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#1
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posted to rec.boats.cruising
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On Jun 15, 9:46 am, Salomon Fringe wrote:
...If you use a main engine or a generator to charge then I think AGM or gel are out of the question. And you believe this because...? I and many others have gotten many years of outstanding service from AGMs used in exactly this way. I've got nothing against regular old flooded batteries. They're certainly the best in terms of capacity per monetary unit or capacity per weight for lead acid. But the article you're quoting is being wildly, even absurdly unfair in its comparison of the types of lead acid batteries. He gives AGMs a particularly bad rap by asserting that they are essentially the same thing as a "maintenance free" starting battery. His argument seems to be "well, they've got thin plates and you can't add water to them so they must outgas like mad if you charge them fast and the plates must fail quickly because they are thin." Of course, if that were true AGMs would die quickly in normal use. Yet, I and many other folks, have AGMs that have lasted for 8+ years despite being deep cycled and charged at significantly faster rates than flooded cells. How can that be? The answer is that the author of your article either doesn't know the differences between an AGM and a cheap maintence free starting battery or is being intentionally misleading. As far as I know all AGMs are "valve regulated". Certainly all the major players are. Under normal charging they recombine virtually all gas. While massive overcharging will cause them to vent, modest amounts of over voltage will not hurt them noticeably. Indeed, all of the manufactures that I've looked at recommend periodically equalizing them. Generally you can put all the amps you've go into them as long as you regulate the voltage (max between 14.0 and 14.6 depending on the temperature and the particular battery). Even so regulated their acceptance rates are higher than deep cycle flooded batteries and charge times are quicker. AGMs do have thin plates. But, those plates are packed tightly into the glass mat and physically very well supported. So, they are less prone to physical failure than the thin plates in flooded starting batteries that need to be largely self-supporting. And, at the same time, they have more surface area than flooded deep cell batteries. The net result is that AGMs have very low internal resistance compared to other deep cycle batteries and are more durable. Low resistance also reduces gassing. .... If you read the article then you will also have read that if you are willing to use 'reasonable charging rates' (=slow charging), standard lead-acid is 'maintenance free' just like AGM and gel. But AGM and gel are much more expensive. I've read the article. It is total BS. AGMs are not gels or cheap sealed starting batteries. All his conclusions follow from a false assumption and no evidence for the conclusions is provided. -- Tom. |
#2
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posted to rec.boats.cruising
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#3
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posted to rec.boats.cruising
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On Jun 15, 12:32 pm, Salomon Fringe wrote:
.... That's interesting. Do you have the actual manufacturers discharge graphs that the author says they -for some reason- don't seem to supply? Just go look them up. There's no secret. I don't know why the author seems to think there is. Indeed, the article you posted in reply to Roger down the thread has some good info on this. Did you read it? In any case, the author of your first link doesn't provide a single test or citation to support his views, so why should we believe him? ... If the AGM manufacturers have nothing to hide then that info will be advertised on their websites. It is. --Tom. |
#4
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posted to rec.boats.cruising
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#5
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posted to rec.boats.cruising
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On Jun 15, 1:23 pm, Salomon Fringe wrote:
.... Yes I actually have the printed version of that doc, but I don't think there is even a hint of being able to use a AGM for 8+ years while deep-cycling... ? Well, I don't think I said that. What I was trying to say is that the author doesn't seem to have had any trouble coming up with published data. For instance he notes that deep cycle flooded cells ("semi- traction") get 350 cycles at 60% DOD (which is deep cycling) while AGMs get 650-800 depending on construction and chemistry. Service life depends on how you use them but the AGMs look much better than the semi-traction batteries for deep cycle use. His service life numbers suggest that some AGMs will be expected to last 10 years. AGMs have only been popular in marine use for less than a decade so it may be hard to get real numbers. My experience has been fantastic. YMMV... I think some of the very negative responses in the "Dutch magazine" (if they exist, got a citation?) might have been for gel cels. AGMs are not gel cells and linking them is bogus (or maybe even dishonest). AGMs have really good cycling numbers and they are published and you've even posted a link to them. So the Sterling guy's conclusion that you should avoid AGMs because they have "poor cycling numbers" is hard to figure. The rest of his arguments seem to be based on straw men and thin air, too. Who is this guy? Although it's a little off topic http://www.proboat-digital.com/proboat/20080203/ is interesting and has some insight into usage issues. .... Err, I was hoping you would have the links handy... ;-) I was hoping you'd do your own. If you can't google I'll do it for you, but last time I looked both Full River and Lifeline (Concord) had graphs and spec sheets on-line for their AGMs. You may have to plot data from your favorite flooded deep cycle battery for comparison but if the flooded guys have nothing to hide their data will be on-line, too... ;-) I'm not trying to sell AGMs. There are good reasons that they don't use them in golf carts, for instance. But the guy at Sterling seems to have decided that he hates AGMs and then gone off to figure out why. --Tom. |
#6
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posted to rec.boats.cruising
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On Sun, 15 Jun 2008 15:20:55 -0700 (PDT), "
wrote: His service life numbers suggest that some AGMs will be expected to last 10 years. AGMs have only been popular in marine use for less than a decade so it may be hard to get real numbers. My experience has been fantastic. I have heard the same from others whom I respect. I will probably convert one of my house banks to AGMs in the future. |
#7
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posted to rec.boats.cruising
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![]() "Wayne.B" wrote in message ... On Sun, 15 Jun 2008 15:20:55 -0700 (PDT), " wrote: His service life numbers suggest that some AGMs will be expected to last 10 years. AGMs have only been popular in marine use for less than a decade so it may be hard to get real numbers. My experience has been fantastic. I have heard the same from others whom I respect. I will probably convert one of my house banks to AGMs in the future. While I cannot comment on AGM batteries, my experience with gel batteries may be of interest. In 2005 I imported a boat from Florida to Norway. The survey was carried out in mid March and the batteries were Ok and powered up all auxiliaries properly. Three months later she arrived in Norway and the batteries were flat because, as recommended by the makers, the refrigerator was connected directly to the batteries rather than going through the panel and nobody had thought to disconnect it. I tried to charge the batteries with a powerful charger and it could get no current at all to pass through the batteries-they blocked the current completely.. I found that very surprising although I had half expected them to accept, but not retain, a charge. |
#8
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posted to rec.boats.cruising
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Wayne.B wrote:
On Sun, 15 Jun 2008 15:20:55 -0700 (PDT), " wrote: His service life numbers suggest that some AGMs will be expected to last 10 years. AGMs have only been popular in marine use for less than a decade so it may be hard to get real numbers. My experience has been fantastic. I have heard the same from others whom I respect. I will probably convert one of my house banks to AGMs in the future. I hope you were also thinking of adding another charger, since if your other bank is not AGM you will need it. |
#10
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posted to rec.boats.cruising
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On Jun 16, 12:58 am, Salomon Fringe wrote:
Well the author of the Victron article really did a good job and I have used his info extensively but I did realize that Victron sells gel and AGM but nothing else in terms of batteries so I assumed a slight nudge towards their product line in the numbers. ... Now wait. You're accusing the guy of lying to sell overpriced batteries that will fail if they ever get used and you're saying you've used his "info" extensively? Is this wise? Also his pricing info in the comparison was way off from what I found, e.g. full traction was just 50% of the price he stated. Pricing changes all the time. Still, I think he was testing 24v full traction batteries which might well explain the difference. ... in real life, a flooded cell will hugely outperform the AGM for cycling use because you can equalize a flooded cell to refresh weak cells, because you cannot monitor the temperature of each battery (let alone every cell) while charging which means guaranteed overcharging of some batteries/cells - destroying your typical AGM cell. Of course it is cheaper, too. Just for the record, you can equalize AGMs periodically without destroying them. The manufacturers even recommend it. I use a temperature compensated charging system with my AGMs. I don't understand what you're saying about not being able to monitor the temp. Your theory about cycling is interesting and testable but it goes against the published data. Given that I think the burden of proof lies with you. Go do some tests that suggest that the datasheets and experts are wrong and you'll garner a lot of attention. .... I would like to know from people who have REALLY deepcycled their AGM's 500 times (anybody counting?) and are still using them. If these exist I believe that you will find they paid as much for their AGMS as they would have for equivalent capacity traction - which would last at least twice as long. I presume what you're saying here is that my experience of REALLY sailing three times around the Pacific and REALLY living on my boat full time and REALLY charging my batteries using my engines is REALLY not valid because you REALLY don't want to hear it? I'm not claiming to be a representative sample but my experience suggests to me that some of your concerns about AGMs are overstated. I cruise extensively and keep in touch with many who do the same and I haven't heard any negative feedback about AGMs. Again, that's not a random sampling, but still, here we are in a widely read newsgroup discussing AGMs. Where are the voices saying "damn, I put one of those in and smoked it in a week"? Where are the 500 e-mailers who wrote into the Dutch magazine to complain about AGMs? I think Roger is right. The discussion has wandered off a bit. I'm not trying to get into a ****ing match. I don't sell batteries. When I bought my AGMs it wasn't a slam-dunk, easy decision. I can understand why lots of folks choose differently. I've been very happy with the way my AGMs have worked, but performance was not the only criteria in my decision. As I type this at my nav station, I have two 8D AGMs just a foot or so away from my toes. Safety and aesthetics have some value for me, too. AGMs are much more shock resistant than flooded or gel batteries and that makes them less prone to internal plate failures and shorts. Reliability is important, too. And so it goes. In different circumstances I can easily see myself doing things differently. There's lots of room for discussion of the pros and cons of various systems. My only serious beef with the discussion so far is with some of the arguments and assertions in your first link which are, to be kind, bogus. --Tom. |
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