Mick,
Forget isolators. Old
school, and not needed. Paul mentioned one of their limitations...voltage drop.
Consider yourself lucky: no wires left in place. This is an ideal way to start. Now, you can do it right.
What's right? Experts may have slightly different takes on it, but these days "right" is often defined as these 5 elements:
1.
a starting battery, dedicated to the
engine starting chore only and, as Paul says, with it's own robust ON/OFF switch.
2.
a house bank of adequate size, built up by paralleling 12V batteries (or 12v battery banks made up of 2V or 6V units). The size will depend upon your needs. The type of battery will depend on your desires, your wallet, and available space. These house batteries should also have a robust ON/OFF switch (my preference) or, optionally, a robust ONE/TWO/BOTH switch so you can switch them to the starting circuit if needed. Personally, I prefer just the ON/OFF switch, and a short piece of wire or jumper cable kept handy in the VERY UNLIKELY event that your starting battery goes dead.
3.
adequate charging devices: alternator and smart
regulator;
wind generator;
solar panels; mains-powered battery
charger; onboard
generator; etc. All charging sources should be connected to the HOUSE BATTERIES, i.e., they should be used primarily to charge the house batteries.
4.
an EchoCharge device, or a "battery combiner" which is used to charge the starting battery. I much prefer the EchoCharge...a $100 solution which is trouble-free and which will keep your starting battery topped off.
5.
a means of measuring battery voltage or, if you prefer, of monitoring battery usage. I prefer just a digital voltmeter. Many others prefer a device like the Link
monitor system which keeps track of amps in and amps out, and gives some indication of battery state-of-charge.
Remember that a starting battery is called upon to provide a great deal of
current...sometimes upwards of 250 amps....to start the engine, but for a VERY SHORT TIME. Do the math. A 250-amp draw for even 30 seconds (and if your engine takes longer than this its got real trouble) is only a tiny draw in amp-hours....only about 2AH. It doesn't take long to replenish this tiny draw in your starting battery.
What DOES take time is to replenish the 100-200 AH
lost from your house batteries each day (on a typical 40-50 footer). So, you wanna optimize the way in which these house batteries are replenished. They should never be drawn below about 50% charge (12.2V resting voltage), and they should be recharged as quickly and as fully as possible when cruising, remembering that
undercharging is the main killer of batteries.
To recap: (1)
a starting battery with its own ON/OFF switch; (2) an
adequately sized house battery bank with its own ON/OFF switch; (3) all
charging sources connected to the house batteries; (4)
an EchoCharge device to keep the starter battery topped off; and (5) a means of
battery monitoring.
Needless to say, all connections should be clean and tight, and all
wiring should be of adequate size. The ABYC
electrical code provides good guidance on wiring practice (particularly, the E-11 "AC and DC Electrical Systems on Boats").
That summarizes the
current "best practice".
Final note: battery switches are not created equal. IMHO, you're better off investing in a very robust battery swich, rather than the flimsy ones at the low end of the market.
Hope this helps a bit,
Bill
Linear Mode
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