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mrspudandcompany(at)veriz
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 Posted: Mon Mar 29, 2010 5:49 am Post subject: Schumacher SC-600A |
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Bob,
I have a Schumacher SC-600A. It is a switchable 6/12 volt automatic charger
/ maintainer with 3 selectable charging rates of 2, 4, or 6 amp output, with
a microprocessor control. They recommend using the 2 amp for trickle charge
or charging small batteries such as lawn tractor or motorcycle. The 4 amp
is for medium charge of automotive batteries, and the 6 amp for fast charge
of automotive / light truck batteries.
In your years of experience with charge rates of batteries, do you think the
higher rate of 6 amps would even damage a small garden tractor battery?
When I look at automotive alternators with 50 amp outputs I wonder what are
the limits that will cause damage or shortening of useful life of a battery,
provided you don't overcharge?
Roger
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nuckolls.bob(at)aeroelect
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| Posted: Tue Mar 30, 2010 5:41 am Post subject: Schumacher SC-600A |
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At 08:40 AM 3/29/2010, you wrote:
<mrspudandcompany(at)verizon.net>
Bob,
I have a Schumacher SC-600A. It is a switchable 6/12 volt automatic charger/
maintainer with 3 selectable charging rates of 2, 4, or 6 amp output, with
a microprocessor control. They recommend using the 2 amp for trickle charge
or charging small batteries such as lawn tractor or motorcycle. The 4 amp
is for medium charge of automotive batteries, and the 6 amp for fast charge
of automotive / light truck batteries.
Yeah, I've got one of those too . . . or maybe it's the 2500. Got
it at Walmart . . .
In your years of experience with charge rates of batteries, do you think the
higher rate of 6 amps would even damage a small garden tractor battery?
When I look at automotive alternators with 50 amp outputs I wonder what are
the limits that will cause damage or shortening of useful life of a battery,
provided you don't overcharge?
Very astute observations! There's a common faulty assumption
that if one connects a monster charger to a 2 a.h. battery that
the beastly machine will smoke the little battery. The ratings
on any charging system come with two values. Set point voltages
and maximum available recharge current. Batteries come with
two values, state of charge and internal resistance. The battery's
ability to accept recharge energy is what sets how much and how
fast it will accept energy from the charging source.
As a rule, smaller, completely discharged batteries placed across
a rigid bus will initially draw large values of current but it quickly
falls to values that are commensurate with the battery's physics
and relatively independent of charging system's characteristics.
Let's recall that battery performance is a function of chemistry
mass which set capacity and surface area of exposed chemistry
which sets internal impedance. The greatest performing batteries
(Enersys and competing products) have lots of thin plates that
are a finely tuned compromise for optimum mass/area ratio. These
batteries are also exemplary in their ability to accept charge.
In fact, the Genesis series batteries I helped STC onto TC aircraft
with B&C have no published limits for rate of recharge.
At the other end of spectrum, smaller batteries with fewer,
thicker plates may appear to be accepting a charge when their
recharge current drops off rapidly while in fact, chemistry
on the surface of the plates is what has become recharged and
chemistry deeper in the chemical cell-mass (isolated by internal
impedance features) are coming along more slowly. If you leave
the itty-bitty battery connected to the monster bus long
enough, it will eventually get recharged.
Damage? During the initial stages of a rushed recharge,
energy is being dissipated internally to the battery in its
relatively poor connection between and internal to individual
chemical cell sites. This warms the battery up and is not
good for battery longevity. Hence, the poorer the construction,
the more care in recharging is necessary for maximum service
life. As a rule, tiny 'back up' batteries in airplanes
are not well construction (i.e. like an Enersys). These
batteries do benefit from careful maintenance and generally
don't have good service lives. This is why ALL of my suggested
two-battery systems feature identical batteries with engine
cranking abilities. They require a minimum of maintenance
and smoothly integrate into a "new battery every year"
rotation protocol.
Most of this discussion about battery chargers is
academic for the manner in which we use batteries. In
the auto/aeromotive worlds we depend on batteries to
start engines. After that, the well design charging
system replaces a few percent of expended battery energy
and supports all vehicle loads for the remainder of
the operating cycle. We don't routinely deeply discharge
our batteries.
It's only the deeply discharged battery that will
benefit from recharge protocols finely tuned to
it's physics. The smaller/cheaper the battery, the more
it benefits from fine tuning. So unless your airplane's
alternator runs too slow to support ship's loads while taxiing
miles to the hangar with all the electro-whizzies
turned on, then there's little or no benefit for
connecting any kind of charger until the next flight.
Even the smallest chargers (.8A Battery Tender) will
recharge the largest of our batteries if given
sufficient time. Further the time they spend in
top-off mode isn't real critical either . . . it
just doesn't want to be sustained over many weeks
or months while an airplane is being stored or waiting
for flying weather to improve.
Bob . . .
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