[aprssig] Negative Fuses

Curt, WE7U archer at eskimo.com
Wed Jan 25 10:46:13 EST 2006

On Tue, 24 Jan 2006, Robert Bruninga wrote:

> >>> rgilson at adelphia.net 01/24/06 7:45 PM >>>
> > I can't help but wonder why for many many years
> >Motorola or GE  never put a fuse in the ground of
> >their commercial radios(tubes and transistors).
> Because you dont need one if you connect the
> negative lead of the radio independently to
> FRAME ground near the battery.  A failure of
> the battery connection cannot then damage your
> radio.
> But you MUST have a fuse in the negative lead if you
> connect your negative lead *directly* to the battery.
> Ham equipment comes with the fuse, because they
> assume the ham might connect it that way.
> A pro installer would never do that.

Now _that_ makes sense!

I've been tweaking my install methods over the years hoping to come
up with the perfect method.  Every time I see the issue discussed I
get different info.  One of the things I've been trying to minimize
in the past is engine noise coming into the radio via the power
wires, so I've tried to take both leads straight to the battery, or
as near as I can get, with #10 or so wires to minimize drop/give me
max power out when I need it.  The Jeep has the red wire doing to
the power distribution stud right next to the battery, the black
wire going right to the battery terminal.  I thought that was the
"right" way to do things.

Now:  If the strap from the battery to the frame goes bad I have a
good solid high-current connection from the frame to the battery via
the antenna (or perhaps through the radio mounting bracket), through
the radio, through that #10 ground lead right to my battery.  I have
both leads fused right near the battery so I shouldn't get a fire or
anything, but I still will get excessive currents flowing right
through my radio until that ground-lead fuse blows.

If instead I take that #10 wire and put it to the frame as close to
the battery as I can electrically (but NOT to the stud where the
strap attaches!), then if the cable from the frame to the battery
goes bad I won't end up replacing that connection with my radio.  I
think I have all that straight now.

So, this covers me if the battery->frame cable isn't making
connection properly.  What about when the engine->frame strap isn't
making connection?  In that case, it doesn't appear that it'll go
through the radio with either wiring method, but the starter motor
won't get any juice.  Do I have it right now?

Even though I might not need the fuse in the negative lead with this
better wiring method, because of my prior experiences I'd put one in

Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
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