There are pros and cons.
Nothing beats the reliability and speed of fuses, but they are inconvenient
to replace. Circuit breakers are more convenient although less reliable, but
is a happy medium. Polyswitches are useful in unreachable areas, but are
slower to trip and sensitive to ambient temperature.
It depends on what you are trying to protect. If you are trying to protect
your electronics from surges, then polyswitches are probably the least
favorable. Your electronics would probably be fried before the switch trips.
But in mechanical drives and motors they could be ok.
On Sat, Jan 10, 2009 at 9:50 AM, Frans Veldman <frans@paardnatuurlijk.nl>wrote:
> >
>
> craig bastin wrote:
> craigb@onthenet.com.au>
> >
> > for those of you up to the electrics stage, i found these
> >
> > http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2592
> >
> > they look like they might be a good replacement for circuit breakers
>
> It appears to me that these are PTC-resistors. Downside of these things
> are that they will never really cut the power, but remain in such a
> state that the heat development is just enough to increase the
> resistance enough to remain in some sort of balance. Another problem is
> their relatively high resistance. You will loose some voltage over these
> things, depending on the amount of current you are asking. Near their
> cut-off current, the voltage drop is sufficient to convert some of the
> energy into heat, it is the heat which will increase resistance even
> further, and that is why there is some limit in the amount of current
> you can ask from it.
> With other words: These things have no clear on-off states, but
> everything in between instead. Depending on your purpose, this is
> allowable, or it is not.
>
> It might be an option to power non-trivial small devices through them
> (like a GPS) where the current remains significant below the cut-off
> current, but I would not use them for, let's say, the fuel pumps, the
> flaps, or the radio. In general, all equipment with changing current
> demands and higher current demands are unsuitable.
>
> Oh, and you can't instantly reset them. They need to cool down first
> after they "tripped". Not bad for your GPS (unless you are in the middel
> of an GPS-IFR-approach), but not so smart for the fuel-pumps, flaps, etc.
>
> Actually, I would stay away from them.
>
> Just my 2 cents.
>
> --
> Frans Veldman
>
>
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