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102808_CAPAC_MANUAL_MODEL_90W12D_SYSTEM.doc
Section V
Service
General Theory
The Model 90W12D system is composed of four major components: The
reference cell, the controller, the anode(s) and the CAPAC
®
Monitor. These units
perform the following functions:
A. The reference electrode produces a voltage, which is related to the amount of
protection received by the hull.
B. The controller compares the voltage produced by the reference cell with an
internal voltage set by the factory. The output of the controller is automatically
adjusted to keep the reference voltage at the same value as the factory set
voltage.
C. The anode(s) is an electrically insulated element located outside the boat’s
hull through which current flows from the controller into the water and back
into the hull or bonded fittings.
The amount of anode current delivered by the controller is dependent upon
factors such as: The physical dimensions of the hull, the condition of the paint on the
hull, conductivity of the sea water, and the speed of the boat. For this reason the
operating current of the controller is difficult to predict.
1. When the anodes fitted to the hull or fitting emit current, the protection given to
the hull gradually increases and corrosion is reduced. This process is called
polarization.
2. As this anode current increases, the voltage between the reference electrode
and hull increases gradually.
3. Tests have shown that there is an optimum reference electrode voltage (hull
potential). Increasing anode current to give a higher reference electrode
voltage gives no further reduction in corrosion and wastes current. Excessive
current, such as created by magnesium anodes, may even cause paint
damage.
When the reference electrode voltage is below the optimum voltage set by the
factory, output of the controller increases until the reference voltage equals the
set voltage. A reference voltage greater than the set voltage causes a
decrease in controller output.
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