Charge rate up to 40%

[Don Bradner]

In general it is true that bigger is better. With 3-stage chargers, though, you
do not get 33% faster full charge with 100 amps than you do with 75 amps

That is because, after the initial bulk charge has brought the voltage up to
14.x volts the amps start to drop. Once the output of the 100-amp charger has
dropped to 75 amps the time advantage has been exhausted, and the remainder of
the charge will take the same amount of time with each charger.

My charger puts out 105 amps peak. When my 660AH of batteries are around 50%
depleted it runs at that 105 amps for about 1 hour before reaching peak voltage
and beginning to drop. At that point it still has over 200AH left to put into
the batteries, and will take several hours to get there. Real-world says that
100 amps would do it in about 5 hours, and 75 amps in about 6 hours.

Because of that, when boondocking, I don't run the generator to anywhere near
full charge most of the time. Once the charge rate drops off to between 60 and
80 amps I turn the generator off.

This is not the best thing for the batteries, and shortens their life by some
percentage, but when you figure the cost of running a 15KW generator just to put
30-40 amps into the batteries to top them off I figure to save enough on fuel to
make the loss of battery life (which will still be many years with AGMs)
reasonable.

With my method, having more amps of charging is a good thing. I wouldn't mind
having 200 amps of charge, but you have to realize if you do that it will finish
bulk really quickly and rapidly drop off from there.

On 2/22/2008 at 8:20 PM Ross MacKillop wrote:

>How much faster would 110a (two 55's) be over a 75?
>
>With three 210 Ah batteries half discharged
>
>2 hours 47 minutes--- generator run time with 100 AMP charger or
>4 hours 10 minutes-- generator run time with 75 amp charger.
>
>100 amp Overkill? No By this article maximum charger could higher.-- from
>boatus ttp://www.boatus.com/boattech/battchg.htm
>
>If you own a small boat and
> you only need battery power at dockside intermittently for things
>like
> lights and bilge pumps, an SCR (silicone-controlled rectifier)
> charger may work best for you. It varies its charge to keep your
>battery
> at a constant 13.4 volts. The ones we carry are fully automatic
>and have
> multiple charging capabilities.
>
>
> Live-aboards and larger boats with many 12-volt accessories
>usually
> have ferro-resonant chargers that put out 12 volts continuously
> to keep up with constant power demands. Ours are fully
>automatic, self-regulating,
> and ruggedly built to give many years of dependable service.
>
>
> Experts agree that the best way to replace the energy you
>consume from
> your boat's batteries is through a controlled, multi-stage
>process.
> Both conventional lead-acid (flooded) batteries and gel cells
>will charge
> faster and last longer if they are charged in distinct phases
>that take
> into account their chemical and physical complexities. The
>recommended
> three-stage charging process works as follows:
>
> 1.
> Bulk Stage: This first stage provides a constant amperage bulk
>charge
> of 25-40% of the battery's capacity (in amp hours, Ah) up to
>about 14.4
> volts (14.2 for gel cells). This bulk charge will restore about
>75%
> of the battery's total capacity. It takes less time than
>tapering chargers,
> like ferro-resonant and SCR chargers, because the smart charger
>delivers
> greater current to the batteries which can accept greater
>current loads
> when they are discharged.
>
> 2.
> Absorption Stage: The remaining 25% of capacity is restored at a
> decreasing rate. Maintaining the battery at 14.4 volts (14.2 for
>gel),
> the amperage is steadily reduced. The battery is considered
>fully charged
> when it will accept only 2-4% of its amp-hour capacity at 14.4
>volts.
>
> 3.
> Float Phase: The charge amperage has declined to 2-4% of the
>battery's
> capacity, and voltage drops to 13.5 (13.8 for gel cells). This
>maintains
> the battery without losing electrolyte from gassing.
>
> 4.
> Equalization: Applies to lead-acid batteries only. This fourth,
> manually triggered stage prevents lead-acid batteries from aging
>prematurely
> by applying a small, constant current until the battery reaches
>16 volts,
> which dissolves the hardened lead sulfate crystals on the
>battery plates
> and prolongs battery life.
>
>
>
>
>
>
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