage is that it can be serviced with bare hands. The key cartridge has a characteristic rim; a special key is needed to maintain it, which is not always convenient.

Since we are talking about the cartridge, an important criterion is the maximum diameter of its opening. the larger it is, the more different nozzles can be used.

Maximum torque is a measure of how hard the nozzle will rotate. This indicator does not always directly depend on the power of the motor, sometimes it can be increased due to the gearbox, but it is always desirable that the maximum torque be quite high. Models with stepless torque control are in priority, since they are more sparing for fasteners and surfaces that are drilled.

The last, but very important criterion for choosing a tool is its weight. Unfortunately, it is impossible to create a lightweight, and at the same time powerful and multifunctional device, therefore it is necessary to decide which is more important: lightness or performance. Keep in mind that with constant daily work, the first factor may be much more important.

Impact screwdrivers: what is it and how is it different from shockless screwdrivers?

  • What is it and what is it for?
  • Views
  • Distinctive features
  • How to choose?
  • Operating rules
  • Care Tips

One of the original criteria for assessing the masculinity of the owner of the house is considered to be his ability to drive a nail (or, in a modern way, screw a screw) into the wall. Without this elementary skill, it will not be possible to hang a shelf, decorate a room with a picture, or install a curtain rod.

An electric screwdriver is called upon to cope with this task faster and without unnecessary effort, and the impact screwdriver is especially often praised, but not everyone understands what it is and why.

Distinctive features

When deciding whether to choose an impact or a shockless model of a screwdriver, first you need to figure out how they differ.

Many consumers who have managed to evaluate the operation of the striking mechanism will say that such a unit is better, and this is how they are ready to substantiate their point of view.

  • Directed impacts increase the torque of the impact tool to a range of 80-250 N / m, making it possible to break through the most difficult obstacles. It is significant that in the process there is even no need to firmly press the case against the wall. the tool bites into it even without significant pressing.
  • Without the need for constant physical effort applied to the tool, the wrist and hand of the master are much less tired, which allows you to increase the same productivity.
  • Considering that even a solid wall is not able to successfully withstand the onslaught of such a tool, it usually does not deform the fasteners, which will allow it to be removed without additional efforts in the future. over, many models also provide for the reverse function of removing old fasteners from the walls, and even the fact that, due to long-term use, it has experienced strong deformation.
  • The screwdriver works not only with bolts, but also with nuts, in each case achieving the most tight tightening. A “smart” car usually automatically switches from shockless mode to shock mode when it senses that the nut has become tighter at a certain moment.

Unfortunately, this solution also has certain drawbacks, which may never allow it to completely supplant unstressed models. Thus, an impressive twisting speed is observed only in the shockless mode; when switching to impacts, it significantly decreases.

Chucks for such a tool are not suitable for any. you need strictly hex. Most models do not have a limiting sleeve, so the degree of tightening must be carefully monitored by the operator, otherwise damage to the wall or parts will not be done. Finally, at high speeds, such a unit is capable of producing deafening construction noise, therefore constant work with it requires the mandatory use of protective equipment.

Care Tips

If you purchased a rechargeable model, remember that the battery should always be in the disconnected position, except for direct work. In this case, the nickel-cadmium battery must be completely discharged before turning off the device, and then immediately put it on charge. Among other things, it is still not capable of storing a charge for a long time even when it is idle, therefore sometimes it needs to be recharged, even if you have not used it.

A screwdriver gearbox may require periodic lubrication, an indicator that such a moment has already come is a characteristic unpleasant sound and a tight movement of the chuck when trying to rotate it by hand.

In the next video, you will find an overview of the impact and non-impact screwdrivers: AEG BS12CS vs BSB12C2.

What other factors do the battery capacity depend on??

End discharge voltage

Each time the battery is discharged, the voltage on it gradually drops, and upon reaching the so-called final discharge voltage, it is imperative to disconnect the battery. over, the lower this characteristic is, the correspondingly higher will be the actual capacity of the battery. As a rule, manufacturers indicate on their own batteries the minimum value of the final discharge voltage, which in turn depends on what current the discharge is made with. There are situations when the voltage of the energy source drops below this value (they forgot to disconnect the battery in time or this could not be done, since it was impossible to de-energize the load for a long period). Then a phenomenon called deep battery discharge occurs. If the battery is frequently discharged deeply, it can quickly fail.

An example of calculating the required capacity

As you know, the calculation of the consumed power is carried out in W, and the battery capacity for the UPS is in Ah. To calculate the required battery capacity for powering a particular technique, it is necessary to make some recalculation. For a better understanding, consider a specific example. Let’s say you have a critical load of 500 W that needs to be backed up for 3 hours. Since the amount of accumulated energy depends not only on the capacity of the battery, but also on its voltage, for the calculation we divide the total power of the redundant equipment by their operating voltage (often confused with the open circuit voltage of a fully charged battery). For a standard 12V battery, the required battery capacity is:

Q = (Pt) / Vk

where Q is the required battery capacity, Ah;

P. available load, W;

V is the voltage of each storage battery, V;

t is the backup time, h;

k is the utilization factor of battery capacity (the amount of electrical energy allowed for use by consumers).

The need to introduce the coefficient k is due to the possibility of incomplete battery charging. In addition to this, a strong (deep) discharge following a small number of charge and discharge cycles leads to premature wear and damage of the battery. For example, if a new battery is discharged by 30% of its total capacity, and then immediately recharged, it can withstand about 1000 such cycles. If the discharge value decreases to 70%, then the number of these cycles will decrease by about 200.

In total, we find that to power this load for a specified period of time it will take:

Q = 500 3/12 0.7 = 178.6 Ah.

Teardown of the Hanmatek Electric Screwdriver

This is the minimum required battery capacity for the case under consideration. Ideally, it is better to take a power source with a small margin (about 20%) in order not to completely discharge it every time. this will help maintain the performance of the battery for as long as possible.

Q = 178.6 1.2 = 214.3 Ah.

This means that to solve the problem, it is necessary to purchase batteries with a total capacity of at least 215 Ah. When using a UPS in tandem with a generator, it is recommended to reduce the capacity correction factor to 0.4, since in such a bundle, batteries are most often used to maintain continuous power supply until the power plant is turned on and the entire load is transferred to it. At the same time, if the value of the coefficient 0.4 is to include the loss of battery capacity during its aging, due to the peculiarity of the pulse converter and others, then on average the discharge of the battery can reach 50% of its nominal capacity.

In the case when several batteries are used to back up the load, the amount of energy accumulated in them does not depend at all on the type of their connection. parallel, serial, or mixed. Given this feature, it is necessary to substitute the voltage of one battery in the formula for determining the total capacity of the batteries, but at the same time it is allowed to use only batteries with the same technical characteristics.

Battery indicators, with which the concept of capacity is inextricably linked

Dependence of battery capacity on its discharge current.

This dependence is based on the following fact: when the protected load is connected to the battery without using a converter, then the amount of current consumed by the battery is unchanged. In this case, the operating time of the connected electrical consumers will be determined as the ratio of the taken capacity to the consumed current. In a more familiar form, this formula is written as follows:

Q = I T

where Q is the battery capacity, Ah (mAh);

I is the constant discharge current of the battery, A;

T. battery discharge time, h.

If we are dealing with large values ​​of the consumed current, then the real power indicators are often lower than the nominal ones indicated in the passport.

Dependence of battery capacity on energy

Today, among users, the opinion is quite widespread that the capacity of a storage battery is a value that fully characterizes its electrical energy, accumulated in the battery 100% charged. This statement is not entirely correct. Here it is also necessary to make a reservation that the ability to store energy in a battery directly depends on its voltage and the higher it is, the more energy the battery can store. In fact, electrical energy is defined as the product of the charging current, battery voltage and the time this current flows:

where W is the energy accumulated by the battery, J;

U. battery voltage, V;

I is the constant discharge current of the battery, A;

T. battery discharge time, h.

Based on the fact that the product of the current and the charging time gives us the capacity of the battery (as discussed above), it turns out that the electrical energy of the battery is found by multiplying the nominal voltage of the battery and its capacity:

where W is the energy accumulated by the battery, Wh;

Q. battery capacity, Ah;

U. battery voltage, V.

When several batteries of the same capacity are connected in series, the total indicator of this bundle is equal to the sum of the capacities of all batteries included in its composition. In this case, the energy of the resulting battery pack will be determined as the product of the electricity of one battery by their number.

The concept of the energy capacity of the battery

An equally useful indicator of storage batteries for the consumer is their energy capacity, measured in units such as W / cell. This concept characterizes the capacity of the battery for a certain short period of time, which is most often no more than 15 minutes, in constant power mode. This indicator is most widespread in the United States, but recently it is gaining popularity among consumers in many other countries. For an approximate calculation of the capacity of a storage battery, measured in Ah by the value of its energy capacity in W / cell for a period of 15 minutes, use the formula:

Q = W / 4

where Q is the battery capacity, Ah;

W. energy capacity of the battery, W / cell.

Battery backup capacity

For car batteries, another characteristic is distinguished. a reserve capacity, which indicates the ability of the battery to power the electrical equipment of a moving car when the vehicle’s standard generator is not working. This parameter is also better known in the USA and is called “reserve capacity”. It is measured in minutes of battery discharge with a current of 25 A. For an approximate estimate of the nominal capacity of the battery according to its reserve capacity indicated in minutes, you must use the formula:

Q = T / 2

where Q is the battery capacity, Ah;

T. battery backup capacity, min.

What is battery capacity? Methodology for its calculation

Battery capacity and charge (charge)

Another fairly popular misconception is the identification of the concepts of battery capacity for and its charge (charge). Let’s dot all the “and”. Capacity is understood as the maximum potential of the battery, that is, the amount of energy that it can store in a fully charged state. The charge, in turn, represents this energy required to power the load in an autonomous mode. Hence the conclusion that the amount of charge of the same battery can be different depending on the charging time of the battery, and the value of its capacity in the discharged and charged states is the same. Here you can draw an analogy with a glass into which water is poured. The volume of the device will represent a capacity. this is a value that does not depend on whether the glass is full or empty, and the most poured water is a charge.

Temperature

Such an important factor as the ambient temperature in the place where the battery is used has a very strong effect on the capacity of the latter. In the case of an increase in temperature from 20 ° C to 40 ° C, the battery capacity indicator increases by 5%, and when it decreases to 0 ° C, it decreases on average by 15%. A further decrease in the air temperature leads to a drop in the specified parameter by another 25% relative to the nominal value.

Discharge current

Those battery capacity indicators that can be found in their technical documentation and on the product case are indicated by the manufacturer based on the results of test measurements made according to the above formula (Q = I T) with a standard discharge duration (10, 20, 100 hours, etc.). etc.). Accordingly, the capacitance is also designated. Q10, Q20 and Q100, as well as the discharge current. I10, I20 and I100. In this case, the amount of current flowing through the load at a discharge time of 20 hours is determined by the formula:

Cordless Screwdriver or Cordless Drill?

I20 = Q20 / 20

Following this logic, we can assume that with a discharge lasting a quarter of an hour (15 minutes), the current will be equal to Q20 x 4. However, this is not the case, as practice shows, in the case of a 15-minute discharge, the capacity of a standard lead battery will be no more than half of its nominal capacity. Accordingly, the value of the parameter I0.25 will be slightly less than Q20 x 2. Hence, we can conclude that characteristics such as time and discharge current are not proportional to each other.