T&T: Ramifications of AGM's

[Robin Brueckner]

 In general, AGM's are evolutionary rather revolutionary.

I've  posted detailed technical information here before on AGM  vs wet
cells/lead acid batteries and I won't rehash that now(since I don't remember
it all). In essence AGM's can offer improved life cyle power delivery
(somewhat lower cost per amp hour over the battery life), about four times the
bulk charge rate of wet cells (you can charge a 220 amp hout AGM at nearly 220
amps vs only 55 amps for a traditional leadacid wet cell) and only about 2% to
4%  power loss (mostly as heat) during charge vs about 20% (if I recall
correctly) for wet cells. I forget if there is any difference in power
stored/lb of battery....I don't think enough to warrant much consideration
" In other words, would being able to quickly store a LOT of juice change our
perception of what is possible electrically on our boats, including how big a
battery bank we could handle?"

Not really, just reduced charged time, reduced generator run time if you
invest in a bigger and more expensive charger/alternator and more expensive
batteries.   "..Similarly, AGM's store more energy much faster for longer
periods than, say, cold plate systems. So, where does that send the "best
reefer" conversation? .."

Good question...the answer depends on how you cruise and use your equipment.
For those who cruise frequently enough to keep a cold plate system cold, AGM's
don't mean anything because they won't be used. If you sit for days on end,
then reduced genny run time due to faster and more efficient charging might be
a benefit...but not if you need to run the genny for, say, hot water or
cooking,anyway.... you get little benefit in reduced run time.
Heating water and cooling air is very power intensive and in general is not
very feasible using dc battery sources. (Not unless you are extremely frugal).

But MODEST heating and cooling can be achieved. A 3,500 BTU air conditioner,
for example, (rather small) can be run off an 8D battery overnight..but the
battery requires charging before another night of use. (Was that discussion
here last month?)

Heating water from a battery is also tough: To heat 5 gallons of water enough
to raise it only 70 degrees requires about: ( 5 gal x 8.33lbs/gal x 70 or)
2915 BTU, and since a watt-hr gives 3.4 BTU's, this takes about 857 watt-hr;
at 12 volts this is about 71.3 amp hours....about 40 to 50% of the useful
energy from a 12v 8D battery assuming no energy losses.


So I don't believe AGM technology by itself offers a revolutionary change in
the choice of  other components on boats.
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