ELECTRICS UPGRADE, PART III
Alternators – how do they work?
To understand how a regulator works the batteries via the rectifier diodes, varies in
you need to have some grasp on how an direct proportion to the voltage fed into this
alternator operates. field coil.
An alternator uses the magnetic field of The field voltage – and consequently the
the rotor to induce an alternating current in alternator’s output – is controlled by the
the fixed (stator) coils mounted around it. The regulator. But rather than being set at a
rotor is wound with an electro-magnetic coil fixed level, a smart regulator adjusts the field
called the ‘field’ and the AC voltage induced voltage according to the output level required
in the stator coils, which is output as DC to during each charging phase.
Do I need a
smart regulator?
Will my alternator need modifying?
The main benefit of installing an
intelligent regulator is that it is fully There are two basic alternators types – ‘N’ Serious damage can be done to the
automatic and it considerably reduces the and ‘P’, depending on whether they have alternator if these modifications are done
time taken for the batteries to become negative (N) or positive (P) field coil switching. incorrectly, so if in doubt have it
fully charged. This saves fuel, cuts engine N-types, which comprise most standard done professionally.
wear and greatly extends the period automotive alternators, need to be adapted If you chose to fit a higher output alternator
between charges – as well as increasing by cutting the wire to the negative field brush at the same time, remember the engine,
the life of the batteries. and diverting the circuit through the smart pulleys, belt and electrical system must be
Temperature monitoring is also an regulator. P-types, designed more specifically capable of taking the extra load. Cabling,
important aspect of proper charging. for marine or leisure use, are usually much diode splitters, ammeters and shunts must all
The cooler the battery, the greater the simpler to modify by replacing the field wire be upgraded as well.
charge current required. A standard with the field output from the smart regulator. You should also make sure the new
regulator senses only alternator The type of alternator you have can be regulator has a ‘soft start’ delay feature that
temperature (usually considerably higher determined by setting a multimeter to x1 in allows the engine to warm up and a ‘ramped’
than that of the batteries), but most smart the resistance range and measuring between charging rate, which progressively increases
regulators have one or more battery the brushes and battery negative. A dead the power.
temperature sensors, which alter the short on one brush indicates an N-type, high There are some systems available
charge rate accordingly. In hotter climates resistance a P-type. whereby the alternator needs no
this prevents overheating, over gassing modification at all.
and dehydration of the cells. The Pro-Alt charger from Sterling
Upgrade yoUr electrics
Power operates in a similar fashion to
a multi-stage shore power charger, by
What is multi-
taking the output from the alternator
stage charging?
and putting it through a DC/DC
converter first to regulate the
Just as with modern mains battery voltage, before stepping it up to
chargers, multi-stage smart the required charging voltage.
regulators can also cycle The system is said to
the batteries using the bulk, double the charge capacity
absorption and float regime of a normal alternator
generally accepted as being without any
the optimum charging method complex wiring
for deep-cycle batteries. modifications
Depending on the depth of and even has
discharge, this may or may an integral
not be a useful feature. If splitter giving
your batteries are kept fully separate
charged on shore power during outputs for
the week and you only use the the start and
boat for weekends it is unlikely domestic battery
you will need a lengthy bulk charge banks to avoid
stage, so careful control of the second overcharging.
(absorption) and third (float) modes will
be less important.
On the other hand, if the engine is your
main, or only method of charging your
>>
September 09 Sailing Today 117
ST149 Practical_Electrics
RTG.in115 115 17/7/09 15:22:46
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