ELECTRICS UPGRADE, PART 1
Table A
Battery types
BATTERY TYPE (12V) COST PER NO. OF 50% COST PER
You will often hear the expressions ‘starter’, ‘leisure’
100AH CYCLES AMP-HOUR
and ‘deep-cycle’ referring to marine batteries and,
apart from their differing physical attributes, there is
Ordinary low cost lead-acid £75 100 £0.015p
also a considerable difference in cost. They all work
Heavy-duty truck battery £100 200 £0.010p on the same principle, but their make-up varies.
Semi-traction multi-purpose £125 400 £0.006p
Engine start batteries (aka starter, cranking,
Deep-cycle lead-acid £150 600 £0.005p
or engine batteries) have a large number of thin
AGM £250 800 £0.006p
plates with plenty of surface area to supply heaps
Gel deep-cycle £200 1,000 £0.004p
of amperage over the short period it should take to
start an engine. The thin plates, however, are easily
damaged if the battery is deeply discharged
fully recharged at least once again, you can stick with the over a long period, so they are not suitable
every 10 cycles. The rule lower cost wet batteries, but for use as service batteries.
with these types of batteries you will need to carry a supply
is ‘the heavier the better’. of de-ionised water and check Deep-cycle (aka traction) batteries have
Generally, if the battery the electrolyte levels regularly much thicker plates, which can’t provide
is extremely heavy, its – especially if you are charging such a sudden surge of current, but can be
plates are likely to be quite them at a high current. slowly discharged to a reasonable depth
thick and should last some time. Another For those who are a little more without damage. These batteries are much
tip is to look for the longest warranty fastidious in such matters, or who larger, heavier and more costly, but they
period – a manufacturer will only give plan to set off ocean cruising, will last a great deal longer than an ordinary
a three-year guarantee if it has full deep-cycle dry cell batteries are car battery when used in a service bank.
confidence in its product. the favoured solution. Either gel or
The modern way of organising your AGM will give better performance Leisure batteries (aka semi-traction or
electrical system is by splitting the engine than wet cell types and will last dual-purpose) are a compromise between the
and service batteries into separate banks. considerably longer if treated with two. The plates are thin enough to start an engine,
This enables you to have a cheap engine respect. Both AGM and gel batteries can but thicker than normal start batteries so that they
start battery, whilst investing more in a give 1200-1500 cycles if they are only can be used for moderate service supply.
decent, deep-cycle service bank. Once discharged by a quarter of their stated
>>
High performance batteries regulated charge sources or a split- The electrical characteristics of AGMs
charge management device that can are remarkably similar to standard
Advances in technology have better solution for the supply charge at different rates to each lead-acid wet batteries – they recover
introduced various marine environment battery bank. Most ‘smart’ regulators equally well from deep discharges with
improvements in battery and, if treated well, can be set either for lead-acid or no ill effects and they can be charged
design over the last they can last up to gel battery charging, but rarely both in the same way with the same
few decades. Some of four times longer independently, except in the most equipment. Unlike lead-acids, however,
these have been quite than liquid electrolyte expensive units. they have very little self-discharge, so
successful, others not so. batteries. they can be stored fully charged for
They are fully sealed AGM (Absorbed Glass Mat) batteries long periods. With a life expectancy of
Lead-acid batteries are and can be mounted at an have been hailed as the new ‘sliced three times that of lead-acid batteries,
fast becoming a thing of the angle, but they require a more precise bread’ of marine batteries. Developed the initial expense is soon recovered.
past for serious marine applications. charging routine and accurate charging originally for the MOD, AGMs
Yes, they supply power for a relatively equipment. Unlike are similar to gels in that Nickel-Cadmium batteries have
small financial outlay, but they have standard lead-acids, they are completely been tried in marine applications, but
to be regularly topped up and there is which can take up spill-proof, but the their huge cost and exacting charging
a danger of excessive gassing when to a 15.25V charge electrolyte in an AGM regimen really makes them unsuitable
charging or of electrolyte leakage without damage, gels is fully absorbed into a for general cruising purposes.
at steep angles of heel. Low- or no- must never be charged glassfibre matting that
maintenance types are better, but they above 14.1V or at best completely envelops Lithium-Ion As with Ni-Cads, these
will still gas and dry out if overcharged. you will risk fatally the internal lead plates. are currently just too expensive to be a
damaging the battery, at Their size and weight is greater than feasible solution.
Gel batteries, where the electrolyte worst it can literally blow up. standard deep-cycle
is a silica gel rather than a water/acid Also, they are not generally suitable lead-acids, but a little
combination, cannot be spilled and for engine starting, so you will need a under that of gels. They
cannot be topped up. These were separate (usually lead-acid) cranking are totally sealed, don’t
a boon to boat owners when they battery. This is not uncommon, emit dangerous gasses, can
became generally available and are but creates a problem in that you be mounted at any angle and
still popular today. They do provide a will either need two independently require zero maintenance.
July 09 Sailing Today 111
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Practical_Electrics_RTG.in115 115 14/5/09 15:09:36
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