T&T: Advice charging inverter bank from alternator

[Mark Richter]

Steve,
The stock alternator on your Cummins 5.9B is more likely 70-80 amps, rather
than 150.

The mixture you have of AGM's and wet batteries is likely to cause you some
trouble, as these two types cannot be charged by the same sources.  Either
constant undercharging of the wet batts, or damaging overcharging of the
AGM's will result.  Your stock alternator has a fixed voltage setting,
probably 14.0 to 14.1, and will cook those expensive AGM's if left connected
during long cruising days. You can get along with the present system with
some careful charge management.   Unless you are willing to make some
substantial and fairly expensive changes, you may as well leave the system
as it is.

If you want to make the change, here's what I'd do.  Keep the 24v AGM's and
separate 24v charger for the thruster as it is.  Keep the genset battery as
it is, charging from the genset alternator and independent from the rest of
the boat's electrical system.

Throw away the battery isolator(s).  Combine the start, house, and inverter
banks, by replacing them all with a large bank of new wet golf-carts ( told
you it wouldn't be cheap).  You can't mix the battery types you have, and
mixing older with newer batteries isn't wise, either.  The alternator
charges the large bank directly, and the engine starts directly from the
large bank.  The inverter charges the large bank directly (through a manual
on-off switch and a 300 amp type-J fuse).  Keep the phase III charger for
backup in case the inverter goes tits up.  It can also be connected to
charge the genset battery at the dock if not using the genset for an
extended period.

Run a pair of 10 ga wires fitted with a 40a breaker from the main panel (if
a spare position is available) to the dinghy lift batteries for charging
from the main batteries.  The long run should prevent blowing the fuse by
resistance limiting the current flow.  Turn the breaker on to charge, off to
isolate this pair.  Don't leave the switch on too much, or the charging
voltages set for your wet cells may damage the AGM's on the boat deck.
Alternately, you could run a pair of larger battery cables to the upper deck
(fuse and battery switch) and do away with that pair of AGM's entirely.

Good luck, and let us know what you decide to do.

Mark Richter, m/v Winnie thePooh, Ortona, FL on the Okeechobee Waterway
Mark's Mobile Marine, electrical systems design, installation, and repair.

> .... Briefly as I can, battery inventory is:
> 8D start
> 4D gen
> (2) 8D house
> (4) GC AGM- 3kw Freedom inverter
> (2) GC wet- on boat deck for boom winch
> AGM -24V thruster
>
> Charging is accomplished by:
>
> Alternator (stock 150A? on Cummins 5.9BTD) does house & start -via an
> isolator.
> Inverter bank stands alone, charge via inverter only (genset or shore
> power req'd)
> Boat deck by portable 15A manually (ditto genset or shore power)
> A phase III charger does house, gen, start (ditto power)
> thruster via dedicated charger (ditto power)
>
> Not what you'd call integrated systems. It works OK, but
>
> I'd like to be able to charge the inverter while underway, but the
> inverter bank is AGM, the rest are wet.
> I'd like not to have to drag out the portable charger for the boat deck
> bank.
> I considered an echo charger or a current limiting battery link for the
> boat deck bank, makes sense to charge it from the engine. (Cabling is
> not easily accessible)
> I'd prefer to eliminate the isolator in favor of a combiner, although
> charging the house bank is not a problem.
> I'd like to end up with a smart charging regulator for the alternator,
> but the differing battery types are a problem. (I am adding ventilation
> for the alternator & E/R.)
>
> Any suggestions on how to progress to a more integrated system while
> accomplishing some of my objectives on the way, and not backtrack? Or
> should I start over? <G> Our long-term objective will entail more
> anchoring and cruising than marina stays by at least 4:1.