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Old 19-03-2010, 21:51   #1
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Battery Charging Problem

I am using this forum as a last resort. I am having cronic problems with my charging and battery system and i am in the middle of the Pacific, in Micronesia. A year and a half ago I replaced the engine of my boat with a Volvo D2-55 which comes with a 115A alternator. I also had work done on the electical system, which has a starter battery, 4 x 100A house batteries and a zantrex pathmaker and isolator switches. Since then we have be on the move and have had consitant problems with the batteries and charging systems. I have replaced the batteries twice as they have died - once in Tahiti (with automotive batteries - the only ones i could get) and again in Fanning Island with Interstate SRM-24 (again the only batteries i could get). The new batteries seem fine for a while - say 2 months, but them seem to die and will not accept charge even after I equalize. The voltage goes up to 14.2 after about 15-20 mins of charging, and the amperage drops right down.

I have checked all connections ect, and I cannot find the souce of the problem, however I have a few theories:
1- The batteries are undercharging due to a voltage drop caused by the pathfinder?
2 - The alternator regulator is faulty
3 - The alternator is overcharging the batteries as it does not drop the voltage to below 14.2
Any comments regarding this or new theories. My next stop is Papau New Guinea and I will not beable to get batteries there, so i am thinking of getting new ones here. They have Excide Nautica batteries for sale - the only ones close to a deep cycle. Again I would appreciate any comments regarding this.

Many thanks,

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Old 19-03-2010, 22:12   #2
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You need a trusted voltmeter and a hydrometer. The voltmeter to measure the actual voltage at the actual terminal (not the clamp) of the battery. The hydrometer to indicate the actual level of charge. Make both measurements after that 15-20 minute charge...while charging.

Theories are fun, but science gets results.

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Old 19-03-2010, 22:24   #3
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Originally Posted by skatrijk View Post
The voltage goes up to 14.2 after about 15-20 mins of charging, and the amperage drops right down.
This is completely normal if your batteries were not deeply discharged and were already at or near 80% state of charge. Wet cell batteries accept very little amps as they near full or get above 80% state of charge. At roughly a 50% state of charge they can accept about 25% of the total 20 hour rated Ah capacity.

So the max a 400 Ah bank could theoretically accept is about 100 amps but that is when they are pretty depleted. At 90% state of charge and up you will be lucky to be getting much more than few amps into them.

This is why cruisers generally cycle their banks between 50% & 80% of capacity because the last 20% of charge takes a long, long time to put back into the batts due to acceptance.

Another thought is that you are deeply cycling your batts and prematurely killing them?

How are you monitoring your state of charge? In order to get an accurate read on SOC the batteries should have rested with no incoming or outgoing current for a good deal of time to attain any real level of accuracy. With some thick plate batts it can take 12 -24 hours of resting (nothing in or out) before an accurate measurement can be taken..
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Old 19-03-2010, 22:41   #4
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Thanks for the responses.
To respond to the first post...I have both and have been montering the voltage and the Specific gravity. They voltmeter indicates that the voltage at the post is correct (around 14.2 after 20mins). The specific gravity is way low at around 1175. So I know the voltage is correct and that the batteries are undercharged. I have also been montering the amperage flow while charging with a clamp on ampmeter (i had a link 10 - but it died - no chance of a replacement where i am!)

With regard to the second post, yes that is correct, but the batteries are deeply discharged. The voltage drops to 12 volts and under - 11.8 volts sometimes (in the morning) before I have a chance to charge. In addition to this the hydrometer reading indicates that the batteries are deeply discharged - they should be accepting more charge.
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Old 19-03-2010, 22:46   #5
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Yes, it certainly sounds like failed batteries. Next time you have new ones you should monitor them carefully. Modern auto batteries really cannot be deep discharged. In my experience they only survive a few deep discharges. So if you must use 'starting' batteries you'd best not discharge them much - which I realize make little sense.....
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Old 20-03-2010, 06:02   #6
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Is there any possibility of replacing the automotive-type batteries (which, surely, are a good part of your problem) with 6V deep-cycle golf-cart batteries? These are available almost everywhere. Four golf-cart batteries would give you 225AH X 4 = 450AH capacity for the house bank.

Also, if it were me I'd lose the Xantrex Pathmaker (battery combiner) and replace it with an EchoCharge or DuoCharge device.

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Old 20-03-2010, 06:31   #7
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Rijk, Making what seems like a change for the better sometimes produces unexpected results. Without full details of the systems & load requirements advice is a bit limited. Xantrex added results in maybe less total capacity for the house load (sounds like the starter battery may have added to the total capacity) but now you have protection for the starting battery. If getting to the house batteries to service them & space to install them is not a problem then the use of the golf-cart batteries is the best cost of ownership. The SRM-24 seems to be only a 80amp @ 5amps for 16hrs & you might have lost more capacity than you think with the combiner/isolator being added. 14.2v will not damage the batteries & you know by the need to top up the water level very frequently if you were overcharging.

regards Bill Goodward

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