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Exploding Batteries and Boats
Introduction
There have been many tons of tons of batteries destroyed from
overcharing, so don't feel lonely if you just replaced a
relatively new set.
Liquid electrolyte batteries have been around for over a hundred
years, so they are understood better than gel batteries which are a
relative newcomer.
Are gel batteries that much different than liquid types? It's
always difficult to give a yes or no answer to any question more
complicated than ``do you sleep'', but for the gel battery question
we tend to favor a ``no'' answer.
Actual differences are subtle ...what complicates the subject
for many people is the claim that gel batteries are sealed.
In 1996, a sailboat operating in the Carribean had an explosion in
the battery compartment ...gel batteries. Fortunately, no one
was injured, but the
repair bill was significant, and as a result there will now be
a flurry of discussions about the place of gel batteries in boats,
and you can expect greater scrutiny of electrical systems from
the insurance companies. Let's review some basics.
Using Liquid Batteries
- Liquid batteries should be located in a cool, well ventilated
space, preferably
not in living quarters because of emissions of arsine and stabine gasses.
- The batteries should be secured so that movement is not possible in
expected conditions. This means more than a single nylon strap
with plastic buckles routed over the top of the battery. Batteries
should not be enclosed so tightly, however, that normal expansion
and contraction of the case is impeded.
- The batteries should be mounted in a watertight tray big enough to
hold all of the electrolyte in the event of battery case fracture.
- The battery should be maintained with a charging system, (charger,
alternator, etc.), that actually
measures battery temperature and corrects the applied voltage accordingly.
- An instrumentation system should be connected to the battery that
provides alarms for the following abnormal conditions:
- high battery voltage;
- low battery voltage;
- high battery temperature;
- high battery current; and
- low state of charge.
- If multi-step charging is used, the systems should be designed so
that it trips from the absorption voltage to the float voltage based
on Volts and Amps through the battery, rather than just timing the
absorption charge.
Using Gel Batteries
For the most part, gel batteries should be used exactly the
same as liquid batteries. The possible exception is the requirement
for an electrolyte container. First, gel batteries use a tougher
case than typical liquid batteries, so case fractures are infrequent,
and the electrolyte is much like a paste and will only ooze from
a fracture. Obviously, using a container is playing it safe.
Case by Case Analysis
- Keeping batteries cool is always, well cool!
Typically gel batteries don't gas, but in the event they do, the
same explosive mixture is produced. Planning for the day that the
charging systems fails, and no one is around to hear the alarms from
the instrumentation system is prudent ...provide plenty of ventilation.
- Gel batteries are no more sensitive to
temperature than liquid batteries, and might even be less sensitive
regarding gas emissions. However, effects from gassing a liquid
battery can be hidden by the addition of water to the cells. That
can't be done with a gel battery. Conclusion: There is no safety
difference related to temperature between gel and liquid batteries,
just an economic difference.
- Instrumentation System: Operating any electrical system without
alarms is for risk takers, not for the prudent. Battery type
makes no difference.
| What Went Wrong?
In the case of the explosion mentioned earlier a plethura of things
probably went wrong.
From reliable sources we've heard that the
batteries weren't
secured properly, insufficient ventilation was provided, temperature
measurement and
compensation was lacking, instrumentation was limited, no alarms
for abnormal conditions were present, and multi-step charging was
being used without battery state-of-charge controls. While there was an Ample
Power Energy Monitor onboard, battery temperature sensors had not been
connected, and no alarms had been activated in the Energy Monitor. Had the
sensors been wired, and alarms enabled, the Energy Monitor would have sounded
and alarm long before an explosion happened!
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The first temperature sensing alternator regulator was the original
3-Step unit introduced by Ample Power Company in 1987. Alarms
have been available since 1989. Monitor/Regulator interfaces to
smartly terminate absorption charging have been offered since 1992.
In 1996,
a lot of Ample Power gear could have been purchased for the reported
$100,000.00 repair bill!
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