[SI-LIST] Re: Can a thin PCB trace be used as a reliable fuse
- From: "Brent DeWitt" <bdewitt@xxxxxxxxxxxxx>
- To: "'Si-List'" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 25 Aug 2004 20:52:12 -0600
I'm not a safety guy, but it would seem there are situations where a
non-repairable fuse makes sense. All you have to do is justify the cost
savings per board times the probability of failure and compare it against
the total board replacement cost (including service). Cheap boards with
highly unlikely failures might make a whole lot of sense.
Brent DeWitt
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Kai Keskinen
> Sent: Wednesday, August 25, 2004 6:42 PM
> To: Mark.Hofmann@xxxxxxxxxxxxxxx; a.ingraham@xxxxxxxx; 'Si-List'
> Subject: [SI-LIST] Re: Can a thin PCB trace be used as a reliable fuse
>
>
> Yes, you can use a thin trace as fuse. How do you fix the thing when the
> "fuse" goes? Do you build a new pcb and populate it again? The whole point
> of a fuse is that you change the fuse if there is a fault. You don't throw
> away the PCB.
>
> Cheers,
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Hofmann, Mark
> Sent: Wednesday, August 25, 2004 10:59 AM
> To: 'a.ingraham@xxxxxxxx'; 'Si-List'
> Subject: [SI-LIST] Re: Can a thin PCB trace be used as a reliable fuse
>
>
> Well, I hate to say this, but this very thing was done at a company that
> makes fire alarm panels. If UL allowed that, they'll probably allow it in
> your application as well. Just remember that the i2t value of
> the trace can
> vary WIDELY. How wide? I think it was on the order of +/- 50%.
>
> Mark Hofmann
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Andrew Ingraham
> Sent: Wednesday, August 25, 2004 9:47 AM
> To: Si-List
> Subject: [SI-LIST] Re: Can a thin PCB trace be used as a reliable fuse
>
> I don't know the regulatory details here ...
>
> ... but I'd be very concerned about things like fire. When a trace blows,
> is there a flame? In a packaged fuse, it would be contained within the
> package. Not so with an open trace.
>
> Even if no flame, does something melt, and could it fall somewhere else?
>
> Are toxic materials released, due to the uncontained nature of your
> makeshift fuse?
>
> I would not think that a thin board trace would make a very reliable fuse
> with good repeatability, but that's not much more than a guess. External
> layers have loose tolerances on trace thickness, because of the
> way they are
> made and because it has minimal effect on Zo.
>
> Also I'd think that the heat sinking properties of the board
> might make it a
> rather slow acting fuse, and in the meantime a lot of the board "cooks" as
> well as all nearby components (you did say you are tight on space).
>
> Even attaching short lengths of nichrome wire might be better (if nichrome
> makes a good fuse)...
>
> Regards,
> Andy
>
>
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