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It's another question on batteries & wiring circuits
Not so. Re-read my post. The only time the extra battery is connected
is when the engine is running; all batteries are at 13+ volts at the terminals, regardless of their charge state, b/c the alternator is running. The small battery will never be charging the house bank while the alternator is running. If the house bank is depleted, the worst that happens is the alternator is trying to keep up with the house bank and runs at 13 volts or so until the house bank charges up some, at which point the alternator's output will rise in voltage. This is still above 12.8 volts, the full-charge resting voltage of a battery. Even if the small battery lost no charge during the month and is at 12.8 volts, there's no way the small battery can drain into the house bank. Ditto the sparking issue. Connecting a battery at 12.5 volts and one at 14 volts won't likely cause any sparking. Shouldn't be an issue anyway, b/c your box is properly vented, right? Finally, the loss issue. True. But: High quality, well maintained jumpers make a difference. Clean the connections first. Make sure the "small" battery isn't sized to just barely start your engine, but has some hefty reserve to it. Did this with an old 8D starting battery for a 120 h.p. diesel. Tried it out, worked fine. How big is your engine? Rich Mechaber MIDEMETZ wrote: The only possible problem with your idea is if you run down the main battery it will over load the small extra battery. There is lot of loss with jumper cables plus if you can't disconcert the dead batteries they pull a lot out of the good battery. Not to mention the probably sparking during hook up. Problem never happen in good conditions. At least for me anyway. Mike *********** I would echo what others have contributed about not routinely drawing from the house battery for starting if you set up as you describe. What surprises me is that almost no one selects a setup I prefer: a large-ish bank of house/starting batteries, without switches, relays, or problems. "What if you drain the batteries down?" For this purpose, and for this purpose _only_, I bought a cheap starting battery. Unconnected to anything. Once a month, I would affix heavy gauge jumper cables from it to the main bank during a 6-hour motor to re-charge the self-dischaged capacity. Left the cover off the battery compartment while under way so there was no way to forget to remove the cables later. ("Gee, why are the batteries visible from the saloon?") Cables served for the emergency start, if needed, connected directly to the starter solenoid. HTH, Rich Mechaber |
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