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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 10-24-2010
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AGM batteries with Lead Acid Charger

Has anyone had a problem using an existing charging system made for lead acid batteries then replacing lead acid with AGM batteries?
I have a PD 2030 charger from Progressive Dynamics which is designed for lead acid only. (Of course the new design 2130 has the ability to change to one of 3 battery types, but I don't want to pay to upgrade.) I am putting in 4 - 6 volt AGM batteries. BTW the alternator on the engine is OEM and is set for Lead acid as well.
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Jamie
1983 Morgan 384
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Old 10-24-2010
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Lead acid and AGM batteries are very close in charge parameters. It shouldn't be a problem.
What are your reasons for choosing AGM?

.1 volt difference with a design tolerance of .1 volts +/-
From Xantrex charger manual:
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AGM batteries with Lead Acid Charger-1.jpg  
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Old 10-24-2010
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+ what mitiempo said.

However, your alternator might be a problem. The four AGM golfcarts are capable of accepting very high amperage....at least 400 amps....for a substantial period of time.

The OEM alternator, probably with an internal regulator, isn't designed to put out high amperage for long periods. Typically, these are automotive alternators designed to put out high amperage for a very short period of time (minutes only) after which they ramp down considerably. Typical flooded lead-acid batteries will only take about 20% of their capacity in charging amps, while AGM's will accept well over 100%, and can overtax your alternator.

I see quite a few such mismatches, and burned out alternators as a result. If you're going to switch to AGMs and if you're going to cruise with them -- not sit at dockside with the charger plugged in -- then you'd be well advised to consider whether your engine's alternator is up to the task. If not, you'll need to go to a high-output alternator AND an external regulator.

Bill
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Old 10-24-2010
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One solution is an external regulator like Balmar's MC-612 which lets you adjust the alternator output and has temp sensors as well.
Switching to AGM batteries without other changes is not always a good plan and often is just a beginning of problems and further upgrades are often necessary.
You might find this recent thread interesting.
AGM Batteries
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Old 10-24-2010
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Brian, superb link. And it includes one of Maine Sail's "classic" discussions, the one on page 6 or so with Balmar's discussion of acceptance and the higher voltages now being used for dumb or internal regulators.

Here's the Small Engine Mode in action: Alternator Output Management with External Regulators [Small Engine Mode]

Folks might wanna read the embedded links in that topic, too.
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Old 10-27-2010
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Thanks for the replies. I have ripped out the wiring the previous installer put in. Found a dead battery as well. Have installed 4 six volt AGMs and one of the previous Optima batteries for a starter. Will change out the altenator when I can, before going offshore.
Jamie
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Old 10-27-2010
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Jamie, an AGM battery IS a "lead" battery, and you will find different ones suggest different charging voltages, within the same general range as wet lead batteries. You need to check the manufacturer's specs for your batteries and compare them to your alternator/regulator. In the case of an Optima, it is designed to replace a wet lead battery and should work perfectly well on the same equipment, even if the optimum (no pun) voltages are slightly different.

With regard to AGM sucking the life out of an alternator...Bear in mind that depending on the overall capacity of your battery bank(s) and how deeply you discharge them, you can control that to some extent just by noting how much charge you need (i.e. 50% of 400AH? 75% of 800AH?) and not letting the demand go too far beyond what your alternator/regulator can accomodate.

Marine installations can kill alternators from heat, so good venting to the alternator, a blower if needed, or dual fans (at both ends) of the alternator can all help that.
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Old 10-27-2010
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Quote:
Originally Posted by hellosailor View Post

With regard to AGM sucking the life out of an alternator...Bear in mind that depending on the overall capacity of your battery bank(s) and how deeply you discharge them, you can control that to some extent just by noting how much charge you need (i.e. 50% of 400AH? 75% of 800AH?) and not letting the demand go too far beyond what your alternator/regulator can accommodate.
You're quite right about the heat. (4) 6V batteries would be 400 to 450 AH. @ 50% SOC they would most likely "accept" up to 50A. An internally regulated alternator would attempt to provide that load, and an OEM alternator, regardless of regulator (unless you have one like the MC-612 which has Amp Manager and Small Engine Mode).

So you need to match your alternator size to the acceptance of the house bank @ 50%, which usually results in a 100 A alternator working at 50% of its total capacity.

Millions have gone through this same exercise, and those are the numbers that come out and get you, most all of the time. Why? Balances output, storage capacity and input from the alternator.

hellos is right, and AGMs will accept a higher rate of charge than wet cells, so re-check your alternator sizing.
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Stu, the thing about OEM alternators is that the gods must love them, they keep creating so many more kinds. Oh wait, no, maybe that's "better idiots" they keep making.

Either way, about the only thing we can be sure an anonymous "auto" alternator shares in common with the next one is that it is not designed to run at 100% power for long, and the internal regulator is designed to not overcharge a battery during long use. As opposed to charging one quickly.

Charging voltages, temperature protection, surge protection, many things vary from one to the next but if someone is working with limited time, or money, and has to upgrade one piece at a time, usually starting with "Oh damn, I need new batteries NOW" it may not be the best solution, but upgrading piecemeal can be made to work.
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I agree. Two issues are bank capacity compounded by AGMs higher acceptance, when combined with a small OEM (automobile) alternator. imply ends up with an alternator that;s too small for the intended use and that lovely "sucking sound" from a large bank with the AGM's increased ability to absorb amperage.

Can be made to work? Hmm, I don't see how without an external regulator with amp manager or small engine mode.
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Last edited by Stu Jackson; 10-27-2010 at 10:08 PM.
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