[Elecraft] OT: 2017 Chevy Silverado 1500 power outlets

[Clay Autery]

For some reason, the following detailed response did not "reflect"...
Resending...
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1) There is NO GROUND in an automobile.  There is a return plane that
effectively ACTS as a ground.... if you choose to look at it that way.
2) The "Negative" terminal of the battery IS the return point...  The
theoretical point of lowest potential...  (not really, but that's a
whole other discussion that would just confuse the issue here).
3) EVERY other so-called "ground" in the ENTIRE system is an
APPROXIMATION of THE return at the Batt (-) post.
4) I don't "suppose" anything in my circuit design.... TWO
hypotheticals?  BUT...
5) Yes, we'll assume hypothetical #1....  I am ABSOLUTELY going to
connect my HF radio, along with my also very expensive stereo DIRECTLY
to the battery via BOTH BATT (+) and BATT (-) using VERY large
conductors in order to keep the resistance as low as possible.
6) Hypothetical #2 is simply laughable... ANY system that has only ONE
low resistance return path to BATT (-).  Even the STOCK electrical
design had more than one "ground" path back to BATT (-)....  In fact,
there were returns from every major metal structure in the truck... 
Front clip, LH frame, RH frame, engine, cab, middle frame, bed, rear
frame left and right, receiver and several other smaller/minor ones
dedicated to specific purposes...  aka: ECU has it's own ground, et al.
7) Any engineer worth his salt plans for failures...  I increased the
size and rerouted returns more efficiently to cause the return
resistance to BATT (-) to be approximately the same from ALL points in
the truck (rear frame grounds have not yet been replaced, but are
spec'd. Average resistance from any return tie to frame/body panel, etc.
is LESS than 1 Ohm.... a lot less.... like 0.2 Ohms.
8)  Assuming I was ignorant enough to ONLY have a single engine return
to BATT (-) for instance...  The current would find returns via the
motor mount to frame bond which would be still less than 1 Ohm.  Same
with starter solenoid and/or starter relay...
9) Additionally, the direct cabling from the battery to the in-cab
distro point is FUSED on BOTH the BATT (+) and BATT (-) with fast blow
fuses range selected to open BEFORE catastrophic current spikes can hit
the accessories.

And finally....  As a properly trained aviator, I don't crank my vehicle
with direct connected accessories on...  That's simply poor operator
procedure.  Even the original factory circuit interrupted the circuit to
the factory stereo when the key was in the START position.

FACT:  There is no electrical difference between a 0.2 Ohm return path
DIRECTLY to the battery than there is a 0.2 Ohm return path that runs
from the accessory to frame or engine ground point and THEN to Batt (-).

Take-away:  Design your return plane such that you 1) incorporate EVERY
appreciable piece of metal in the vehicle... frame, engine, body panels,
suspension, etc.  AND design it such that all returns are redundant and
have approximately the same resistance in the path to Batt (-).

Poor design/engineering, exceedingly poor maintenance, poor operator
training lead the list of stupid things one can do if you are TRYING to
create a potential damage situation...  But generally, it takes a
failure in TWO of the three domains to realize any damage.

I think the smallest return wire I have in my truck carrying more than 1
amp is 4 AWG.

Bottom Line: understand DC... don't do stupid stuff.  :)

73, Vic....  this was mostly in response to the original post and the
false absolutes stated in the article....  If we allowed articles like
that to guide our science, we would never have gone to space because we
can't jump into orbit using human leg power...  <grin>

______________________
Clay Autery, KY5G

On 6/27/2017 10:52 AM, Vic Rosenthal wrote:
> I don't think math or difficult physics is needed. Suppose you connect the radio directly to battery, and then suppose the battery to ground cable becomes partially or completely disconnected. Finally, suppose you then try to start the engine. When the starter solenoid closes, some of the high current from the battery negative terminal flows through the negative lead to the radio, and then to ground through the radio's mounting bracket, the coax to the antenna, etc. The no. 10 ground wire might have to carry several hundred amps! Lots of things can be damaged.
> This is why negative leads should be fused, at least.
>
> Vic 4X6GP 
>
>> On 27 Jun 2017, at 18:21, Clay Autery <KY5G at montac.com> wrote:
>>
>> Horse puckey!  I DEFY you to prove the physics OR math of that
>> ridiculous statement.
>>
>> ______________________
>> Clay Autery, KY5G
>>
>>> On 6/27/2017 9:55 AM, donovanf at starpower.net wrote:
>>> WARNING! 
>>>
>>>
>>> For extremely important safety and fire prevention reasons reasons, 
>>> no accessory should ever be connected directly to the negative 
>>> terminal of an automotive battery . Just like when charging an 
>>> automotive battery, the negative lead of a cable running directly 
>>> to the battery should always connect to the engine block and never 
>>> directly to the battery. 
>>>
>>>
>>> The positive lead must be fused where it connects to the battery. 
>>>
>>>
>>> There's an excellent discussion here: 
>>>
>>> https://www.w8ji.com/negative_lead_to_battery.htm 
>>>
>>>
>>> 73 
>>> Frank 
>>> W3LPL 
>>>