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From: Robin Brueckner (no email)
Date: Mon Feb 04 2008 - 09:31:15 EST
Statements and my comments:
"....pretty pathetic compared to most everybody elses' banks, but that's all
the boat designer left room for!!."
Comment:
Don't pay attention to what others have...it's irrelevant...likely they know
less than you and have no idea if their system best meets even their own
needs...certainly not yours. Determine what YOU need based on how you use your
boat and your objectives.
".. I THINK I'll bite the bullet and get four 12volt AGM's for the house
bank,
Comment:
What's your criteria? What's your objective? Without usage input data or at
least usage experience no one can comment nor provide sensible
advice/suggestions. What's wrong qith the 200 map hours you have??
For example, if you anchor out five nights annually, one at a time, you are
probably just wasting money. If you anchor out dozens and dozens of nights
annually and want to have three days battery capacity your criteria will be
totally different.
You should size your house bank at three to four times your total amp hour
usage...a three day battery bank supply will be triple the size of a daily
bank, for example.
..."Victron, but I think it is still the best choice.
Comment: That's one good brand, but I have absolutely no idea if it's "best".
Ask owners here....",,, is a significant risk of shorting a flooded cell in a
parallel bank and having that battery hog the charge out of it's neighbors and
overheat
Comment: That can happen for many reasons, the most common one being faulty
charging or misue. It's not in any way "significant" in my experience, but is
a potentially legitimate concern. To reduce this risk: replace all batts in a
bank at the same time, use a smart charger, keep batts properly filled with
water, don't regularly discharge more than 40 to 50%, monitor specific gravity
or note changes in recharge times, size banks to their load.
"... I feel AGM's are mostly immune to that risk ..."
Comment; Could be, but if any evidence existed, manufacturers would claim
it...don't kid yourself...
".. (put)AGM's in and get eight times the charge acceptance rate (four times
from upgrading to AGM and two times for doubling the size of the bank).
Comment: in practice, you might get somewhat less. However you also reduce 20%
power (heat) loss to about 2% or 4% over wet cell, so this figure might be ok.
In addition, you may need a bigger charger and alternator and even generator
to achieve this....more expense consideration.
My Bold New Plan also calls for adding two more remote batteries: (1) a
biggish single AGM start type way up forward to start the genset and run the
windlass, with a nearby small independent charger, and (2) a deep cycle AGM
under the flybridge to provide power for the VHF and SSB radios -- completely
isolated from the rest of the boat, and with another small independent charger
nearby which is fitted with a relay to automatically disconnect this charger
when either radio is on -- eliminating noise issues on the radios as well as
to and from everything else on the boat.
Comment: Good plan overall. Also a good idea is to run navigation electronics
from a house bank ,not starting bank, as electronics can reset from voltage
drop at starting....A switch at the flybridge permitting alternative power
sources is ideal.
I plan to use the automatic combiner I already have (and the heavy cables
formerly used to bring 12 volt windlass power forward) to provide emergency
support between the genset/windlass system and the house bank/Victron. I
will provide a small charger for the two independent start batteries and add a
manually switched fused jumper between them. They will remain the 'no
maintenance' semi-sealed automotive flooded cell batteries, and not connected
to the house bank.
Comment: A combiner may not be a good way to parallel banks: unless voltage is
at the "combine" level, say 13.2 volts, you may not be able to provide
emergency support. This depends on the brand combiner you use. I like a manual
switch in addition to a combiner....I used mine once when a battery bank began
to fail during my six month summer getaway. At the same time I want to install
independent 12 volt and 120 volt outlets in every accessible space aboard for
work lights, power tools, emergency pumps, etc. without extension cords
running through unclosable hatches and doors.
Comment: Think abou where you need both voltage sources: I added 120 and 12v
in my engine room just as you described because I fuss around down there a
lot. Most other areas I've rarely had the need. "...Listees, feel free to
sharpshoot my plan. I have mostly book learning and less real experience at
some parts of this. I want a safe, versatile and effective system and I also
want to spend my boat bucks wisely.
Comments: Overall, you've proposed a pretty sophisticated system, relatively
expensive, which is fine if you use your boat a lot away from the dock. Or if
you just like to tinker in a cool season, that's reason enough....
I'd suggest you consider writing down all your objectives before you start to
be sure they all all addressed....and you can prioritize to start on what's
most important to you...
A way to approach this is incrementally....make a change or two at a time and
see how it goes..what you learn....I used my Hatteras two long seasons before
adding a third battery bank and a second refrigeration system...those based on
my use and experience with that particular boat.
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