T&L Publications

How about a not-a-fuse fuse?

In a test-bench situation:

• A fuse blows, that's annoying
  A solid state fuse can oscillate. ( set-reset loop )
  A resettable fuse can oscillate. ( set-reset loop )

So, what else?

How about this. Lets say you want to replace a 10 A fuse at x volts. What if this "fuse" only allows 10 amps even at a short circuit? That way there will never be a short-circuit.

And you want that for alternating and direct current ?

DC battery pack.
I just built a 3 cell lithium pack. So about 9 - 12 volts.
I also built one last year that uses one cell lithium ion pack at 3 - 4 volt.

Look into the way a programmable power supply works. The kind where you can set both voltage and current.

"A solid state fuse can oscillate. ( set-reset loop )
A resettable fuse can oscillate. ( set-reset loop )"

Can you give an example of a fuse or circuit breaker that self resets without user intervention? Something called a "fuse" should not self reset

What is a solid state fuse? Do you mean a voltage or current limiting circuit?

There are many types of fuses and the time to blow relative to a given continuous current is one of the selection specs. For example, compare fast blow and slow blow fuse specs for the same current rating. Slow blow fuses are used when that margin is small and it is allowed to come close to or even slightly exceed the rating periodically, it prevents unnecessary blows during short surges and works best for motors and inductive loads. Fast blow or instrument fuses blow quickly close to the rated value to protect more sensitive electronics from secondary failures resulting from a primary short circuit failure.

You should not use a fuse as a current limiter, it is intended to be protection of last resort and normally requiring operator inspection prior to resetting to discover the reason. Ideally it has a rating well above what the circuit needs to operate and well below what any conductor would need to get hot in a short circuit fault situation.

I think what you are saying is that if you place a fuse with a rating higher than the current limit of the supply it should never blow. For example a 10A fuse should not blow if the supply is limited to 10A or less. True, but a fuse is not there to protect against normal operation. If the supply has a failure that damages the ability to limit current, more than 10A may be possible, that's when the fuse does its job. That job is not to prevent that initial failure, it was to prevent a fire that may have resulted from greater than 10A through a wire for too long.

Extending from that, putting a 20A or greater fuse on an AC power cord is a waste of time because the circuit breaker in the panel should blow at 15A or 20A (for most US household branch circuits). Since a fuse's purpose is to prevent fires, it should carry a rating lower than the smallest conductor current rating in the assembly so any dead short does not generate enough heat to cause a fire.

For some ideas, look on XrayTonyB's YouTube channel. His recent video, https://youtu.be/aIdVdDziOCs , shows the electronic circuit breaker he built, based on Glasslinger's design, around 21 minutes in. You can go back about a year (2019 +- ) and find the build.

A PTC Resettable Fuse will reset once the current is reduced.
User intervention, like turning something off may be needed to stop the current, but the device itself does not need replacement or resetting.
If the fault current burns the short clear, then it will reset, but by then, there may be no current to restore!

I see, I had not paid much attention to those before, Here is a bunch more info
https://www.littelfuse.com/products/pol ... -ptcs.aspx

In the OP application, unless you strap one of these to a heat source, one should not experience oscillation if the right device is selected. They seem to have hysteresis between when they trip and when they reset and the amount is a selection parameter.