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Subject: TWL: Re: Re: Re: AGM Battery justification
From: Richard Tomkinson (capnrich31@XXX.XXX)
Date: Sun Mar 11 2001 - 23:47:41 EST
Jim says:
> 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.
Obfuscation extordinaire!
1. Your system should be able to fully recharge from the alternator
underway.
2. Any level of discharge is responded to by the regulator through its
program. If the program is set for AGM, then it will stay in full charge for
the *first*, bulk stage for a much longer time than for a flooded program.
This is not interpretation, it is fact. If you snapshot power restored after
one hour on an AGM program vs a flooded program for any moderate size
alternator, you will find a very significant difference in energy restored
irrespective of the state of discharge. As time goes on the difference will
lessen ... thats arithmetic.
The benefit is clear: Full charge faster without damage.
>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.
Not so. AGM programs are available from several vendors in the recreational
marine market.
>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.
Some long while ago I replaced the 55A Motorola alternator that came with my
Lehman. If that same 55A alternator ran through a properly wired system and
an AGM program regulator, it would serve well to charge 600A Hr AGMs, it
would not serve to charge this same value of flooded batteries in most
coastal cruising situations.
>
> 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.
Again, high marks for obfuscation.
The point is that in any finite charge time window longer than the flooded
bulk time period (which is very short), the AGM program will deliver the
marginal difference between absorption and bulk rate over the time period.
This energy difference is substantial.
>
> 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.
So you have a 44' Taiwan trawler with 1200AHr and you are maxed for space
for batteries. What then?
>For high speed planing hulls it is probable that the
> exotic battery technologies will clean the clock of any Lead/Acid system.
AGM is neither exotic or new, but it is Lead/Acid.
> 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.
And if your boat can house batteries that require a crane to install and
have a case size some 16" high.
>
> 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.
You haven't been listening. For any given A/Hr, AGM are lighter. Read, less
lead, longer life.
> Heavy, thick plates last longer than thinner ones.
Based on what evidence? I agree when comparing flooded/flooded.
>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.
OK
Richard
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