DC/AC Systems

An efficient electrical system can be designed to run for a day off a house bank. A separate AC generator is not required.
© 2008 David Shaw

Design Considerations

In the previous chapter, we established that “the design objective of Sharina’s electrical system is to run as much as possible on the DC system and use an inverter for AC while, hopefully, eliminating the need for a separate AC generator.” In addition, it should run on shore power anywhere in the world.

We then outlined a scenario that maximised the use of DC, and used AC only where it made most sense. This minimises the size and cost of the inverter.

The assumption in not having a genset is that the boat will be underway at least one hour every day, or shore power will be available, or you can simply run the engine for an hour if you are moored.

If you plan to be moored extensively in other circumstances, then you should consider a genset. It doesn’t make sense to run a 200-300 horsepower (hp) engine for long periods to provide charging when a 20-hp engine will suffice. But remember that you should run the main engines to operating temperature at least once a day to eliminate condensation in the cylinders, anyway, so we might as well use this period to charge the batteries.

In designing the system, the DC and AC systems should be loosely, not tightly coupled, with no single point of failure, as discussed in Chapter Two. Both AC and DC systems should have surge protection. A trickle-charge system will provide some degree of backup to the alternator and charger.

The worst-case scenarios we want to cover for Sharina’s intended usage are:

• The AC system fails, but the boat’s critical systems continue running on DC.
• Both the AC and main DC systems fail, but there is a backup DC system for super-critical instruments and navigation systems.
• The main charging system and/or shore power fail while the boat is unattended, but there is a backup trickle-charge system.

The shore-power requirement is complicated by the various standards around the world. But first, some background.

Because the voltage at your house will be lower than at the power station, 120 VAC is sometimes referred to as 110, 115 and sometimes 117 V. Similarly, 240 VAC is often called 220 V.

AC does not have the same energy as direct current because it reverses polarity, swinging from positive to zero to negative to zero and back to positive. To equate the two, most AC voltages are given as the root-mean-square (RMS) voltage, which simply means the equivalent-to-DC voltage (Vrms = 0.7 * Vpeak). This makes power calculations easier, i.e., a Watt is a Watt is a Watt.

In North America, AC systems are 60-Hz and either 120 or 240 Vrms. Because the 240 VAC circuit consists of two 120-VAC circuits stacked together, the AC is double-phase. Service is usually available in 30, 50, 100 or 200 amps. While homes used to function adequately on 50 A, most modern homes have 200-A service. In Europe and elsewhere, service is usually 50-Hz 230 VAC single phase, i.e., a single circuit.

For simplicity, in most of this chapter we will refer to AC only without specifying the voltage. DC systems are usually 12, 24 or 48 V. Again, for simplicity, we will refer just to DC.

In general, DC is somewhat safer than AC in that an accidental shock is less likely to fibrillate the heart. All the same, note that in either case:

• 1 mA causes a tingle
• 5 mA causes a slight shock
• 50 to 150 mA can result in death through muscle breakdown and renal failure
• 1 to 4 A can cause death through fibrillation of the heart
• 10 A causes cardiac arrest

As a good practice, treat both AC and DC with the same trepidation.

The DC Primary System

12 or 24

The boat's primary electrical system is DC. In the size of boat we are discussing, 48 VDC is uncommon, so we will be choosing between 12 or 24 VDC. Generally, 24 VDC is preferable but, as noted in the previous chapter, some equipment may be available only in 12 VDC.

24-VDC is better because for a given amount of energy consumption in Watts, it requires fewer amps running through the wires than a 12-VDC system. The lower the voltage the higher the current (amps = Watts/Volts). For example, a 100-W device draws approximately 8.3 A at 12 V and 4.2 A at 24 V.

Higher current has disadvantages. The higher the current draw, the thicker the wiring is required (and the bigger the spark when you accidentally ground it). Thick wiring is more expensive and hard to install and maintain – think jumper cables for boosting your car.

Higher voltages are also feasible. Large ships have long used a higher voltage DC bus. Glacier Bay [25] is pioneering the adaptation of this technology to smaller yachts. Its OSS system runs at around 150 VDC. Some of the advantages this yields are smaller wiring, more efficient thrusters and windlasses, and compatibility with most shore power around the world and existing resistive devices like stoves.

Wires also have resistance and, when a current passes through them, this causes a voltage drop along the length of the wire. The higher the current, the higher is the drop in voltage. This voltage drop limits the practical length of a wire. The maximum run for 12-VDC wiring is around 30-35 ft, which translates into a boat length of around 50 ft, given a midships battery, and the need to run wires around corners.

Also, for various reasons the efficiency of DC-AC inverter circuits is better the higher the DC input voltage. Therefore, a 24- or even 48-VDC system is better than a 12-V one. As mentioned, the downside to 24 V is the wider range of equipment available for 12 V.

To accommodate both 12- and 24-VDC equipment, it is possible to design a battery system for 12/24, in somewhat the same way that North American houses have 110/220 VAC. This system would use high-amperage blocking diodes to split the two voltage circuits.

A better approach, if you select a 24-VDC system and some equipment is available only in 12 VDC, is to use individual 24-12 VDC, solid-state, low-noise controllers with voltage regulation. These start as low as $16 for a unit suited to power a radio. Obviously you should keep some spares on board. Using the individual controllers eliminates the need for an extra wiring system, complexity in the house bank, and dependence on a single set of high-performance diodes.

At this stage, in the first iteration, Sharina was going to have a 12-VDC electrical system. This design hit the wall when I worked out the specification for the watermaker. The key differentiating factor here is the number of people on board. More people need more water and, above a certain size, watermakers are 24 VDC.

The trend in the market is to 24 VDC, so that should be your first choice, anyway. However, if your boat is less than 50 ft, 12 VDC is probably still your best price-performance option.

Second only to discussions about one house bank or two, are discussions about bonding or not bonding the electrical circuits. The simple fact is that all electrical circuits have to have a common ‘ground’. On shore, this is often the earth. Bonding means connecting all the ground points together with an extra run of wires.

In all cases, the DC system must be a "floating ground" (DC negative bus) type of system, with an insulated return, fully isolated from the hull and all the hull fittings. This means that no electrical items (including common appliances) have a local ground to the hull (remember the double pin lamps in the previous chapter?). Instead, all ground returns are tied to a Common Grounding Point (CCG).

For example, all engine fittings are double insulated. The engine is electrically isolated from the hull via flexible mounts and flexible coupling. A grounding wire runs from the alternators to the DC negative bus. This might seem confusing, because the CCG itself is grounded to the hull. However, a CCG avoids stray electrical currents running through the hull and causing electrolysis. It also provides a grounding point for the lightening-protection system.

Having selected the voltage, the next phase in the design of the electrical system is to determine the requirements for the DC battery primary system – the house bank. The main considerations are:

• Load
• Battery type
• Layout
• Capacity
• Alternator
• Trickle charge

Load

Load is measured in total daily amp-hours (AH), which is simply the average current drawn per hour times 24 hours. Calculating this is a major task subject to much second-guessing. The first step in calculating load is to determine the combined DC and AC AH load for all ‘appliances’. Use a spreadsheet to list each item and its wattage or current draw, depending on which is available. For the DC, make sure you work entirely in either 12 or 24 V.

For each item, estimate the duty cycle (how long it will be used each day). Do a separate tally for fixed loads (e.g., instruments) and intermittent loads (e.g., coffee maker). If in doubt it is safer to over-estimate the duty cycle. But don’t go overboard. If you overestimate too much you might have to go back and tweak the numbers more realistically when you realize that you need to tow a substation behind you on a barge to supply your electrical requirements. All estimating processes must be subject to a reality check. It’s better to get each number as exact as possible, then add a fudge factor to the total, rather than fudge numbers individually.

In addition, you need to calculate the peak and surge requirements. To estimate the peak demand, determine which of the largest appliances will be used simultaneously. To estimate the surge demand, determine the surge on start up of large AC motors. (DC motors do not have a surge.)

Use whichever number is the highest for all future calculations. Let’s call this the Total Daily Load.

Battery Types

Battery types can be classified half a dozen different ways, so we will cut to the chase. On board a trawler, we need rechargeable lead-acid batteries for three different applications:

• Starting the engines
• Emergency lighting in the passageways
• Powering the equipment

These applications require different types of battery.

Starting the engines requires a vehicular-type battery that can provide a very short burst of very high current to crank the engine and provide ignition. This is sometimes called an SLI battery (starting, lighting, ignition). SLI batteries are slow to recharge. Other vehicular types are traction (also called RV and marine) and stationary (also called standby and float). Traction batteries are used in golf carts and (I guess) RVs.

For emergency lighting and backup power supplies, standby batteries, e.g., lead-calcium, are used. Typically they will provide juice to a lamp for 1.5 hours.

For the house bank, although traction batteries are sometimes used, what we really need is a true deep-discharge (DD) battery. Unlike an SLI, a DD provides high levels of current for a long period, and re-charges very quickly. Traction batteries have a slightly lower cost, but overall efficiency and performance will be better with DD batteries.

All of the above types are available in flooded or sealed sub-types. Flooded batteries are an older design. Internally they emit oxygen from the positive electrode and hydrogen from the negative one. This has to be vented to the outside to release pressure, i.e., they lose water and you have to top them up regularly. They have a relatively high internal resistance, which causes them to lose their charge by as much as 1% per day. During charging, they can lose 15-20% in heat losses.

Sealed batteries are just that, and they require no topping up. They use gel or absorption glass mat (AGM) to immobilize the acid solution. Unlike flooded batteries, they are not prohibited from air shipment. Gel batteries use a thickening agent like fumed silica to immobilize the electrolyte.

AGM batteries were originally developed for use in aircraft. In AGM batteries a fine fibreglass mat between the lead plates absorbs and immobilizes the acid. This makes the acid more available, enhancing the reaction between the acid and the plates. Consequently AGM batteries can be discharged and recharged at higher amperages than other types of construction [1]. They are also resistant to vibration, operate in any position and will survive submerging.

Gels and AGMs have a lower internal resistance, losing only 1-3% per month due to internal discharge. Gel cells lose 10-16% to heat during charging while AGMs lose as little as 4%, meaning that the charging system can be smaller.

All of these types are built in different physical sizes. The most appropriate size for a boat’s starter and house banks is 8D. Types cannot be mixed in a house bank, because they have different discharge and charging rates. In fact, all batteries in any battery bank (not just on a boat) should be of the same brand, type and size and, preferably, batch number. Lifeline, Optima® and Rolls Surrette are typical AGM brands.

Lead battery lifespan is reduced at temperatures over 77 F, so put the batteries low and as close to the keel as possible to keep them cool. It is a good practice to have the house bank fused internally as well as externally. This will keep a battery gone bad from shorting and discharging the entire bank. Some batteries are built so you can replace individual cells.

Layout

There is a lot of discussion about whether you should have one or two separate house banks. The idea behind two banks is that you also have two separate charging systems, thus there is good redundancy in the system. But it is clear that for maximum electrical efficiency and battery life, you should have one virtual house bank [2]. One house bank also satisfies Occam’s razor (see Chapter 2). If necessary, this virtual house bank can be divided into two physical banks to better distribute weight.

The exception is that you could put a separate battery in the Pilot House, for all instruments and emergency lights. Normally, it would be in the charging circuit for the house bank, but in an emergency it could be switched out and isolated using a fail-open relay with a manual bypass switch. In an emergency, this will preserve communications and navigation instrumentation independently of other demands.

The major disadvantage is having to run long heavy-duty cables from the engine room to the pilothouse. The distance will not be too long with a midships engine room, but an aft engine room could require 40-50 ft of cable. In this situation, you are strongly advised to plan for a 24-VDC or higher system.

Bilge pumps may be wired directly to the batteries, and if so, are provided with in-line fuses. The battery banks are fully metered.

Each engine fitted has its own starter battery, and a 1-2-Both switch that will allow it to be started by either start battery or, in an emergency, the house bank.

Capacity

When you have determined the Total Daily Load in AH, multiply it by the desired Charging Interval (days) to determine the Battery Drain Between Charges. Once a day seems like a common-sense choice. With less than a day, there will be a tendency for charging cycles to run into each other, along with all the extra fuss for your neighbours at the anchorage. With more than a day, you will need an ever bigger and more expensive house bank and alternator. With once a day, you exercise the system every day, keep the engine from rusting out, produce minimal fuss, and keep battery and alternator costs in a reasonable range.

Basic layout of the house bank: (a) engine starter, (b) house supply, (c) instruments, (d) 1-2-both switch, (e) isolation switch and/or fail-open relay

There are several approaches to determine the House Bank Required. A common one is to size the bank so that it cycles between 50% and 80% charged. Using this approach, you would simply multiply the Battery Drain Between Charges by 333% and throw in a 15% fudge factor for good measure, i.e., multiply the Battery Drain Between Charges by 350%.

However, batteries are constrained by their discharge/charge rate. For example, flooded-cell batteries cannot discharge at a rate more than 25% of their capacity. A better way is to base the size on the discharge/charge rate of the selected battery type. For a flooded cell, you would apply a factor of 400% to determine the total capacity required. (Refer to Table 8-1 for a working example.) For gel and AGM cells, you could go as low as 300%; although in all cases more battery is better than less. The resultant is the House Bank Required.

Divide this number by the AH rating of your chosen battery type, to determine the number of batteries in the house bank. Typically, for a passagemaker under 65 ft, the house bank will have four to ten 8D deep-discharge batteries with a capacity of 1,100-2,800 AH.

Alternator

Each engine (if there is more than one) has a high-capacity dual-output alternator and multistage regulator, with separate charging circuits for the starter and house batteries. The charging sources (alternators, trickle and charger) are automatically switched. A backup manual switch and regulator are provided. The regulator must be suited to the type of battery: Flooded cells require an equalization charge after the main charge; whereas gel and AGM cells usually do not. Typical vendors are: Ample Power [3], Balmar [4], Ferris [5], Hehr [6], JackRabbit Marine [7], and SALT [8].

Sharina is designed to be left unattended for a week. So to keep the batteries charged at least one engine must autostart.

The Charging Factor determines the required capacity of the charging system (see again Table 8-1). This rate of charge will damage the battery if it is too high. If it is too low, the batteries will be chronically under charged. The rule of thumb is to charge a deep-discharge flooded-cell battery at a rate of 25% of the listed AH. A gel cell can be charged at 40%; while an AGM can take an unlimited charge.

To determine the Basic Charging AH, multiply the House Bank Required in AH by the Charging Factor. To this, add the battery load while charging, i.e., the Fixed DC Load, Fixed AC Load and Other DC Loads. This total gives you the Required Charging Capacity AH. The larger this is, the bigger and more expensive the alternator required.

Finally, we need a reality check. How long will it take each day to re-charge the batteries? An hour would be nice. Several hours would be insufferable, and counter-productive. To determine the daily charging period, divide the Battery Drain Between Charges by the Required Charging Capacity (other loads net out). In the example shown, a flooded cell bank will take 55 min to charge, a gel cell 34 min and an AGM cell 28 min. Obviously a gel or AGM is the way to go, provided you can manage the larger alternator and charger system. Remember that these times are for a hypothetical house bank of 1100 AH capacity. A real example is likely to be several times larger.

Trickle Charge System

In case the main charging system fails while Sharina is unattended, a DC trickle-charge system is provided. Trickle charging is also a good idea because there are usually parasitic loads on a battery system that will slowly discharge it. Deep discharge batteries do not want to be trickle charged at a high rate: 3% is recommended. Thus a trawler with a house bank of 1000 AH requires a trickle charge of 30 AH.

Table 8-1 House Bank Calculation - Example
Line	Item	Amount	Calculation	Comments
A	Total Daily Load AC AH	200		Normalize to 12 or 24 V
B	Total Daily Load DC AH	50		Normalize to 12 or 24 V
C	Total Daily Load AH	250 A+B
D	Charging Interval (days)	1
E	Battery Drain Between Charges AH	250	C*D	Amount to recharge
F	Battery Efficiency Factor	1.1		Typically 90%
G	Charging (Safety) Factor %	400		Use 350-400+
H	House Bank Required AH	1100	E*F*G
I	Battery AH	275		Use the AH rating of selected battery
J	Number of 8D Batteries	4	H/I
K	Battery Capacity	1100	I*J	Reality check in case H and K are not equal.
L	Charging Factor %	33		25% is the norm for flooded cell; 40% for gel cell; 50+% for AGM
M	Basic Charging Rate AH	363	K*L
N	Fixed DC Load AH	5		Load while charging
O	Fixed AC Load AH	50
P	Other DC Load AH	0
Q	Required Charging Capacity AH	418	M+N+O+P
R	Time to Charge Hours	0.7	E/M

Wind turbines and solar panels are ideal for a trickle-charge system; although they are not suited as a main power source.

Unfortunately, as a main power source, each of them has a significant performance drawback in the context of a small- to medium-size long-range trawler. They simply need too much real estate.

Air X Marine wind turbine – Photo with permission © Northern Arizona Wind & Sun, http://www.solar-electric.com/

For traditional horizontal-axis wind turbines (HAWT), the drawback is the size of the rotor, the noise they make, low efficiency (25-40%) and the constant output. As a main power source, you would need a propeller the size of a house. To be economical, commercial wind turbines need an average wind speed of 25 km/h.

Vertical-axis wind turbines (VAHT) are more efficient (43-45%) and scale better, but not available yet in marine models.

But for trickle charging, a 400-watt HAWT like the Southwest Windpower AIR-X produces a maximum of 33 AH, just right for our house bank of 1000 AH [9, 10]. The catch is that the AIR-X has a noisy 46-in rotor whizzing above your head. Larger units have comparably larger rotors. Rotors can be made smaller if the turbine is engineered to turn faster, but this requires a stronger wind. Wind turbines make noise when they flutter, and sometimes they growl. They have to be mounted as high as possible, and produce vibration.

They are active generators, producing power whenever the wind blows. If the batteries are fully charged, the output of the turbine must be diverted somehow, e.g., to a water heater or some other electrical system.

They also have no output when the wind stops. Denmark invested in 6,000 wind turbines on the national grid, theoretically providing 19% of demand. But they have to keep conventional plants running at full capacity in case the wind drops.

Water turbines, like the Ampair Aquair 100, are also available. But these are designed primarily for cruising sail boats [11]. They use the energy from the forward motion of the boat to turn the turbine. Since in a powerboat the engine generates that forward-motion energy, a water turbine doesn’t make sense. It’s better to mount the generator on the engine directly.

Because of the real-estate constraint, solar panels can’t provide primary power either. This is too bad because the sun delivers around 1000 Watts per square metre at the surface of the earth. A 100% efficient panel 5 x 2 m would deliver 10,000 Watts (833 AH). But commercial solar panels are only about 13% efficient with an optimum sun angle. A trawler needing 1000 AH at 12 V would need more than 100 panels on a barge as a primary power source.

For a trickle-charge system, solar panels are less intrusive than a wind turbine. Unlike turbines, solar panels are passive devices. They produce no current when they are disconnected.

So both wind turbines and solar panels are suited for trickle charging the house bank. Because of their passive nature (no noise or vibration, no moving parts, no active current) solar panels are a more elegant choice. They are also lightweight, easy to install, clean, low maintenance and have a long life. Their disadvantages are limited power, poor performance on cloudy days, and no performance at night.

Most solar panels from 5 to 120 Watts are 12 V, the rest up to 200 W are 24 V. After that, you’re into units designed for tying into the electrical grid. A single high-efficiency 125-W solar panel like the Kyocera KC125G measures 56.1 x 25.7 x 2.0 in (1425 x 652 x 52 mm), and outputs 7 AH while the sun is up [12]. Note that ratings are given for one peak sun hour at 25 C so performance deteriorates at off-peak hours and with temperature changes. Peak time is noon, when the distance from the sun to your location is the shortest.

In our simplified example, a house bank of 1000 AH, a trickle charge of 30 AH would need four of the above panels. On a trawler with a beam of 15 ft (180 in), you could mount six 25-in wide panels side by side on the boat deck or on the flybridge roof, if it had one. This would yield around 42 A for, say, an average of 5 h/day, or 8.75 AH per day. The most efficient way to use this is with a linear-shunt regulator as follows. If the battery is:

• Under load, feed the load directly
• Discharged, charge it
• At rest, trickle charge it

There are three common panel technologies: single-crystal silicon, polycrystalline, and thin-film amorphous cells. Single-crystal silicon cells are rigid and expensive to manufacture but provide the greatest efficiencies and have a stable output during their lifetime. Polycrystalline cells are also rigid, cost less but have lower efficiencies. Thin-film amorphous cells are inexpensive to manufacture, but are not as stable as single crystal or polycrystalline cells. Amorphous panels are made in rigid or flexible panels with the flexible panels costing a bit more.

Solar panels range from 5 to 200 Watts output in full sunlight
– Photo with permission © Northern Arizona Wind & Sun, http://www.solar-electric.com/

An interesting new solar technology is PV-TV, a semi-transparent coating for windows. Developed by MSK Corporation, it passes 10% of visible light while generating 38 W from a 1-m x 1-m window [13]. It provides shading against excessive sunlight, reduces solar gain, gives UV protection, and acts as thermal insulation. It also works as a rear-projection display screen at night (if you want to use your windows as a billboard). To produce a 30-AH trickle charge we would need 10 such windows on the sunny side.

Other improvements are coming. Researchers at the University of Toronto have developed a flexible plastic panel that is 30% efficient [24]. It operates in the infrared spectrum. Nanosolar has developed a printing process to make rolls of thin-film solar cells [26]. In July 2007 the New Jersey Institute of Technology also announced a polymer process to print sheets of carbon-nanotube solar cells. Other companies in Europe, China and Japan are racing to develop thin-film technology.

Any selected solar panels should have a rigid frame, and be designed for marine use with a floating ground. For maximum efficiency, they should be mounted perpendicular to the angle of the sun. In practice, it is best to mount them flat at a 10-degree angle and forget about the complications of tracking the sun. Most rigid panels have an aluminium frame, which must be isolated from a steel hull. The panels should clear the deck by at least 1.5 in, to allow circulation of cooling air, and be free of any shade.

Mounting them at a small angle allows rain to run off. Consider a mount that lets you adjust the angular setting, depending on seasons, latitudes and moorings. Note that fungus tends to grow where the frame meets the panel.

Panels should be fitted with individual inline over-current fuses, to protect against ground faults. Each panel should also be fitted with a bypass diode, to shunt the panel if it fails or is shaded. The overall solar system should also be fitted with blocking diodes, to prevent reverse currents from the battery to the solar cells at night. Some installers are concerned that the resistance of fuses and blocking diodes reduces the available voltage during the day. This is less of a concern in 24 V systems than 12 V ones [14].

The AC Secondary System

The ship's secondary electrical system is AC. In Europe it will be designed for 230-VAC single phase. In North America it will be either 120-VAC single phase or 240-VAC double phase. A manual switch in the Pilothouse selects "boat power" (inverter) or "shore power" as the power source, with automatic detection of the voltage and frequency of the shore power. In the boat, the green AC ground wire is connected to the Common Grounding Point – the white ground wire is left floating. AC wiring should be stranded copper, not solid or tinned, to better resist breaking from vibration. All AC light bulbs adjacent to metal, especially in the engine room, are protected as shock hazards. All AC outlets are equipped with ground-fault-circuit-interruption (GFCI) circuit breakers.

Inverter/Charger

A combination inverter/charger is attached to the house bank for generating AC when offshore, and/or charging the batteries from shore power when in port. Points to consider in an inverter/charger are:

• Peak power output
• Peak charging current
• Continuous charging current
• Battery size AH
• Output voltage
• Output current regulation
• Safety factor of 30%

Sharina’s design requires an inverter with a capacity of about 7,000 W, which is high by normal standards for this size of boat. However, Sharina’s design goal is not to provide the minimum for casual use but to provide at-home comfort at all times.

Shore Power

Because Sharina is intended for passage making, she has to operate on shore power almost anywhere in the world. To do this requires voltage conversion and frequency conversion.

AC voltage conversion is readily done with a transformer having multiple taps that can step-up or step-down a range of voltages. For a specific input voltage, the corresponding tap is selected manually or automatically. The transformer then delivers the correct output voltage.

This fits well with best practices. Although there are several ways of bringing aboard AC, the best way is an ABYC-approved isolation transformer between the shore power inlet and the breaker panel. This avoids polarization issues and doesn’t require a reverse-polarity indicator. AC shore power is brought aboard through an electrically isolated marine-rated receptacle in the side of the Deckhouse. A multi-tap isolation transformer meets this specification.

The incoming AC is grounded (green wire) at the shore end but is not grounded to the hull.

Frequency conversion may or may not be critical. Most modern electronic equipment is designed for 50-60 Hz, and should operate without difficulty (check the label).

The problem areas are timing devices that reference the AC, microwave ovens and AC motors, including those in domestic refrigerators. AC motors designed for 60 Hz will run more slowly on 50 Hz, and tend to overheat. To avoid this, you can:

• Use DC motors only.
• Put AC motors on the inverter power only, not on shore power.
• Install a voltage- and frequency-converting inverter/charger.

Sharina’s approach consists both of using DC motors only and a voltage- and frequency-converting inverter/charger. The design objective of her electrical system is to run as much as possible off the DC primary system. Vendors include: ASEA, Atlas, Charles Industries, Failsafe Power, Magnus Marine, Mastervolt, Stored Energy, Olsun, Xantrex [15-23].

An example of a controller for the electrical system
– Graphic with permission © Ample Technology, http://www.amplepower.com/

Controller

The controller in our scheme is a single point of failure, so a backup controller or a bypass system should be provided.

Distribution Panel

The AC/DC distribution panel is located in the pilothouse. Remote latching relays disconnect the batteries in the event of an electrical fire.

Summary

An efficient electrical system can be designed to run for a day off a house bank. A separate genset is not required. The design maximizes DC services while minimizing AC. The charging period is around one hour per day. The preferred DC voltage is 24 V, with solid-state DC-DC converters for 12-V equipment. There is a single house bank with a high-capacity dual-output alternator and multistage regulator. Trickle charging is solar. Shore power uses voltage- and frequency-conversion for global compatibility.

References

1. DC Battery Specialists, http://www.dcbattery.com/agmtech.html

2. Boatowner’s Mechanical and Electrical Manual, Nigel Calder, McGraw Hill, ISBN 0-07-009618-x.

3. Ample Power, http://www.amplepower.com/

4. Balmar, http://www.balmar.net/

5. Ferris Power Products, http://www.charternet.com/greatgear/hamiltonferris/

6. Hehr Power Systems, http://www.hehrpowersystems.com/

7. JackRabbit Marine, http://www.jackrabbitmarine.com/

8. Sea Air Land Technologies, Inc., http://www.salt-systems.com/

9. Southwest Wind Power, Inc., http://www.windenergy.com/

10. Power Performance Test Report for the Southwest Windpower AIR-X Wind Turbine, National Renewable Energy Laboratory, NREL/TP-500-34756, September 2003, http://www.nrel.gov/docs/fy03osti/34756.pdf

11. AMPAIR Natural Energy, http://www.ampair.com/

12. Kyocera, http://global.kyocera.com/

13. MSK Corporation, http://www.msk.ne.jp/english/company/

14. Blocking Diodes and Fuses in Low Voltage PV Systems, John C. Wiles, Southwest Technology Development Institute, and David L. King, Sandia National Laboratories, Presented at the 26th IEEE Photovoltaic Specialists Conference, September 29-October 3, 1997, Anaheim, California.

15. ASEA Power Systems, http://www.aseapower.com/

16. Atlas Energy Systems, http://www.shorepower.com/

17. Charles Industries, http://www.charlesindustries.com/

18. Mastervolt, http://www.mastervolt.com/

19. Olsun Electronics Corp, http://www.olsun.com/

20. Xantrex Technology, http://www.xantrex.com/

21. Magnus Marine, http://www.magnusmarine.com/

22. Stored Energy Technology Limited, http://www.set.gb.com/

23. Failsafe Power, http://www.failsafepower.com/

24. Ted Sargent, Nature Materials, January 9, 2005, http://www.nature.com/nmat/

25. Glacier Bay, http://www.glacierbay.com/

26. Nanosolar, http://www.nanosolar.com/