Quality Resistors

Resistors are used in the manufacture of virtually every piece of electrical or electronic equipment. Any device that is powered by an Alternating Current (AC) or a Direct Current (DC) source incorporates resistors in their use. Without them, there would be no stereos, computers, mobile phones, tablets, televisions, and a wealth of other electronic technologies upon which to depend.

Resistors are manufactured from wire coated with resistive materials and then sealed with an insulator. The type and corresponding properties of the resistive materials used determine its overall strength. There are different types of resistors, but the most common types are the carbon, metal film, which includes metal oxide and thick film, and wirewound. Selection of one type of resistor over another other depends on the application, cost, and technical specifications of the resistor itself.

A current shunt resistor is a low Ohm, high precision resistor which is used to measure the current flowing through a circuit. Current is calculated by dividing the voltage drop of the resistor by the resistance of the resistor (I=V/R). These resistors are sometime referred to as “ammeter shunts” because of their ability to measure amperes. They are used when the current to be measured is out of the range of the measuring device. Depending on their rating, shunt resistors are usually designed to drop voltage by 50mV, 75mV or 100mV.

Pulse resustors are specifically used in a circuit to literally "withstand" the excess load and heating that accompanies a transient energy event. Hence, they are typically known as Power Withstanding Resistors (PWRs). Fusing with flameproof protection, under specific fault conditions, can also be designed into the resistor performance where necessary. The types of resistor technologies available are wirewound, metal film, metal oxide, and surface mount. Telecommunications, computers, consumer electronics, and office equipment are just a few of the applications in which a pulse resistor may be used.

Resistors

Electrical resistors are an important part of just about any electrical circuit board schematic one can think of. They are generally quite numerous in just about all electronic products. All of them are not made equal, however. For a high-quality design, one should pick high quality components, and although some may overlook quality for pricing, all the parts should be up to specification with whatever project it is going into.

One thing to look at is tolerance to actual resistance specification of resistors. If the manufacturer states a 5% tolerance to the ohm spec, it really needs to be at or below that number. Another thing to check is how much voltage it can handle. This should be listed in the spec sheet for each particular resistor. Depending on whether the design is for a high-power application like a power supply or something much lower, like a calculator, one needs to watch for that. Lead sizing should fit the design. For example, one should not buy a through-hole type when a surface mount design is preferable during the engineering phase. Also, temperature specifications should be looked at to ensure thermal breakdown does not become a problem during peak performance of the resistor. It needs to be able to handle rapid fluctuation in temperatures, as various devices can change temperature quickly in real world applications.

A general quality check should be performed as well by quality assurance personnel on site at the time of delivery to ensure that the parts looks up to par. Just a little glance under a monocle will tell them whether it is well made, and of the correct material. Going by particular brands that are reputable can often be a great first step in quality assurance.

In general, breaking down of these specific parts is uncommon in a well-designed circuit; however, a bad part can make even the best design fail due to inferior parts. High quality parts go a long way toward end user satisfaction, so one should always be sure to pick the right parts from the start whenever possible to avoid frustration and loss of company dollars.

What is a Pulse Resistor?

Electronic engineers and manufacturers are realizing the increasing importance for "designing in" an adequate margin of safety to protect against high energy, short term current surges or voltage spikes. Likewise, protection also needs to be considered in the final circuit design where there exists a potential for more frequent, but less intense power surges.

These transient events, such as a lightning strike, or in the case of electrical switching, can produce high energy and result in significant heating within a circuit element, affecting its performance, and possibly result in premature component failure, or catastrophic damage to other components throughout the circuit. Repair or replacement of circuit components not only has devastating financial consequences, but causes significant downtime to be incurred. Therefore, use of pulse resistors when designing a circuit should be considered.

Pulse resustors are specifically used in a circuit to literally "withstand" the excess load and heating that accompanies a transient energy event. Hence, they are typically known as Power Withstanding Resistors (PWRs). Fusing with flameproof protection, under specific fault conditions, can also be designed into the resistor performance where necessary. The types of resistor technologies available are wirewound, metal film, metal oxide, and surface mount. Telecommunications, computers, consumer electronics, and office equipment are just a few of the applications in which a pulse resistor may be used.

Guard Against Inrush Current

"Inrush current" is current in a circuit that is generated by the initial magnetizing of a transformer or by the initial capacitor charging. Although for only a short period of time, the circuit components are subjected to significantly higher current than normal, and over time, can result in damage or premature failure of the component. Use of a with fusing characteristics helps to extend the life of the circuitry by dissipating and limiting the adverse effects of inrush current to circuitry downstream.

Short Circuit Protection

A PWR is used to provide short circuit or overload protection. Overload protection can also be referred to as overcurrent protection. Today, current output in circuits is monitored electronically, where resistors are used to divert or limit that is allowed to be ultimately passed through the circuit. A series voltage regulator with constant current limiting capability is one example.

When selecting pulse resustors for use in a circuit, it is important to properly size the resistor to meet the desired performance requirements and determine which resistor technology best matches your application.

What is a current shunt resistor?

A current shunt resistor is a low Ohm, high precision resistor which is used to measure the current flowing through a circuit. Current is calculated by dividing the voltage drop of the resistor by the resistance of the resistor (I=V/R). These resistors are sometime referred to as “ammeter shunts” because of their ability to measure amperes. They are used when the current to be measured is out of the range of the measuring device. Depending on their rating, shunt resistors are usually designed to drop voltage by 50mV, 75mV or 100mV.

Let’s say you have a 100 Amp current shunt resistor used to measure the current flowing in or out the the battery bank of a renewable energy system, such as solar or wind turbine. You can connect a standard multimeter (0-100mV) to the shunt resistor’s leads to monitor how much current the batteries output or how much current is being used to charge the batteries.

In our example, the 100 Amp shunt resistor is configured to drop the voltage by 100mv when the current flowing through it is 100 Amps. The resistance of the shunt resistor is calculated by dividing the voltage by the current 0.1/100=0.001 Ohms. The resistance value changes in linear proportion to the current flowing through the circuit. You can determine the amount of voltage dropped in a circuit using a standard multimeter. If the voltage drops by 18mv then the current flowing though the circuit can be determined by dividing the voltage drop by the resistance (0.018/0.001= 18 Amps)

There is, of course, a “cost of doing business” with a shunt resistor. The power lost when the shunt resistor is doing it’s work is calculated by multiplying the voltage by the current. In the previous example that would be 0.018V * 18 Amps = 0.32 Watts.

Current shunt resistors are not designed to be used at their full capacity continuously. “Continuously” is defined as being more than 2 minutes of use. Doing so could overheat and damage the resistors which would give inaccurate measurements. If a shunt resistor becomes too hot for too long will be permanently damaged. Most shunt resistors have a “derating factor” of 66%. This means that you would not operate the 100Amp shunt resistor in our example at more than 66 Amps.

Current shunt resistors can be used in a wide variety of applications including automotive, marine and renewable energy systems.