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Marine Electrical Systems on Auxiliary Sailboats. Topics To Discuss. Major AC and DC electrical systems typically found on small to medium size auxiliary sailboats. Tools and supplies needed to install or repair those systems. Troubleshooting techniques for common problems. Safety.
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Topics To Discuss • Major AC and DC electrical systems typically found on small to medium size auxiliary sailboats. • Tools and supplies needed to install or repair those systems. • Troubleshooting techniques for common problems. • Safety
Nomenclature • AC – Alternating Current (120 volts AC) • DC – Direct Current (12 volts DC) • V – voltage - volts • I – current – amperage or amps • R – resistance - ohms
AC Systems & Components • Shore Power Connection • AC Electrical Panel • Cabin Outlets • Battery Charger • Inverter / Chargers • Hot Water Heater • Galvanic Isolator
AC Panel • Sometimes separate but often integrated with the DC Panel. • AC Main circuit breaker - 30 amp. • Individual load circuit breakers - 15 amp. • Reverse Polarity Indicator – warning when neutral line is not at ground potential.
Reverse AC Polarity Problem • AC circuit breakers are single pole which means they only disconnect hot wire. • If polarity is reversed then neutral is hot and not switched. • If neutral is tied to the metal case of an appliance then there is a shock hazard. • Reverse polarity indicator will not function if ground is missing. • Always best to disconnect shore power cord when working on AC systems.
AC Outlets Same as those in your house – 120 volts 15 amps
Battery Charger • Typically provides 10 to 50 amps of charging current depending on manufacture and model. • Normally has charge state indicators but often mounted where they cannot be seen. • Better models provide 3 charge stages; bulk, absorption, and float.
Battery Chargers 50 amps max 20 amps max
Inverter / Charger • At the dock charges the both house and starting batteries. • Away from the dock provides 120 Volts AC from the house battery. • Usually include automatic transfer switch for AC loads. • Available battery charging current and AC power output depends on size.
Hot Water Heater • Typically 120 Volts, 1500 watts, 12.5 amps • Can be round or rectangular, horizontal, or vertical. • Often include a heat exchanger that uses engine coolant to heat water when under power.
Galvanic Isolator • Not really an AC system but is connected in the AC line. • Isolator prevents low voltage DC path in shore power ground wire. • Engine, metal through hulls, prop and shaft are often all electrically connected or bonded together and connected to boat ground. • Zincs attached to shaft and bonding system are sacrificial anodes to prevent corrosion of bronze prop and through hulls • Common shore power ground will provide conduction path to other boats and dock with potential corrosion problem.
DC Systems • Main Battery Switch • DC Panel • Batteries • Engine Alternator • Engine Starting Motor • Typical Loads
Main Battery Switch • All major connections to batteries go through this switch. • Exceptions are battery chargers and auto bilge pumps • Allows selection of Battery 1, Battery 2, Both or Off (None)
DC Panel • Sometime separate but often integrated with the AC Panel. • Usually has a MAIN DC circuit breaker. • Circuit breakers for individual loads. • DC Voltmeters and Ammeters.
Typical DC Loads • Starter Motor • Lights • VHF Radio • Instruments (Depth, Speed, Wind) • GPS – Chart Plotter • Auto Pilot • Stereo • Water Pressure Pump
Batteries • Lead, Lead Dioxide, Sulfuric Acid • Normally 12 Volts DC, sometimes two 6 volt batteries connected in series for 12 volts. • Sometimes grouped in parallel for higher current. • 12 volt battery constructed of 6 individual cells that are two volts each. • Types: Starting, Deep Cycle, and Marine/Hybrid/Dual Purpose • Construction: Wet Cell, Gell Cell, AGM (Absorbed Glass Mat)
Series / Parallel Configurations Two 6 Volt Batteries in Series Two 12 volt batteries in parallel
Starting Battery • Designed for high current - short duration use. • Large number of thin plates for maximum surface area. • May last for thousands of 2% to 5% of capacity discharges. • However, if deep cycled the thin plates will quickly be consumed and fall to the bottom of the cells. • Will generally fail after 30 to 150 deep cycles of 20% to 80% depending on design.
Deep Cycle • Designed to be discharged down to as much as 80% of capacity. • Thicker plates than a starting battery. • Fewer thicker plates mean less surface area and therefore less current capability. • However, Deep Cycle batteries can still be used for starting if large enough.
Marine / Hybrid / Dual Purpose • Designed as a compromise between Starting and Deep Cycle. • Some Marine batteries are actually Deep Cycle. • In some hybrid designs plates are composed of lead sponge but coarser than true Starting batteries. • Often hard to tell what it is without opening the case which is not an option.
Wet / Flooded Cell Batteries • Most common and usually least expensive. • Can be designed for starting, deep cycle or hybrid use. • Liquid electrolyte so mounting is important, must be mounted horizontally. • May vent hydrogen and oxygen generated by electrolysis at end of charge or if overcharged. • Cases need to be vented. • Electrolyte level must be monitored and topped up periodically.
Gel Cell Batteries • Normally designed for deep cycle applications. • A thickening agent immobilizes the electrolyte. • Valve-regulated design means batteries are sealed so mounting is not critical. • However, if overcharge hydrogen and oxygen will escape through valves. • Since batteries are sealed and cannot be refilled with electrolyte charging is more critical. • Gel cells use slightly lower charging voltages than wet cells and thus the set-points for charging equipment have to be adjusted
AGM, (Absorbed Glass Mat) Batteries • Normally designed for deep cycle applications. • Liquid electrolyte. • Uses a fiberglass like separator to hold the electrolyte in place by capillary action. • Physical bond between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact resistant lead-acid batteries. • Valve-regulated, sealed, so electrolyte cannot be replaced. • Small amounts of hydrogen and oxygen will be trapped and recombine. Large amounts will vent. • AGMs use almost the same voltage set-points as flooded cells and thus can be used as drop-in replacements for flooded cells.
Why Batteries Fail • Leaving batteries in a discharged state which leads to Lead Sulfation. • Deep discharging a Starting Battery which damages the plates. • Excessive vibration and shock damaging the plates. • Long term sulfation due to normal battery use.
Lead Sulfation • When batteries are discharged amorphous lead sulfate is formed on the plates. • If recharged soon the lead sulfate is easily converted back to lead, lead dioxide, and sulfuric acid. • However, if the battery is left in a discharged state too long the lead sulfate will convert to a crystalline form and will not convert back to lead, etc., during normal charging. • This process will eventually coat the plates with non-conductive crystalline lead sulfate and kill the battery.
Lead Acid Battery Charge Stages • Bulk – Charge current is set to maximum safe rate batteries will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. • Absorption - Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts. • Float - After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life.
Battery Maintenance • Keep correct electrolyte level using only distilled water. (Wet cells only) • Keep terminals clean. • Keep batteries dry, especially the top. • Make sure charging levels are correct. • Keep batteries fully charged.
Battery Safety Issues • Batteries contain sulfuric acid which can cause eye and skin burns and damage clothes. • A charging battery may contain significant amounts of hydrogen which could explode if ignited. • Batteries can source hundreds of amps of current and can melt jewelry around your finger or arm. Therefore: • DO - wear safety glasses and protective clothing. • DON’T - wear rings, bracelets or expensive clothes. • DON’T – allow sparks or flames near batteries, especially when they are charging.
