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Old 13-05-2020, 04:13   #1
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AGM Query

My RV and Catamaran were built before AGM batterys were invented,
They both came with lead acid batterys,

My Query is, would the standard alternators on the diesels in both, charge a 200 amhr AGM battery, Or kill them,

Or do I need a specific AGM alternator to charge the AGM battery bank,
They have been charging the batterys to date, But I notice my AGM'a are not holding a charge for any length of time,

My batterys are charged with 500 watts of solar through a 100 amp controller, as well as the diesel alternator when the diesel is running,
200 amphr AGM battery, and a seperate start battery,

Thanks in advance, Brian,
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Old 13-05-2020, 04:33   #2
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Re: AGM Query

A lot of variables here. Alternator regulator setting is a big one. Also which AGMs you have. There are big differences between AGMs from different manufacturers.

Without knowing any specifics, I would say it's unlikely you are doing anything wrong vs wet cell batteries. AGM absorption voltages are pretty similar to wet cell. Not like gel cells which are considerably lower.

Take a multimeter and measure the battery voltage during engine charging. Compare with manufacturers charging voltage stipulations.
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Old 13-05-2020, 06:11   #3
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Re: AGM Query

DefinitelyMe speaks with wisdom. That's very practical advice. take a look at this discussion of AGMs versus floodeds, and "Check with your physcian to see if AGMs are right for you." I switched to them for trail motor bikes because the bumps kept destroying flooded ones.

https://lifelinebatteries.com/2019/1...agm-batteries/
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Old 13-05-2020, 09:01   #4
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Re: AGM Query

Three inter-related issues arise when switching from FLA to AGM batteries: absorption voltage, absorption time and temperature sensing. The bulk/absorption knee varies with the AGM manufacturer from a low of 14.3V to a high of 14.7V. These voltages are at 77F. Lead acid batteries (FLA, AGM, GEL) have a negative temperature coefficient (NTC) which means as the battery temperature rises, the required charging voltage declines and vice versa.

The time that the charging source keeps the batteries at absorption voltage is critical to ensuring the AGMs are fully charged on nearly every cycle. If AGM batteries are not fully charged frequently, they will be chronically under charged, sulfate, stratify and die a premature death.

So, for optimum AGM service life, the charging source should have an adjustable absorption voltage set point, temperature sensing at the battery bank to adjust the charging profile and an adjustable absorption time or other method to determine when the bank is fully charged. No stock alternator that I am aware of has these attributes.
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Old 13-05-2020, 11:53   #5
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Re: AGM Query

Quote:
Originally Posted by Mr B View Post
My RV and Catamaran were built before AGM batterys were invented,

They both came with lead acid batterys,



My Query is, would the standard alternators on the diesels in both, charge a 200 amhr AGM battery, Or kill them,



Or do I need a specific AGM alternator to charge the AGM battery bank,

They have been charging the batterys to date, But I notice my AGM'a are not holding a charge for any length of time,



My batterys are charged with 500 watts of solar through a 100 amp controller, as well as the diesel alternator when the diesel is running,

200 amphr AGM battery, and a seperate start battery,



Thanks in advance, Brian,


The absorption voltage setting for your battery should be per battery manufacturer unless it’s some off brand that doesn’t provide that info.

Incorrect setting of alternator could kill the batteries if it’s set for just a regular starting battery. If it has a smartish regulator it’s probably close unless somebody messed with it.

Going the other way the AGMs could kill your alternator if the regulator doesn’t limit max current. AGMs and LiFePos can accept huge currents, more than most alternators can produce.

Why the switch?
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Old 13-05-2020, 21:42   #6
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Re: AGM Query

Quote:
Originally Posted by Adelie View Post
The absorption voltage setting for your battery should be per battery manufacturer unless it’s some off brand that doesn’t provide that info.

Incorrect setting of alternator could kill the batteries if it’s set for just a regular starting battery. If it has a smartish regulator it’s probably close unless somebody messed with it.

Going the other way the AGMs could kill your alternator if the regulator doesn’t limit max current. AGMs and LiFePos can accept huge currents, more than most alternators can produce.

Why the switch?
Its quite simple, The switch,
AGM's because I thought they were better batterys and no maintenance,
Very Difficult to get at for adding water to them,
And myself being a Dummy with electrics, Not Knowing,

My RV's batterys were over 20 years old when I got them, One was very dead and the other was well on the way out,
I replaced with an AGM 200 Amphr about 5 years ago, Mutlimeter on it and its not holding a charge for a week or so, down 10.7 volts,
It fully charges when the diesel is running,

My boats batterys got drowned and needed replacing, They were Kaput,
I replaced with an AGM 200 Amphr that I got for a slab of beer, No guarantee it would even work,
It was charged fully with an AGM battery charger, 14.4 Volts,
500 watts of solar connected to it, 100 watt solar controller,
It goes up to 14,4 on the solar,
But no sun and the battery was 10.6volts after two nights with all nav lights, GPS, cabin lights, Laptop, Fridge, Etc running,
The diesel alternator charges the batterys fully when its running,

The alternator was fully rebuilt after it got drowned and was rusted out inside after 7 years of just quietly rusting away,
I have no idea on its output or what it will charge other than a Lead acid battery that it was originally built for,
It was rebuilt as a Mitsubishi 3 cylinder diesel alternator,
Not as a Westerbeke alternator, They had never heard of Westerbeke and didnt know what Westerbeke was, Im in Australia,
Other than it works efficiently and does charge the flat batterys in a very quick time, I have no other info on it at all,

After stuffing around and rewiring my boat, It suddenly occured to me as AGM's need a special Battery charger, 240 Volt, which I have purchased specifically for my AGM's,
Will the Alternators on the RV and the Diesel on my boat, need a special Charger, ( alternator) for the AGM's as well, This I dont know,


My bike is a different issue, It ran an AGM from New,

I need a new battery for my boat anyway, 200 amphr, Minimum,
Every thing works for lead acid,
Should I buy lead acid again, or can I put AGM's in with my current system set up, ????????? With out the existing alternators killing the AGM's, ,
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Old 14-05-2020, 05:46   #7
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Re: AGM Query

Mr. B #6:
Quote:
Should I buy lead acid again, or can I put AGM's in with my current system set up, ????????? With out the existing alternators killing the AGM's, ,
To optimize the service life of AGM’s, see Posts #2, #3, #4 and#5 for answers to your
question.
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Old 14-05-2020, 06:57   #8
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Re: AGM Query

To optomize the life of any lead acid battery a “smart” charge source is necessary, personally I won’t buy one that isn’t programmable, the dip switch settings for AGM, flooded etc most likely isn’t correct.

However from my perspective it seems to me that any battery that is actually used and by that I mean actually cycled not shallowly and often it seems most last 5 years. Many get more, far more, but I believe they don’t use much power and very shallow cycle them, or stay plugged in a lot.
I get the 5 years from personal use, airplanes, motorcycles, tractors, cars, RV’s and my house bank on my boat is beginning to tell me it’s losing capacity. Only because I watch and compute capacity regularly, if I didn’t I’d still think everything is fine.

In my opinion AGM’s are often poor quality, unless you get the ones that are known for quality, and cost much more than flooded, and the only real advantage they have is that you don’t have to water them, if not watering them is worth the extra money then you will like them, just don’t expect more from them than a flooded bank, cause I don’t think there is more.

I hope the Fireflies are the exception, but it’s tough to believe the hype, can anything really be that good?
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Old 14-05-2020, 09:43   #9
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Re: AGM Query

Quote:
Originally Posted by Mr B View Post
Its quite simple, The switch,

AGM's because I thought they were better batterys and no maintenance,

Very Difficult to get at for adding water to them,

And myself being a Dummy with electrics, Not Knowing,



.....


AGMs are better for certain things. Vibration resistance, slightly faster charging, high output current, maintenance free, odd installed orientation.

For a cruising house battery much better bang for the buck are Gels and FLAs.

Gels are also maintenance free, more tolerant of PartialStateOfCharge and get about twice the cycle life for slightly less cost.

FLAs are much cheaper, have the same or better cycle life, are more tolerant of PSoC, and can be repaired to some extent if they are accidentally abused.

I would use AGMs in a dinghy where a use was expected.
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Old 14-05-2020, 10:04   #10
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Re: AGM Query

#9
Quote:
AGMs are better for certain things. Vibration resistance, slightly faster charging, high output current, maintenance free, odd installed orientation.
FLA have a charge acceptance rate (CAR) of < 0.2C; AGMs have a CAR as high as 1C.

Quote:
For a cruising house battery much better bang for the buck are Gels and FLAs.
This is misleading. GELs are fussy in that they typically have a lower absorption voltage than other LA batteries and are very sensitive to charging voltage just a few 0.1VDC above specification. Charge above the spec, and the GEL battery is destroyed. FLA's have a CAR significantly less than the AGMs which equates to having to charge longer to fully charge the bank.

Quote:
FLAs are much cheaper, have the same or better cycle life, are more tolerant of PSoC, and can be repaired to some extent if they are accidentally abused.
>> Yes, FLAs are cheaper.
>> FLAs cycle life is usually in the 500 cycle range whereas properly maintained AGMs can have as many as 1200 cycles.
>> Yes FLAs are more tolerant of PSOC, but AGMs are on the market with special chemical formulations that make them insensitive to PSOC.
>> FLAs can be "repaired" by an equalization charge. Some AGMs can be too.
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Old 14-05-2020, 10:29   #11
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Re: AGM Query

Where good gel batteries excel is with extremely long life in deep cycle operation (for lead acid batteries). I have had 15+ years service from these batteries in reasonably demanding marine applications.

They have a reputation for being sensitive to charging voltages (which should not be a problem with modern regulators), but I have used these batteries when dumb or manual regulation was typical. Despite all too frequent over-voltage problems, the deep cycle life was great.

The best gel batteries are expensive so the “bang for the buck” performance is not necessarily better, but they provide the closest to “fit and forget” (for a long time) available in lead acid chemistry, with the posible exception of carbon/foam (time will tell).
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Old 14-05-2020, 10:36   #12
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Re: AGM Query

Starting at 50% DoD or lower an AGM will charge faster. Once they hit absorption at about 70% charging will be voltage limited and all types of lead acid batteries will charge at pretty much the same rate. From 50% the time saving will be on the order of 20-30min for a 6-7hr charging cycle. To get this faster charging you will need a high capacity alternator, driven by a serpentine belt and a smart regulator. Figure an extra $1k or so. Alternatively a generator and a big mains charger, figure $1500. If you don’t get a souped up charging system the it will take the same amount of time regardless of what type of battery you have. If you are going to run the engine or a generator to recharge, best use is for about 1hr first thing in the morning to get thru bulk charging then let solar panels charge thru the absorption stage for the next 5-6hr.

The hybrid FLA batteries many marine stores sell as deep cycle probably only get 500 cycles. Real deep cycle FLAs can get 1000+.

I distrust the AGM manufacturers that advertise 1200 cycles.

Yes Gels are pickier about their charging, but if you can do it they will likely have the longest life from what I read by disinterested testers. Yes they are slower to charge but if most or all of that is off solar does it really matter?

The only AGMs I’m aware that are really tolerant of PSoC are CarbonFoam which are a bird of a different feather and are in a completely different price category for it.

Yes, some AGMs can be equalised, most can not. None can have electrolyte added back if the are overcharged.
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Old 14-05-2020, 11:49   #13
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Re: AGM Query

#12
OK.
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Old 14-05-2020, 15:03   #14
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Re: AGM Query

Post #12 is right on the money. AGM batteries CAN often be charged at a higher rate during the constant-current (bulk) part of the charge cycle. But just run the numbers. Four series-parallel T-105s are about 450 AH. They’ll quite nicely charge at .2C or 90 amps. Any more charge capacity than that requires a huge alternator, big cables, etc. The majority of the boats that I’ve seen over the years have nowhere near enough charging capacity to charge a big AGM bank. And certainly not any faster.
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Old 14-05-2020, 15:29   #15
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Re: AGM Query

AGM doesn’t really charge any faster, it still takes 6 hours to fully charge. They will initially charge faster though, I can charge mine at 185 amps with the generator and if I started my engine at about 285 amps, but if they are close or 50% when they were new that would take that for 20 min, then start backing down, so I’d guess they would accept 285 for 5 or 10 min or so.

I don’t know why but I have talked to several with Gel batteries that didn’t get a good life, and they talked like they knew what they were doing and were using the correct charge voltage, I can only assume they were discharging deeper than others that get long lives.
If you look at almost any batteries life vs discharge chart, you get about twice the Life if you discharge 25% as opposed to 50% often more.
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