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Old 16-01-2019, 12:47   #1
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Battery charger for AGM batteries

The flooded lead acid batteries on my 30 foot trawler have been replaced with Lifeline AGMs. The start battery is a 4D. The house bank has a pair of 8Ds connected in parallel. The existing 15 amp charger was not designed to charge AGM batteries. I am searching for a charger for the new batteries. The marine electrician who installed the batteries recommends a Pro Mariner Pro Nautic 1250 charger. A Lifeline Battery service tech suggested a 50 amp Victron charger yesterday. A different Lifeline Battery service tech suggested the Pro Nautic 1250 charger today. An Amazon review of the Pro Nautic 1250 charger by Aphrael does not recommend it for charging AGM batteries.
I have the following comments/questions:
1. Why should the battery charger need to be 50 amps? I could understand the recommendation, if the vessel was a sailboat. A 30 amp charger would double the existing charger output.
2. The Amazon review on 10/17/16 by Aphrael states that the Pro Nautic charges should not be used to charge AGM batteries. In addition, he states that the output is the same to all battery banks. Is this a problem? I do not have the training or expertise to properly evaluate the review by Aphrael.
3. What other brands of battery chargers should I consider?
Thanks
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Old 16-01-2019, 13:44   #2
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Re: Battery charger for AGM batteries

Silly reviewer, ignore.

Those are among the best. Otherwise Sterling Power ProCharge Ultra. Both user-custom setpoints.

How big is the bank? Lifeline reco is .4C as a minimum rate.
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Old 16-01-2019, 13:59   #3
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Battery charger for AGM batteries

Yeah, you want a BIG one, reason is to extend the life of the Lifeline battery, apparently itís good for them to be charged with a big charger.
Other than money spent you canít go too big, the battery will only accept the amount that is safe, any unsafe current as long as the voltage is correct wonít be accepted.
Plus donít forget if your house load is 10 amps, then you only have 20 left over to charge if your a 30 amp charger.
Only way a lead acid battery can be overcharged is if the voltage is too high, voltage is pressure and to push in the current, you raise the pressure.

Download and read the Lifeline Manual, itís likely the most comprehensive battery manual that exists.
http://lifelinebatteries.com/wp-cont...cal-Manual.pdf
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Old 16-01-2019, 14:02   #4
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Re: Battery charger for AGM batteries

Quote:
Originally Posted by DLECF View Post
I have the following comments/questions:

1. Why should the battery charger need to be 50 amps? I could understand the recommendation, if the vessel was a sailboat. A 30 amp charger would double the existing charger output.
The larger the charger, the faster it will charge a large battery bank.

Quote:
Originally Posted by DLECF View Post
2. The Amazon review on 10/17/16 by Aphrael states that the Pro Nautic charges should not be used to charge AGM batteries. In addition, he states that the output is the same to all battery banks. Is this a problem?
ProNautic 1250P | ProMariner

According to the ProNautic documentation they fully support AGM


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3. What other brands of battery chargers should I consider?
Sterling, Xantrex, Charles
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Old 16-01-2019, 14:35   #5
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Battery charger for AGM batteries

Just be sure whatever charger, you can set absorption to 14.3V and float to 13.3, and itís temperature compensated.
Going big really isnít about charging fast, itís about best for the Lifeline battery. A bigger charger wonít actually fully charge all that much faster, and the higher the SOC is to begin with, the less the difference as acceptance rate drops with SOC of course.
I have 185 amps of total charger available and usually only discharge my 660 AH bank by 150 AH, at that SOC often as high as 80%, the bank wonít accept the full 185 amps and if it will, itís only for a few minutes at most.
This article is specifically about how fast can I charge my Lifeline AGM battery.
There are many other articles, all worth reading
https://marinehowto.com/how-fast-can...ry-be-charged/
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Old 16-01-2019, 21:14   #6
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Re: Battery charger for AGM batteries

with ~500ah of house bank. I bet lifeline wants more like a 100a charger. (charging at 20%)

50a is actually on the small side for max battery life. but should work ok.

15a is simply worseless unless it's a 15' dingy.

the promariner have 6 different programmed settings. and I think custom as well but I haven't tried that.

every single battery charger will put out the same voltage on all 3 outputs. nothing you can do about that. since both your banks are the same voltage settings it's fine. if you had one agm bank and one flooded bank. you might have wanted 2 different chargers.
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Old 17-01-2019, 05:09   #7
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Re: Battery charger for AGM batteries

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with ~500ah of house bank. I bet lifeline wants more like a 100a charger. (charging at 20%)
Try 200A, .4C is their reco **minimum**

Can stack a 120A and an 80A if you want.

Need robust wiring of course
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Old 17-01-2019, 05:51   #8
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Re: Battery charger for AGM batteries

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Originally Posted by a64pilot View Post
Yeah, you want a BIG one, reason is to extend the life of the Lifeline battery, apparently itís good for them to be charged with a big charger.
Other than money spent you canít go too big, the battery will only accept the amount that is safe, any unsafe current as long as the voltage is correct wonít be accepted.
Plus donít forget if your house load is 10 amps, then you only have 20 left over to charge if your a 30 amp charger.
Only way a lead acid battery can be overcharged is if the voltage is too high, voltage is pressure and to push in the current, you raise the pressure.

Download and read the Lifeline Manual, itís likely the most comprehensive battery manual that exists.
http://lifelinebatteries.com/wp-cont...cal-Manual.pdf
Is that really true (bold part)? Just never heard it before
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Old 17-01-2019, 05:53   #9
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Re: Battery charger for AGM batteries

Take a look at Blue Seas Systems P12 battery chargers. I have had excellent service from my 40 amp unit charging my 3 batt banks.

https://www.bluesea.com/products/cat...ttery_Chargers
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Old 17-01-2019, 06:02   #10
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Re: Battery charger for AGM batteries

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Is that really true (bold part)? Just never heard it before
Some chemistries like GEL are more sensitive, and the caveats I posted above are very real, but yes.

Letting voltage climb or holding charging V too long can be fatal, high heat always reduces longevity, many rigs have dangerously dodgy wiring incapable of safely handling 200A.

But otherwise as a generalization, max current specs on FLA and AGM batts can be ignored, I think mfg lawyers worry about that last bit.
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Old 17-01-2019, 06:04   #11
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Re: Battery charger for AGM batteries

Power supplies, alternators, batteries, none "push" amps, they just make a max current **available**.

The load determines the current actually drawn.

If more is "requested" than the supply can safely deliver, that is when overcurrent protection is required, to protect the source. Makes things lots more expensive, usually cheaper to just buy a higher current output.
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Old 17-01-2019, 10:46   #12
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Battery charger for AGM batteries

Quote:
Originally Posted by Trackskinz View Post
Is that really true (bold part)? Just never heard it before


Yes it is true and is easily seen.
The first stage is bulk, bulk means that the battery can accept more than a charger can supply, so the voltage is lower than set point, if you could supply more power then voltage would be higher.

If you had a truly huge Charger, there would never be any bulk, voltage would rise straight to absorption

You can connect a 1000 amp charger to a single 100 AH battery, and as long as the voltage is correct the battery will only accept what it can, the charger will not push more current than the battery can safely accept, voltage is what controls how much current a battery will take, plus of course how much current is available, turn the volts up and more power is accepted, if itís available.
That is why an alternator has a voltage regulator, current into the battery is controlled by controlling voltage.

Once the batteries ability to accept current drops to be equal to what the charger can make, then your in absorption, where voltage is tightly controlled, in a 12V Lifeline itís 14.3 + or - .1V, but voltage remains steady and current continues to drop until ideally current is .5% of the rated capacity of the bank, so for my 660 AH bank, that is 3.3amps at 14.3 VDC.

At that point you are fully, 100% charged and the charger should drop into float, float for a 12 V Lifeline is 13.3 VDC, float is not meant to charge, but to maintain a charge, without overcharging the battery.
Almost all chargers drop into float prematurely, many can be brought back into absorption by turning them off and back on, sometimes a couple of times are required until you get to .5% of rated AH.

Higher voltages will ďPushĒ higher current into a battery, often resulting in damage. You can argue semantics whether the battery is accepting higher current or the source is pushing higher current, but it doesnít matter, end result is the same, a damaged battery.
You must control voltage to safeguard the battery, that is one reason that proper voltage is so important and not just selecting an AGM program, because the programmed voltages are very likely to be incorrect.

The hotter a battery is, the lower the voltage needs to be, and the colder, the higher, that is why itís best to have a charger that is temp compensated, that is it has a temp sensor that mounts on the battery and adjusts voltage based on battery temp.
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Old 17-01-2019, 10:55   #13
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Re: Battery charger for AGM batteries

Way back in the day automotive chargers put out quite high voltage, and what kept them from damaging a battery is that they were small, just couldnít supply enough current to hurt anything, but if you left one on, they could cook a battery.

Now better chargers are three stage and voltage is tightly controlled, so itís safe to hook up a really huge charger to even a small battery
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Old 17-01-2019, 18:10   #14
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Re: Battery charger for AGM batteries

Does Lifeline make chargers for their own batteries? I'm asking for I have three Odyssey AGMs in our smallish sailboat (31'). Odyssey sells chargers in 3 sizes - we bought the largest (20 amp). It's set up to do regular charging of their AGM as well as reconditioning cycles to (hopefully) remove sulfation.

We have light house load of around 3 amps, so we're nothing comparable to a larger boat with big fridge, AC or what have you. But we also have a smallish (160 watt nominal) solar panel, so we worry about our AGMs living in a chronic PSOC. Therefore, we run a reconditioning charge cycle 3 or 4 times each summer (we're in Maine where the summer is, well, not longish).

The batteries are 5 years old and still take/hold a good charge, so we can't be doing too much harm.

We also replaced the solar controller last year to ensure that the AGMs were getting the proper voltage (14.7 for part of the charging cycle).

Good luck with charger selection. There's a lot of them out there.

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Old 17-01-2019, 18:13   #15
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Re: Battery charger for AGM batteries

1) Lifeline doesn't make chargers but does make good batteries
2) Both Victron and ProNautic make great chargers (so does Mastervolt)
3) Sterling and ProNautic are, for all intents and purposes, the sme
4) Bigger is better with AGM's; I like .25C
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