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Old 08-03-2007, 22:09   #1
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AGM?

I am planning on 700-800 amp hour deep cycle battery bank with a gasoline powered 120- 150amp alternator.

If I go with wet cell open batteries (trojan golf cart) I am told it will take forever to charge up the bank even with a smart charger. A Maximum of 80 amps/hour at first and then dropping off to a very slow rate of charge??
I don't want the sound of the gas motor any longer than necessary.

If I go AGM it is going to cost more. Is charging AGM that much faster?
I don't mind paying the extra for AGM if I am getting value.
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Old 09-03-2007, 01:04   #2
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To the main question, yes you can charge AGM's just a little faster. But it is because you can charge with a slightly higher charge rate, not that the AGM charges any faster. The more current you put in, the less time to charge of course.
However, I think you have some confusing points in your post.
So for us to answer more accurately, please clarify a couple of points.
Alternator! Can this supply 150A @ 12V ??
Smart charger! is this an alternator powered charger? and is this limitied to 80A??
The reason why I ask is that an 800Ah bank will handle a charge rate of 150A with no harm.
If you only have a 80A smart charger, then you can only put in 80A, no matter if the batteries are wet or AGM or Gel or whatever. So any bank type would take ruffly the same time to recharge. The rule of thumb is, what comes out must go back in, plus the losses.
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Old 09-03-2007, 02:31   #3
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How "fast" you can reliably charge your battery.
Started by Rick, our resident battery & charging Guhru.
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Old 09-03-2007, 03:44   #4
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AGM does have other advantages. Especially if you should happen to be rolled over.
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Old 09-03-2007, 09:37   #5
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To put a finer point on what Alan said, you can charge up to 25% of the aH capacity of the battery bank, in this case 200 amps with an 800 aH wet cell bank.
With AGM you can charge up to 100% of aH, so with 800 aH worth of AGM you could charge up to an 800 amp rate.

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Old 09-03-2007, 12:35   #6
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Quote:
With AGM you can charge up to 100% of aH, so with 800 aH worth of AGM you could charge up to an 800 amp rate.
NO!!!!! Maximum charge rate for wet is 25%. Max charge rate for AGM is 33%.
So for 800Ah, wet would be 200A and AGM would be 264A. So the time difference is not greatly so. So the time difference charging the 800Ah bank would be ruffly 4hrs for the wet and maybe 3.5hrs for the AGM, using the respective charge currents.
That is the bulk charging time, not including the equalize stage.
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Old 09-03-2007, 13:00   #7
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Again, the charge rate is...

Please refer to Gord's reference above. AGM batteries are merely a sub-set of lead-acid electrochemistry and, therefore, still adhere to the principles of charging.

As previously stated, ANY lead-acid battery designed to deliver performance for cruising boats can be charged with a current equal to the number of Amp-hours "missing" from the battery without excessive gassing or temperature rise. This "Amp-hour law" establishes a safe boundary for charging and should be used to put to rest all of those myths and "rules of thumb" regarding just how fast a battery can be reliably charged.

Keep in mind that the Amp-hour law CAN be exceeded, especially for short periods of time yet that is another subject.

Using the Amp-hour law to charge the Trojan batteries you can completely charge them from "dead" in slightly less than 4 hours. With AGM batteries you can completely charge them from "dead" in less than 3 1/2 hours. Obviously a smaller depth of discharge will take less time than that to reach full charge using this method.

Adjustable 3-step chargers can be used to approximate an Amp-hour law charge regimen using a "real" battery monitor to tell you when to make changes in the charging current. It is not critical to micro-manage these settings.
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Old 09-03-2007, 13:06   #8
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As was said before, there are a lot more advantages to AGMs than just the charge rate. Let me post this straight from Lifeline:

LIFELINE MARINE BATTERY BENEFITS
User Safe
sealed construction
non-spillable
install in any position if properly supported.
submersible without damage
Maintenance free (no adding water or repairing corroded terminals)
Fastest recharge. (no current limitations with voltage regulated recharging)
Deep Cycle (thick positive plates to provide real deep cycle performance)
Outstanding cranking performance (aircraft cell construction lowers internal resistance)
Best charge retention (especially against flooded cell types)
Lowest discharge rates (Less that 3 percent per month unattended)
Easily shipped (even via UPS except GPL-8D and GPLAD because of weight)
Shock and vibration resistant. (100% of plates are covered with separator liners)
Properly supported, LIFELINE AGM batteries with absorbed electrolyte can be installed and operated on their side.


I have cruised with wets and now lifeline agms. No comparisson. I know Nigel Calder said a really good wet may be superior to an AGM, but that is probably something like a Rolls. Why bother? For those of you that cruise, you are so tied up with so many things, I GUARANTEE YOU THAT YOU WILL FORGET TO CHECK THE WATER LEVEL OF YOUR BATTS SOONER OR LATER! The only negative I can think of with a top of the line AGM is cost. THey are expensive.

I will also give you another real life example: I ended up having to leave my agms in the dock box in sub freezing temps over the winter. Four months later, came and hooked them up. Barely discharged at all. How would that Rolls have held up??

I consider Surrette to be one of the leading manufacturers of wets. At a 20hr rate, they have a rated cap of 185 AH as posted online. Lifeline AGM, same rate, 210 AH. THis is for their 4d's on both.

In all seriousness, please enlighten me why anyone would buy a wet cell anymore?? Becuase you MAY be able to get more cycles out of it? Well, how many assumptions follow that 20 year lifespan? A lifeline will be around a LONG TIME too.

Seriously, I am not being argumentative. Please explain to me why anyone cruising and not weekending would use a wet??
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Old 09-03-2007, 13:20   #9
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Yea, Cruisingdad!

One reason that many people keep buying flooded-cell constructed batteries is that they believe the claims stated by the marketing departments of the companies selling them. So-called "technical" articles appearing in sailing magazines parrot these unverified claims (such as Amp-hour ratings and more).

My testing of various batteries over the years have rarely varified the stated Amp-hour claims. Trojan batteries have, in general, been "honest". Believe it or not, Surrette and Rolls have not, in my experience...as expensive as they are. One HUGE disadvantage of Rolls and Surrette type batteries is their overly high (in my opinion) internal resistance which results in excessively large terminal voltage drop when large loads are applied. This means that if such a battery is sized to start an engine then it has to be 4 times or more larger in size and weight than a good start-only-start battery. Obviously one should not use an undersized deep-discharge flooded-cell battery for a starting battery. In my opinion Rolls batteries are antiquated technology best used for powering loads relatively small over long periods of time.

IN addition, what is missisng from stated specifications is the true energy stored which is Amp-hours times voltage over discharge time, otherwise known as kilo-Watt-hours. Any AGM or gel-cell battery truly rated equal to a wet-cell Amp-hour value will have LARGER kilo-Watt-hour ratings due to the higher terminal voltage over the discharge time. Forget Amp-hours in the face of kilo-Watt-hours!

AGM or gel-cell batteries can make good start batteries in addition to having deep-discharge capabilities with good longevity.
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Old 09-03-2007, 13:40   #10
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Rick,

As I recall, AGM's have very low resitance compared to the other types. I think personally gells have NO advantage to AGMs and will dissapear.

Have you done any comparissons between AGM manufacturers? I went Concored (lifeline), but what about Deka? They are building on that market (probably due to cost). Deka's are a lot cheaper, but in my research between the two companies, the Concorde was more commercial oriented versus the Deka seemed more price oriented. I even told Concorde I was seriously considering equipping with Dekas and they went on a very long description of why their batteries were not even comparable. Unfortunately, I could not write it all down!!

In the end, most of the cruisers I know go with Lifeline/Concorde. But I would be interested if anyone that is knowledgeable in that business (Rick??) can spell out the difference.

- CD
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Old 09-03-2007, 13:52   #11
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Thank you everybody, for your help.
I was told by the battery supplier that with an 800amp hour battery bank of wet cell batteries I could ONLY charge up to 10% or 80 amps.
Is this correct or not?
I have the ability to charge up to 150 amps.

I also was told that with wet cell I could really only discharge them to 50% which would mean I don't have 800 amps only 400amps

I like the idea of AGM but it will come down to total capacity/cost/value
What is the recommended discharge of AGM is it any higher than 50%
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Old 09-03-2007, 14:30   #12
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Beau,

You should go and get Nigel Calders Guide to Marine Electrical Systems... (or something like that). Not hard to find. Excellent book and well written and very detailed. It has a place on every boat - especially one that is going cruising. Chapmans Piloting and Rousmanieres (sp, sorry I know you frequent this site and Sailnet) Annapolis Book of Seamanship. Great books, all three of them.

The 50% rule is in place for all batteries, in general. Without too much detail, I will say that by taking a DEEP CYCLE BATTERY below 50% multiple times will result in a very early demise of the battery, exponentially so. In fact, if you go a lot LESS than 50% depetion, say 10 or 20%, you seriously stretch out the life of your batts - but for many marine based systems, that is impractical as the load versus bank size. Thus, you can only count (as a general rule) half of your battery cap toward what you can use before recharging. Also, you cannot just do a basic bulk and expect to have a full 100% of the batt. It needs a 3 stage charge, at the very least once every couple of weeks or the sulfation will start to become a problem and what once might have been 3 days to 50% will now be two, then one... etc.

I have been trying to put some thought into writing up an electrical budget diagram for people that want to go cruising. Maybe this is the place - I will post on Sailnet too.

There is more to buying batteries than cost so make sure you are really examining what you are buying. A cheap battery is... cheap. It is the heart of your system. I rate my cruising gear as such:

1) Safety gear.
2) Ground tackle.
3) Battery system.
(others)

There are many numbers after that, but in general, as a cruiser and not a weekender, you do not want to skimp on those three. Just my opinion, others dissagree. You will know those who disagree when you see them. They are usually being pulled off a reef, towed back to shore, or written up in the OBITS with a nice little picture.

- CD
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Old 09-03-2007, 14:45   #13
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HOW MUCH CURRENT?

Over and over again I repeat: NO SINGLE CHARGE CURRENT VALUE is valid as an absolute for a limit in charging a lead-acid battery! If one refers to the "Amp-hour charging law" the answer is evident. This information has been published in electrochemistry battery textbooks since 1930 or so!

The REASON that some battery distributors and/or marketing dept. published charge current values are single-valued is because they must limit their liability exposure for warranty claims by users having crude chargers. Therefore, when anyone claims that you can only charge at 10% or 25% or (fill in the blank) it is incorrect (translation: "wrong").

A 50% DOD (depth-of-discharge) limit for any lead-acid deep-discharge battery (AGM, flooded, gel-cell) is an ECONOMIC optimum guideline. Using a 50% DOD value when repetitively cycling batteries results in the lowest number of pennies spent per Amp-hour-cycle over the life of the battery. Less levels of discharge limits result in longer life yet cost more because the battery bank must be initially sized larger for a given cyclical energy usage. A deeper DOD results in shorter battery life yet the bank initially costs less because it is smaller and, in either case, results in higher lifetime cost than the case of the 50% DOD designed limit.

It is not true that flooded-cell batteries can only be discharged to 50% as per the above discussion.

I tend to agree with Cruisingdad's comments regarding gel-cell batteries in that they will probably ultimately lose out in competition with AGM products which will profliferate much more than the gel-cell products. There is no doubt that the gel-cell batteries have proven to be quite rugged, long-lasting and also have low internal resistance.

In the case of manufacturing technology the ultra-pure techniques of the latest production from Fulriver, for example, has proven that the self-discharge to be superior to Deka or Lifeline along with repeatable low internal resistance.
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Old 09-03-2007, 18:05   #14
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A 50% DOD (depth-of-discharge) limit for any lead-acid deep-discharge battery (AGM, flooded, gel-cell) is an ECONOMIC optimum guideline. Using a 50% DOD value when repetitively cycling batteries results in the lowest number of pennies spent per Amp-hour-cycle over the life of the battery. Less levels of discharge limits result in longer life yet cost more because the battery bank must be initially sized larger for a given cyclical energy usage. A deeper DOD results in shorter battery life yet the bank initially costs less because it is smaller and, in either case, results in higher lifetime cost than the case of the 50% DOD designed limit.
The table at the bottom of this webpage illustrates the above.

http://www.glacierbay.com/1batcrg.asp


The copy of Charlie Wing's book that I have is old enough that he only compares flooded to gel cells, but it looks like if your priorities are economics then golf cart batteries cost way less than anything else per kWhr according to Wing. Another way he shows to save money, he has a graph showing how much more it costs you in engine wear in $/kWhr charging your batteries than your batteries cost you with the price skyrocketing for engine costs as you decrease the depth of discharge of your batteries, so even if you discharge your batteries deeper than nominal you would still be way ahead in total money spent, that is if you mostly run your engine to charge your batteries.

Yes I would love to have AGMs for the many reasons listed above, but I can't afford to double or triple my costs on disposables.

John
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Old 09-03-2007, 21:20   #15
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Quote:
Originally Posted by Alan Wheeler
NO!!!!! Maximum charge rate for wet is 25%. Max charge rate for AGM is 33%.
So for 800Ah, wet would be 200A and AGM would be 264A. So the time difference is not greatly so. So the time difference charging the 800Ah bank would be ruffly 4hrs for the wet and maybe 3.5hrs for the AGM, using the respective charge currents.
That is the bulk charging time, not including the equalize stage.
From the Northstarbattery.com website:
http://northstarbattery.com/SES-544-01.pdf
About 60% of the way down the page,
The low internal resistance of the NSB battery allows for very high charge acceptance. These batteries also do not require the charge current to be artificially limited, as long as constant voltage (CV) charging is used. This characteristic helps the battery reach a very high (>85%) state of charge (SOC) in less than one hour with a charge current of the order of 1C amps where C is the rated capacity of the battery. Thus, 1C for a 100 Ah battery would be 100 amps.

I have 8 of these in my house (my REAL house) with a Airex 403 wind generator (and a grid 75 amp CV charger) for backup power. Whidbey Island WA has lousy grid power reliability.

My current boat has 4 Trojan T105's and an alternator with a couple of wussie flexible solar panels.


Steve B.
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