For HF mobile installation, GM and others recommend that the radio NOT be grounded in the cabin. Both battery leads should be fused at the battery. The reason for the negitive side fuse is in the event that the battery ground lead to the engine block should go open or have a high resistance there will be very high current trying to find ground when you start the engine. Starter motor current can be in the hundreds of amps. You do NOT want that amount of current flowing thru your rig!>>
The problem actually comes from what is inside the radio, not what GM thinks is inside our radios or how GM thinks the system works. The main problem is connecting the radio negative lead to the battery negative terminal. That's a bad idea, and it applies to our station wiring as well as car wiring. We can have similar destructive ground loops in station wiring. Our radios and accessories have small thin foil traces and small components like RF chokes on the ground leads of many accessories connectors. Blow a negative fuse or lose a ground connection on the negative supply lead and you can damage components inside the radio. The jacks and plugs become the negative high current return path. Our power supplies either need to be ground isolated, which they often can't be, or they need to bond the negative into a solid ground buss, and all the negative supply leads need to connect solidly to that buss. Otherwise we risk damaging our equipment from something as simple as a bad connection or blown fuse. In your car, the battery should have a heavy return to the engine for alternator or starter current. It should have a lighter, but still reasonably heavy, connection at the battery to the chassis. The radio should be grounded on the same sheet metal near the point, but not on the point, where the battery is grounded to the chassis. There should be no negative fuse. It should be a solid connection and NOT common with the bolt grounding the battery. Then if the battery negative comes loose, current will never flow through the radio or radio wiring. It can't set the car on fire, it can't blow out automotive electronics, and it can't damage the radio. Every passenger area accessory connects to the chassis as a return, and so do the lights and other things. They would never run their stuff, other than the starter and alternator back to a negative battery post, so why should we do that with our radios? It is foolish and unsafe to ground radio to the battery post upstream of the vehicle chassis ground, just as it is unsafe to ground equipment at home directly to the negative rail of high current 12 V supplies instead of a ground buss or common ground point, no matter who says otherwise. Without a common reference point all it takes is a high current load negative to come detached, or a positive lead low resistance fault to ground, and we have equipment damage. I learned this years ago when my radio lost the keying line ground trace on a circuit board because the radio negative lead fuse developed a bad connection, and the radio primarily grounded through the keyer path. 73 Tom ______________________________________________________________ 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
