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 Captain Charlie Johnson, PE
 JTB Marine Service
 St. Petersburg, FL
 cjohnson@jtbmarine.com
 727.323.2500

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 This presentation will not make you into a competent marine electrician
 JTB Marine Corporation and the presenter assume no responsibility for
the use of any of the materials, calculations or methods described in
this presentation.

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 Mechanical Engineer
 Retired Naval Engineer: Submarine Maintenance and Repair
 100 Ton Master
 ABYC Certified Marine Electrician
 Amateur Radio Operator: Advanced License
 Live aboard a 53’ Gulfstar Trawler; ten years
 Extensive cruising experience; three years “Down Island mon” in the
Eastern Caribbean
 All round nice guy……..

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 System Design
 Equipment Selection
 System Installation

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 The Energy Equation:
 Energy In = Energy Out Plus Inefficiencies

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 The Energy Equation Restated:
 Sources of energy = Users of energy plus inefficiencies

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 On today’s yacht:
 What are some sources of energy?
 What are some users of energy?
 What inefficiencies are encountered?

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 Load calculations
 Battery bank sizing
 Wiring considerations
 Circuit protection devices
 Switches

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 Be brutally honest...do not hedge your numbers!!
 The goal is to arrive at the realistic amount of power that your battery
bank is going to have to produce to supply your 120 VAC loads.

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 First some definitions:
 Energy is a measure of the ability of a system to do work; the units
are watthrs
 Power is rate of energy delivery; the units are watts
 One thousand watts are equal to one kilowatt
 The discharge cycle is the amount of time that the house bank will be
providing energy to the normal 12 VDC loads and the inverter before
being recharged

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 …and now some simple mathematics:
 Power equals voltage x current
 (Watts) = (Voltage) x (Current)

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 Example:
 Label plate on the new FRAMUS states:
 Voltage: 120 VAC
 Frequency: 60 Hz
 Current: 1.5 amps
 What is the power consumed by the new FRAMUS?

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 Recalling our formula:
 Power equals voltage x current
 …and substituting for V and I, we get:
 P=120 VAC x 1.5 amps
 =180 watts

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 The instantaneous power consumption of the FRAMUS is 180 watts…
 …however we need the estimation of the duration that this appliance will
be used in order to calculate the energy (watthours) requirement

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 This part is easy; the energy requirement is simply the power
requirement multiplied by the duration of use

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 Continuing with our example; the Admiral is going to use the FRAMUS for
one hour per discharge cycle
 The energy consumed will be:
 Energy=power x time of usage
 Therefore; the energy requirement is:
 E=180 watts x 1 hour = 180 watthours

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 Repeat this process for all of your 120 VAC loads
 Most of the standard texts have estimates if you cannot find the label
plate data
 A simple spreadsheet would be helpful
 Remember…no cheating!!

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 In a perfect world, energy conversion would take place with 100 %
efficiency…there would be no losses
 In our real world, we have to account for losses
 Recall that our 120 VAC loads were calculated to be 7,032 watts; or
about
 7 kW

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 …a little more mathematics:
 Energy out = Efficiency x Energy in
 Solving for Energy in:
 Energy in = Energy out /Efficiency
 So, for our example:
 Energy in = 7,000 watts/0.85
 = 8,235 watts

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 Converting Watts
amphours
 Recall that: Power = volts x amps
 And: Energy = Power x time
 Therefore: Energy = volts x (amps x time)
 The amphour concept is handy to introduce:
 One amp being consumed for one hour is one amphour

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 Continuing with our example:
 Initial Battery Loads = Energy in/12 VDC
 = 8,200 watts/12
 = 683 amphour

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 This is only for the 120 VAC loads supplied by the inverter…
 Must add normal hotel loads for the 12 VDC appliances aboard
 Again, be brutally honest…a spreadsheet approach can help
 For our example; I am assuming 117 amphours of 12 VDC load

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 The Final Battery Loads =
 683 amphours + 117 amphours
 (120 VAC loads) (12 VDC loads)
 = 800 amphours
 This is not a day sailor!!

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 Some practical considerations…
 Deep cycle batteries live longest if you only discharge them to 50% of
their total capacity
 Getting the last 15% of a battery’s capacity back into the battery
takes a disproportionate amount of time

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 We arrive at the ideal battery capacity (C) with a little more math:
 Battery Loads = (0.50.15)C
 Solving for C:
 C = Battery Loads / 0.35

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 The Ideal Battery Bank for our example would be:
 C = 800 amphrs/0.35
 = 2,286 amphrs

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 Considering only flooded, true deep cycle batteries…

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 Direct Current Connections
 Heavier is better
 Use the 3% voltage drop tables
 Use only Tinned Boat Cable
 BC5W2
 Insulation rated for 105°C dry
 Insulation rated for 75° C wet
 UL 1426
 Type 3

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 Direct Current Connections
 Do not use SAE Boat Cable
 On average; approximately 12% less crosssectional area for the same
wire gage
 Use properly sized, tinned, closed end lugs
 Crimp lugs using a box crimping tool
 Do not us hammer blow type crimpers
 Use heavy duty heat shrink on lugs

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 If the tables don’t allow for the expected current; calculate using this
formula:

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 Where:
 CM is the req’d. circular mil area of the conductor
 K is a constant regarding the properties of copper, 10.75
 I is the current in amps
 E is the voltage drop; a 3% voltage drop in a 12 VDC system is 0.36
 L is the round trip conductor length in feet

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 For a sample calculation, assume the following:
 The maximum current will be 200 amps
 The round trip from the B+ bus bar to the inverter/charger and back to
the B bus is 18 feet
 3% allowable voltage drop; 0.36

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 Calculating the required CM:
 CM = 10.75 x 200 amp x 18 ft
 0.36 volts
 CM = 107,500

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 From Table XII, we need 2/0 cable
 We need to check to see if 2/0 cable with 105°C insulation can handle
this kind of load in the engine room.

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 Alternating Current Connections
 Use BC5W2 three conductor AWG #10
 Run a separate case grounding wire (safety green wire) from the
grounding stud provide on the inverter/charger to the 120 VAC safety
ground bus

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 Install a Class T fuse of the size specified by the manufacturer within
7 inches of connection to the B+ bus
 If the conductor is sheathed, the fuse can be a maximum of 40 inches
from the connection to the B+ bus

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 Install a remotely accessible
inverter/charger disconnect switch in the B+ conductor
 Ensure that the output from the inverter is protected so that the boat’s
120 VAC power panel can only be supplied by ONE SOURCE at a time

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 Inverter/Charger
 Sine wave or modified sine wave
 Charger requirement
 Charging starting batteries
 Battery Isolators
 Battery Combiners
 Echo Charging
 Battery Monitoring System
 One bank or two
 Used to control inverter/charger…or not

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 With the possible exception of the main engine starter, an
inverter/charger is the largest 12 VDC load on the entire boat
 Wiring and installation MUST be workmanlike to the extreme…serious
problems can occur if corners are cut
 If you do not have the requisite skill, tools and material to properly
install the inverter/charger…do not attempt to do it yourself.

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 There are real design issues that have to be considered on how to route
120 VAC power to and from the inverter/charger
 If you are not comfortable working on alternating current circuits, hire
a knowledgeable ABYC Certified Electrician and help him so you can
learn.

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 Alternating current can KILL YOU DEAD.

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 If you are not comfortable working on alternating current circuits, hire
a knowledgeable ABYC Certified Electrician
 Work with the Electrician and learn some of the techniques for wiring
alternating current circuits

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 This presentation did not make you into a competent marine electrician
 JTB Marine Corporation assumes no responsibility for the use of any of
the materials, calculations or methods described in this presentation.

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 This presentation has provided you with:
 the information that you need to
ensure that your inverter/charger is designed properly
 some of the details to ensure that the installation is properly
installed
 If you are the least bit uncomfortable with dealing with extremely large
amounts of DC energy or the 120 VAC system….

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 Engage the services of an ABYC Certified Electrician and discuss your
planned installation using this presentation as a guide….

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 References
 ABYC Standards and Technical Information Reports for Small Craft
 Boatowner’s Mechanical and Electrical Manual; 2^{nd} Ed.; Nigel
Calder
 Powerboater’s Guide to Electrical Systems; Ed Sherman
 Blue Sea Systems; http://www.bluesea.com/
 Xantrex; http://www.xantrex.com/

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