[amsat-bb] Re: FT-847 Disaster - THE PAIN!
ham at g4dmf.co.uk
Fri Dec 28 03:38:00 PST 2007
> > In the commercial world of radio's (R/T) the Tait/Motorola/etc rigs have
> > all sorts of "idiot proofing" built in....the most useful ones being
> > FAST blow fuses or circuit breakers combined with a very large (>100
> > amp) suicide diode in the main power leads to remove power really,
> > really fast in the event of a major problem.
>Just remember, as soon as you make something "idiot-proof", nature will
>invent a better idiot...
A fuse and sacrificial diode are all very well, BUT.. Fuses take time
to rupture, and a power transisistor always has, and always will be
the fastest fuse on 3 legs... or 4 or whatever.
For higher power items, I prefer the Idiot-Proofing method of a big
relay!... Car accessory type of thing, in series with the input line,
and the coil energized with a smaller diode!.. Wrong polarity, no
coil current, so no power to item. It also has a zero volt-drop
advantage. Smaller items are catered for with a SERIES diode, the
0.7V volt drop rarely has any effect on smaller items, as they tend
to be internally regulated to lower voltages anyway.
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