Corrosion problems can pop up when you are passing current through areas
where it wasn't intended to go.   My gear takes hot and ground directly
from the battery, with fuses in both lines.


On Sat, Dec 28, 2013 at 7:39 AM, Matt Bennett <mattpiclist@hazmat.com>wrote=
:

> On Fri, December 27, 2013 8:24 pm, Justin Richards wrote:
> > There has been several discussions regarding the best practice with
> > regards
> > to grounding devices and batteries in vehicles.
> >
> > Some recommend that the device is grounded as close as possible to the
> > device to the chassis.
> >
> > Other suggest running a negative lead all the back to the battery or to
> > the
> > battery earth point.
> >
> > I once considered it best to run both a negative and positive lead all
> the
> > way to the battery.  However, over time I have been convinced that usin=
g
> > the chassis provides a superior return as it will offer less resistance
> > and
> > reduce ground loops. (Reduce ground loops as in the case where the
> chassis
> > of the device comes into electrical contact with the chassis of the
> > vehicle
> > and there is also a negative return lead to the battery).
>
> Grounds in vehicles can be really flaky- Big hunks of steel or aluminum
> can have pretty low resistance, but the impedance (as you go up in
> frequency) gets pretty poor. All that said, the biggest source of problem=
s
> is the connection- you can get rust and other corrosion with 2 dissimilar
> metals in contact with each other.
>
> Since there is higher impedance with the chassis ground- current across
> that ground conductor causes a voltage, and if you are referencing signal=
s
> between 2 different points on the chassis, there can be a lot of
> difference particularly with higher frequency signals.
>
> Since you mention (in a later/separate message) that it is for an
> auxilliary battery for a fridge--- I doubt it cares too much about higher
> frequencies, though compressor motors can draw very high current when
> starting. If the compressor motor sounds like it is struggling to start,
> you need a better ground. In that case, big copper wires are your friend.
>
>
>
> Matt Bennett
> Just outside of Austin, TX
> 30.51,-97.91
>
> The views I express are my own, not that of my employer, a large
> multinational corporation that you are familiar with.
> --
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>
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