Fuse Limits
Fuses are representations of the weakest link within a circuit; should a problem occur within the circuit, such as too much amperage, a fuse will "blow" and the next weakest link within the circuit, such as the wiring, to fail.
In an attempt to blow a fuse, an 8-amp fuse was used with a power supply capable of producing up to 10 amps at a constant 12 volts. This setup represents the circuit that can be found in an older car. Older cars are prone to blown fuses, and this experiment is an attempt to learn how many amps are required for the fuse to fail. The assumption is that 8 amps is the maximum amperes that the fuse is designed to withstand, and 9, or 10 even, will cause the fuse to blow.
During the experiment, the power supply was connected with the fuse, with a multimeter verifying the amperes in the system. 12 volts was initiated and the amperes were increased from 0 to nearly 10 amps. During this time the fuse did not blow. Once the amperes reached a maximum value, the power supply continued to produce the same 12 volts and 8 amps for several moments; still, no result.
With further research, it was discovered that there is a curve for every fuse with axis amperes vs. time. Two asymptotes separate the curve into the positive quadrant, as shown in the figure to the right.
[GRAPH]
A value of extremely large amperage will cause a fuse of this type to blow in an extremely small amount of time; conversely, an amperage slightly above the rated value of the fuse will cause a failure in a long amount of time.
Using this new concept for understanding the maximum load in a fuse and reflecting back and the experiment, it becomes obvious that the value of 10 amps will not produce a failure for at least 100 seconds. This suggests that failures within the circuit of a car are most likely due to very high amperes for a short amount of time, rather than slightly high amperage for a lengthy amount of time. This is concluded with consideration of the fact that a car would be designed with fuses that meet the requirements that will not be reached, rather than a car being designed with amperage slightly above, at, or above the maximum rated value.
Source of graph:
Electronic Fuse Catalog
http://www.circuitprotection.ca/
