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Old 05-08-2013, 21:51   #1
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Are my AGMs Done?

Hi all,

I have had my boat for about a year and a half. It has 6 WM AGM 6 volt batteries, wired in series to give me 525 amps of 12v. They are kept connected to shore power which runs through a Xantrex 3000w inverter charger. I just returned from a weekend trip where I motored for 100 miles, arriving with fully charged batteries. With a steady load of 4-6 ah, plus some smaller temporary loads, my batteries dropped to 70% in less than 24 hours. I brought them back up with my Honda 2000, only to have them drop by the same amount a day later.
This is a pretty good sized house bank, so they should not be getting depleted so quickly. What do you all think?

Thanks, Bill
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Old 05-08-2013, 22:15   #2
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Re: Are my AGMs Done?

Bill...

I am not the AGM expert, but this doesn't seem to bode well at all....

Check for current draw... and obviously batt connections...

I once had a bad alternator connection that "appeared to" be giving my house a full topping off, but was actually giving some sort of false report of "Hey everybody! The batts are FULLY charged" AND THEN... bleeding current back through the alt system

Similar symptoms to yours...

I would buy a battery load tester, disconnect and individually charge each battery, and test each one... Maybe you have only one going bad, pulling the rest down...

More of a post bump than anything... There are far more qualified battery guys here!
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Old 06-08-2013, 01:44   #3
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Re: Are my AGMs Done?

where are you reading the 70%? the battery monitor? if so, you are probably just drawing more then you think. or it's set up to the wrong AH.

6 Goft carts at 12v should be in the 600-700ah range.

a battery monitor will not tell if you have bad batteries. if it says 70%, that means you have in fact draw 30% of the AH number that is progranmed into it out. the default is probably 200ah

with good or bad batteries it will still say 70%. with good ones you can keep going. with bad ones the voltage will drop too low if you keep going.
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Old 06-08-2013, 03:36   #4
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Re: Are my AGMs Done?

A 6A average load over 24hours is 144AHrs. Deducting 144AHrs from your 525AHr batteries mean they should be at 73%.

This is the only calculation the battery monitor makes. The battery monitor just deducts the AHrs you used off the total AHrs of the battery bank that you have programmed in. When setting the total battery AHrs on the monitor it is often not possible to select precise figures like 525 AHrs. It is better to set it lower so whoever set yours up probably put in 500 AHrs. This would make the 144 AHrs 71%, closely agreeing with your 70%.


The battery % tells you nothing about the health of your batteries.

Your batteries and system are fine.
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Old 06-08-2013, 03:43   #5
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Re: Are my AGMs Done?

if you've ran 150ams plus for the day (not unusual) then 70 percent remaining would be a fairly good figure to start off the day with, ten percent is 52 amp hours, so 150amps would use 30% of your bank, it all sounds about right.
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Old 07-08-2013, 17:08   #6
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Re: Are my AGMs Done?

I went to the boat today and checked the settings on my charger. My house bank was listed as 600AH and is only 525AH, so I changed it to 500AH (increments of 100). Shouldn't that give me a more accurate picture of my percent of charge on my battery monitor? Will changing this setting limit the amount of juice that goes into my batteries compared to before the change?

As you can tell, I have lots to learn .

Thanks, Bill
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Old 08-08-2013, 04:30   #7
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Re: Are my AGMs Done?

its worth checking the rest voltage as well, the battery monitor assumes the batteries are at capacity
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Old 08-08-2013, 04:47   #8
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Re: Are my AGMs Done?

Quote:
Originally Posted by montenido View Post
As you can tell, I have lots to learn .

Thanks, Bill


Hi Bill,

The thing you have still to learn is that calculations don't mean diddly-squat. If you were using your boat every day you would see that your figures are about 'normal'.

A 24 hour drain is a long time and in normal circumstances you would never have a 24 hour drain because, if you were cruising, you would be topping up with solar (etc).

So with a 6 amp load constantly (I've never had a load anywhere near that. My fridge cycles at that) + extras (that suck more than you think) for 24 hours on 550amp hours only dropping to 70% is EXCELLENT!!!!!!!!

70% = 12.40V aprox.

Over 24 hours you can let it cycle down to 12.24 volts (50%) so you have only half used your batteries.

If topping up with solar you would only be dropping down 15% each day! Thats truly excellent and you could pile more electrical goodies on-board.


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Old 08-08-2013, 05:06   #9
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Re: Are my AGMs Done?

Quote:
Originally Posted by montenido View Post
I went to the boat today and checked the settings on my charger. My house bank was listed as 600AH and is only 525AH, so I changed it to 500AH (increments of 100). Shouldn't that give me a more accurate picture of my percent of charge on my battery monitor? Will changing this setting limit the amount of juice that goes into my batteries compared to before the change?

As you can tell, I have lots to learn .

Thanks, Bill
Yes that is the right thing to do.
No it will not effect the charging in any. The only change will be in the % discharge. If you have discharge a 100Ahrs with the battery capacity set at 600 AHrs his would be displayed as (600-100)/600= 83% verses (500-100)/500=80%

The 80% is more accurate for your batteries as the 525 AHrs is for brand new batteries very carefully charged by the factory to 100% (I will ignore the Pukerts equation because it depends a bit on the typical loads and is usually a small factor)
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