RTFDS -- and if there's no datasheet, run like hell!
e.g.
formatting link
Note the time current curves: it can take very long indeed for a 1A fuse to open at, say, 1.9A (hours) -- down in the range where ambient temperature and vibration matters.
The response gets fast when the element melts, slumps and vaporizes faster than the blink of an eye, which may give closer to your estimated 3x multiplier (< 0.1s say).
Note also those curves are average. The min/max are given on the first page. 1A at 275% says max 2s, min 50ms.
Fuses are most effective at stopping fault currents, typically hundreds of amperes for residential mains. Potentially, hundreds of kiloamperes for industrial and distribution applications! Moreover, fuses that blow too quickly are seen as a nuisance, not a safety feature -- can you imagine! Often, handling a 100A inrush surge for a couple cycles is a requirement.
Keep this in mind when designing fuses and surrounding circuitry.
One final note, remember the transistor dies in a hundred microseconds. Ten thousand microseconds later, the fuse begins to melt. The transistor protects the fuse, never the other way around.
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
wrote in message
news:e45d5436-af22-4bea-9c3a-baad00a1dd90@googlegroups.com...
I was curious about the actual current needed to blow my newly purchased set
of 250V 20mm fuses. Half a dozen experiments with 0.5A, 1A and 2A samples
indicated a multiplier of 3.0-3.5. For example, 3.4A to blow a 1A fuse. Is
that typical?
P.S: While googling about fuses I came across this scary incident on a
rather larger scale:
https://m.youtube.com/watch?v=GPqcPoZgPMk&t=529s
incident is at 08:49.
Terry, East Grinstead, UK