Weak Batteries! Dead Batteries! Stop it!

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Weak Dead Battery BankYou know it's coming, the engine starts to crank a little slower, the house battery bank doesn't seem to last as long and you are now only two, maybe three years into the batteries

Cruisers are by far the biggest abuser of batteries because they typically do not fully recharged them except when they use the iron jib for excessive times of 8 to 10 hours. This typically makes the onboard crew very annoyed from the noise, smell and vibration and let's not forget the cost of fuel. It's not comfortable, practical or effective.

The inevitable will happen soon, the batteries will need to be replaced. You know it in your “gut”.

Here's the quick set of recommendations.

How the problem be solved (this is typical for flooded or AGM type batteries) is simple, just bring to batteries to full 100% charge and keep them topped off until needed. Batteries are funny animals they take time to receive a charge, hungry at first (this stage is called "bulk" charge) they grab almost as much energy as can be thrown at them until about 85% charge is achieved and then the batteries need to slowly absorb the balance of the charge (this stage is called "absorption" charge) which requires several hours of charge time regardless of the overcapacity of the charging source.

Keep in mind the daily maximum depth of discharge should not exceed 50% (always check the battery manufacturers for exact specifications/ recommendations). Most cruisers are well aware of this bottom limit and respect it. The problem is on the charging side of things. To get the batteries back up from 50% to 85% can be done relatively quickly by running the drive engines or on board generator.

But do most run their engines for 6 to 8 hours needed to get to 100%?

Probably not! Most of the time engines run 3 to 4 hours bringing the batteries up to 85 or maybe 90% charge. And so the cycle begins the next day with a repeat of discharge to 50% from an inadequate recharge. The battery bank is heading to a premature death.

When the boat is tied up at the dock with shore power and a battery charger active, the charger has the ability, over 24+ hours, to recharge the battery to 100% (provided the battery charger is large enough to overcome the onboard loads and is adjusted to the proper charge level). So the problem typically is on boats used during cruising or when tied up on a mooring.

In the later case, the solution is simple, utilize a charging source that can patiently recharge your batteries to full 100% charge and then keep them correctly topped off. The most practical solution is to use a renewable energy source such as a wind generator or solar PV panels. The best solution is dictated by your geographical location, budget and personal preference. Northern climates typically have good winds for recharging while near equator areas have excessive sun.

One would be quite surprised to realize that 140W of solar PV is capable of fully recharging a 400 A-Hr battery bank (with minimal loads on board). The solar works all day and quietly operates in the background pumping low amounts of energy into the battery bank and bring it up to that happy 100% charge. Larger renewable energy systems can quickly recharge house battery bank’s eliminating the need to run the engines unless weather conditions limit their production capabilities.

You don't have to be a cruising sailor to abuse your battery. Power Boaters are equally as offensive by letting their boats sit idle at the docks or on a trailer for days or weeks at a time while the battery slowly discharges (due to its own internal resistance). The addition of a single small solar panel (6-20W) can extend that battery life 2+ years and assuring that nice solid cranking sound when it is time to start your boating adventure.

1 comment(s)
Ken @ Primus Wind Power July 13, 2015 4:38 PM reply

Great Article and information eMarine - I see and hear about this situation all the time in many off gird situations. In the Marine world, it tends to be the most common. Bringing that battery bank up to 100% will greatly increase the life of the battery. In addition, limiting the DOD (depth of discharge) is another very critical component to extend the battery life. At Primus, we speak with customers all the time about this charging topic and utilizing two renewable charging sources, such as wind and solar in a Hybrid system is the best solution. Solar is great and should be installed but for charging at night, during storm periods and winter months (depending on where you are in the world), a wind turbine, such as the Primus built AIR Breeze or AIR Silent X is a great solution. Very quiet and reliable, the AIR units can be easily mounted to the stern or on the mast and do not take up as much room on the decks or stern as larger solar panels.

Wind power complements solar power because it often produces the most power precisely when solar power is reduced or unavailable, such as at night, in inclement weather, and during winter. Wind often blows during long winter nights and is, on average, actually stronger in stormy weather. During winter, average wind speed is highest, as is air density, both factors that contribute to wind generating more power when solar power tends to be least available. Hybrid systems that incorporate both solar panels and wind turbines, it turns out, form a perfect complementary relationship with each compensating for the weaknesses of the other system. Where solar is best during the daytime, wind power works throughout the night. Where solar is better through the summer months, wind power is better in winter months. And, on stormy and overcast days, wind power is the only option for generating power. Go to www.primuswindpower.com to learn more about the AIR Breeze and the latest AIR turbine.

1 comment(s)
JV July 20, 2015 2:14 PM reply

I agree with Ken (above). This is a good article which touches on an important subject we run into all the time. Keeping your batteries 100% charged and not discharging them more than 50% of their capacity will definitely extend the life of the battery - typically the most expensive component of your off-grid system. When it comes to solar, in order to properly charge your batteries on a consistent basis you should look for a high quality MPPT solar charge controller such as that offered by Genasun or the Blue Sky Energy product line of products with their patented MPPT algorithm and three stage charging technology. A well-designed system will include a controller providing an auxiliary charge connector which could be used to trickle charge an auxiliary battery, such as a start engine battery, when there is enough solar power available. So, whether you have been sitting idle at a dock or simply not had a chance to get on the water as much as you had hoped to, this is a great feature to have in order to ensure you always have enough juice to start your engines. Some of the Blue Sky Energy's products, such as SB3024, SB2512iX-HV, SB1524iX and SB3000i can provide this added security allowing you to be rest assured. For those that have incorporated wind into their systems, such as the turbines offered by Primus, the SB3024(D)iL DUO may be a formidable option. This allows you to have a hybrid system charging the same battery bank while making use of a dump load for any excess power. My advice - don't ignore this issue. Also, don't risk it when trying to determine which solar charge controller best suits your needs. Make sure you reach out to one of the many experienced professionals at e-Marine for advice. Making an error that may affect the performance or longevity of your batteries is often overlooked, but, one that most can ill-afford. For more information on Blue Sky Energy and Genasun product lines, please visit the links below: http://www.blues

2 comment(s)
e Marine Systems (Store Admin) (Post Author) May 5, 2016 11:34 AM reply
One of our customers Earl - What I am questioning is the absorb and float voltages for the pkgc-5 225 amp 6 volt flooded lead acid. I use these batteries in my solar system in series of 8 batteries to give me 48 volts by 4 banks a total of 32 batteries in all. I have been told all sorts of specs including absorb voltages of 57.6 up to 59.2 the later which makes the batteries run rather warm to hot. Can you verify the absorb, float and Eq voltages for me please along with a possible temperature compensation value. My batteries normally hover around 109 to 111 degrees Fahrenheit . Also how long should I keep them in absorb charge before letting them switch to float. I have been told to use half an hour per 100 amps so with 4 banks at 225 amps per bank I work that to around 4 and a half hours.

2 comment(s)
e Marine Systems (Store Admin) (Post Author) May 5, 2016 11:36 AM reply
We love it when our Vendor can directly assist Earl's questions directly..... Hopefully we can answer some questions. I always tell people to revert back to your manufacturer of the charger for maximum efficiency. For instance a smart charger technology may function differently from older technology. Bulk stage in a 48 volt charger involves about 80% of the recharge, wherein the charge current is held constant and voltage increases. The properly size charger will give the battery as much current as it will accept up to 25% of battery capacity in ampere hours and not raise a wet battery over 125 degrees F. The target voltage for a 48 volt system is 2.4 volts to 2.45 volts or 57.6 to 58.8 volts. The 59.2 volts you mentioned will heat up the batteries. The absorption stage is the other 20% and has the charger holding at 57.6 and 58.8 volts ( if set properly) and decreasing the current until the batteries are fully charged. In terms of time , this should be a function of your charger which should be automatic. I cannot guess how long this should take. You may have to use a volt meter or a hydrometer to help determine whether the battery is fully charged. If the battery is warm or hot the specific gravity will be higher than its true reading after it cools down or a load is put on it. This is called a surface charge. Again, if you can adjust your charger between 57.6 and 58.8 VDC this will be in the right range. The float state is where the charge voltage is reduced to 2.25 volts per cell, which is around 54.0 VDC and held constant, while the current is reduced to less than 1% of battery capacity. Some chargers hold this indefinitely and some shut off completely. Equalization should not be used in AGM and Gel batteries since the design of these batteries should all but eliminate stratification. In wet batteries, the electrolyte can stratify over time if not cycled properly. However, if you properly maintain a charged system you

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