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Old 17-04-2009, 19:30   #1
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Batteries, again, sorry

Batteries, again, sorry


I suspect that this has already been discussed, but since I don't have
access to the archives, I beg your indulgence...

We have new, L16H batteries in our 880AH house bank, flooded cell. In
a perfect world to make them last longest, I know that they'd never be
allowed to drop below 100% capacity - but then, what's the point of
having a battery?

I also know that running them down to 20% on a regular basis will make
for a short life span.

So, the question (well, maybe two) is:

What is the recommended, real-world cycle? That is, how low do you
take your flooded batteries on a regular basis? Related, is there a
readily available source for information on the numbers of cycles to a
given percentage of discharge in a battery life span? I.e., 500
cycles to 50% and back to 100% but only 100 cycles to 20% and up to
75%, or the like (recognizing that these numbers have no relation to
any battery made)?

Second, what do those of you with flooded cells, not connected to the
shore power all the time (that is, full-time cruisers or rarely
connected to the utility-based power cord) have as a practice? What
charge regime, and how, do you observe? Never below X%, seldom above
Y%/Always more than Y% of capacity?

We have a variety of charging sources and differing loads which makes
for days when we may see close to 50%, and days when it never leaves
"full" - and since we can't "force" "full" reasonably, we want to make
sure we're not unreasonably asking for our batteries performance.

Knowledgeable assistance appreciated, and your practice, whether
empirical or just "is" would also be appreciated.

Thanks.

L8R

Skip (Gundlach) and crew, lying Lucaya, over (what else??) wifi among
the 14 available open sites we can see

Morgan 461 #2 St. Thomas USVI
SV Flying Pig KI4MPC
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quite alone on a wide, wide sea, it is apt to occur to you that in the
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surface of the ocean; and are not nearly so important or as
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as you thought you were. Which is an exceedingly wholesome thought,
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Old 17-04-2009, 19:46   #2
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Comparing marine batteries (Gel, Absorbed Glass Mat (AGM), flooded lead acid)
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Old 17-04-2009, 20:45   #3
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Quote:
Originally Posted by skipgundlach View Post
Batteries, again, sorry
So, the question (well, maybe two) is:

What is the recommended, real-world cycle? That is, how low do you
take your flooded batteries on a regular basis? Related, is there a
readily available source for information on the numbers of cycles to a
given percentage of discharge in a battery life span? I.e., 500
cycles to 50% and back to 100% but only 100 cycles to 20% and up to
75%, or the like (recognizing that these numbers have no relation to
any battery made)?

Second, what do those of you with flooded cells, not connected to the
shore power all the time (that is, full-time cruisers or rarely
connected to the utility-based power cord) have as a practice? What
charge regime, and how, do you observe? Never below X%, seldom above
Y%/Always more than Y% of capacity?

We have a variety of charging sources and differing loads which makes
for days when we may see close to 50%, and days when it never leaves
"full" - and since we can't "force" "full" reasonably, we want to make
sure we're not unreasonably asking for our batteries performance.

Knowledgeable assistance appreciated, and your practice, whether
empirical or just "is" would also be appreciated.
Skip...here is a cycle life chart for ONE pretty good battery from a respected manufacturer. Cycles you get are on the left hand side and DEPTH of discharge runs along the bottom. 30% depth of discharge= 70% full. I would suggest that this is good guidance for your own planning on how deep to discharge but would note that all batteries are different and may have somewhat different slopes to their cycle life. Hope that helps you.

I would also add in answer to your second question that the MOST important thing you can do living on the hook is to insure that your batteries are not only charged properly but BROUGHT to 100% full as often as possible and not longer than a week or two at less than 100%.
Furthermore...NEVER trust a voltmeter for providing state of charge in the real world of living on a boat. With passive sources like you have you will NEVER eliminate surface charge or small loads and thus never know your real depth of discharge. A Link type amp hour monitor or similar is needed to do so properly. If you already have one...great but hopefully this will be useful to others as well.
We chose 50% as our depth of discharge limit before recharging but obviouly...that is just where it made sense for us and where we were happiest with the charging cycles. Don't forget...you can put a lot of amphours into a well discharged battery in a short time. It is a lot less efficient to start at 80% charged and try to cram amp hours in....especially when you consider the cost of fuel to run an engine or generator. It takes about twice as long in my experience to go from 80 to 100% charged than it takes to go from 50 to 80 % charged. We would put in THAT 30% on a daily basis and then once every couple of weeks at anchor we would go all the way to 100%....if we hadn't pulled into and plugged into a dockside power cube.
Worked for us...your mileage may vary!
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Old 18-04-2009, 04:37   #4
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Hi, Skip.

You do have access to "The Archives", by the way.

Just use the Google search feature in the small "Search" pull-down menu in the upper right of the page. Tons and tons of stuff about batteries there. In particular, posts by Rick are always helpful and to the point.
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Old 19-04-2009, 08:08   #5
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Skip...I just noticed my graphic did not post in #3 above. Sorry! Here it is:
Click image for larger version

Name:	cycles.JPG
Views:	256
Size:	11.2 KB
ID:	7839
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Old 19-04-2009, 09:59   #6
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“Cycles you get are on the left hand side and DEPTH of discharge runs along the bottom. 30% depth of discharge= 70% full.”
20*900 = 18000
30*768 = 23040
40*672 = 26880
50*576 = 28800
60*504 = 30240
70*432 = 30240
80*360 = 28800
Interesting graph, according to it you get more Amps at 60 or 70% discharge or is it the other way around?
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Old 19-04-2009, 10:21   #7
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Yes...for THIS battery you get more amp hours over the full life at 60% discharge than at 20% discharge. Other batteries may have a steeper slope which is probably why 50% discharge is the oft quoted optimum depth of discharge and I have graphs on another battery which offers LESS of an advantage at 60%..but still a quite clear advantage on the order of a 60% gain in amphours delivered. You would have to have cycles cut by 2/3's to come out even and I'm pretty sure any quality deep cycle battery will NOT have cycles reduced by that much.
Given the extra efficiency in charging costs in BULK charging, it is quite clear to me that relatively deep discharging a house bank rather than 20% in and out...is much more economical in the long run.
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Old 19-04-2009, 10:24   #8
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By the way an Amp meter is a Voltmeter.
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