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Old 02-05-2010
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AGMs and standard alternators

My current project is new batteries and cable, with some rewiring. I've gotten some valuable help here, all appreciated!

Current issue: we have space/location issues with the batteries, which has me considering 2 Group 24s as the house bank. The 160 AH (usable 80 at 50%) should serve our modest electrical budget.

The same space/location issues make AGMs attractive, but we have the standard (assume 35A) alternator on a Yanmar 2GM20F. No $ in budget to go with a new one and external regulator--shoot, I'm not even sure the budget can stand the AGM $$, but I'm pretending it can.

So, should I even be considering AGMs with this alternator/regulator? Would we fry the alternator if we took the bank down to 50% and then motored for a few hours at 2600 rpm, where the alternator would be putting out 25 or 30 amps and I guess the AGMS would be slurping up all the amps they could get?

Thanks all!
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Old 02-05-2010
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Arf,

Consider 2 AGM 6 volt and put them in series. That would give you about 225 ah. We bought 6- lifeline 6volt AGM. Thats about 775 ah. We chose themfor the following reasons. 1. Lifeline 6 volt have a smaller footprint than most 2. Twice a many deep cycles as the average wet cell 3. No maintainence 4. They can be laid on their sides if necessary. 5 They accept a charge more quickly than wet cell 6. They generally can be discharged more deeply than wet cell. Iy is true that they are twice as much money, and lifelines are a little more expensive than most other brands, but the have over twice the number of discharges so they really are not twice the money in the long run if you excercise care with them.

You would get more bang for you buck with AGMs and also twice the ah with2- 6 volts for as the 2-6 v yake up about the same space as 1 Group 31 12 volt

Dave
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Arf145,

Guess I have a different view. I would NOT consider AGMs in your situation. Yes, they could very well burn up your 35A alternator, trying to keep up with their charging needs when 50% discharged or more.

Interestingly, I'm in the middle of a project right now for an owner who already made the shift to AGMs, but didn't consider the requirements for their charging or possible damage to his small alternator. He's chosen to go with a major upgrade: new large alternator with external regulator, etc.

Truth is, for the type of weekend sailing many persons do, AGMs just don't make sense. And, no matter how you do the math, flooded batteries are still the best bang for the buck, IMHO.

BTW, see you're in the Chesapeake region. If you'd like to discuss, give me a buzz. My email is bill at wdsg dot com

Bill
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Old 02-05-2010
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Quote:
Originally Posted by btrayfors View Post
Arf145,

Guess I have a different view. I would NOT consider AGMs in your situation. Yes, they could very well burn up your 35A alternator, trying to keep up with their charging needs when 50% discharged or more.

Bill
Bill, I totally agree that flooded batts are by far the best bang/buck for our use. The only AGM feature that caught my attention is the ability to stick them in some spots that flooded batts can't go.

But the alternator situation makes it moot--which is good! Fewer options to consider.

Thanks!
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arf145,

Good thinking!

BTW, I do agree with the idea of using 6V batteries, in series, but flooded golf-carts. If you have the room, it's hard to beat them. Two T-105s in series will give you 225AH @ 12 volts, require fewer cable connections (paralleling 12-volt batteries actually requires more connections), and have true deep-cycle performance.

Bill
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Old 02-05-2010
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The deep cycle lifeline agm can be cycled 1000 times while the trojan 105 500. The argumernt more bang for your buck does not really apply as you have to replace the trojan batteries once to equal the lifeline agm thus equalizing their price. The trojan 105 are good batteries also. It is all according to how much time and energy you want to spend on battery maintainence and their replacement. If you do not go for long cruising...they may be the way to go. It is true your alternator must match your bank so if that is the determining factor, then go with wet. You must maintain them though or they will be useless and you will not even get the 500 cycles, so if they are in a hard to reach spot go agm. Again the Lifeline AGM golf cart are low profile and you will never worry about having the room as 2 of them are smaller than the 2 group 24 you have with double the ah. The Trojan 105 are much higher by about 4 inches I beleive.

The following is an exerpt from an article
Battery Types: Flooded versus AGM and Gel
On the kinds of batteries we may use on board:
The most common kind of battery in Marine use today is the lead acid battery. Using an electrolyte consisting of sulphuric acid, these cells can store impressive amounts of electrical energy in a relatively small space. This energy is stored in chemical form within lead grids mounted inside the battery. The reliance on lead grids and paste explains the great heft of lead-acid batteries.

The battery universe is further divided along the lines of battery construction. Currently, there are three common lead-acid battery technologies: Flooded, Gel, and AGM.

Flooded or Wet Cells are the most common lead-acid battery-type in use today. They offer the most size and design options and are built for many different uses. In the marine business, they usually are not sealed so the user can replenish any electrolyte the battery vented while charging the battery. Typically, the cells can be access via small ~1/2" holes in the top casing of the battery.

The plastic container used for flooded cells will have one or more cells molded into it. Each cell will feature a grid of lead plates along with an electrolyte based on sulphuric acid. Since the grid is not supported except at the edges, flooded lead-acid batteries are mechanically the weakest batteries.

Since the container is not sealed, great care has to be taken to ensure that the electrolyte does not come into contact with you (burns!) or seawater (chlorine gas!). The water needs of flooded cells can be reduced via the use of Hydrocaps, which facilitate the recombination of Oxygen and Hydrogen during the charging process.
Gel Cells use a thickening agent like fumed silica to immobilize the electrolyte. Thus, if the battery container cracks or is breached, the cell will continue to function. Furthermore, the thickening agent prevents stratification by preventing the movement of electrolyte.

As Gel cells are sealed and cannot be re-filled with electrolyte, controlling the rate of charge is very important or the battery will be ruined in short order. Furthermore, gel cells use slightly lower charging voltages than flooded cells and thus the set-points for charging equipment have to be adjusted.
Absorbed Glass Mat (AGM) batteries are the latest step in the evolution of lead-acid batteries. Instead of using a gel, an AGM uses a fiberglass like separator to hold the electrolyte in place. The physical bond between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact resistant lead-acid batteries available today. Even better, AGMs use almost the same voltage set-points as flooded cells and thus can be used as drop-in replacements for flooded cells.

Basically, an AGM can do anything a Gel-cell can, only better. However, since they are also sealed, charging has to be controlled carefully or they too can be ruined in short order.
Gel and Absorbed Glass Mat batteries are relative newcomers but are rapdily gaining acceptance. There are some very compelling reasons to use VRLAs:

Gel and Absorbed Glass Mat (AGM) batteries can dispense charge at a higher rate than flooded cells due to their lower Peukerts exponent. Deep-cycle Flooded Cells cannot deliver more than 25% of their rated amp-hour capacity in amps without plummeting Available Capacity.
Deep-Cycle Flooded cell battery manufacturers recommend a 4 to 1 ratio between battery bank size and the largest load encountered on board.
AGM and Gel cell manufacturers recommend a ratio of at least 3 to 1, a significant difference for loads such as the engine starter or windlass.
Virtually no gassing under normal operating conditions: Unlike flooded cells, gel cells and AGMs are hermetically sealed and operate under pressure to recombine the oxygen and hydrogen produced during the charge process back into water. You find VRLAs in the bilges of high end yachts such as Hinckley, Hans Christian, Island Packet, etc.. Every boat benefits from a low center of gravity over the keel (good for righting purposes) and the minimal venting requirements make it possible.
The ability to put VRLAs in the bilges (they can operate under water should you hole yourself) also lengthens their lives: For every additional 15 degrees of heat over 77 deg F, lead acid battery life (regardless of type) is cut in half (batteries self-destruct with time, you can only slow that process). Chances are, the bilges are the coldest place on board (outside the freezer) and the keel provides protection.
VRLAs can operate in any orientation (although you may lose some capacity that way) and even if a container is broken, a VRLA will not leak. This is a feature particularly important to blue water sailors who may encounter survival storms - you don't want to coat the inside of your boat with sulfuric acid if you ever get rolled. Proper (heavy duty) battery restraints are a must, regardless of battery type.
Gel cells and AGMs require no maintenance once the charging system has been properly set up. No equalization charges (usually), no electrolyte to replenish, no specific gravity checks, no additional safety gear to carry on board in order to protect yourself. If you want to be anal retentive about VRLAs you can load test them. However, proper charge control and protection is much more important with VRLAs because once fried it is impossible to revive them.
The charge acceptance of AGMs can burn up an alternator if the charging system is not adequate for extended runtimes at full power. The larger the battery bank and the harder the charger is made to work, the more attention I would pay to ensuring that the charging system can handle the currents for extended periods of time. This caveat does not really apply to low-duty applications like starter banks, since they usually need so little charge to be topped up. Even the puny alternators found in Jet Skis should be able to handler an AGM starter battery, as long as that battery is just used for that - starting.
On the other hand, if you need a large house bank and want to rely on a single charge source for much of the power, I'd aim for a high quality charge system from a respected company such as Ample Power, Balmar, Ferris, Hehr, JackRabbit Marine, SALT, etc. Ensure that the alternator receives enough cooling air as a hot alternator will produce less energy than a cool one and last longer to boot. AGMs and to a lesser extent gel cell systems can benefit from using the thermal alternator protection offered by the Balmar MaxCharge series of regulators, particularly if you expect to bulk charge your system for extended periods of time and don't have good engine compartment ventilation.
The higher charge efficiency of AGMs allows you to recharge with less energy: Flooded cells convert 15-20% of the electrical energy into heat instead of potential power. Gel-cells lose 10-16% but AGMs as little as 4%. The higher charge efficiency of AGMs can contribute to significant savings when it comes to the use of expensive renewable energy sources (wind generators, solar panels, etc.) as your charging system can be 15% smaller (or just charge faster).
While flooded cells lose up to 1% per day due to self-discharge, VRLAs lose 1-3% per month. Why employ a solar charger to trickle-charge your battery banks if you don't have to?
High vibration resistance: The construction of AGMs allows them to be used in environments where other batteries would literally fall to pieces. This is another reason why AGMs see broad use in the aviation and the RV industry.
Thus, there are some significant differences between battery types in terms of features and construction. However, there are also some very important figures to consider when it comes to choosing the right battery: Various capacities, cost, warranty, etc. The following table tries to summarize across brands using batteries as close to the 8D Group Size as possible

ix.
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Last edited by chef2sail; 02-05-2010 at 08:38 PM.
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Old 02-05-2010
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AGM batteries have what seems like a lot of advantages. But not everybody can take advantage of them. It's true that AGM batteries can deliver a much higher current but this is really not much use to the average sailor. A big advantage for an electric car (or boat) though. Maintenance is less with no fluid ever being required as is freedom of placement.
If you discharge an AGM more than 50% it will shorten its life like any battery.
They have more lifecycles than most flooded batteries. But not by enough when price is factored in. Based on my research a Lifeline AGM will survive about 1000 cycles to 50% while a T-105 Trojan about 750 cycles (other Trojan batteries a lot less). And some premium flooded will outcycle AGM batteries.
The biggest reason as far as I can tell to go to AGM batteries would be their greater charge acceptance, the ability to push basically as many amps as you are able to into them as quickly as possible. Lifeline AGM batteries will accept upto 5 times their capacity in charge current. In other words a 100 AH battery will accept upto 500 amps of charge current in bulk charge mode. But to really take advantage of this the alternator has to be upgraded to a much larger one, a proper 3 stage regulator is needed as are temperature sensors for the alternator and maybe the battery temp as well. And increased engine compartment cooling is a good idea as well. For a weekend sailor this doesn't make economic sense I don't think. And if you can't take advantage of this major bonus of AGM batteries I don't think their price of about double a Trojan T-105 is justifiable. However if you are long term cruising it makes a great deal of sense. A flooded battery like the T-105 needs no great expense in charging systems although certainly gains from a 3 stage regulator and I think is still the best buy for most people.
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Chef... Umm.. 3 x 225 = 675, not 775.

You should also post a link to the original article that you're quoting from.
Quote:
Originally Posted by chef2sail View Post
Arf,

Consider 2 AGM 6 volt and put them in series. That would give you about 225 ah. We bought 6- lifeline 6volt AGM. Thats about 775 ah. We chose themfor the following reasons. 1. Lifeline 6 volt have a smaller footprint than most 2. Twice a many deep cycles as the average wet cell 3. No maintainence 4. They can be laid on their sides if necessary. 5 They accept a charge more quickly than wet cell 6. They generally can be discharged more deeply than wet cell. Iy is true that they are twice as much money, and lifelines are a little more expensive than most other brands, but the have over twice the number of discharges so they really are not twice the money in the long run if you excercise care with them.

You would get more bang for you buck with AGMs and also twice the ah with2- 6 volts for as the 2-6 v yake up about the same space as 1 Group 31 12 volt

Dave
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Old 02-05-2010
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For me, it's about relevant bang for buck. And cash flow buck. We're not cruisers--if these batts only make it 5 years instead of 8 or whatever, it's not that big of a thing. And it's about partnership bucks when I try to explain to my less-frequent-user boat partner, my brother, the functional importance and technical beauty of all these under-the-skin projects that, when I complete them, seem to have changed nothing significant so far as he can see

The fact is, we've actually gotten by for two years on the two lame, abused Walmart floodeds that have never been able to be charged higher than 12.4 volts.
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Old 02-05-2010
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Originally Posted by chef2sail View Post
The deep cycle lifeline agm can be cycled 1000 times while the trojan 105 500. The argumernt more bang for your buck does not really apply as you have to replace the trojan batteries once to equal the lifeline agm thus equalizing their price.
Sadly the realities of marketing claims have not come through in the real world as I have seen it with AGM's. My friend Dave is a battery distributor and sells/distributes Lifeline, Trojan, Deka and many others. When I ask him about AGM longevity vs. deep cycle wet cells he just smirks and chuckles, then I hear something like "on paper blah, blah, blah...BUT"

Just last week he had no less than 20 AGM batts on core pallets. The oldest date code of the 20 +/- AGM's was 6 years, but the average was under 5 years. I look at the pallets and dates, as I have been, since my buddy Tom's premature failures of Lifeline's. Dave also had a fair slug of Trojan's and other deep cycle golf/industrial batteries. The average date codes on the deep cycle wets were 6+ years.

In my own personal experience I have not seen anywhere near the length of service the AGM makers claim. There are numeraous complaints on the many sailing forums of short lived AGM's despite proper care and feeding.

I installed 6 Lifeline batts on my friend Tom's boat, along with a gourmet charging system to match it. Nearly 3.5k worth of upgrades in just material costs.

Everything was done to Lifeline's requirements, charge profile, winter storage, float, absorption etc. etc.. Tom babies his batteries and treats them better than I do yet last spring he brought them over to me asking what I thought was wrong?

Took them over to the distributor and they were DEAD. Called Lifeline and was told this in not unusual and that he got a good service life? Really? He had nowhere near 1000 cycles, not even 500..?

His previous bank was T105's on a dumb regulator and fero charger and they lasted him 8 years and were still going strong when he made the change to Lifeline's. I have personally seen more than one bank of Trojans older than ten years and still going. Perhaps we will see this with AGM's but I have yet to.

I have yet to see many AGM's live up to the claims by the makers other than fast charging and non-spillable etc..

I was going to switch my own boat over to them last season, still ahve the new alt and regulator on my bench, but decided against it as the math just does not seem to add up in the real world. Besides my buddy Dave has talked me clean out if it by showing me under five year old AGM's that are dead on pallets every time I walk in the shop.

Wet's require maintenance but it takes me all of five minutes a couple times a year with some distilled water. I pay $144.00 for 225 Ah's with 6V wets and would pay about $588.00 for 220 Ah's with two 6V Lifeline's.

I could buy FOUR banks of wets, 4 X $144.00 = $576.00 for less than the price of one bank of Lifeline's. For those prices they should last twenty years minimum. Perhaps some have lasted 7-10 years but neither myself nor my friend Dave, who has been distributing AGM's for years, has seen it regularly.

My cost in Maine:
6V Wet Cells/225 Ah = $0.64 per Ah
6V Lifeline's/220 Ah = $2.67 per Ah

Don't get me wrong I like AGM's, and the technology, and they DO have their merits, but the manufacturers longevity claims have not stood up in the real world IMHO and with access to a distributor I can see and confirm this on a regular basis.

If you want to argue the merits of AGM's, and there are many, it is best to leave any sort of cost calculation out of it. We all know even the poorest treated 6V batts will last four to five years. Four banks of those @ 5 years life is 20 years. When AGM's start lasting 20 years, which would be $ for $ Ah for Ah, maybe then we can draw a cost comparison.

As Bill said above AGM's and lightly built alternators are a bad recipe and the alt will not usually last very long running at near full output. I have seen this on multiple occasions.

Get yourself a set of the Johnson Controls "Energizer" brand GC2 6V batts at Sam's Club. They run between $68.00 and $76.00 depending upon the club. I have a few friends going on 7 years with these as I type.. For those prices even if they last four years your still ahead of the game..
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