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[aprssig] RE: D700 Honda Odyssey Mounting Options

Dave Baxter dave at emv.co.uk
Wed Nov 16 09:49:42 UTC 2005


It was actualy me that wrote the first bit!...

> Brad [VE3BSM] wrote:
> 
> >If you run a seperate power cable for the rig, including the 
> -ve lead 
> >direct to the battery, remember to fuse the -ve wire too, or a loose 
> >battery ground strap (it does happen) can become very expensive when 
> >you next try to start the engine!..
> >  
> >
> Sorry, I still don't see this.  Would not the starter be a 
> parallel connection?  If the Battery groud lead was 
> disconnected how would the starter current go through the 
> radio?  Assuming the radio power leads run directly to the 
> battery (Both + and - leads).
> 
> I believe I am missing something but just don't see it yet, sorry. 
> Working on cars is one thing I attempt to avoid at all costs.

OK...

Typical system, engine and battery have seperate grounds to the frame.

If one fails, the battery is dificult to charge, and the engine is
difcult to start, due to the extra losses...

However, if there is a parallel ground path between the batt' -ve and
frame (the radio lead, radio, coax etc) then if the battery ground goes
iffy, when you try and start the engine, "quite a lot" of current will
flow via the radio ground.   It's that current that can and will totaly
fry a radio if it happens.  From the sound of it, at least one other on
this list has had experience of that in the past.

Before that happens, the charge current from the alternator will also
travel that route.  And we all know what alternator whine sounds like.
Posibly an indication of faulty earthing, more often thatn not though,
sign of one phase of the alternator failing.  (They are 3 phase
machines, with at most 6 point recitification)

Note, I made no mention of the +ve side.  That's rarely a problem as far
as failure due to "Ground Fault Currents"...

Hope that helps explain the posible problem...

Dave  G0WBX.

PS:	Out of office for the next two days...  Ah, peace and quiet!...




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