or vent fitting could be routed to the deck,
provided it’s done in a manner that will
ensure water cannot enter. The box would
not necessarily need to be airtight per
se, however, extraction vent fittings must
be located at the apex of the lid, where
gasses will collect.
In order to provide adequate heat
removal it would be advisable to utilize
two vents or ducts, one at each end, or
one duct and holes in the side of the
box that would allow air from the space
in which the batteries are installed to
enter. ABYC guidelines require electrolyte
containment, however, it need not be able
to contain 100% of the electrolyte, so
holes at the mid-level of the box side are
allowable.
If you opt for forced ventilation, a
continuous duty, low volume ignition
protected extraction fan could be
installed in the vent duct. Duct material
is not critical, however, it should be acid
resistant. A 4-inch non-metallic bilge
blower or dryer type duct would work
and it would support a fan as well. It’s
important that even if the fan is not
operating that hydrogen gas be able to
escape from the box passively, without
the fan operating. Finally, the entire
installation must comply with ABYC
standards E- 10 ‘Storage Batteries’ and
E- 11 ‘AC and DC Electrical Systems’.
—Steve D’Antonio
A/C BLEED VALVE
Steve, read your article on air
conditioning in latest PassageMaker
and on page 88 you refer to having a
bronze bleed valve for use with a non-self-priming pump. This past summer
I have had to disconnect the pump a
number of times to prime it. Having a
bleed valve makes perfect sense, but
can’t find anyone who makes them or
carries them.
Can you give me the name of a
supplier?
Jim Purvis
San Rafael, California
Jim, one of the most important aspects
of installing and maintaining any
raw-water system is alloy selection,
and nowhere is that selection more
insidiously fraught with potential for
disaster than in the case of brass
vs. bronze hardware. Bronze is well
known for its durability and corrosion
resistance, while brass, because of its
zinc content, should never be used in
any raw-water plumbing application.
The problem is they look the same, and
as such the user must be extremely
cautious when making his or her
selection. For more on this subject see
PassageMaker Channels, “Don’t Fall for
the Brass Line.”
The good news is small bronze valves
are available. Make certain the valve
you select is indeed bronze and not
brass. McMaster Carr caries ¼-inch
and 1/8-inch bronze and petcocks,
access them at www.mcmastercarr.
com.—Steve D’Antonio
CHARGING
Steve, I saw your article, printed as
a Gearhead series some time ago,
“Advanced, high output DC charging
systems demystified” and it prompted
a question. If you have covered this
in additional articles, a pointer would
be great. I’m an EE by education so I
understand the basics of electricity. My
question is this. I have a coach with a
12 volt house bank of 1500AH using 6
Lifeline AGM batteries (all in parallel of
course). I have a Trace SW2512 inverter
charger which will charge at 150A max.
I have a genset that will put out 14kw (at
120VAC)!
So my frustration is, to recharge my
house bank from a deep discharge of
50% (I never discharge more than that), it
would take many hours even at 150A and
of course the charge current tapers as the
bank comes up in charge level. Also, I’m
barely putting any load on the big genset.
My question is has anyone used an
approach of somehow breaking the bank
down into segments or even individual
batteries, and charging them using separate
smaller chargers? AGMs can take a lot
of charge current and when running the
genset, I have LOTS of current available
(equivalent to over 1000 amps at 12v, if
converted from the 120VAC), of course at
a cost of burning a bit more fuel I would
think—energy can’t be free.
In the extreme, what if I had a
separate 100A 3-stage charger for each
battery? The genset could handle this,
and it would seem that it would charge all
the batteries in potentially 1/6 of the time.
Would it be necessary to actually separate
the batteries electrically from each other
with switches or relays or something?
The objective is to reduce the genset
run time and speed the recharging of the
bank. Is this workable or am I missing
something?
Barclay Brown
Green Cove Springs, Florida
Barclay, you pose some very good, and
somewhat complex, questions.
The problem you face is one
encountered by many cruisers. Ideally,
it’s preferred to discharge and recharge
a large battery bank as a whole, rather
than separating it into two or more
smaller banks. Separating the bank into
individual batteries will likely have little
effect on recharging them, the amp-hours must be replaced regardless. It
may have the side effect of unbalancing
them when they are reconnected for use,
which can prove problematic. Individually
charging the batteries will also be very
complicated as each battery would need
to be isolated from the others (every
battery would need to be isolated during
charging).
Regrettably, there are no silver bullets
to solve this problem, short of adding
more charge capacity for the bulk phase.
Adding chargers to the bank as a whole
will have an effect on the initial bulk
charge, as AGM batteries can accept
up to and in some cases more than 100
percent of their amp-hour capacity.
As that charge tapers off, however,
additional chargers will become
redundant and some will likely shut
themselves off as they “see” output
from other chargers. In the end, the final
10%-15% charge will be replaced slowly
regardless of whether the batteries are
charged as a group or individually.
Charging the batteries individually will
not, however, reduce the time required
for charging to 1/6. Remember, the
amount of charge the battery accepts
tapers off after the bulk stage, as the
battery’s charge increases, so too does
its internal resistance, and the charge
process is not linear; i.e., replacing 100
amp hours using a 100 amp charger
doesn’t take just one (it could take 1. 75
or 2 hours for a full 100% charge, which
may be impractical) hour because the
battery will only accept 100 amps
initially.—Steve D’Antonio
Ask Steve
