pracTical
part iii: on
board charging &
alternator regulators
The MaxCharge regulator
installed with a diode isolator
Upgrade yoUr electrics
Last month Duncan Kent looked into how best to keep your battery banks
fully charged when in reach of shore power. This month he takes an in-
depth look at the most effective charging methods when you’re under way.
N
early all alternators supplied by is designed to operate at 14.0V and will percent gain over the standard.
production boat builders are standard probably start charging at around 20A, What is needed is a way of forcing
automotive units, complete with internal rapidly dropping off to 5A or less after just the alternator to output its maximum,
regulator and integral temperature a few minutes. At this rate of charge the or near to maximum, until the batteries
compensation. They are usually rated at average domestic bank of around 200Ah are at least 90 percent charged. Some
around 35-55A, depending on the engine would take days to replenish, in fact never cruising yachtsmen override the regulator
size, but in a car they seldom need to actually reaching its full capacity. It is for to achieve this by disconnecting the
put out anywhere near this current as this reason that most boats operate almost integral field sensor and fitting a switch or
automotive batteries are rarely discharged continuously with under-charged batteries. variable resistor, but this entails keeping
below 5-10 percent of their total capacity. Some boat owners mistakenly assume a regular watch on the situation to avoid
Deep-cycle marine batteries, however, that upgrading their alternator to, say, a overcharging the battery, or overheating
are intended to be discharged to around 100A unit, will enable the batteries to be the alternator. A more controlled way of
50 percent of their total capacity, and so charged more quickly. But if you still rely achieving the ideal charging current is
require a much higher charging current. on the built-in regulator it is unlikely that to use what has become known as a
The standard voltage-sensing regulator this would offer much more than a 5-10 ‘smart alternator regulator’.
116 Sailing Today September 09
ST149 Practical_Electrics
RTG.in114 114 17/7/09 15:22:37
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