Once upon a time there was an old man and an old woman, they had a daughter, Alyonushka, and a son, Ivanushka. An old man...
Electric heating elements are used in household and industrial equipment. The use of various heaters is known to all. These are electric stoves, ovens and ovens, electric coffee makers, electric kettles and heaters of various designs.
Electric water heaters, more often referred to as, also contain heating elements. The basis of many heating elements is a wire with high electrical resistance. And most often this wire is made of nichrome.
Open nichrome helix
The oldest heating element is perhaps the usual nichrome coil. Once upon a time, homemade electric stoves, water boilers and goat heaters were in use. Having a nichrome wire at hand, which could be "get hold of" in production, it was not a problem to make a spiral of the required power.
The end of the wire of the required length is inserted into the cut of the wrench, the wire itself is passed between two wooden blocks. The vise must be clamped so that the entire structure is held as shown in the figure. The clamping force should be such that the wire passes through the bars with some force. If the clamping force is large, then the wire will simply break.
Figure 1. Coiling a nichrome spiral
By rotating the knob, the wire is pulled through the wooden bars, and carefully, coil to coil, is placed on a metal rod. In the arsenal of electricians there was a whole set of knobs of various diameters from 1.5 to 10 mm, which made it possible to wind spirals for all occasions.
It was known what diameter the wire was and what length was required to wind the spiral of the required power. These magic numbers can still be found on the Internet. Figure 2 shows a table that shows data on spirals of various capacities at a supply voltage of 220V.
Figure 2. Calculation of the electric spiral of the heating element (click on the figure to enlarge)
Everything is simple and clear here. Having asked for the required power and the diameter of the nichrome wire available at hand, it remains only to cut off a piece of the desired length and wind it onto a mandrel of the appropriate diameter. In this case, the length of the resulting spiral is indicated in the table. But what if there is a wire with a diameter not indicated in the table? In this case, the spiral will simply have to be calculated.
If necessary, calculate the spiral is quite simple. As an example, the calculation of a spiral made of nichrome wire with a diameter of 0.45 mm (there is no such diameter in the table) with a power of 600 W for a voltage of 220 V is given. All calculations are performed according to Ohm's law.
How to convert amps to watts and vice versa, watts to amps:
I = P/U = 600/220 = 2.72A
To do this, it is enough to divide the given power by the voltage and get the amount of current passing through the spiral. Power in watts, voltage in volts, result in amps. All according to the SI system.
The formula for calculating the resistance of the conductor R=ρ*L/S,
where ρ is the specific resistance of the conductor (for nichrome 1.0÷1.2 Ohm.mm2/m), L is the length of the conductor in meters, S is the cross section of the conductor in square millimeters. For a conductor with a diameter of 0.45 mm, the cross section will be 0.159 mm2.
Hence L = S * R / ρ = 0.159 * 81 / 1.1 = 1170 mm, or 11.7 m.
In general, it turns out not so complicated calculation. Yes, in fact, the manufacture of a spiral is not so difficult, which, undoubtedly, is the advantage of ordinary nichrome spirals. But this advantage is covered by many disadvantages inherent in open spirals.
First of all, this is a rather high heating temperature - 700 ... 800˚C. The heated coil has a faint red glow, accidental contact with it can cause a burn. In addition, electric shock may result. A red-hot spiral burns out the oxygen of the air, attracts dust particles, which, when burnt out, give a very unpleasant odor.
But the main disadvantage of open spirals should be considered their high fire hazard. Therefore, the fire department simply prohibits the use of heaters with an open coil. These heaters, first of all, include the so-called "goat", the design of which is shown in Figure 3.
Figure 3. Homemade heater "goat"
Here is such a wild "goat" turned out: it was made deliberately carelessly, simply, even very badly. A fire with such a heater will not have to wait long. A more advanced design of such a heater is shown in Figure 4.
Figure 4. "Goat" home
It is easy to see that the spiral is closed with a metal casing, this is what prevents touching the heated current-carrying parts. The fire hazard of such a device is much less than that shown in the previous figure.
Once upon a time, reflector heaters were produced in the USSR. In the center of the nickel-plated reflector there was a ceramic cartridge, into which, like a light bulb with an E27 base, a 500W heater was screwed. The fire hazard of such a reflector is also very high. Well, somehow they didn’t think in those days what the use of such heaters could lead to.
Figure 5. Reflector type heater
It is quite obvious that various heaters with an open coil can, contrary to the requirements of the fire inspectorate, be used only under vigilant supervision: left the room - turn off the heater! Better yet, just stop using heaters of this type.
Closed coil heating elements
To get rid of the open coil, Tubular Electric Heaters - TENs were invented. The design of the heating element is shown in Figure 6.
Figure 6. The design of the heating element
The nichrome coil 1 is hidden inside a thin-walled metal tube 2. The coil is insulated from the tube by filler 3 with high thermal conductivity and high electrical resistance. The most commonly used filler is periclase (a crystalline mixture of magnesium oxide MgO, sometimes with impurities of other oxides).
After filling with an insulating compound, the tube is pressed, and under high pressure, the periclase turns into a monolith. After such an operation, the spiral is rigidly fixed, therefore, electrical contact with the body - the tube is completely excluded. The design is so strong that any heating element can be bent if the design of the heater requires it. Some heating elements have a very bizarre shape.
The spiral is connected to the metal terminals 4, which go out through the insulators 5. The lead wires are connected to the threaded ends of the terminals 4 with the help of nuts and washers 7. The heating elements are fastened in the device case with the help of nuts and washers 6, providing, if necessary, the tightness of the connection.
Subject to the operating conditions, such a design is quite reliable and durable. This is what led to the very widespread use of heating elements in devices for various purposes and designs.
According to the operating conditions, heating elements are divided into two large groups: air and water. But it's just a name. In fact, air heating elements are designed to operate in various gaseous media. Even ordinary atmospheric air is a mixture of several gases: oxygen, nitrogen, carbon dioxide, there are even impurities of argon, neon, krypton, etc.
The air environment is very diverse. It can be calm atmospheric air or a stream of air moving at a speed of up to several meters per second, as in fan heaters or heat guns.
The heating of the heating element shell can reach 450 ˚C and even more. Therefore, various materials are used for the manufacture of the outer tubular shell. It can be ordinary carbon steel, stainless steel or high temperature, heat resistant steel. Everything depends on the environment.
To improve heat transfer, some heating elements are equipped with fins on tubes in the form of a wound metal tape. Such heaters are called finned. The use of such elements is most appropriate in a moving air environment, for example, in fan heaters and heat guns.
Water heating elements are also not necessarily used in water, this is the general name for various liquid media. It can be oil, fuel oil and even various aggressive liquids. Liquid heating elements, distillers, electric sea water desalters and simply in titanium for boiling drinking water.
The thermal conductivity and heat capacity of water is much higher than that of air and other gaseous media, which provides, in comparison with the air environment, better, faster heat removal from the heating element. Therefore, with the same electric power, the water heater has smaller geometric dimensions.
Here you can give a simple example: when water boils away in an ordinary electric kettle, the heating element can heat up red-hot, and then burn out to holes. The same picture can be observed with ordinary boilers designed to boil water in a glass or in a bucket.
The given example clearly shows that water heaters should never be used to work in an air environment. Air heaters can be used to heat water, but you just have to wait a long time until the water boils.
The layer of scale that forms during operation will not benefit water heating elements. Scale, as a rule, has a porous structure, and its thermal conductivity is low. Therefore, the heat generated by the spiral does not go well into the liquid, but the spiral itself inside the heater heats up to a very high temperature, which sooner or later will lead to its burnout.
To prevent this from happening, it is advisable to periodically clean the heating elements using various chemicals. For example, TV commercials recommend Calgon for protecting washing machine heaters. Although there are many different opinions about this tool.
How to get rid of scale
In addition to chemical anti-scale agents, various devices are used. First of all, these are magnetic water converters. In a powerful magnetic field, crystals of "hard" salts change their structure, turn into flakes, become smaller. From such flakes, scale is formed less actively, most of the flakes are simply washed away with a stream of water. This is how the protection of heaters and pipelines from scale is achieved. Magnetic filters-converters are produced by many foreign firms, such firms exist in Russia as well. Such filters are available as mortise and overhead type.
Electronic water softeners
Recently, electronic water softeners have become more and more popular. Outwardly, everything looks very simple. A small box is installed on the pipe, from which antenna wires come out. The wires are wound around the pipe, without even having to peel off the paint. You can install the device in any accessible place, as shown in Figure 7.
Figure 7. Electronic water softener
The only thing you need to connect the device is a 220V socket. The device is designed to be turned on for a long time, it does not need to be turned off periodically, since turning it off will cause the water to become hard again and scale will form again.
The principle of operation of the device is reduced to the emission of oscillations in the range of ultrasonic frequencies, which can reach up to 50 kHz. The oscillation frequency is regulated by the control panel of the device. Emissions are produced in packets several times per second, which is achieved using the built-in microcontroller. The vibration power is small, therefore, such devices do not pose any threat to human health.
It is quite easy to determine the feasibility of installing such devices. It all comes down to determining how hard the water is flowing from the water pipe. You don’t even need any “abstruse” devices here: if after washing your skin becomes dry, white stains appear on the tile from water splashes, scale appears in the kettle, the washing machine erases more slowly than at the beginning of operation - definitely hard water flows from the tap. All this can lead to failure of the heating elements, and, consequently, the kettles or washing machines themselves.
Hard water does not dissolve well various detergents - from ordinary soap to trendy washing powders. As a result, you have to put more powders, but this does not help much, since hardness salt crystals linger in the fabrics, the quality of washing leaves much to be desired. All of the listed signs of water hardness eloquently indicate that it is necessary to install water softeners.
Connecting and checking heating elements
When connecting the heating element, a wire of a suitable cross section must be used. It all depends on the current flowing through the heater. Most often, two parameters are known. This is the power of the heater itself and the supply voltage. In order to determine the current, it is enough to divide the power by the supply voltage.
A simple example. Let there be a heating element with a power of 1 kW (1000 W) for a supply voltage of 220 V. For such a heater, it turns out that the current will be
I \u003d P / U \u003d 1000/220 \u003d 4.545A.
According to the tables posted in the PUE, such a current can be provided by a wire with a cross section of 0.5 mm2 (11A), but in order to ensure mechanical strength, it is better to use a wire with a cross section of at least 2.5 mm2. Just such a wire is most often used to supply electricity to sockets.
But before you make the connection, you should make sure that even the new, just purchased heating element is working. First of all, it is necessary to measure its resistance and check the integrity of the insulation. The resistance of the heating element is quite simple to calculate. To do this, you need to square the supply voltage, and divide by the power. For example, for a 1000W heater, this calculation looks like this:
220*220/1000=48.4ohm.
Such resistance should show a multimeter when connected to the terminals of the heating element. If the spiral is broken, then, naturally, the multimeter will show a break. If you take a heating element of a different power, then the resistance, of course, will be different.
To check the integrity of the insulation, measure the resistance between any of the terminals and the metal case of the heating element. The resistance of the filler-insulator is such that at any measurement limit the multimeter should show a break. If it turns out that the resistance is zero, then the spiral has contact with the metal body of the heater. This can happen even with a new, just bought heating element.
In general, it is used to check insulation, but not always and not everyone has it at hand. So checking with a regular multimeter is quite suitable. At the very least, such a check should be done.
As already mentioned, heating elements can be bent even after filling with an insulator. There are heaters of the most diverse forms: in the form of a straight tube, U-shaped, coiled into a ring, a snake or a spiral. It all depends on the device of the heating device in which the heating element is supposed to be installed. For example, in the instantaneous water heater of a washing machine, coiled heating elements are used.
Some heating elements have protection elements. The simplest protection is a thermal fuse. If it burned out, then you have to change the entire heating element, but it will not come to a fire. There is also a more complex protection system that allows you to use the heating element after it has been triggered.
One of these protections is protection based on a bimetallic plate: heat from an overheated heating element bends the bimetallic plate, which opens the contact and de-energizes the heating element. After the temperature drops to an acceptable value, the bimetallic plate unbends, the contact closes and the heating element is ready for operation again.
Heating elements with thermostat
In the absence of hot water supply, you have to use boilers. The design of the boilers is quite simple. This is a metal container hidden in a “fur coat” made of a heat insulator, on top of which there is a decorative metal case. A thermometer is embedded in the body, showing the temperature of the water. The design of the boiler is shown in Figure 8.
Figure 8. Storage type boiler
Some boilers contain a magnesium anode. Its purpose is corrosion protection of the heater and the inner tank of the boiler. The magnesium anode is a consumable item, it has to be changed periodically when servicing the boiler. But in some boilers, apparently of a cheap price category, such protection is not provided.
As a heating element in boilers, a heating element with a thermostat is used, the design of one of them is shown in Figure 9.
Figure 9. Heating element with thermostat
A microswitch is located in a plastic box, which is triggered by a liquid temperature sensor (a straight tube next to the heating element). The shape of the heating element itself can be very diverse, the figure shows the simplest. It all depends on the power and design of the boiler. The degree of heating is regulated by the position of the mechanical contact, controlled by a white round knob located at the bottom of the box. There are also terminals for the supply of electric current. The heater is fastened with a thread.
Wet and dry heaters
Such a heater is in direct contact with water, therefore such a heating element is called "wet". The service life of a "wet" heating element is in the range of 2 ... 5 years, after which it has to be changed. In general, the service life is short.
To increase the service life of the heating element and the entire boiler as a whole, the French company Atlantic in the 90s of the last century developed the design of a “dry” heating element. To put it simply, the heater was hidden in a metal protective flask, which excludes direct contact with water: the heating element is heated inside the flask, which transfers heat to the water.
Naturally, the temperature of the flask is much lower than the actual heating element, so the formation of scale at the same water hardness is not so intense, more heat is transferred to the water. The service life of such heaters reaches 10…15 years. This is true for good operating conditions, especially the stability of the supply voltage. But even in good conditions, "dry" heating elements also develop their resource, and they have to be changed.
This is where another advantage of the "dry" heating element technology is revealed: when replacing the heater, there is no need to drain the water from the boiler, for which it should be disconnected from the pipeline. Simply unscrew the heater and replace it with a new one.
Atlantic, of course, patented its invention, after which it began to license it to other firms. Currently, boilers with a "dry" heating element are also produced by other companies, for example, Electrolux and Gorenje. The design of a boiler with a "dry" heating element is shown in Figure 10.
Figure 10. Boiler with dry heater
By the way, the figure shows a boiler with a ceramic steatite heater. The device of such a heater is shown in Figure 11.
Figure 11. Ceramic heater
Mounted on a ceramic base is an ordinary open helix of high resistance wire. The heating temperature of the spiral reaches 800 degrees and is transferred to the environment (air under the protective shell) by convection and heat radiation. Naturally, such a heater in relation to boilers can only work in a protective shell, in an air environment, direct contact with water is simply excluded.
The spiral can be wound in several sections, as evidenced by the presence of several terminals for connection. This allows you to change the power of the heater. The maximum specific power of such heaters does not exceed 9 W/cm 2 .
The condition for the normal operation of such a heater is the absence of mechanical loads, bends and vibrations. The surface must be free of rust and oil stains. And, of course, the more stable the supply voltage is, without surges and surges, the more durable the heater's operation.
But electrical engineering does not stand still. Technologies are developing and improving, therefore, in addition to heating elements, a wide variety of heating elements have now been developed and successfully used. These are ceramic heating elements, carbon heating elements, infrared heating elements, but that will be a topic for another article.
When repairing or when making an electric soldering iron or any other heating device on your own, you have to wind the heating winding from nichrome wire. The initial data for the calculation and selection of wire is the resistance of the winding of the soldering iron or heater, which is determined based on its power and supply voltage. You can calculate what the resistance of the winding of a soldering iron or heater should be using the table.
Knowing the supply voltage and measuring resistance any heating appliance, such as a soldering iron, or an electric iron, you can find out the power consumption of this household appliance. b. For example, the resistance of a 1.5 kW electric kettle will be 32.2 ohms.
| Table for determining the resistance of a nichrome spiral depending on the power and supply voltage of electrical appliances, Ohm | |||||
|---|---|---|---|---|---|
| Power consumption soldering iron, W | Soldering iron supply voltage, V | ||||
| 12 | 24 | 36 | 127 | 220 | |
| 12 | 12 | 48,0 | 108 | 1344 | 4033 |
| 24 | 6,0 | 24,0 | 54 | 672 | 2016 |
| 36 | 4,0 | 16,0 | 36 | 448 | 1344 |
| 42 | 3,4 | 13,7 | 31 | 384 | 1152 |
| 60 | 2,4 | 9,6 | 22 | 269 | 806 |
| 75 | 1.9 | 7.7 | 17 | 215 | 645 |
| 100 | 1,4 | 5,7 | 13 | 161 | 484 |
| 150 | 0,96 | 3,84 | 8,6 | 107 | 332 |
| 200 | 0,72 | 2,88 | 6,5 | 80,6 | 242 |
| 300 | 0,48 | 1,92 | 4,3 | 53,8 | 161 |
| 400 | 0,36 | 1,44 | 3,2 | 40,3 | 121 |
| 500 | 0,29 | 1,15 | 2,6 | 32,3 | 96,8 |
| 700 | 0,21 | 0,83 | 1,85 | 23,0 | 69,1 |
| 900 | 0,16 | 0,64 | 1,44 | 17,9 | 53,8 |
| 1000 | 0,14 | 0,57 | 1,30 | 16,1 | 48,4 |
| 1500 | 0,10 | 0,38 | 0,86 | 10,8 | 32,3 |
| 2000 | 0,07 | 0,29 | 0,65 | 8,06 | 24,2 |
| 2500 | 0,06 | 0,23 | 0,52 | 6,45 | 19,4 |
| 3000 | 0,05 | 0,19 | 0,43 | 5,38 | 16,1 |
Let's look at an example of how to use the table. Let's say you need to rewind a 60 W soldering iron designed for a supply voltage of 220 V. Select 60 W from the leftmost column of the table. On the upper horizontal line, select 220 V. As a result of the calculation, it turns out that the resistance of the soldering iron winding, regardless of the material of the winding, should be equal to 806 ohms.
If you needed to make a soldering iron with a power of 60 W, designed for a voltage of 220 V, a soldering iron for power from a 36 V network, then the resistance of the new winding should already be 22 ohms. You can independently calculate the winding resistance of any electric heater using an online calculator.
After determining the required resistance value of the soldering iron winding, from the table below, the appropriate diameter of the nichrome wire is selected based on the geometric dimensions of the winding. Nichrome wire is a chromium-nickel alloy that can withstand heating temperatures up to 1000˚C and is marked X20H80. This means that the alloy contains 20% chromium and 80% nickel.
To wind a soldering iron spiral with a resistance of 806 ohms from the example above, you will need 5.75 meters of nichrome wire with a diameter of 0.1 mm (you need to divide 806 by 140), or 25.4 m of wire with a diameter of 0.2 mm, and so on.
When winding the soldering iron spiral, the turns are stacked close to each other. When heated, the red-hot surface of the nichrome wire oxidizes and forms an insulating surface. If the entire length of the wire does not fit on the sleeve in one layer, then the wound layer is covered with mica and the second one is wound.
For electrical and thermal insulation of the heating element winding, the best materials are mica, fiberglass cloth and asbestos. Asbestos has an interesting property, it can be soaked with water and it becomes soft, allows you to give it any shape, and after drying it has sufficient mechanical strength. When insulating the winding of the soldering iron with wet asbestos, it should be taken into account that wet asbestos conducts eclectic current well and it will be possible to turn on the soldering iron in the mains only after the asbestos has completely dried.
When winding a nichrome spiral for heating elements, the operation is often performed by trial and error, and then voltage is applied to the spiral and by heating the nichrome wire, the threads select the required number of turns.
Usually, such a procedure takes a long time, and nichrome loses its characteristics with multiple kinks, which leads to rapid burnout in places of deformation. In the worst case, nichrome scrap is obtained from business nichrome.
With its help, you can accurately determine the length of the winding turn to turn. Depending on the Ø of the nichrome wire and the Ø of the rod on which the nichrome spiral is wound. It is not difficult to recalculate the length of a nichrome spiral to a different voltage using a simple mathematical proportion.
The length of the nichrome spiral depending on the diameter of the nichrome and the diameter of the rod
|
Ø nichrome 0.2 mm |
Ø nichrome 0.3 mm | nichrome 0.4 mm | Ø nichrome 0.5 mm | Ø nichrome 0.6 mm | Ø nichrome 0.7 mm | ||||||
| rod Ø, mm | spiral length, cm |
Ø rod, mm |
spiral length, cm |
Ø rod, mm |
spiral length, cm |
Ø rod, mm |
spiral length, cm |
Ø rod, mm |
spiral length, cm |
Ø rod, mm |
spiral length, cm |
| 1,5 | 49 | 1,5 | 59 | 1,5 | 77 | 2 | 64 | 2 | 76 | 2 | 84 |
| 2 | 30 | 2 | 43 | 2 | 68 | 3 | 46 | 3 | 53 | 3 | 64 |
| 3 | 21 | 3 | 30 | 3 | 40 | 4 | 36 | 4 | 40 | 4 | 49 |
| 4 | 16 | 4 | 22 | 4 | 28 | 5 | 30 | 5 | 33 | 5 | 40 |
| 5 | 13 | 5 | 18 | 5 | 24 | 6 | 26 | 6 | 30 | 6 | 34 |
| 6 | 20 | 8 | 22 | 8 | 26 | ||||||
For example, it is required to determine the length of a nichrome spiral for a voltage of 380 V from a wire Ø 0.3 mm, a winding rod Ø 4 mm. The table shows that the length of such a spiral for a voltage of 220 V will be 22 cm. Let's make a simple ratio:
220 V - 22 cm
380 V - X cm
then:
X = 380 22 / 220 = 38 cm
Having wound a nichrome spiral, connect it without cutting it to a voltage source and make sure that the winding is correct. For closed spirals, the winding length is increased by 1/3 of the value given in the table.
Calculation of electric heating elements from nichrome wire
The length of the nichrome wire for the manufacture of the spiral is determined based on the required power.
Example: Determine the length of nichrome wire for a tile heating element with a power P= 600 W at U networks = 220 V.
Solution:
1) I=P/U= 600/220 = 2.72A
2) R = U/I= 220 / 2.72 = 81 ohms
3) Based on these data (see Table 1), we select d=0,45; S=0,159
then the length of nichrome
l = SR / ρ\u003d 0.159 81 / 1.1 \u003d 11.6 m
where l- wire length (m)
S- wire section (mm 2)
R- wire resistance (Ohm)
ρ - resistivity (for nichrome ρ=1.0÷1.2 Ohm mm 2 /m)
| Permissible current (l), A | |||||||
| Ø nichrome at 700 °C , mm |
0,17 |
0,45 |
0,55 |
0.65 It is convenient and profitable to buy a nichrome spiral in the PARTAL company - online order Delivery of orders in Russia, Kazakhstan and Belarus |
Calculation of a nichrome spiral. Ready for you to make a nichrome spiral. Nichrome length at 220 volts
Calculation of a nichrome spiral. Ready for you to make a nichrome spiral
When winding a nichrome spiral for heating elements, the operation is often performed by trial and error, and then voltage is applied to the spiral and by heating the nichrome wire, the threads select the required number of turns.
Usually, such a procedure takes a long time, and nichrome loses its characteristics with multiple kinks, which leads to rapid burnout in places of deformation. In the worst case, nichrome scrap is obtained from business nichrome.
With its help, you can accurately determine the length of the winding turn to turn. Depending on the Ø of the nichrome wire and the Ø of the rod on which the nichrome spiral is wound. It is not difficult to recalculate the length of a nichrome spiral to a different voltage using a simple mathematical proportion.
|
Ø nichrome 0.2 mm |
Ø nichrome 0.3 mm | nichrome 0.4 mm | Ø nichrome 0.5 mm | Ø nichrome 0.6 mm | Ø nichrome 0.7 mm | ||||||
| rod Ø, mm | spiral length, cm |
rod, mm |
spiral length, cm |
rod, mm |
spiral length, cm |
rod, mm |
spiral length, cm |
rod, mm |
spiral length, cm |
rod, mm |
spiral length, cm |
| 1,5 | 49 | 1,5 | 59 | 1,5 | 77 | 2 | 64 | 2 | 76 | 2 | 84 |
| 2 | 30 | 2 | 43 | 2 | 68 | 3 | 46 | 3 | 53 | 3 | 64 |
| 3 | 21 | 3 | 30 | 3 | 40 | 4 | 36 | 4 | 40 | 4 | 49 |
| 4 | 16 | 4 | 22 | 4 | 28 | 5 | 30 | 5 | 33 | 5 | 40 |
| 5 | 13 | 5 | 18 | 5 | 24 | 6 | 26 | 6 | 30 | 6 | 34 |
| 6 | 20 | 8 | 22 | 8 | 26 | ||||||
For example, it is required to determine the length of a nichrome spiral for a voltage of 380 V from a wire Ø 0.3 mm, a winding rod Ø 4 mm. The table shows that the length of such a spiral for a voltage of 220 V will be 22 cm. Let's make a simple ratio:
220 V - 22 cm
380 V - X cm
X = 380 22 / 220 = 38 cm
Calculation of electric heating elements from nichrome wire
The length of the nichrome wire for the manufacture of the spiral is determined based on the required power.
Example: Determine the length of a nichrome wire for a tile heating element with a power of P = 600 W at Unetwork = 220 V.
1) I = P/U = 600/220 = 2.72 A
2) R \u003d U / I \u003d 220 / 2.72 \u003d 81 ohms
3) Based on these data (see Table 1), we choose d=0.45; S=0.159
then the length of nichrome
l \u003d SR / ρ \u003d 0.159 81 / 1.1 \u003d 11.6 m
where l - wire length (m)
S - wire section (mm2)
R - wire resistance (Ohm)
ρ - resistivity (for nichrome ρ=1.0÷1.2 Ohm mm2/m)
Our Company PARTAL is ready to produce a nichrome spiral according to the specifications and sketches of the customer
It is profitable to buy a nichrome spiral in the PARTAL company
Nichrome for high quality spiral only Russian production. Strict compliance with quality and brand
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Calculation of nichrome spiral | Useful
The calculation of a nichrome spiral is, in fact, a very important process. Very often, in factories, industries, factories, this is neglected and the calculation is made “by eye”, after which the spiral is connected to the network, and then the required number of turns is selected depending on the heating of the nichrome wire. Perhaps this procedure is very simple, but it takes a long time and part of the nichrome is simply wasted.
However, this procedure can be performed much more accurately, easier and faster. In order to rationalize your work, to calculate a nichrome spiral for a voltage of 220 volts, you can use the table below. Based on the fact that the resistivity of nichrome is (Ohm mm2 / m) C, you can quickly calculate the winding length turn to turn depending on the diameter of the rod on which the nichrome thread is wound, and directly on the very thickness of the nichrome wire. And using a simple mathematical proportion, you can easily calculate the length of the spiral for a different voltage.
For example, you need to determine the length of a nichrome spiral for a voltage of 127 volts from a wire whose thickness is 0.3 mm, and a winding rod 4 mm in diameter. Looking at the table, it can be seen that the length of this spiral for a voltage of 220 volts will be 22 cm. We make a simple ratio: 220 V - 22 cm 127 V - X cm then: X \u003d 127 22 / 220 \u003d 12.7 cm
Having wound a nichrome spiral, carefully connect it, without cutting it, to a voltage source and make sure in your calculations, or rather, in the calculations of the correct winding. And it is worth remembering that for closed spirals, the winding length is increased by a third of the value given in this table.
Nichrome wire, nichrome weight calculation, nichrome application
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We produce electric spirals from NICHROMA according to the specifications and sketches of the customer
Nichrome spiral
Everyone knows what a nichrome spiral is. This is a heating element in the form of a wire coiled with a screw for compact placement.
This wire is made from nichrome, a precision alloy whose main components are nickel and chromium.
The "classic" composition of this alloy is 80% nickel, 20% chromium.
The composition of the names of these metals formed the name that denotes the group of chromium-nickel alloys - "nichrome".
The most famous brands of nichrome are X20H80 and X15H60. The first of them is close to the "classics". It contains 72-73% nickel and 20-23% chromium.
The second is designed to reduce the cost and improve the machinability of the wire.
On the basis of these alloys, their modifications with higher survivability and resistance to oxidation at high temperatures were obtained.
These are the Kh20N80-N (-N-VI) and Kh15N60 (-N-VI) brands. They are used for heating elements in contact with air. The recommended maximum operating temperature is from 1100 to 1220 °C
The use of nichrome wire
The main quality of nichrome is its high resistance to electric current. It defines the scope of the alloy.
The nichrome spiral is used in two qualities - as a heating element or as a material for the electrical resistance of electrical circuits.
For heaters, an electric spiral made of Kh20N80-N and Kh15N60-N alloys is used.
Application examples:
- household thermal reflectors and fan heaters;
- Heating elements for household heating appliances and electric heating;
- heaters for industrial furnaces and thermal equipment.
Alloys Kh15N60-N-VI and Kh20N80-N-VI obtained in vacuum induction furnaces are used in industrial equipment of increased reliability.
A nichrome spiral of grades Х15Н60, Х20Н80, Х20Н80-VI, Н80ХУД-VI differs in that its electrical resistance changes little with temperature.
Resistors, connectors of electronic circuits, critical parts of vacuum devices are made from it.
How to wind a spiral from nichrome
A resistive or heating coil can be made at home. To do this, you need a nichrome wire of a suitable brand and the correct calculation of the required length.
The calculation of a nichrome spiral is based on the resistivity of the wire and the required power or resistance, depending on the purpose of the spiral. When calculating the power, it is necessary to take into account the maximum allowable current at which the coil heats up to a certain temperature.
Temperature accounting
For example, a wire with a diameter of 0.3 mm at a current of 2.7 A will heat up to 700 ° C, and a current of 3.4 A will heat it up to 900 ° C.
To calculate the temperature and current, there are reference tables. But you still need to consider the operating conditions of the heater.
When immersed in water, heat transfer increases, then the maximum current can be increased by up to 50% of the calculated one.
A closed tubular heater, on the contrary, impairs heat dissipation. In this case, the permissible current must also be reduced by 10-50%.
The intensity of heat removal, and hence the temperature of the heater, is affected by the winding pitch of the spiral.
Tightly spaced coils provide more heat, larger pitch enhances cooling.
It should be noted that all tabular calculations are given for a heater located horizontally. When the angle to the horizon changes, the conditions for heat removal worsen.
Calculation of the resistance of a nichrome spiral and its length
Having decided on the power, we proceed to the calculation of the required resistance.
If the determining parameter is power, then first we find the required current according to the formula I \u003d P / U.
Having the strength of the current, we determine the required resistance. To do this, we use Ohm's law: R=U/I.
The designations here are generally accepted:
- P is the released power;
- U is the voltage at the ends of the spiral;
- R is the resistance of the coil;
- I - current strength.
The calculation of the resistance of nichrome wire is ready.
Now let's determine the length we need. It depends on the resistivity and wire diameter.
You can make a calculation based on the resistivity of nichrome: L=(Rπd2)/4ρ.
- L is the desired length;
- R is the resistance of the wire;
- d is the wire diameter;
- ρ is the resistivity of nichrome;
- π is the constant 3.14.
But it is easier to take a ready-made linear resistance from the tables of GOST 12766.1-90. You can also take temperature corrections there, if you need to take into account the change in resistance during heating.
In this case, the calculation will look like this: L=R/ρld, where ρld is the resistance of one meter of wire with a diameter of d.
Spiral winding
Now let's make a geometric calculation of the nichrome spiral. We have chosen the wire diameter d, determined the required length L and have a rod with a diameter D for winding. How many turns do you need to make? The length of one turn is: π(D+d/2). The number of turns is N=L/(π(D+d/2)). Calculation completed.
practical solution
In practice, rarely anyone is engaged in independent winding of wire for a resistor or heater.
It is easier to buy a nichrome spiral with the required parameters and, if necessary, separate the required number of turns from it.
To do this, you should contact the PARTAL company, which since 1995 has been a major supplier of precision alloys, including nichrome wire, tape and coils for heaters.
Our company is able to completely remove the question of where to buy a nichrome spiral, since we are ready to make it to order according to the sketches and specifications of the customer.
partalstalina.ru
Calculation and repair of the heating winding of the soldering iron
When repairing or when making an electric soldering iron or any other heating device on your own, you have to wind the heating winding from nichrome wire. The initial data for the calculation and selection of wire is the resistance of the winding of the soldering iron or heater, which is determined based on its power and supply voltage. You can calculate what the resistance of the winding of a soldering iron or heater should be using the table.
Knowing the supply voltage and measuring the resistance of any heating appliance, such as a soldering iron, electric kettle, electric heater or electric iron, you can find out the power consumed by this household appliance. For example, the resistance of a 1.5 kW electric kettle will be 32.2 ohms.
| 12 | 48,0 | 108 | 1344 | 4033 |
| 6,0 | 24,0 | 54 | 672 | 2016 |
| 4,0 | 16,0 | 36 | 448 | 1344 |
| 3,4 | 13,7 | 31 | 384 | 1152 |
| 2,4 | 9,6 | 22 | 269 | 806 |
| 1.9 | 7.7 | 17 | 215 | 645 |
| 1,4 | 5,7 | 13 | 161 | 484 |
| 0,96 | 3,84 | 8,6 | 107 | 332 |
| 0,72 | 2,88 | 6,5 | 80,6 | 242 |
| 0,48 | 1,92 | 4,3 | 53,8 | 161 |
| 0,36 | 1,44 | 3,2 | 40,3 | 121 |
| 0,29 | 1,15 | 2,6 | 32,3 | 96,8 |
| 0,21 | 0,83 | 1,85 | 23,0 | 69,1 |
| 0,16 | 0,64 | 1,44 | 17,9 | 53,8 |
| 0,14 | 0,57 | 1,30 | 16,1 | 48,4 |
| 0,10 | 0,38 | 0,86 | 10,8 | 32,3 |
| 0,07 | 0,29 | 0,65 | 8,06 | 24,2 |
| 0,06 | 0,23 | 0,52 | 6,45 | 19,4 |
| 0,05 | 0,19 | 0,43 | 5,38 | 16,1 |
Let's look at an example of how to use the table. Let's say you need to rewind a 60 W soldering iron designed for a supply voltage of 220 V. Select 60 W from the leftmost column of the table. On the upper horizontal line, select 220 V. As a result of the calculation, it turns out that the resistance of the soldering iron winding, regardless of the material of the winding, should be equal to 806 ohms.
If you needed to make a soldering iron with a power of 60 W, designed for a voltage of 220 V, a soldering iron for power from a 36 V network, then the resistance of the new winding should already be 22 ohms. You can independently calculate the winding resistance of any electric heater using an online calculator.
After determining the required resistance value of the soldering iron winding, from the table below, the appropriate diameter of the nichrome wire is selected based on the geometric dimensions of the winding. Nichrome wire is a chromium-nickel alloy that can withstand heating temperatures up to 1000˚C and is marked X20H80. This means that the alloy contains 20% chromium and 80% nickel.
To wind a soldering iron spiral with a resistance of 806 ohms from the example above, you will need 5.75 meters of nichrome wire with a diameter of 0.1 mm (you need to divide 806 by 140), or 25.4 m of wire with a diameter of 0.2 mm, and so on.
When winding the soldering iron spiral, the turns are stacked close to each other. When heated, the red-hot surface of the nichrome wire oxidizes and forms an insulating surface. If the entire length of the wire does not fit on the sleeve in one layer, then the wound layer is covered with mica and the second one is wound.
For electrical and thermal insulation of the heating element winding, the best materials are mica, fiberglass cloth and asbestos. Asbestos has an interesting property, it can be soaked with water and it becomes soft, allows you to give it any shape, and after drying it has sufficient mechanical strength. When insulating the winding of the soldering iron with wet asbestos, it should be taken into account that wet asbestos conducts eclectic current well and it will be possible to turn on the soldering iron in the mains only after the asbestos has completely dried.
felstar.mypage.ru
HOW TO CALCULATE A SPIRAL FROM NICHROME?
Post written by admin at 18.01.2015 23:23Categories: 3. Home electrical, Electrical workshop
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The winding of a nichrome spiral for heating devices is often performed “by eye”, and then, including the spiral in the network, the required number of turns is selected by heating the nichrome wire. Usually such a procedure takes a lot of time, and nichrome is wasted.
When using a spiral for a voltage of 220 V, you can use the data given in the table, on the basis that the resistivity of nichrome ρ = (Ohm mm2 / m). Using this formula, you can quickly determine the length of the winding turn to turn, depending on the thickness of the nichrome wire and the diameter of the rod on which the spiral is wound.
For example, if you want to determine the length of a spiral for a voltage of 127 V from a nichrome wire 0.3 mm thick, a winding rod dia. 4 mm. The table shows that the length of such a spiral for a voltage of 220 V will be 22 cm.
Let's make a simple ratio:
220 V - 22 cm
X \u003d 127 * 22 / 220 \u003d 12.7 cm.
After winding the spiral, connect it without cutting it to a voltage source and make sure that the winding is correct. For closed spirals, the winding length is increased by 1/3 of the value given in the table.
Symbols in the table: D - rod diameter, mm; L is the length of the spiral, cm.
| diam. nichrome 0.2 mm | diam. nichrome 0.3 mm | diam. nichrome 0.4 mm | diam. nichrome 0.5 mm | diam. nichrome 0.6 mm | diam. nichrome 0.7 mm | diam. nichrome 0.8 mm | diam. nichrome 0.9 mm | diam. nichrome 1.0 mm | |||||||||
| D | L | D | L | D | L | D | L | D | L | D | L | D | L | D | L | D | L |
| 1,5 | 49 | 1,5 | 59 | 1,5 | 77 | 2 | 64 | 2 | 76 | 2 | 84 | 3 | 68 | 3 | 78 | 3 | 75 |
| 2 | 30 | 2 | 43 | 2 | 68 | 3 | 46 | 3 | 53 | 3 | 62 | 4 | 54 | 4 | 72 | 4 | 63 |
| 3 | 21 | 3 | 30 | 3 | 40 | 4 | 36 | 4 | 40 | 4 | 49 | 5 | 46 | 6 | 68 | 5 | 54 |
| 4 | 16 | 4 | 22 | 4 | 28 | 5 | 30 | 5 | 33 | 5 | 40 | 6 | 40 | 8 | 52 | 6 | 48 |
| 5 | 13 | 5 | 18 | 5 | 24 | 6 | 26 | 6 | 30 | 6 | 34 | 8 | 31 | 8 | 33 | ||
| 6 | 20 | 8 | 22 | 8 | 26 | 10 | 24 | 10 | 30 | ||||||||
| 10 | 22 | ||||||||||||||||
elctricvs.ru
Electrical resistance is one of the most important characteristics of nichrome. It is determined by many factors, in particular, the electrical resistance of nichrome depends on the size of the wire or tape, alloy grade. The general formula for active resistance is: R = ρ l / S R - active electrical resistance (Ohm), ρ - electrical resistivity (Ohm mm), l - conductor length (m), S - cross-sectional area (mm2)
To rationalize this work when using a nichrome spiral for a voltage of 220 V, I propose to use the data given in the table, on the basis that the resistivity of nichrome = (Ohm mm2 / m) C. With its help, you can quickly determine the length of the winding turn to turn, depending on the thickness of the nichrome wire and the diameter of the rod on which the nichrome spiral is wound. It is not difficult to recalculate the length of a nichrome spiral to a different voltage using a simple mathematical proportion.
For example, it is required to determine the length of a nichrome spiral for a voltage of 380 V from a wire 0.3 mm thick, a winding rod Ø 4 mm. The table shows that the length of such a spiral for a voltage of 220 V will be 22 cm. Let's make a simple ratio: 220 V - 22 cm 380 V - X cm then: X = 380 22 / 220 = 38 cm Having wound a nichrome spiral, connect it without cutting it to a voltage source and make sure that the winding is correct. For closed spirals, the winding length is increased by 1/3 of the value given in the table. This table shows the theoretical weight of 1 meter of nichrome wire and tape. It varies depending on the size of the product.
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www.metotech.ru
| Heating element calculation Calculation example. Given: U=220V, t=700°C, type Х20Н80, d=0.5mm-----------L,P-? corresponds to S = 0.196 mm², and the current at 700 ° C I = 5.2 A. The type of alloy X20H80 is nichrome, the specific resistance of which is ρ = 1.11 μOhm m. We determine the resistance R = U / I = 220 / 5.2 = 42.3 Ohm. From here we calculate the length of the wire: L = RS / ρ = 42.3 0.196 / 1.11 = 7.47 m. We determine the power of the heating element: P = U I = 220 5.2 = 1.15 kW .When winding the spiral, the following ratio is observed: D=(7÷10)d, where D is the diameter of the spiral, mm, d is the diameter of the wire, mm. Note: - if the heaters are inside the heated liquid, then the load (current) can be increased by 1 ,1-1.5 times; - in the closed version of the heater, the current should be reduced by 1.2-1.5 times. A smaller coefficient is taken for a thicker wire, a larger one for a thin one. For the first case, the coefficient is chosen exactly the opposite. I will make a reservation: we are talking about a simplified calculation of the heating element. Perhaps someone will need a table of electrical resistance values \u200b\u200bfor 1 m of nichrome wire, as well as its weight Table 1. Permissible current strength of nichrome wire at normal temperature
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www.elektrikii.ru
If a home master, by the nature of the work he performs, needs a muffle furnace, then, of course, he can purchase a finished device in a store or through advertisements. However, such factory-made equipment is very expensive. Therefore, many craftsmen take up the manufacture of such furnaces on their own.
The main "working unit" of an electric muffle furnace is a heater, which in handicraft production is usually made in the form of a spiral of special wire with high resistance and thermal efficiency. Its characteristics must strictly correspond to the power of the equipment being created, the expected temperature conditions of operation, and also meet some other requirements. If you plan to independently manufacture the device, then we recommend using the algorithm proposed below and convenient calculators for calculating the muffle furnace heater.
The calculation requires certain explanations, which we will try to state as clearly as possible.
Algorithm and calculators for calculating the heater of a muffle furnace
What are heating coils made of?
To begin with, just a few words about the wire that is used for winding heating coils. Usually, nichrome or fechral is used for such purposes.
- Nichrome(from abbreviations nickel + chromium) is most often represented by alloys Kh20N80-N, Kh15N60 or Kh15N60-N.
muffle furnace prices
muffle furnace
Her dignity :
- high margin of safety at any heating temperature;
- plastic, easy to process, amenable to welding;
- durability, resistance to corrosion, lack of magnetic qualities.
Flaws :
- high price;
- lower heating rates and thermal stability compared to Fechraleva.
- Fekhraleva(from abbreviations ferrum, chromium, aluminum) - in our time, material from the Kh23Yu 5T alloy is more often used.
Advantages fehral:
- much cheaper than nichrome, due to which the material is mainly popular;
- has more significant indicators of resistance and resistive heating;
- high heat resistance.
Flaws :
- low strength, and after even a single heating over 1000 degrees - pronounced fragility of the spiral;
- outstanding durability;
- the presence of magnetic qualities, susceptibility to corrosion due to the presence of iron in the composition;
- unnecessary chemical activity - it is able to react with the material of the fireclay lining of the furnace;
- excessively large thermal linear expansion.
Each of the masters is free to choose any of the listed materials, having analyzed their pros and cons. The calculation algorithm takes into account the features of such a choice.
Step 1 - determining the power of the furnace and the strength of the current passing through the heater.
In order not to go into unnecessary given case of details, we will immediately say that there are empirical compliance standardsvolumemuffle furnace working chamber and her power. They are shown in the table below:
If there are design sketches of the future device, then the volume of the muffle chamber is easy to determine - the product of height, width and depth. Then the volume is converted to liters and multiplied by the recommended power rates indicated in the table. So we get the power of the furnace in watts.
Table values are given in some ranges, so either use interpolation or take an approximate average value.
The found power, with a known mains voltage (220 volts), allows you to immediately determine the strength of the current that will pass through the heating element.
I=P/U.
I- current strength.
R– the power of the muffle furnace determined above;
U- supply voltage.
This entire first step of calculation can be done very easily and quickly with the help of a calculator: all tabular values \u200b\u200bare already entered into the calculation program.
