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 <[email protected]> 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, [email protected] 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 >>> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
