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Old 08-06-2008, 07:50   #1
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Location: Miami, Valencia-Spain, Panama
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AGM Batteries

Is anyone familiar and or with expertise on these new batteries? (I have two alternators 60 amp ea. and three 4d batteries) From what I read it seems they are a great solution for sailing vessels. The one thing I am concerned with is the enormous amount of amperage they draw from the alternators and whether they will be able to handle with reasonable or controllable overheating Thanks
S/V Le Freak

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Old 08-06-2008, 08:57   #2
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No problem if you have a hi output alternator and a smart regulator. If your alternators are internally regulated I doubt you'd ever be able to charge them up. I have 2 4D AGM's and am thinking of adding another one. I have the Balmar 100 amp alternator and smart regulator. You just set the regulator to AGM's with the little magnetic pointer they give you.

Rick I
Toronto in summer, Bahamas in winter.
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Old 08-06-2008, 17:14   #3
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Endless debate on the merits of AGM batteries. They are not new by the way. Look down near the bottom of this page for links to threads discussing AGMs.
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Old 08-06-2008, 17:36   #4
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High Quality AGM's can accept up to their amp hour rating as a charge rate...lesser AGMs will at least allow 50% of capacity charge rates. In any event, since you have about 450 amp hours total in 3 x 4D's..... getting down 50% of capacity will create a charging need for 225 amp hours...with your 120amps of alternator power, you will be able to put all but the last 10% of that back (call it 200 amphours) in less than 2 hours of run time.

Now lets look at wet cells as an can put back in about 20% of rated capacity during bulk charging which means about 90 amps per hour. So in 2 hours you will have put back about 180 amps...very close to what you can do with the AGM's... your boat, with your charging system, AGM's will not appreciably reduce charging time and at 2-3 times the price will not have an economic payback. Your decision to invest in AGM's will need to be based on other factors such as no maintenance, spill proof, doesn't lose much charge when not in use. Otherwise stick with decent flooded cells.
To be clear...I am speaking about YOUR situation. I have AGM's and love them AND can justify them economically in MY situation!

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