Originally Posted by maxxx
I am mounting a second battery (Odyssey ER 30) in the rear of my 1999 VW passat wagon and plan to ground it in the rear to the same part of the chassis that the rear metal bumper is attached to. All of the stereo equipment hooked up to it (including the head unit) will be ground at the same point. FYI I will be using a pheonix gold capacitor power grid, which centralizes power and ground and makes it a little neater.
Any advice on grounding this setup? The stereo will be entirely isolated to the rear battery (even going as far as using relays for illumination, ignition, etc.) and as such I figure there should be no ground loop coming from the difference in potential between the two different battery ground points. Still, in addition to a substantial ground wiring setup for the system and the battery, I was considering running a ground wire (just a simple 8awg) from the rear ground point to the front battery's ground point. Is there any advantage to this, and if so should I consider using a heavier gauge? Or should I even consider not grounding the rear battery to the car but only running a heavy gauge ground all the way up to the primary battery? Has anyone actually done a long ground run? I'll be honest I don't like the idea of a long ground run as an exclusive means of grounding a battery or system, particularly for a battery.
As you can imagine I will have an isolator in between the two batteries, and a Soundgate ICB100 (intelligent fuse), not that either of those matter to my questions. Thanks in advance for your input!
I would select a point on the chassis of the car as close to the secondary battery location as possible to ground it to. You can check the resistance from the stock battery negative terminal to the point at which it is grounded and try to find a point in the rear of the car with the same resistance (from the stock battery to a point in the rear of the car). You can do this by extending on of the test leads on a DVM, then touching the leads together to allow the meter to zero out and compensate for the longer leads.
I would not run a ground cable between the batteries, as this will invite ground loops.
Since the isolator is already installed, you should check the voltage loss from the terminal that comes from the alternator or front battery. Iíve seen 1.5 volt losses through isolators before, which is significant loss. The only real benefit of an isolator is to prevent the failure of one battery from crippling the pair. Otherwise, the potential voltage loss is not worth using an isolator. Proper fusing, which you seem to have, will provide the protection the vehicle needs from any shorts.