I wanted to do a test on a PTC Resettable Fuse because I have never used them before and I wanted to personally see it work. The test was done on a breadboard and basically is a simple circuit with a Bourns MF-R050-2 connected as a short across a mechanical switch to a 5V lab power supply with 5A current limitation turned on. The fuse is about half on ohm cold. When the switch is closed the lab power supply spikes to 5A and immediately ramps down, quickly settling at 0.19A. The polyfuse gets hot. If I trip off the power and test the hot fuse by applying probes as fast as possible, resistance is about 10 ohm, quickly ramping down. It must have been around 26 ohms with power applied. I suppose this is expected behavior, right?
Only question, how reliable are these things after abusing them like this? Should I put it back into the kit or toss it now? Forty-six cent question, please answer carefully.
MarkT:
The clue is in the word "resettable" or do I miss something?
It gets pretty hot under these conditions. But I guess that is what it does well. So no matter to what level it is abused, it will always still be in new condition?
MarkT:
The clue is in the word "resettable" or do I miss something?
It gets pretty hot under these conditions. But I guess that is what it does well. So no matter to what level it is abused, it will always still be in new condition?
Your particular part is spec'd that testing with voltage and amperage 60V and 40A (the maximums) that there is no visible damage after 100 trips.
I had your same question as well and was digging through spec sheets from Polyfuse for the answer. They don't specify any type of trip limit either. I suppose the assumption that they can trip "forever" would be accurate.
I've used a 5A resettable fuse to charge a 1 Farad capacitor ... its been working steady for 8 years. They're commonly used in automotive power window circuits and are subjected to daily shorts without failure. For reliability, I think the only thing to be concerned about is keeping within the voltage rating.
