Table of Contents
What is a Wirewound Resistors?
A wirewound resistors is a small, strong part used in electrical circuits. Its main job is to control the flow of electric current -kind of like a traffic signal for electricity.
Inside this resistor, there is a thin metal wire. This wire is wrapped around a solid core made of a material that does not conduct electricity, like ceramic or glass. That wire is made from special metals like Nichrome or Manganin, which are known for resisting the flow of electricity just the right amount.
Let’s take an example: a 20-watt wirewound resistors with a 5-ohm rating. This means it can handle a lot of electrical power and slow down the current by just the right amount — not too much, not too little.
Wirewound resistors have been around for a long time. They are still widely used because they are strong, very accurate, and great for handling high power.
Definition of Wirewound Resistors
A wirewound resistors is a special type of resistor made by tightly winding a thin wire around a strong, non-metal core. This wire is usually made from a material that resists the flow of electricity. Because of this resistance, it helps control how much electric current flows through a circuit.
Construction of Wirewound Resistors
Wirewound resistors are made in a very simple and smart way. As the name suggests, a special kind of wire is wound around a strong core (usually a stick or cylinder). This wire controls how much resistance the resistor gives in an electric circuit.
The resistance depends on three things:
- What the wire is made of (its material),
- How thick the wire is,
- And how long the wire is.
If you need more resistance, you use a longer and thinner wire. If you need less resistance, you use a shorter and thicker wire. This helps us get the exact resistance we want. Because these things can be carefully measured and controlled, wirewound resistors can be very accurate.
Sometimes, we need very precise resistors. In that case, the wire is cut to the exact length needed after checking its resistance.
These resistors are usually made for low resistance values, because making very high resistance would need super long and super thin wires — and that’s not easy to handle. Thin wires are delicate and can break easily, so they must be handled with great care.
After the wire is wound, it is protected properly. This keeps it safe from moisture or water, which could cause damage over time.
There are also heavy-duty wirewound resistors made to handle high power — like 50 watts or more. These ones are built a bit differently. They use thicker and stronger wire, so they are more durable and can manage higher amounts of electricity without getting damaged.
Compared to other types of resistors like metal film, wirewound resistors are more rugged when built for high power.
Resistivity of a wirewound resistors
The resistance in a wirewound resistors depends on the type of metal used for the wire.
If the metal wire has high resistance, it stops or slows down a lot of electric current. This means the wirewound resistors will give strong resistance to the current.
But if the metal wire has low resistance, it only slows down a little bit of the electric current. So, the wirewound resistors will give low resistance to the current.
In short, the kind of metal wire decides how much the resistor can block the electric current.
Length of a wirewound resistors Affects
When you have a metal wire, the longer it is, the harder it is for electricity to pass through. This means the wire’s resistance gets bigger as the wire gets longer.
Why does this happen? Well, electricity flows because tiny particles called free electrons move through the wire. If the wire is very long, these electrons have to travel a longer distance. While moving, they bump into atoms inside the metal.
Every time the electrons bump into atoms, they lose some energy. This lost energy turns into heat. Because of all these bumps, fewer electrons can move freely through the wire, so less electric current can flow.
Short metal wires have very little resistance because the electrons inside them only need to move a short distance. This means they don’t bump into the atoms very often. When only a few electrons collide with atoms, they lose just a little energy as heat. Most electrons keep moving freely, carrying the electric current smoothly. Because of this, a large amount of electric current can pass through a wire wound resistor made with short metal wires.
Cross-Sectional Area of wirewound resistors
The resistance of a wire depends on how thick or thin the wire is. This thickness is called the cross-sectional area.
If the wire is thin (small cross-sectional area), there isn’t much space inside for the tiny particles called electrons to move. Because of this tight space, the electrons bump into the atoms in the wire more often. This makes it harder for electricity to flow, so only a small electric current can pass through.
If the wire is thick (large cross-sectional area), there is plenty of room for the electrons to move around without bumping into the atoms too much. This makes it easier for electricity to flow, so a larger electric current can pass through the wire.
wirewound resistors Materials
Resistors are tiny parts used in electronics to control the flow of electricity. Some special types, called wirewound resistors, are made by wrapping a wire around a core. But not just any wire will do.
Why don’t we use pure metals?
Pure metals like copper or iron change too much when they get hot. This change is called the temperature coefficient of resistance (TCR). In simple words, it means how much a wire’s resistance (its ability to slow down electricity) changes when the temperature goes up or down.
A small change is better. That’s why we often use metal mixtures—called alloys—because they handle heat much better and keep the resistance stable.
But in some very high-temperature situations, we do use certain pure metals. Tungsten, for example, is a strong choice when things get really hot.
What is TCR, really?
TCR tells us how steady the resistor is when temperatures change. For example, if a resistor has a TCR of 50 ppm/°C, it means the resistance might only change a tiny bit—like 50 ohms for every 1 million ohms—when the temperature goes up or down by 1°C. That’s a very small change, which is good.
Common resistor wire materials:
To make sure resistors work well and stay stable, these are the materials most often used:
- Copper alloys – Mixes of copper with other metals
- Silver alloys – Silver blended with other elements
- Nickel-chromium alloys – Strong, reliable wires used in many resistors
- Iron-chromium alloys – Tough and heat-resistant
- Iron-chromium-aluminum alloys – Great for very high temperatures
the Properties of Common Alloys
Alloys are special materials made by mixing different metals together. This is done to give them better strength, resistance, or special electrical properties. Let’s take a look at some of the most common alloys, their makeup, and what makes each one special.
1. Copper-Based Alloys
- Constantan
Made with copper (54%), nickel (45%), and a tiny bit of manganese (1%).
It resists electricity moderately and doesn’t change much with temperature.
Can handle heat up to 400°C.
Used in sensors and instruments. - Nickelin
Contains more copper (67%) and less nickel (30%) than Constantan, with a small amount of manganese.
Has slightly lower resistance and works well up to 300°C. - Manganin
Has even more copper (86%) and more manganese (12%) but very little nickel.
This alloy is very stable—its resistance barely changes with temperature.
Can also work up to 300°C.
Perfect for precise measuring tools.
2. Silver-Based Alloys (NBW Series)
These alloys are made mostly of silver with some manganese and tin added. They are used when both beauty and performance are needed.
- NBW 109
82% silver, 10% manganese, 8% tin.
A strong and shiny metal, with very little resistance change as it heats. - NBW 139
Slightly different mix: 78% silver, 13% manganese, 9% tin.
Works best between 0 to 150°C. - NBW 173
80% silver, more manganese (17%), and less tin (3%).
Can be used in hotter places—up to 200°C.
3. Nickel-Chromium Alloys
These are known for their toughness and ability to handle very high temperatures.
- Nichrome
Has about 77-80% nickel and 20% chromium, sometimes a little manganese.
Used in things like heaters and toasters.
Can work up to 1100–1150°C!
4. Iron-Chromium Alloys
These include nickel, iron, chromium, and manganese.
- CrNiFe 1
Strong and heat-resistant.
Good up to 1050–1100°C. - CrNiFe 2
A slightly different mix but used for similar high-temperature tasks.
5. Iron-Chromium-Aluminum Alloys
These are some of the most heat-resistant materials.
- Kanthal A
Made from iron, chromium, aluminum, and a bit of cobalt.
Handles heat up to 1300°C. - Cekas
A simpler version of Kanthal, without cobalt.
Same heat resistance: 1300°C. - Megapyr
Has even more chromium.
Can go up to 1350°C—great for extreme heat applications.
6. Pure Metal
- Tungsten
Pure metal—100% tungsten.
Very low resistance but changes a lot with temperature.
Extremely heat-resistant: works between 1500 and 1700°C.
Used in high-tech devices like light bulb filaments and aerospace parts.
In high-precision measurement work, even tiny things can make a big difference. One such thing is the type of metal used in a resistor and the wires connected to it.
When the resistor wire and the connecting leads are made of different materials, a problem can happen where they meet. If the temperature changes, it can create a small, unwanted voltage at the connection point. This tiny voltage can affect the accuracy of your readings.
This problem is known as the thermoelectric effect — and while it might seem small, in precise measurements, every little detail matters.
High Frequency Effects: Induction and Capacitance in Wirewound Resistors
Wirewound resistors are made by winding a wire into a coil. Because of this, they naturally have some small electric effects called parasitic inductance and parasitic capacitance. These are like tiny hidden parts that affect how electricity flows through the resistor, especially when the electric current changes direction quickly (which is what happens in alternating current or AC).
For steady, one-way electric flow (direct current or DC), these small effects don’t cause much trouble. But for AC, especially at high frequencies, they can change how the resistor works and cause problems.
The main reason is that a wire coil acts a bit like a tiny magnet, making the resistor behave like an inductor. This makes wirewound resistors the least suitable kind of resistor when dealing with very high frequencies.
To fix this, engineers have invented special ways to wind the wire so these unwanted effects get smaller. Some of these winding styles are:
- Bifilar winding: Two wires are wound together to cancel out the magnetic effects.
- Winding on a flat base: Instead of winding in a coil shape, the wire is wound flat to reduce those effects.
- Ayrton-Perry winding: A special winding pattern that reduces inductance a lot.
These special windings help make the resistors work better in high-frequency circuits, such as in measuring tools or devices that need very precise resistance.
Bifilar Winding
A bifilar winding is made by folding a wire in half and then winding this double wire around a base. This way of winding helps keep the self-induction very low, which means it doesn’t create extra magnetic effects inside. However, because the two wires are close together, there is more electrical “parasitic” capacitance between them.
Simple Winding on a Flat Former
Another way to lower the capacitance is by winding the wire simply on a flat surface called a former. When the base is thin, the wires on the front and back are very close, and their magnetic fields cancel out. This reduces the unwanted inductance in the coil.
Ayrton-Perry Winding
For circuits that need the best performance, the Ayrton-Perry winding is used. It looks like the simple flat winding but uses two windings going in opposite directions. The wires carrying current in opposite directions sit close together, which cancels out self-induction completely. The points where the two windings cross have the same electrical potential, so the capacitance between them stays very low.
Types of Wirewound Resistors
Wirewound resistors come in two main types: precision and power. Precision resistors are made to be very accurate, while power resistors are built to handle higher amounts of electricity. These resistors are flexible and can be changed to work as parts in different devices, like sensors that measure current or temperature, or as adjustable controls called potentiometers. Because of this, wirewound resistors are useful in many different machines and tools.
Precision Wirewound Resistors
Precision wirewound resistors are special parts used in electronics when exact values are very important. You can find them in things like sound equipment, measuring tools, and devices that need very careful calibration.
These resistors are made to be very accurate. Their resistance value usually stays within 0.1% of what is needed, which means they are very close to perfect. They also don’t change much when the temperature changes—only about 5 parts per million for each degree Celsius, which is much better than many other types of resistors.
They are very stable, too. Even after working hard for a whole year, their resistance value changes very little. When they get warm during use, they don’t get too hot—usually less than 30 degrees Celsius above the surrounding temperature. This means they can be safely covered with a protective resin coating.
Sometimes, designers want even more accuracy, like within 0.05% or better. To be sure the resistor stays that accurate over time and with temperature changes, they might choose one with a tolerance of just 0.01%. This way, the resistor always works exactly as needed, keeping the whole circuit running perfectly.
Power Wirewound Resistors:
Power wirewound resistors are special parts used in electronics when a lot of power needs to be handled safely. They come in many sizes and strengths, from small ones that handle about half a watt to very big ones that can handle more than a thousand watts.
These resistors are made in different styles depending on how they are covered or coated to protect them and help them work better.
- Silicone Resin Coating:
This type is used for resistors that don’t need to handle very high power. They are small but tough and can get very hot—up to 300 degrees Celsius hotter than the surrounding air—and still work well. - Vitreous Enamel Coating:
This is a classic coating that insulates the resistor well when it’s cool. But when it gets very hot, it doesn’t protect as well, so it’s not used as much anymore. These resistors can get as hot as 400 degrees Celsius on the surface and usually have resistance values between 1 ohm and 10,000 ohms. - Ceramic Coating with Ceramic Core:
Most power wirewound resistors are built this way. The ceramic inside helps keep the resistor safe and cool. They can handle medium power, usually between 4 and 17 watts. Their surface temperature can reach about 300 degrees Celsius. These resistors have resistance values from 10,000 ohms to 22,000 ohms. They often come with wires (called leads) that let you put them in different positions on a circuit board. - Aluminum Case with Cooling Fins:
For the strongest resistors that handle the most power, an aluminum case with fins is used. These fins spread out heat to keep the resistor from getting too hot. Inside, there’s a ceramic core and a silicone coating. The aluminum is treated to keep electricity from leaking. These resistors handle between 25 and 50 watts, but they work best when attached to a metal surface that helps cool them down. They can get up to 300 degrees Celsius on the surface, and their resistance changes very little with temperature for values over 50 ohms.
Wirewound Potentiometers
A potentiometer is a special kind of resistor with three connection points. What makes it different is one of these points can move along the resistor to change how much resistance there is. This helps control things like volume, brightness, or speed in many devices.
Wirewound potentiometers are made using a strong wire wrapped tightly around a core. This design makes them very tough and long-lasting. Because of this, wirewound potentiometers work really well when you need reliable and steady control in your electronics.
Properties of Wirewound Resistors
These resistors are designed to work well in many different situations because of their powerful features. Here’s what makes them special:
- Handle High Power: They are built to manage a lot of power without getting damaged.
- Low Noise: They help reduce unwanted electrical noise, making them great for clean and clear performance.
- High Accuracy: These resistors are made with very tight tolerance, which means they work with great precision.
- Custom-Friendly: If you have unique needs, these resistors can be made to fit your exact requirements.
- Pulse Resistant: They can absorb sudden bursts of energy (pulses) without breaking down.
- Heat Strong: They can work well even in places where the temperature gets really high.
- Long-Term Stability: Once installed, they stay reliable and consistent over time.
General Specification –Wirewound Resistors
We offer high-quality resistors made with either vitreous enamel (ceramic coating) or silicon coating. These resistors are built to last, perform reliably, and handle a wide range of power and resistance levels.
Types Available:
- Silicon Coated Wire Resistors
- Wound Resistors
Resistance Range:
- From 0.025 Ohm up to 100,000 Ohms (100 K Ohm)
Power Rating:
- From 1 Watt up to 200 Watts
(For some types, the range is from 1 to 20 Watts)
Tolerance (Accuracy):
- Above 1 Ohm:
- ±1% or ±5%
- Below 1 Ohm:
- ±10%
Temperature Coefficient:
- From 100 PPM/°C to 1500 PPM/°C
(Some types may have a fixed value like 200 PPM/°C)
Important Notes About the Wirewound Resistors
Machine and Equipment Costs
The prices given for machines and equipment are just estimates. They are based on a specific brand and model, so the actual cost may be a little more or less.
Break-Even Point
The break-even point mentioned is based on the full use of the factory or unit. This means it applies when you are using 100% of the capacity.
Project Preparation Cost
If needed, the money spent on planning and setting up the project can be included as part of the early (pre-operative) costs.
Machines and Testing Tools
The most important machines and testing tools needed to make the product have been listed.
If the unit doesn’t have its own testing tools, it can use shared testing centers. These are available at special government-supported labs, like Electronics Test and Development Centres (ETDCs) and Electronic Regional Test Laboratories (ERTLs).
How We Calculated Production Capacity
We have calculated our production capacity based on working in one shift a day, at 75% efficiency. This means we are not assuming everything will run perfectly, but at a good, realistic pace.
How Much We Plan to Use This Capacity
We plan to run the unit for 300 days in a year.
- In the first year, we expect to use 60% of the total capacity.
- In the second year, this will go up to 80%.
- From the third year onward, we aim to use the full capacity.
What Our Cost Estimates Are Based On
We have worked out costs like salaries, wages, raw materials, electricity, water, rent, etc., based on the current rates in and around Guwahati.
WireWound Resistors Are Used
Wirewound resistors are important parts used in many machines and devices. They help control electricity in a safe and steady way. Here are some common places where you can find them:
- Telecommunication: They help in devices that let us talk and send messages over long distances.
- Computers: Inside computers, they keep the electricity just right so the parts work well.
- Audio and Video Equipment: They make sure sound and pictures come out clear on things like speakers and TVs.
- Medical Devices: They help machines that doctors use to check and treat people.
- Defense and Space: Used in equipment for the army and space missions where things have to work perfectly.
- Telephone Systems: They help switch and connect phone calls properly.
- Sensors and Instruments: They are part of devices that measure things like temperature or pressure.
- Balancing Electricity: They help keep the flow of current and voltage steady in electric circuits.
- Current Sensing: They are used to detect how much electric current is flowing in a system.
Advantages of WireWound Resistors
- They are affordable and don’t cost much.
- They give very accurate resistance values.
- They stay stable and don’t change much over time.
- You can find them in many different resistance sizes.
Disadvantages of WireWound Resistors
- They work well only at low frequencies.
- At high frequencies, they don’t behave like regular resistors—they act more like coils (inductors).
- Because of this, they aren’t good for high-frequency circuits unless a special type called non-inductive wire wound resistors is used.
Easy Ways to Save Electrical Energy
Saving electricity is not hard. With some smart choices and good habits, we can use less power and still get the job done well. Here are some simple steps that can help:
- Use Energy-Saving Tools
Choose machines and tools that are made to save energy. These can help us do the same work but use less electricity. - Work Smarter, Not Harder
Use machines the right way so they work better and waste less power. Take care of the tools we use for making and testing things, so they don’t use more energy than needed. - Control Heat During Soldering
When we need to heat something, like in soldering, use tools that can control the temperature properly. This helps save electricity and keeps the job safe. - Keep Machines in Good Shape
Take care of motors, compressors, and other machines. If we check and clean them often, they run better and use less electricity. - Improve Power Use
Use special devices called power factor correction capacitors to make sure our power use is efficient. Also, plan the lighting well:- Turn off lights when not needed
- Use energy-saving lights like CFLs (compact fluorescent lamps)
- Place lights where they’re really needed
FAQ
Definition of Wirewound Resistors
A wirewound resistors is a special type of resistor made by tightly winding a thin wire around a strong, non-metal core. This wire is usually made from a material that resists the flow of electricity. Because of this resistance, it helps control how much electric current flows through a circuit.
Construction of Wirewound Resistors
Wirewound resistors are made in a very simple and smart way. As the name suggests, a special kind of wire is wound around a strong core (usually a stick or cylinder). This wire controls how much resistance the resistor gives in an electric circuit.
The resistance depends on three things:
What the wire is made of (its material),
How thick the wire is,
And how long the wire is.