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Subject: TWL: RE: Re: Re: AGM Battery justification
From: Jim Donohue (jim_donohue@XXX.XXX)
Date: Sun Mar 11 2001 - 22:20:54 EST
But here we go again. One does not fully restore charge in the cruising
environment. One also avoids anthing near full discharge. One simply cycles
between something less than fully charged and something well less than fully
discharged. One does this of course, because, as you point out, the last
couple of hours are very inefficient. So to actually work out the
difference between AGM and floods we will have to agree upon the optimum
strategy for each and then run some model to see what the actual difference
is. The full discharged to fully charged analysis is almost to the level of
a marketing pitch.
There is some indication with AGM that very high current charging is very
good for extending life. I do not think a high charge regime is necessarily
a bad thing - merely that it is not in keeping with the generally available
gear on recreational boats. It may well turn out that heavy duty
alternators, chargers or generators will vastly increase the utility of
AGMs - but that is for the future.
Note that both deliver roughly the charge during the bulk period. So if one
simply charges for the bulk charge time it will make no difference which
battery type one uses. Under such a regime I suspect the AGMs lose badly on
an economic analysis.
Wider will increase the weight - but it may well still be cheaper than AGM.
For the same dollars you get a bank that is discharged relatively less and
lasts a lot longer. For high speed planing hulls it is probable that the
exotic battery technologies will clean the clock of any Lead/Acid system.
If money is not an object there are better ways. I would think it simple to
surpass AGM by a factor greater than 2 if cost is not a problem.
When you shake it all down - regardless of the particular technology used it
appears that the weight of the lead involved is the major predictor of life.
Heavy, thick plates last longer than thinner ones. I suspect the same will
prove to be the case in AGM. We will see over time but I certainly would
not concede the point on any evidence presently available.
Jim
Increased
> acceptance rate means that the same alternator (with an appropriate
> regulator program) will deliver the same Amp/Hrs in half the
> time. Think of
> it as bulk charge time lasting four or five times longer. In both
> cases the
> alternator must restore the same watts plus 20-30% for losses. The program
> for flooded cells is remarkably short for bulk charge, then the 130A max
> alternator switches to absorption. The alternator is now putting
> out perhaps
> 75 Amps.
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