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Full Battery Charging Concerns

I've been doing lots of research lately regarding battery banks, chargers, and alternators (as indicated by my recent posts/questions).

One scenario that I haven't seen discussed in detail, but is of course quite common, is a boat that spends most of its time connected to a shore charger or solar (such that batteries are fully charged), and then departs for what might be a long session of motoring (such as on a windless day) -- perhaps many hours in the case of a long transit.

How important would a smart alternator regulator be in a case like this, since a dumb regulator would be applying charge voltage well in excess of float levels?

1981 Spirit 28 "Bonnie Lass"
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Re: Full Battery Charging Concerns

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Originally Posted by Rusty123 View Post
I've been doing lots of research lately regarding battery banks, chargers, and alternators (as indicated by my recent posts/questions).

One scenario that I haven't seen discussed in detail, but is of course quite common, is a boat that spends most of its time connected to a shore charger or solar (such that batteries are fully charged), and then departs for what might be a long session of motoring (such as on a windless day) -- perhaps many hours in the case of a long transit.

How important would a smart alternator regulator be in a case like this, since a dumb regulator would be applying charge voltage well in excess of float levels?
A good gassing voltage is good for the batteries every now and then. In fact most good quality "smart chargers" will revert to an absorption level voltage to periodically gas the batteries.

Living on float constantly can still lead to stratification and with a low enough float voltage and warm enough temps even sulfation. My buddy does UPS systems for banks, pharma and credit card companies. The Enersys batteries he often uses are floated and boost charged. They still shed hard lead sulfate into the bottoms of the clear cases despite never being below 100% SOC for very long. Some of these installs swap out the UPS batteries as early as two years....




The idea that alternators on sailboats must have float voltage is, well, a lot of good marketing.

Let us not forget that nearly every car, truck tractor, bus or other vehicle with an alternator does not use a float voltage when running. They also use the identical battery technology we do on boats...

My wife and I have had numerous car batteries last well over 7 years and 140,000 + miles at 14.2V to 14.5V constant voltage alternator charging. I have two vehicles in my driveway right now that charge in excess of 14.3V. One of them has 174,000 miles and the battery in it is 6.5 years old. The other has 155,000 miles and is a 2005 with the original factory battery.

Don't worry about this on a sailboat. If you are in a trawler then it might be worth it.....

Chronic undercharging is by far and away the biggest issue we face on sailboats. Up until last year our own boat ran a dumb regulated alt (14.4V) and solar, so she was always charged when we went to use her.. The batteries lasted 6 hard seasons and are still testing at nearly new to this day (actual 20 hour capacity tests). Just three weeks ago they were loaned out to save a boat with a defunct bank due to chronic under charging. That owner now has new batteries and our old bank is back in the shop still going strong despite 6 years of dumb regulation and solar charging...

The boat we currently own is a good case study. She was cruised 24/7 for five straight years with only an 80 watt solar panel / charge controller, and the stock 50 amp Mitsubishi alternator with no smart regulation. Start bank was charged via a Yandina automatic combining relay (ACR).

The batteries were NOT FANCY. They were Wal-Mart / US Battery / Johnson Controls (long story) group 29/31 deep cycles installed new at the beginning of the cruise.

Norm, a retired electrical engineer, & his wife, lived & sailed comfortably, away from dock power, from Labrador, across the pond then back to South America and through the canal to Alaska and back all with NO SMART REGULATION and a "small" by today's standards alt and bank. Throughout this FIVE YEAR time period they logged over 2700 engine hours of charging time at the dreaded non-float voltage of 14.4v.

If you figure that the average coastal cruiser might do 100 hours per year this represents 27 years worth of charge time with dumb regulation set to 14.4 Volts. Remember most all vehicles, including the two we own, charge at 14.2-14.6 for many, many years. My wife's 05 Honda Pilot has 155k on the original factory battery and the alt puts out 14.3 volts all day long..

When I bought the boat from Norm the cheap Wal*Mart deep cycle trolling batts and stock 50 amp alt were still plugging along despite being used about 325 days per year more, over 5 years, than the average coastal cruiser does. Oh no, says the local "dock expert" dumb regulators will "cook" your batteries. Take that advice with a grain of salt.....

BTW the 10 year old starting battery with 2700 hours of dumb charging via a "combiner" was still actually starting my brothers 24 foot Mako as of two years ago. 2700 hours of dumb charging, charged via a battery combiner and it was still going at year ten....

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-Maine Sail / CS-36T


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Last edited by Maine Sail; 10-22-2013 at 06:52 PM.
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Re: Full Battery Charging Concerns

That's got to set a record for the fastest, most detailed reply in history. Thanks!

1981 Spirit 28 "Bonnie Lass"
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