Location: Blown Fuses

Blown Fuses - Why I blew a Fuse! and What to do.

What to do when you blow a fuse, how to select a new fuse, and what not to do. When a fuse blows it is due to a buildup of heat inside the fuse, causing the filament to burn up. So when a fuse in a system that has been perfectly capable of handling the power requirements of a given piece of equipment for a long time blows, replace it with an identical fuse. The manufacturer, designer, or installer chose that size fuse to protect the electronics installed. It is a good idea to follow in the footsteps of giants, rather than try to blaze a new path.

Unfortunately, some people will replace a blown fuse with the next larger fuse size, and this can have really bad effects. When you install a larger fuse than the manufacturer or installer chose, you are taking some very large risks. You aren't taking into consideration that the fuse chosen passed all the tests required to get it onto the market, certified, and so on. You aren't thinking about the temperature changes, the operating considerations of electricity under these conditions and so on. Please consider that the fuse chosen by the manufacturer worked until just now. Please understand, that something just changed, and it either has to do with the power going in, or the amount of power being consumed by the device. Not only that, the amount of power is fairly significant percentage wise.

If you have a piece of equipment, like an amplifier or television, that has played fine for a while with a fuse installed. When the fuse blows, choose the same size fuse, and just replace it. DO NOT replace it with a larger fuse. The larger fuse will simply allow damage to occur in your electronics faster, and actually lessen the protection to the system. If you already have a problem, this magnifies the effects, and doesn't help you run your toys either.

To troubleshoot audio systems, you might even consider using a fuse that is approximately 50% or 1/2 of the rating of the one you have installed. This is especially useful for car stereos, amplifiers, and speaker configurations. You can also do this with many other electronics that can be turned up to full power, and down to idle. To test, you replace a 50 amp blown fuse with a 25 amp fuse temporarily. Now power up the 500 watt amp, and see if the electronics work. If you have a short in the system, you will see the fuse blow immediately, otherwise, you should be able to turn the thing on, power it up, and sit there without load. The system should also work at very low volume, should the fuse blow immediatly, you know you have a major short somewhere in the electronic hardware. If the stereo plays clean on the 25 amp fuse at low output levels, but blows the 50 amp fuse under normal operation, check the amplifier for shorts which show up under power conditions. If the stereo sounds bad, check the speakers and or wiring for shorts.

How a fuse blows: What eventually happens with anything is a failure. When there is a failure inside your electronics, be it a transistor, resistor, capacitor, or other electrical building block, the component fails, due to more or less electricity going through. Less electricity just means the system won't run, but too much electricity can lead to fires and more. A fuse senses the usage of more power than normal, and shuts down operation before the other items in the system have a chance to blow up. Many times when a component fails and the fuse blows, the whole component should be replace before installing another fuse, but this is the real world. Instead the fuse is just replaced and life continues.

Now since the fuse has likely been passing a fair amount of current prior to the failure, enough to make something fail, the fuse was allowed to heat up over time. When you install a new fuse without installing a new component, you insert a new (cool) fuse. This cool fuse will take more current to blow it, even though the fuse is identical to the one prior, because it hasn't heated up to the circuit. When at full load, most electronics are operating at the upper end of their safe area (especially common with budget electronics), and simply replacing the one part doesn't ensure the safe operation of the system. Let the whole system cool to ambient temperature before you try again. The new fuse might not blow before the power supply components (if the short is in the power consumption side), or before the power consumption components (if the short is in the power supply side). If the power supply components are destroyed along with the power consumption components, the repair bill will be significantly higher and the point of the fuse in the system is moot.

When you blow a fuse, check the components around it for problems

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