Homebrew PCBs

I'm a fan of PPTC (Polymer Positive Temperature Coefficient) fuses for on-board protection.  Quick enough for most purposes, self-resetting after the fault is removed, available in many sizes and ratings.

Try a web search for such trade names as: PolySwitch, OptiFuse, Multifuse, Polyfuse or for PPTC

Donald.
----- "Sz G" <the6hu8b@...> wrote:

> Sorry for the inline comments. It wouldn't make any sense otherwise.
> Hope it does this way :)
> 
> > ________________________________
> > From: Stefan Trethan <stefan_trethan@...>
> > To: Homebrew_PCBs@yahoogroups.com
> > Sent: Tue, March 9, 2010 10:25:58 PM
> > Subject: Re: [Homebrew_PCBs] PCB fuse
> > 
> >   
> > You appear to be under the impression that fuses should be
> replaceable?
> > 
> 
> He's not alone. Not sure if anyone cares, but I also think it's a much
> better idea to have a fuse enclosed in an electrically and thermally
> (!) isolated container rather than a trace on the PCB itself. I'd find
> it hard to find any reason to choose the latter over the former. Any
> defect in the manufacturing process (or a minor difference in the
> choice of materials, like using another laminate with slightly
> different properties) could render a "PCB fuse" worthless. Not to
> mention that it could aggravate the issue by creating another possible
> source of fire hazard and damaging the PCB if higher currents are
> involved.
> 
> > Usually this is not the case, fuses are there to prevent fire
> and/or
> > other danger if something goes wrong.
> > Changing the fuse will not solve the problem, since it blew for a
> reason.
> > You are supposed to throw the thing out once it is broken, not
> repair it. ;-)
> > 
> I'm pretty confused now. Sure thing: fuses (in the majority of cases)
> blow because the POS behind them drew more current than it should
> have. But I certainly don't feel like wasting hundreds or thousands of
> $'s worth of fine electronics if an electrolytic capacitor decides to
> give up in a SMPS, even if I'm supposed to. In fact, I believe that no
> one should, at least as long as repairs are (financially) feasible.
> Most people won't even attempt repairing a faulty component on their
> own and if they do, they're aware (or at least they should be) of the
> risks associated with the procedure.
> A skilled technician or engineer on the other hand would find it
> _really_ annoying if they were expected to find a way to "replicate" a
> blown PCB fuse. In fact, the only thing they could responsibly tell
> the customer is to throw it away, because it's clearly not meant to be
> repaired.
> 
> > The only situation where a replaceable fuse makes some sense is if
> you
> > have like an outlet or something to which the user can connect
> stuff.
> > But more and more the trend goes towards not providing a user
> > replaceable fuse because people can't be trusted to replace with
> the
> > same rating, no matter how many warnings you print on.
> > 
> I couldn't agree more. People with no experience working with
> electronics shouldn't be trusted with this. That's why they came to
> mount the fuse holder inside the case on the PCB (or somewhere else
> where it's inaccessible from the outside) - still replaceable, but
> only by those who make an explicit decision to disassemble it.
> 
> Gabor
> 
> > ST
> > 
> On Tue, Mar 9, 2010 at 9:57 PM, David Griffith <dgriffi@....
> edu> wrote:
> 
> > I'm curious why someone would want to use such a fuse in the first
> place.
> > How do you replace it?  Are there pads for adding a fuse holder
> after the
> > PCB fuse blows?
> >
> > --
> > David Griffith
> > dgriffi@.... edu
> >
> 
>  
> 
> 
>       
> 
> 
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