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Fuses as in classical wire types blow when the wire melts or fuses. This gives rise to a current rating, and some overload capability due to the heat capacity of the wire. There is some ambient temperature dependence on the fusing current. Reputable manufacturers state this in their curves. My question is what about air flow? Surely a fuse bathed in lots of turbulent airflow from a fan would would have a higher fusing current? How significant is this? Could you set up a system where if the airflow failed the fuse would blow?

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  • \$\begingroup\$ Perhaps air flow could be a factor. Note that a lot of fuses are placed in an enclosure to protect them from the elements, accidental touch, etc. but also to contain the effects of them rupturing when they are subjected to high current or a high energy pulse. \$\endgroup\$
    – ErikR
    Jun 19, 2021 at 23:36
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    \$\begingroup\$ Could you set up a system where if the airflow failed the fuse would blow? ... google crowbar circuit \$\endgroup\$
    – jsotola
    Jun 20, 2021 at 0:03

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Nearly all fuses are enclosed in a glass or ceramic envelope with no real thermal path from the fuse wire itself to the outside environment, so there shouldn't be much of an impact.

Fuses aren't generally carefully chosen for their tight tolerances on blow time under long-term slight overload conditions, so changing the blow time at some slight overload condition from 10 hours to 10.5 hours isn't exactly a problem--and if it is, you should rethink your system design. Fuses only blow quickly under very large overload conditions, where there wouldn't be time for any significant amount of heat to conduct out of the fuse anyway.

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From your question you want to shut down if there is no airflow. Typically to detect air flow you use a switch called a sail switch. They can be gotten in lots of configurations and are not that expensive. One usage example is for RV furnaces. They must show air flow or the unit will not start or keep running. Search for: "sail switch".

For the temperature you could add a over temper sensing device such as a thermal disk, which are usually rated at a trip temperature. When it trips it can have the logic keep it off until the proper conditions are met that will allow it to reset.

Having the thermal disk blow the fuse is easily accomplished but it would be much more economically to just shut it down.

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