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  #1  
Old 09-30-2012
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AGM Battery Upgrade and Charger

So I upgraded my Starting and House flooded cells (Group 27) to two Group 31 AGMs.

Is there anything that I have to modify to accept these two batteries within the electrical system?

I'm usually on a mooring, so it's not top of mind ... but I notice my pre-existing TrueCharge (Model 20 - 20amp) charging controller has two battery types indicated on its read-out ... Flooded and Gel. Will this work when I'm hooked up to shorepower?
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Re: AGM Battery Upgrade and Charger

If you cut and paste this into a google search line, you will find a lot of discussion on AGM batts:

site:sailnet.com agm batteries

Some quick notes. You will need to have a way to keep them fully charged or get them there often, or they will not last. Harder to do on a mooring. AGMs can take a much larger charging load than other batteries, which can overload your engine alternator and burn it out. I believe it can overload a charger not made for them as well. You typically need a temperature and/or charging regulator with AGMs.

Pros will have better details, but chargers that are made for AGMs, seem to have an AGM setting.
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Old 09-30-2012
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Re: AGM Battery Upgrade and Charger

Also you can ruin them if you charge them with over 14.2V and some alternators go to 15V.

That's one of the reasons a charger regulator (as Minnewaska says) is a must.

Regards

Paulo
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Re: AGM Battery Upgrade and Charger

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Originally Posted by PCP View Post
Also you can ruin them if you charge them with over 14.2V and some alternators go to 15V.

That's one of the reasons a charger regulator (as Minnewaska says) is a must.

Regards

Paulo
Paulo,

I think you're thinking of gelled batteries, not AGMs. In fact, AGMs can and should take a higher absorption voltage...14.6-14.8 VDC and, the faster they can be charged the better (i.e., the largest charging source you can fit on your boat).

As was noted above, AGMs need to regularly be fully charged or they will sulfate and suffer a shortened service lifetime.

This is hard to do on a mooring, unless you have adequate solar power and a proper charge controller.

I'd not choose AGMs for a boat on a mooring UNLESS it had a sizeable solar charging system.

Also, it's true that if the batteries are significantly discharged they may place a very heavy load on your undersized alternator and, with no protection in the way of temp sensors, burn it out. This is because AGMs can take an enormous amount of amperage, will demand it from the alternator, and alternators typically fitted on boats are not capable of putting out high power for a long time.

Battery chargers will not likely be burned out by attaching them to AGMs, but they'll take a long time to charge. This is no problem if at dockside for a long time. If your charger doesn't have an AGM setting, use the flooded setting. Flooded batteries and AGMs have very similar charging profiles.

Bill
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Re: AGM Battery Upgrade and Charger

I have a Westerbeke 30 (1979) 41-9 ... I'll need to research the output of my alternator. I usually have to run the engine for about 20 minutes at a minimum on my final approach. So, hopefully that will top them off. I guess I'll just have to experiment.

I do have a 5w trickle solar charger ... not sure if that is sufficient or if it needs a controller.
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Re: AGM Battery Upgrade and Charger

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Originally Posted by btrayfors View Post
Paulo,

I think you're thinking of gelled batteries, not AGMs. In fact, AGMs can and should take a higher absorption voltage...14.6-14.8 VDC and, the faster they can be charged the better (i.e., the largest charging source you can fit on your boat).

As was noted above, AGMs need to regularly be fully charged or they will sulfate and suffer a shortened service lifetime.

This is hard to do on a mooring, unless you have adequate solar power and a proper charge controller.

I'd not choose AGMs for a boat on a mooring UNLESS it had a sizeable solar charging system.

Also, it's true that if the batteries are significantly discharged they may place a very heavy load on your undersized alternator and, with no protection in the way of temp sensors, burn it out. This is because AGMs can take an enormous amount of amperage, will demand it from the alternator, and alternators typically fitted on boats are not capable of putting out high power for a long time.

Battery chargers will not likely be burned out by attaching them to AGMs, but they'll take a long time to charge. This is no problem if at dockside for a long time. If your charger doesn't have an AGM setting, use the flooded setting. Flooded batteries and AGMs have very similar charging profiles.

Bill
Bill,

No, I am no wrong about the max charge or at least that was explained to me by the technician that recently installed a complete upgrade of the batteries and electrical system in my boat. On the instructions that came with the batteries (AGM Mastervolt) they also say that the max charge should be no more than 14.2V and less than what is optimal for lead batteries.

Their dedicated regulator (Mastervolt) as well as the port charger (220V) also have specific regulations for AGM batteries, with less voltage than for lead batteries.

However you are right about the rest: They like to be fully topped from time to time and they can "absorb" much more electrical energy much faster than lead ones (they can be charged much faster by a big alternator) but that has nothing to do with the max voltage allowed, that is smaller than the one that is optimal for lead batteries.

Regards

Paulo
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Re: AGM Battery Upgrade and Charger

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Originally Posted by PCP View Post
Bill,

No, I am no wrong about the max charge or at least that was explained to me by the technician that recently installed a complete upgrade of the batteries and electrical system in my boat. On the instructions that came with the batteries (AGM Mastervolt) they also say that the max charge should be no more than 14.2V and less than what is optimal for lead batteries.

Their dedicated regulator (Mastervolt) as well as the port charger (220V) also have specific regulations for AGM batteries, with less voltage than for lead batteries.

However you are right about the rest: They like to be fully topped from time to time and they can "absorb" much more electrical energy much faster than lead ones (they can be charged much faster by a big alternator) but that has nothing to do with the max voltage allowed, that is smaller than the one that is optimal for lead batteries.

Regards

Paulo
Most AGM batteries can be charged at much higher voltages than the Mastervolt line. Mastervolt suggests 14.25V absorption voltage at 77F. They also suggest temp compensated charging and not exceeding 5 hours at absorption voltage and also limit charge capability to .3C.

On the other hand Lifeline, Odyssey, Optima and the large private labelers like Deka/East Penn and Full River all suggest significantly higher absorption charging voltages for their AGM's.

I've done one bank of Mastervolt and found them expensive for what they are. I found it frustrating that they limit the charge to .3C. This means they really can't be charged that much faster than wet cells, which is one of the main benefits of owning an AGM bank..

Bottom line is we don't know what brand AGM the OP has so can't really recommend a charging voltage.

What we can recommend are:

*Alternator capability equivalent to the manufacturers MINIMUM standards. Lifeline for example wants a minimum of 20% of bank capacity and sets no limit. Odyssey also sets no limit and wants a minimum of 20% of "C".

*Solar or wind is a MUST for a mooring sailed boat with AGM batteries. If you do not get them full, and the alternator will not do this unless you motor for 10+ hours, they WILL die an early death. With only an alternator expect two maybe three years. With solar you can push 5-6+ years.

*Do not discharge below 50% of capacity very often. The shallower the discharge the longer the bank life.

*Temp compensated charging can be very important with AGM batteries. You'll need a alternator regulator that can compensate for battery temp.

*Charge to full as often as you can. At the least once weekly is much preferred and will yield longer life.

*If you own Lifeline AGM's then you should equalize/condition charge when they begin to show signs of capacity loss.

*Do NOT equalize other brands of AGM batteries without checking with the manufatuerer.

*If you convert to external regulation and a bigger alternator invest the extra $40.00 on an alternator temperature sensor.

*Be sure your pulleys are aligned and CLEAN. With a stock 3/8" or 1/2" belt AGM batteries can eat belts for lunch. Carry a spare.

*Charge the batteries at the manufacturers recommendations or as close as you can get.



There is mounting evidence out there that suggests insufficient charge current can have a negative impact on AGM battery bank life. 20% of a 200Ah bank is and alt that can produce at least 40A when hot. These banks seem to like to be hit with some decent current. Bigger is better in the case of most AGM batteries and 20% of capacity with Lifeline for example is a BARE MINIMUM...
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Re: AGM Battery Upgrade and Charger

Paulo,

The recommended charging voltages for all lead-acid batteries -- of which AGMs are just one type -- vary considerably from one manufacturer to another. In part, this is because of slightly different construction practices. In part, it's because the recommendations tend to be very conservative -- sometimes because of liability concerns. And, in part, it's because the recommendations are sometimes developed by sales and marketing personnel and not the engineers who designed the batteries.

Mastervolt recommends a maximum of 14.3 VDC for absorption charging of their 6V AGMs in series configurations. That's a very conservative rating.

Other manufacturers of 6V AGMs (in series to give 12VDC) recommend higher maximum voltages, viz:

Trojan 14.4-14.7V

Surette AGM 14.9V

Concorde Lifeline 14.6V

In collaboration with a major manufacturer of AGMs and a well-know expert in the field, I've been doing some research on AGM charging for the past few months. We've found that charging AGMs at higher than "recommended" voltages can have several benefits, including cost and longevity.

We have already proven this, and Nigel Calder gave a presentation to that effect at the SSCA Gam in Annapolis just this past weekend. Concorde is right now running a series of tests for us using 14.8VDC absorption voltage and several different maximum charging rates (to simulate what happens with different size chargers and alternators).

By the way, many AGM batteries can take WAY WAY more charging current than Mastervolt specifies. For example, Lifeline AGMs at 50% state of charge (SOC) can take 1.3X their rated 20-hour capacity initially, tapering off quickly thereafter. So, a 100AH AGM which is 50% discharged can take 130 amps initially. If they are more deeply discharged, they can take 5X their rating, i.e., a 100AH battery could accept 500 amps for a short time.

TPPL batteries -- a variant of AGMs -- can take even more charging current that this, reaching truly stupendous levels.

Moreover, these elevated charging currents are good for the batteries! They last longer, and deliver more cycles. In the traction field (forklifts, etc.) a new charging technique called "opportunity charging" has been instituted which involves frequent high-amperage charging whenever possible.

Bottom line for boaters with AGM batteries, however, is to fit large alternators and battery chargers whenever possible and -- most important -- make sure your AGMs receive a full charge frequently. Big chargers and alternators help to cut charging times, but the time required to reach a full charge is still quite long, normally much longer than you'd want to run your engine or generator for. Solar panels, wind generators or shorepower are the only practical solutions to ensure your AGMs reach a true full charge frequently.

Bill

Last edited by btrayfors; 09-30-2012 at 09:40 PM.
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Re: AGM Battery Upgrade and Charger

I have two Deka/East-Penn Group 31 AGM

http://www.dekabatteries.com/assets/base/1741.pdf
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Re: AGM Battery Upgrade and Charger

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I have two Deka/East-Penn Group 31 AGM

http://www.dekabatteries.com/assets/base/1741.pdf
Rated at 105ah, with 2 you can roughly assume you have 100ah usable before you need to top them up fully. The ratings are done assuming you draw at a specific rate and, therefore, their capacity will differ if you draw more or less at a time. Your specific systems will dictate how sufficient. The point is that you don't really want to get below that or you will shorten the life of those expensive batts.

A battery monitor is also a great investment, of you don't already have one.
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