That matches my recollection. The temperature derating is even worse. If you rate for say 1A hold current at 150F, you may end up with 2A or more hold current around 0F, with that 12 seconds being effectively at 4A when cold.
About the only place I'll use a PTC fuse anymore is where there is not likely to be a fault but you want to survive a short anyways. For instance, I'm thinking about adding one in the ground connection on the SiteMonitor bus to help avoid permanent damage when a customer accidentally mixes a positive ground device into a system. On Mar 21, 2016 4:37 PM, "Chuck McCown" <[email protected]> wrote: > 12 seconds at double the hold current at room temp if I am reading the > specs right. > > *From:* Adam Moffett <[email protected]> > *Sent:* Monday, March 21, 2016 2:32 PM > *To:* [email protected] > *Subject:* Re: [AFMUG] Fuse question > > 12 seconds with a dead short, or 12 seconds when slightly over current? > That might be two different answers. > > > > On 3/21/2016 4:17 PM, Chuck McCown wrote: > > Yeah, it does sound a bit pointless. > > *From:* Josh Luthman <[email protected]> > *Sent:* Monday, March 21, 2016 2:16 PM > *To:* [email protected] > *Subject:* Re: [AFMUG] Fuse question > > 12 seconds for a fuse to pop??? How is that event a fuse. That sounds > pointless. > > > Josh Luthman > Office: 937-552-2340 > Direct: 937-552-2343 > 1100 Wayne St > Suite 1337 > Troy, OH 45373 > > On Mon, Mar 21, 2016 at 4:14 PM, Chuck McCown <[email protected]> wrote: > >> The poe card would not be the cause, it would be the victim. The AP or >> wiring would be the cause. >> >> The polyfuse I am looking at takes 12 seconds to blow. Trying to >> protect the power supply and other loads in parallel. >> Not sure if that is fast enough to be of great value. >> >> If one AP shorts out, you don’t want it taking down others that are off >> the same power supply. >> >> *From:* Josh Luthman <[email protected]> >> *Sent:* Monday, March 21, 2016 2:07 PM >> *To:* [email protected] >> *Subject:* Re: [AFMUG] Fuse question >> >> >> Meh just replace the card if it's being troublesome. >> >> Josh Luthman >> Office: 937-552-2340 >> Direct: 937-552-2343 >> 1100 Wayne St >> Suite 1337 >> Troy, OH 45373 >> On Mar 21, 2016 4:05 PM, "Chuck McCown" <[email protected]> wrote: >> >>> Well, they have their downside. >>> A real fuse will be easier to notice when it is blown. >>> A poly fuse just cuts the current way down. >>> More of a troubleshooting issue than anything else. >>> >>> But, if a fuse is blown, then you have to fix the circuit and find a >>> replacement fuse. >>> I do have LEDs and by unplugging the short circuit cable the LED should >>> come back to full brightness. >>> >>> Just thinking out loud here. Want to make the right choice. >>> >>> *From:* Josh Luthman <[email protected]> >>> *Sent:* Monday, March 21, 2016 2:02 PM >>> *To:* [email protected] >>> *Subject:* Re: [AFMUG] Fuse question >>> >>> Cheaper to run a polyfuse...why bother asking??? >>> >>> >>> Josh Luthman >>> Office: 937-552-2340 >>> Direct: 937-552-2343 >>> 1100 Wayne St >>> Suite 1337 >>> Troy, OH 45373 >>> >>> On Mon, Mar 21, 2016 at 4:01 PM, Chuck McCown <[email protected]> wrote: >>> >>>> Still leaning toward the polyfuse. Not a lot of room, fuses and fuse >>>> holders are more money. >>>> >>>> *From:* Bill Prince <[email protected]> >>>> *Sent:* Monday, March 21, 2016 1:51 PM >>>> *To:* [email protected] >>>> *Subject:* Re: [AFMUG] Fuse question >>>> >>>> Most of ours are now the DIN-mounted double feed that uses the 5x20mm >>>> glass fuses. However, we also have a few legacy sites that use the >>>> automotive blade fuses. >>>> >>>> If something new came along, we would use what it uses. >>>> >>>> bp >>>> <part15sbs{at}gmail{dot}com> >>>> >>>> >>>> On 3/21/2016 12:47 PM, Josh Luthman wrote: >>>> >>>> We already stock 5x20mm fuses so keeping with the same form factor >>>> would be nice. Anyone else using those same DIN clip fuse holders have the >>>> same. >>>> >>>> >>>> Josh Luthman >>>> Office: 937-552-2340 >>>> Direct: 937-552-2343 >>>> 1100 Wayne St >>>> Suite 1337 >>>> Troy, OH 45373 >>>> >>>> On Mon, Mar 21, 2016 at 3:40 PM, Adam Moffett <[email protected]> >>>> wrote: >>>> >>>>> I have no strong opinions sir, but if it's a replaceable fuse I do >>>>> like the automotive blades because every gas station has them. >>>>> >>>>> >>>>> On 3/21/2016 2:42 PM, Chuck McCown wrote: >>>>> >>>>> I am considering adding a fuse to a new version of my rack mount POE >>>>> surge suppressors. >>>>> >>>>> I know many of you like PTC resettable solid state fuses. I don’t >>>>> recall ever designing one in to anything. >>>>> Maybe I did on a phone device years ago, but that would have been to >>>>> satisfy a regulatory agency only. >>>>> >>>>> Studying up on them I learn that if you have a 1 amp “hold current” >>>>> the “always trip” current is 2 amps. >>>>> Not like a fuse, which is pretty well guaranteed to trip at any >>>>> current over the rating if you wait long enough. >>>>> >>>>> For a polyfuse, if your load is one amp, you have to have a design >>>>> value of greater than 1 amp hold current. >>>>> But then it takes double that to actually trip.. >>>>> >>>>> And then there is leakage current required to keep it in the tripped >>>>> condition. >>>>> It does not totally break the circuit. >>>>> >>>>> They are fairly inexpensive compared to glass fuses and fuse holders. >>>>> Could do auto blade fuses too. >>>>> >>>>> Not sure I have the room for anything but a polyfuse though. >>>>> >>>>> Anyone have strong opinions about this? >>>>> >>>>> >>>>> >>>> >>>> >>>> >>> >> > > >
