I repeat myself, but my Tiptop Eurorack supply trips right away if I short it. So does the ATX breakout I use on the bench. I don’t know what kind of resettable fuses they use (not through hole, I think) but clearly there are ones that work.
Anyway, the module power consumption is under conditions when you don’t want the fuse to trip, so I don’t see how it’s at all relevant.
I do have some polyfuses I haven’t actually experimented with. I should, I guess.
I mean I suppose if we’re just looking at protecting against a dead short then it really doesn’t matter because your power supply will dump everything it has through that fuse and it will blow.
I still hold that a 60V, 100mA polyfuse won’t trip or will trip much more slowly at 12V 100mA.
It would be easy enough to test. The fuse starts off at around 0 ohms at room temperature, so just put it in series with a 120ohm resistor and a 12v constant voltage source.
Then after it’s cooled down compare it with a 30v constant voltage source (since most bench supplies don’t go to 60v) and a 300ohm resistor.
So, did you make this test ?
At least from a theoretical point of view (I have never used polyfuses, and don’t have any to test…), they will “blow” at exactly the same rate.
I’m curious about this too. My plan for reverse voltage, over-current, and power conditioning in my modules is a pic poly fuse between the IDC header and the rest of the circuit, then a 10uF electro cap and a diode between each rail and ground. My problem is that I know enough to think to put those things into my power circuit, but I’m not enough of an engineer to know what kind of diode or what amperage of fuse to use. I’m guessing that 100mA should be enough since most modules seem to typically draw around 25-50mA. Or should I be using a fuse more closely rated to the actual current draw of the module? I guess I’m joint to have to to some reading on diodes and get some poly fuses and do some experiments. Anyone have suggestions?
I can’t think of a situation a PTC fuse would address other than a power rail short, and then the current will be way over 100 mA. Otherwise for most modules 100 mA would be well over normal current, so I think that’s likely to be good. But a few modules might approach 100 mA normally.
In case of a power cable reversal, diodes to ground will protect your module, but will short your PSU to ground. Of course if there’s a PTC fuse it’ll trip, no harm done, probably. I’d probably go for something like a 1N4004 rectifier in that case. What I always use is 1N5817 Schottky diodes in series on the rails. That drops the voltage by ~200 mA but protects against power reversal with nothing dramatic happening like fried 10R resistors or tripped PTC fuses.