Electronic – Blow MSP430 security fuse with FET430 or MSP-FETFlash programmer

The 180W reasoning is wrong. You don't have the full 12V across the fuse, only a fraction of it. Say the fuse has a 0.1\$\Omega\$ resistance, then 15A will cause a power dissipation of

\$ P = I^2 \cdot R = (15A)^2 \cdot 0.1 \Omega = 22.5W \$.

And that 22.5W in the thin wire is just too much, and the fuse will blow.
Note that the 12V doesn't appear anywhere in this, and you could do the same calculation for 15A at 230V AC. There's a "but", however. Fuses do have a rated voltage. Not for the blowing, as we've seen, but to make sure the remains of the fuse won't cause sparks when at a high voltage. So you can't use a 12V car fuse in a mains appliance, but the other way around should be safe.

Automatic fuses also react on current only. They have a coil which releases a latch if the number of coil-windings exceeds the rated value. Also here it's independent of voltage.

To get useful data points it's helpful to look at what the fuse will likely do from a datasheet:

At the standard temperature (usually 25°C) and 1A, a 600mA-rated fuse will typically blow in about 15 seconds. The time will be less if the ambient temperature is higher, and greater if the temperature is cooler than 25°C, but even a +/-10°C ambient change will only change the effective current rating by about -/+5% (see below).

You can measure the current through the light bulbs without the fuse and see if you can get current values that make sense from the perspective of the fuse characteristics. Putting an overvoltage on an incandescent lamp reduces its life by something like the 13th power of the voltage.. so you may burn out the lamps (keep in mind that the fuse element is thicker and will respond more quickly than the fuse) but you may be able to get useful results. Even if the life of a 1000 hour bulb is reduced 10,000:1 it will still operate for a number of minutes.

Complicating factors:

• Currents in the 1A range are more than what a PP3 9V alkaline battery may be able to supply, and it may significantly reduce the output voltage of even a fresh high-quality AA alkaline cell.

• The lamp filaments will increase in resistance when they get hotter, so with over-voltage they won't give you as much current as you might expect.

If you want to do a useful experiment, you should monitor the current (for sure) and also the voltage.