Fusible Resistor Technology and Cost Efficiency
Fusible resistors combine the requirements of a resistor and fuse, making them ideal for applications where there are low power surge and level requirements. Combining the characteristics of the two components reduces costs and saves space. Certain applications such as utility meters, tools that use electric power, and other commercial equipment require strong resistors within them. Such resistors are designed to tolerate high, short-term pulses, high fluctuations in power, and high temperatures. This is where fusible resistors come into the picture, and they can be further divided into wirewound and fusible film resistors. This blog aims to shed more light on the applicability of fusible resistors in different systems, considering their importance and ease of functionality.
Features of Fusible Film Resistors
Fusible film resistors use a thin film made up of a standard alloy along with other compatible materials that are appropriate for the fusible part. The film’s thickness and its overall composition should be kept uniform throughout the part across the manufacturing batch. Once the resistors are covered with film, they need to be calibrated to regulate their precise resistance value and fusing action. The resistance of a batch of resistors varies with the calibration trimming applied, where an increase of trimming leads to shorter fusing time, and consequently, lower power needed by the resistor for fusing. This fluctuation of resistance values can simultaneously lead to a fluctuation in fusing performance since materials with higher resistance tend to fuse together more quickly. Fusing traits are often expressed in terms of fusing time, that of which follows a magnification power which exists in multiples of 5. Some fusible resistors are also manufactured with absolute resistance tolerances of 5 percent or higher.
Features of Fusible Wirewound Resistors
Fusible wirewound resistors are used to protect a system from a temporary electrical event without failing, such as having a fusible wirewound resistor pass 20 microsecond pulses of 6000 V. Common applications of such resistors include both HVAC systems and fire safety equipment systems. These types of resistors have to be able to fuse quickly without catching fire when they are faced with an overload of 120 V. Although wirewound resistors are easy to build, they are far more difficult to maintain because their fusing properties can cause the device to heat up and generate flames when faced with 6 kV fluctuations. In some instances, manufacturers make a fail-proof design for the fusing action by making the cap weaker on one of the two welding ends. In many instances, the resistor will fuse just fine, while in other instances, the fuse will not occur until the PCB catches on fire.
The trimming process also determines a fusible wirewound resistor’s performance, affecting the wire element and the current that it can possibly carry. The trimming process affects the current carrying capacity of the fusible wirewound resistor by as much as 40%, which does not affect the power tolerance in a steady-state. A 5 W low resistance wirewound fuse can be used to handle around 70 J of energy, whereas the regular commercial variety can be used to handle only around 0.4 J. Although trimming increases costs of fusible wirewound technology, the overall benefits are still worth the price rise.
Rising Interest in Fusible Wirewound Resistors
For the benefit of power supply design, engineers have come up with a single failsafe wirewound to avoid the need for two separate components. This is because single wirewounds will be more reliable than a separate resistor and fuse. Although the usage of a thermal fuse lowers the power handling capability of the resistor, it still produces a significant fusing action that is required for circuit protection. Wirewounds can be very problematic in conditions of extreme overloading. This is because the wirewound will keep heating up until it is so hot that it destroys itself as well as any parts that are kept anywhere around it. As such, they are best for applications where there is a very low risk of a significant overload occuring. Wirewounds find their use in several applications where wirewound resistors are simply not feasible. They are especially cost effective in situations where a device can experience high surges of 6000 kV or more.
If you have been looking for fusible wirewound resistors, or even basic wirewounds for that matter, then Aerospace Buying is your ultimate destination. We at Aerospace Buying pride ourselves in assisting all our customers with a unique parts procurement experience, complete with 24/7x 365 support and fast & competitive quoting. We also offer same-day or next-day shipping on select in-stock items, which you can find in our inventory of more than 2 billion parts. Once you narrow down the part that you want, you can place your order by using the Instant RFQ service available on our website, and a dedicated sales rep will respond within 15 minutes or less.