Donald Phillips wrote:
bruce wrote:

I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce


The way batteries are charged in the factory where they are made is in
series string. This way all batteries receive the same amount of
current and thus the same amount of amp hours. The chargers vary the
voltage to keep the current in spec.

I don't think charging in parallel is the best idea, IMHO.

Most (if not all) charging circuits rely on the voltage to indicate a
full charge, if I remember correctly roughly 14.7v means a fully charged
lead acid batter. Now if you connect them in parallel the voltage seen
at the regulator is going to likely be wrong for both batteries, leading
to slower charging or overcharging.

And don't connect them in series, cause they you've got 24v ;-)

I'd suggest a switch for 1 - both - 2 batteries, and put a seriously
bright red light on the dash to indicate when you're in 'both' mode...
or a buzzer, or something.. Two seperate meters for the batteries, and
you can switch over to one that needs charging the most...