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Old 22-07-2018, 10:12   #1
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Battery Equalization

I’m a bit of a newbie when it comes to maintaining wet cell batteries. The house batteries on our sailboat consists of four 6v golf cart batteries (Crown 235s) wired in series and parallel to create a 400ah 12v bank. They are about 14 months old.

We are full time cruisers so they get cycled every day. We nearly always anchor out, or tie up to a mooring, so these batteries are recharged by the engine, or (mainly) by our 200 watts of solar panels.

Since we we are usually in sunny parts of the world, this has seemingly worked well, but last week I noticed that the batteries just weren’t accepting as much of a charge as they used to. I did some reading, and I now believe that we have been chronically undercharging them all this time. One symptom:although we check the water level frequently, the batteries never need topping up. I thought this was because they were new, but now I read that is a symptom of under charging.

The specific gravity of the cells is 1.1-1.3, even when our solar charger thinks they are fully charged. Shortly after sundown the battery voltage is about 12.05 volts.

There is still enough capacity to run the fridge, fans, and lights, but I think the cells are in desperate need of equalization to reverse the sulphation caused by a year of under charging.

My question: reading about equalization is scary stuff... boiling acid, deadly fumes, peeling paint, sulphuric stench... can it be done with the batteries in place on board, or do they need to be removed from the boat?

Our Xantech 40 amp AC battery charger (never used) has an equalization cycle. Will this be sufficient to restore the batteries? Or are more drastic measures required?

Thanks in advance for any advice.

Author of An Unlikely Voyage -- 2000 Miles on a Small Wooden Boat
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Old 23-07-2018, 05:25   #2
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Re: Battery Equalization

A couple of comments on the info you provided:
Temperature corrected SG should be close to 1.268. Your stated range of 1.1 to 1.3 implies that you have a hydrometer that does not have enough granularity for the task at hand. A hydrometer (a spectrometer can also be used) must be able to read to 3 decimal places to carefully control this process.

A battery resting voltage of 12.05VDC indicates a nearly totally discharged bank. If you have a modest load on the battery, then the bank is significantly discharged or has a much reduced capacity, as you surmised.

Here are a couple of recent Cruisers' Forum Posts on the subject (there are many more):

6vdc Trojan T105 (225ah) Equalization - Cruisers & Sailing Forums
Disconnect bank before Equalizing ? - Cruisers & Sailing Forums

Equalizing even a modest bank such as yours will take several hours after the initial charge and needs to be closely monitored. Equalizing is considered complete when subsequent SG readings cease to increase and the SG between the cells are within a couple of points of each other.

Good luck!
Good luck.

Charlie Johnson
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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Old 23-07-2018, 07:28   #3

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Re: Battery Equalization

Do in place, with mains power. Monthly is a good routine for a regularly cycled bank.

Lots of details covered in the first thread above.
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Old 23-07-2018, 07:52   #4
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Re: Battery Equalization

Not sure it's in one of those threads but after equalization, set your solar charger so that it never comes out of absorption voltages, this will help with chronic undercharging.
The people that think their Banks are fully charged by Noon and I recently read by 10AM are almost certainly mistaken. I don't doubt that is when the charger drops to float, but it unlikely they are fully charged.

Finally not all batteries are allowed to be equalized, not all manufacturers publish a procedure
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