Thursday, May 23, 2013 at 09:56
Roger B
Additional clarifications….
There is no legal requirement for circuit protection for auxiliary battery wiring.
And yes, wiring can be a dangerous practice if not done correctly. Note I say correctly. For many years cars have had batteries located in many areas, sometimes nowhere near the engine. A lot of modern cars have batteries under front/rear seats, in boots, near the boot....you get the idea. And all done without main feed protection. (in the automotive environment, how do you economically protect a feed that needs to supply up to 500 amps cranking current....) Yes ok there are ways, but, as I said, they’re very expensive to do properly.
But you can do it by doing the wiring job properly.
By people (or machines) who know what they're doing.
And here is the GREAT DISCLAIMER.
You take advice from forums such as this as just that....general advice. There are many experts on this, and all other public
forum sites and some even know what they're talking about. However most do not. Their experience is from their experience, or an armchair, and again, forums. So the circle of misinformation/folklore/old wives tales continues.
However you are correct. If the current were to be above the capacity of the cabling, it could overheat. And if you do want to utilise the override function, you will need large cabling. 2 B&S would be suitable. If no override, 4 B&S and you can, if you feel a great need, also put in a 50-80 amp circuit breaker or fuse, but keep in mind this will be the weak point, both physically and electrically. Solder all connections and seal. Crimp, solder and seal if you like. Do not just crimp unless your crimping tool and connections cost you the equivalent of a small house. Insulate the cable run with split tubing or similar, use good quality grommets and clean cut holes (no burrs, sharp edges) where cabling passes through metal panels and make sure you secure with at least good quality uv, heat and oil/petrol stabilised/resistant cable ties. Mount the battery box firmly, not with the 2 plastic clips they usually come with.
Done this way, you minimise the complexity of the system, safeguarding its integrity without introducing components where dirt etc may compromise it (either electrically or physically).
I think you get the idea.
A number of other points have been made. Mount the isolator (if it's a smart one) close to the main charging battery. It’s voltage sensitive so give it the best chance of doing its job properly. If it's just a solenoid (100A for example) wired to the ignition feed, mount it anywhere.
Do put overload protection in the feeds from the auxiliar battery. A simple fuse usually suffices, or a fuse for each item is also acceptable though a bit of overkill as most devices have their own.
AnswerID:
511655