Calculation of a nichrome spiral. We are ready to make a nichrome spiral for you. Nichrome length for 220 volts
Calculation of a nichrome spiral. We are ready to make a nichrome spiral for you
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 after heating the nichrome wire, the threads select the required number of turns.
Typically, such a procedure takes a lot of time, and nichrome loses its characteristics with multiple bends, which leads to rapid burning in places of deformation. In the worst case, business nichrome turns into nichrome scrap.
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.
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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 necessary 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 at a voltage of 220 V will be equal to 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 made of nichrome wire
The length of nichrome wire for making a spiral is determined based on required power.
Example: Determine the length of 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 = U/I = 220/2.72 = 81 Ohm
3) Based on these data (see Table 1), we select d=0.45; S=0.159
then the length of nichrome
l = SR / ρ = 0.159 81 /1.1 = 11.6 m
where l is wire length (m)
S - wire cross-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 customer’s specifications and sketches
It is profitable to buy a nichrome spiral from PARTAL
Nichrome for spiral High Quality only Russian production. Strict compliance in quality and brand
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Calculation of nichrome spiral | Useful
Calculating a nichrome spiral is, in fact, a very important process. Very often, in plants, factories, factories, this is neglected and calculations are made “by eye”, after which they connect the spiral to the network, and then select the required number of turns depending on the heating of the nichrome wire. This procedure may be very simple, but it takes a long period of 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. From the calculation that the resistivity of nichrome is equal to (Ohm mm2 / m)C, you can quickly calculate the length of winding turn to turn depending on the diameter of the rod on which the nichrome thread is wound, and directly on the thickness of the nichrome wire itself. 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 the winding rod is 4 mm in diameter. Looking at the table, you can see that the length of this spiral at a voltage of 220 Volts will be 22 cm. We make a simple ratio: 220 V - 22 cm 127 V - X cm then: X = 127 22 / 220 = 12.7 cm
Having wound the nichrome spiral, carefully connect it, without cutting it, to the voltage source and make sure of your calculations, or rather, the calculations of the correctness of 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, calculation of nichrome weight, use of nichrome
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We produce electrical spirals from NICHROMA according to the customer’s specifications and sketches
Nichrome spiral
Everyone knows what a nichrome spiral is. This is a heating element in the form of a wire, rolled up 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 X20N80 and X15N60. 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 increase the machinability of the wire.
Based on these alloys, modifications with higher survivability and resistance to oxidation at high temperatures were obtained.
These are brands X20N80-N (-N-VI) and X15N60 (-N-VI). They are used for heating elements in contact with air. Recommended maximum operating temperature – from 1100 to 1220 °C
Application of nichrome wire
The main quality of nichrome is its high resistance to electric current. It determines the applications of the alloy.
Nichrome spiral is used in two qualities - as a heating element or as a material for electrical resistances electrical diagrams.
For heaters, an electric spiral made of X20N80-N and X15N60-N alloys is used.
Application examples:
- household thermoreflectors and fan heaters;
- Heating elements for household heating devices and electric heating;
- heaters for industrial furnaces and thermal equipment.
Alloys Kh15N60-N-VI and Kh20N80-N-VI, produced in vacuum induction furnaces, used in industrial equipment increased reliability.
A spiral made of nichrome grades X15N60, X20N80, X20N80-VI, N80HYUD-VI is distinguished by the fact that its electrical resistance changes little with temperature changes.
It is used to make resistors, connectors for electronic circuits, and critical parts of vacuum devices.
How to wind a spiral from nichrome
A resistive or heating coil can be made at home. To do this, you need nichrome wire of a suitable grade 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 power, you need to take into account the maximum permissible 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 to 900 °C.
There are reference tables for calculating temperature and current. But you also need to take into account 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 be reduced by 10-50%.
The intensity of heat removal, and therefore the temperature of the heater, is affected by the pitch of the spiral winding.
Densely spaced coils generate more heat, while a larger pitch increases cooling.
It should be taken into account that all tabular calculations are given for a heater located horizontally. When the angle to the horizon changes, the heat removal conditions worsen.
Calculation of the resistance of a nichrome spiral and its length
Having decided on the power, we proceed to calculate the required resistance.
If the determining parameter is power, then first we find the required current using the formula I=P/U.
Having the current strength, we determine the required resistance. To do this, we use Ohm's law: R=U/I.
The notations here are generally accepted:
- P – allocated power;
- U is the voltage at the ends of the spiral;
- R – spiral resistance;
- 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 – required length;
- R – wire resistance;
- d – wire diameter;
- ρ – resistivity of nichrome;
- π – constant 3.14.
But it’s easier to take 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 changes in resistance when heated.
In this case, the calculation will look like this: L=R/ρld, where ρld is the resistance of one meter of wire having a diameter d.
Spiral winding
Now we will make a geometric calculation of the nichrome spiral. We have selected the wire diameter d, the required length L has been determined, and we have a rod with diameter D for winding. How many turns do you need to make? The length of one turn is: π(D+d/2). Number of turns – N=L/(π(D+d/2)). The calculation is completed.
Practical solution
In practice, rarely does anyone wind their own wire for a resistor or heater.
It’s 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 spirals 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 sketches and technical specifications customer.
partalstalina.ru
Calculation and repair of the heating winding of a soldering iron
During repairs or self-production An electric soldering iron or any other heating device requires winding a heating winding made of nichrome wire. The initial data for calculating and selecting wire is the winding resistance of a soldering iron or heating device, which is determined based on its power and supply voltage. You can calculate what the winding resistance of a soldering iron or heating device should be using the table.
Knowing the supply voltage and measuring the resistance of any heating electrical appliance, such as a soldering iron, electric kettle, electric heater or electric iron, you can find out the power consumed by this household electrical 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. In the leftmost column of the table, select 60 W. From the top 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 winding material, should be equal to 806 Ohms.
If you needed to make a soldering iron from a 60 W soldering iron, designed for a voltage of 220 V, for power supply from a 36 V network, then the resistance of the new winding should already be equal to 22 Ohms. You can independently calculate the winding resistance of any electric heating device using an online calculator.
After determining the required resistance value of the soldering iron winding, the appropriate diameter of the nichrome wire is selected from the table below, 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 X20N80. 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 a soldering iron spiral, the turns are laid close to each other. When heated red-hot, the 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 a second one is wound.
For electrical and thermal insulation of heating element windings the best materials is mica, fiberglass cloth and asbestos. Asbestos has 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 a soldering iron with wet asbestos, it is necessary to take into account that wet asbestos conducts electric current well and it will be possible to turn on the soldering iron into the electrical network only after the asbestos has completely dried.
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HOW TO CALCULATE A NICHROME SPIRAL?
Post written by admin at 01/18/2015 23:23Categories: 3. Home electrical, Electrical workshop
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Winding a nichrome spiral for heating devices is often done “by eye”, and then, including the spiral in the network, the required number of turns is selected based on the heating of the nichrome wire. Usually this procedure takes a lot of time, and nichrome is wasted.
When using a 220 V spiral, you can use the data given in the table, based on the calculation that the resistivity of nichrome ρ=(Ohm mm2/m). Using this formula, you can quickly determine the length of 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 need to determine the length of a spiral for a voltage of 127 V from nichrome wire with a thickness of 0.3 mm, the winding rod dia. 4 mm. The table shows that the length of such a spiral at a voltage of 220 V will be equal to 22 cm.
Let's make a simple ratio:
220 V - 22 cm
X = 127 * 22 / 220 = 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.
Legend in the table: D - diameter of the rod, mm; L - length of the spiral, cm.
| dia. nichrome0.2 mm | dia. nichrome0.3 mm | dia. nichrome0.4 mm | dia. nichrome0.5 mm | dia. nichrome0.6 mm | dia. nichrome0.7 mm | dia. nichrome0.8 mm | dia. nichrome0.9 mm | dia. nichrome1.0 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 | ||||||||||||||||
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Electrical resistance is one of the most important characteristics nichrome. It is determined by many factors, in particular electrical resistance nichrome depends on the size of the wire or tape and the grade of alloy. The general formula for active resistance is: R = ρ l / S R - active electrical resistance (Ohm), ρ - specific electrical resistance (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, based on the calculation that the resistivity of nichrome = (Ohm mm2 / m)C. With its help, you can quickly determine the length of 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, you need 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 at a voltage of 220 V will be equal to 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 the 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
| Calculation of the heating element Calculation example. Given: U=220V,t=700°C, type X20H80, d=0.5mm-----------L,P-?Solution: From Table 1 we find that the diameter d=0.5mm corresponds to S = 0.196 mm², and the current at 700 ° C I = 5.2 A. The type of alloy X20N80 is nichrome, the resistivity 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. Determine the power of the heating element: P = U I = 220 5.2 = 1.15 kW .When winding the spiral, adhere to the following relationship: 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 a closed version of the heater, the current should be reduced by 1.2-1.5 times. A smaller coefficient is taken for thicker wire, a larger one for thinner wire. For the first case, the coefficient is chosen exactly the opposite. I’ll make a reservation: we're talking about about simplified calculation of the heating element. Perhaps someone will need a table of electrical resistance values for 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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Winding a nichrome spiral for further heating is carried out mainly by trial and error. After winding, voltage is applied to the heating element and the required number of turns is determined by how the wire is heated.This process can take a long time. It is worth remembering that nichrome can lose when large quantities bends its characteristics. The wire will quickly burn out in areas of deformation. Ultimately, it may turn out that good material turn into scrap.
For correct calculation nichrome spirals usually use special tables, where the resistivity of nichrome wire = (Ohm mm2 / m). But, these tables display data for a voltage of 220V. To operate the heating element in an industrial environment, you will have to carry out the calculation yourself, substituting the available data.
Using the tabular data, you can accurately determine the winding length and the distance between the turns. Depending on the diameter of the wire and the diameter of the nichrome winding rod, it will not be difficult to recalculate the length of the spiral for operation at a different voltage. Here you need to use a simple mathematical proportion.
For example, if you need to calculate the length of the spiral for a voltage of 380 V using a wire with a diameter of Ø 0.6 mm and a winding rod Ø 6 mm. In the table you can see that the length of the spiral at a voltage of 220 V should be 30 cm. Next, we calculate using the following ratio:
220 V – 30 cm
380 V – X cm
Based on this data:
X= 380 30/220=52 cm
After the spiral has already been wound, it should be connected to the energy carrier and make sure that the winding is correct. In this case, the wound wire is not cut. For a spiral in a closed heater, the winding length should be 1/3 greater than the values given in the table.
Calculation of a heating element made of nichrome wire
The length of the wire is determined based on the indicators required power.As an example, we will carry out the following calculations based on the available indicators.
There are several types of tandoor heating. Today, the electric method is becoming increasingly widespread, since it does not require the purchase of fuel, does not emit combustion products, and makes it easier to use behind the stove.
Collapse
The device is heated by heating the spirals and subsequent uniform heat transfer. The article discusses in detail the features of the tandoor spiral. This information will help you select and install the heating element on the stove correctly.
What is a tandoor spiral?
The spiral is an important element of the tandoor; without it, the device will not work. Warms up quite quickly. Allows you to maintain the required temperature long time, which is especially important if you have to cook on the stove all day.
This is what a spiral looks like
The heating element is made from wire with high electrical resistance. The length of the wire is quite long, so it is twisted in turns for convenience. Spirals can have the shape of cylinders or flat coils and be equipped with contact leads. Heaters are attached to the furnace on ceramic or metal bases with special heat-resistant inserts or insulators.
Purpose of the spiral
The main function of a tandoor coil is incandescence and subsequent uniform distribution of heat. To do this, the element must have the following qualities:
- Heat resistance (does not collapse at high temperatures in tandoors).
- High current resistance (the heating rate, the resulting temperature, and the service life of the element depend on this).
- Constancy of properties (does not change depending on environmental conditions, duration of operation).
Kinds
The most practical materials for heating parts are nichrome and fechral compounds. Let's briefly consider their features.
Nichrome
Nichrome spirals are made from Cr+Ni. This alloy allows the device to heat up to 1200 degrees. It is characterized by creep resistance and oxidation resistance. The downside is the lower temperature range compared to fechral alloys.
The price of nichrome products is affordable. For example, brand Х20Н80(20% chromium, 80% nickel), suitable for a standard voltage of 220 volts will cost 150-170 rubles. per meter
Fechral
Fechral is a combination chromium, iron, aluminum and titanium. The material has good current resistance. It has increased heat resistance: the maximum melting temperature of spirals made of this material reaches 1500 degrees.
Fechral spiral
Types
When selecting a heating device, it is important to pay attention not only to the material, but also to the type of product: a 220 or 380 volt tandoor coil has some differences.
220 V is the standard voltage for home electrical networks (that is, for connecting to regular sockets in apartments and country cottages). Can also be used in small restaurants with low productivity. According to safety rules, spirals with a power of 3.5-7 kilowatts are connected to 220 volts.
A powerful tandoor is not connected to a standard consumer electrical network. This will cause the heater to burn out and short out. Requires connection to an industrial three-phase power supply of 380 volts. The power of each spiral in the tandoor in this case increases to 12 kilowatts. Special requirements for wires used in heating elements: they must have a cross-section of at least 4 mm.
How to choose the right spiral?
The dimensions of the wire used to create heaters are determined by the power of the tandoor, the voltage in the electrical network and the heat that should be produced by the stove. First, you need to determine the current strength using the formula: I = P:U
- P is the technical power of the furnace.
- U is the voltage in the electrical network.
For example, for an 800-watt stove and a mains voltage of 220 volts, the electric current will be 3.6 amperes. Afterwards, using the specified parameters (temperature and electric current), suitable wire dimensions are searched in a special table.
The length of the wire for the spiral is calculated by the formula l=RхS:ρ. For example, with a resistance of 61 Ohms, a cross-sectional size of 0.2 square meters. mm and a resistance of 1.1 requires a spiral made of wire 5.3 meters long.
Installation work
Specialists charge about 2300-3000 rubles for installing heating elements in a furnace. If you want to save money and install the spiral in the tandoor yourself, here are some important tips:
- You should not place the heating element vertically. The hot wire is soft and may bend due to gravity. It is better to lay it horizontally.
- It is not recommended to install the heater close to the insulating brick - the risk of overheating increases. A small “air cushion” is created between the furnace walls and the wire.
- When installing, you need to stretch the spiral so that all the turns are at a small distance from each other (experts recommend the distance between the rings is 1.5-2 times greater than the diameter of the wire).
An alternative option: a heating element (tubular electric heater with a wire spiral inside) is installed at the bottom of the tandoor. This is a convenient and safe option. But as practice shows, heating from the heating element will slower than in the case of an open spiral.
The photographs below show several types of spiral installation:
Example of spiral installation
Another way
heating element instead of a spiral
Conclusion
Correct and safe work tandoor depends on this important element like a spiral. When buying a ready-made stove or making a device with your own hands, it is important to choose suitable material, type, size of heaters. If you do not have confidence in your abilities and knowledge, it is better to entrust the selection and installation of foam spirals to specialists.
←Previous article Next article →In practice home handyman it is necessary to repair or construct heating devices. These can be various ovens, heaters, soldering irons and cutters. Most often, spirals or nichrome wire are used for this. The main task is to determine the length and cross-section of the material. In this article we will talk about how to calculate the length of a nichrome wire or spiral based on power, resistance and temperature.
Basic information and brands of nichrome
Nichrome is an alloy of nickel and chromium with additions of manganese, silicon, iron, and aluminum. The parameters of this material depend on the specific ratio of substances in the alloy, but on average they lie within the limits:
- specific electrical resistance - 1.05-1.4 Ohm*mm 2 /m (depending on the brand of alloy);
- temperature coefficient of resistance - (0.1-0.25)·10 −3 K −1;
- operating temperature - 1100 °C;
- melting point - 1400°C;
In tables, resistivity is often given in µOhm*m (or 10 -6 Ohm*m) - the numerical values are the same, the difference is in dimension.
Currently, there are two most common brands of nichrome wire:
- Х20Н80. It consists of 74% nickel and 23% chromium, as well as 1% each of iron, silicon and manganese. Conductors of this brand can be used at temperatures up to 1250 ᵒ C, the melting point is 1400 ᵒ C. It is also characterized by increased electrical resistance. The alloy is used for the manufacture of elements of heating devices. Specific resistance – 1.03-1.18 µOhm m;
- Х15Н60. Composition: 60% nickel, 25% iron, 15% chromium. Working temperature no more than 1150 ᵒ C. Melting point – 1390 ᵒ C. Contains more iron, which increases magnetic properties alloy and increases its anti-corrosion resistance.
You will learn more about the grades and properties of these alloys from GOST 10994-74, GOST 8803-89, GOST 12766.1-90 and others.
As already mentioned, nichrome wire is used everywhere where heating elements are needed. High resistivity and melting point make it possible to use nichrome as a base for various heating elements, from a kettle or hair dryer to a muffle furnace.
Calculation methods
By resistance
Let's figure out how to calculate the length of nichrome wire based on power and resistance. The calculation begins with determining the required power. Let's imagine that we need a nichrome thread for a small soldering iron with a power of 10 W, which will operate from a 12V power supply. For this we have wire with a diameter of 0.12 mm.
The simplest calculation of the length of nichrome by power without taking into account heating is performed as follows:
Let's determine the current strength:
I=P/U=10/12=0.83 A
We calculate the resistance of nichrome wire according to:
R=U/I=12/0.83=14.5 Ohm
The length of the wire is:
l=SR/ ρ ,
where S is the cross-sectional area, ρ – resistivity.
Or using this formula:
l= (Rπd2)/4 ρ
L=(14.5*3.14*0.12^2)/4*1.1=0.149m=14.9cm
The same can be taken from GOST 12766.1-90 table. 8, where the value of 95.6 Ohm/m is indicated, if you recalculate it, you get almost the same thing:
L=R required /R table =14.4/95.6=0.151m=15.1cm
For a 10 watt heater powered by 12V, you need 15.1cm.
If you need to calculate the number of turns of a spiral to make it from nichrome wire of this length, then use the following formulas:
Length of one turn:
Number of turns:
N=L/(π(D+d/2)),
where L and d are the length and diameter of the wire, D is the diameter of the rod on which the spiral will be wound.
Let's say we wind nichrome wire on a rod with a diameter of 3 mm, then we carry out the calculations in millimeters:
N=151/(3.14(3+0.12/2))=15.71 turns
But at the same time, it is necessary to take into account whether nichrome of such a cross-section is even capable of withstanding this current. Detailed tables for determining the maximum permissible current at a certain temperature for specific sections are given below. In simple words– you determine how many degrees the wire should heat up to and select its cross-section for the calculated current.
Also keep in mind that if the heater is inside a liquid, then the current can be increased by 1.2-1.5 times, and if in a confined space, then vice versa, it can be reduced.
By temperature
The problem with the above calculation is that we calculate the resistance of the cold spiral by the diameter of the nichrome thread and its length. But it depends on the temperature, and you also need to take into account under what conditions it will be possible to achieve it. If such a calculation is still applicable for cutting foam plastic or for a heater, then for muffle furnace he will be too rough.
Let us give an example of calculations of nichrome for a furnace.
First, determine its volume, say 50 liters, then determine the power, for this there is a rule of thumb:
- up to 50 liters – 100 W/l;
- 100-500 liters – 50-70 W/l.
Then in our case:
I=5000/220=22.7 Ampere
R=220/22.7=9.7 Ohm
For 380V when connecting the spirals with a star, the calculation will be as follows.
We divide the power into 3 phases:
Pf=5/3=1.66 kW per phase
When connected by a star, 220V is applied to each branch (phase voltage may differ depending on your electrical installation), then the current:
I=1660/220=7.54 A
Resistance:
R=220/7.54=29.1 Ohm
For a triangle connection, we calculate using a line voltage of 380V:
I=1660/380=4.36 A
R=380/4.36=87.1 Ohm
To determine the diameter, the specific surface power of the heater is taken into account. Let's calculate the length, take the resistivity from the table. 8. GOST 12766.1-90, but first we will determine the diameter.
To calculate the specific surface power of the furnace, use the formula.
Bef (depends on the heat-receiving surface) and a (radiation efficiency coefficient) – are selected according to the following tables.
So, to heat the furnace to 1000 degrees, let’s take the temperature of the spiral at 1100 degrees, then according to the selection table for B eff we select a value of 4.3 W/cm 2, and according to the selection table for coefficient a - 0.2.
V additional = V eff *a = 4.3 * 0.2 = 0.86 W/cm 2 = 0.86 * 10^4 W/m 2
The diameter is determined by the formula:
рт – specific resistance of the heater material at a given t, determined according to GOST 12766.1, table 9 (shown below).
For nichrome Х80Н20 – 1.025
р t =р 20 *р 1000 =1.13*10^6*1.025=1.15*10^6 Ohm/mm
Then to connect to a three-phase network according to the “Star” scheme:
The length is calculated using the formula:
Let's check the values:
L=R/(p*k)=29.1/(0.82*1.033)=34m
The values differ due to the high temperature of the coil; the test does not take into account a number of factors. Therefore, let’s take the length of 1 spiral to be 42 m, then for three spirals you need 126 meters of 1.3 mm nichrome.
Conclusion
- environmental conditions;
- location of heating elements;
- temperature of the coils;
- the temperature to which the surface should heat up and other factors.
Even the above calculation, despite its complexity, cannot be called sufficiently accurate. Because the calculation of heating elements is pure thermodynamics and a number of other factors can be cited that influence its results, for example, the thermal insulation of the furnace and so on.
In practice, after estimated calculations, spirals are added or removed depending on the result obtained, or temperature sensors and devices are used to adjust it.
Materials
Some household heating appliances still use nichrome wire. It has high heat resistance, characteristic of an alloy of nickel and chromium. This material has good ductility, high electrical resistivity and a low temperature coefficient of resistance. Therefore, when calculating nichrome wire for a heater, these parameters must be taken into account. Otherwise, the calculation results will be inaccurate and will not give the desired result.
Using an online calculator in calculations
Quick calculations can be done using an online calculator. With its help, you can calculate and approximately set the required length of nichrome wire. As a rule, we consider the brands that are most widely used in heating devices - X20N80, X20N80-N, X15N60.
To perform calculations, mandatory initial data is required. First of all, this is the amount of heater power that is planned to be obtained, the diameter of the nichrome wire and the value of the supply voltage.
Calculations are carried out as follows. First of all, you need to install it in accordance with the specified parameters, according to the formula: I = P/U. After this, the resistance for the entire heating element is calculated. Next, you will need electrical resistivity for a specific brand of nichrome wire. This value will be needed in order to establish the most optimal length heating element using a different formula: l = SR/ρ. Right choice length will bring the heater resistance R to the desired value.
After performing the calculations, it is recommended to check the obtained data using the table and make sure that the calculated current corresponds to the permissible value. If the calculated current exceeds the permissible limits, repeat calculations should be performed by increasing the diameter of the nichrome wire or reducing the power of the heating element itself. It is necessary to take into account the fact that all the parameters given in the tables are calculated for heaters located in a horizontal position and operating in an air environment.
If you plan to use a nichrome spiral placed in a liquid, the value of the permissible current should be multiplied by a factor of 1.1-1.5. With a closed spiral arrangement, on the contrary, it is necessary to reduce it by 1.2-1.5 times.
