Understanding Boat Batteries and Battery Charging 157409162X, 2002154369

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Other Books by John C. Payne

The Fisherman's

Electrical

The Great Cruising Cookbook: An Marine

Electrical

Motorboat

International Galley Guide

and Electronics

Electrical

Manual

Bible,

Second Edition

and Electronics Manual

Understanding Boat Wiring

Understanding Boat Batteries and

Battery Charging John C. Payne

S SHERIDAN HOUSE

This edition

first

published 2003 by

Sheridan House Inc.

145 Palisade

Street,

Dobbs

NY

Ferry,

Copyright

©

10522

2003 by John

All rights reserved,

C

no part of

Payne this publication

may

be reproduced,

stored in any retrieval system, or transmitted in any form by any

means, electronic, mechanical, photocopying, recording or otherwise without permission

in writing of

Sheridan house.

The publisher takes no responsibility for the use of any of the materials or methods described in the book, or for the products thereof.

Library of Congress Cataloging-ln-Publication Data

Payne, John C.

Understanding boat batteries and battery charging

/

John C. Payne, p.

cm.

ISBN 1-57409-162-X 1. I.

(alk.

paper)

Storage batteries. 2. Boats and boating-Electric equipment

Title.

VM367.S7 P39 2003 623.8'503-dc21

Printed in the United States of America

ISBN 1-57409-162-X

2002154369

Contents

1. Batteries

1 2.

Lead Acid Batteries 5 3.

AGM

Batteries

13 4. Gel Batteries

15 5.

General Information on Battery Types

17 6. Battery Ratings

and Selection

19 7. Safety, Installation

and Maintenance

31 8. Charging, Alternators

and Regulators

35 9.

Charging Circuit System

59 10. Battery Chargers

69 11. Alternative Charging, Solar and Wind

74 Index

87

1.

What

is

BATTERIES

the purpose of a boat battery?

power storage device that is used to start the engine or to power lights and accessories, such as radios, pumps and electronics. The battery also acts as a "buffer" which absorbs the power surges and disturbances that occur during battery charging and discharging.

The

battery

is

the

What type The type of

of battery is required?

battery required depends

on the

service or

power

dis-

charge requirements of the boat. The service requirements can be

grouped under house power, deep cycle or service loads; the other requirements are starting or high current loads.

load type

This

may

is

When

the

decided, the type of battery chemistry can be chosen.

be the lead-acid flooded

cell;

the gel

cell;

the

AGM or

alkaline type battery.

What

is

a service, house power or deep-cycle load?

Deep-cycle, service or house power loads are those loads that

draw current over long periods of gory includes the cabin

time.

Equipment

in this cate-

lights, refrigeration, electronic instru-

ments, radios, radar, autopilots, inverters, trolling motors and entertainment systems. The deep-cycle battery

is

normally used

to supply these applications. Calculations are based

on the max-

imum power consumption over the expected longest period between battery recharging.

1

Understanding Boat Batteries and Battery Charging

2

What

is

a starting or high current load?

Starting loads require large current levels for relatively short pe-

riods of time such as the engine starting motor.

Loads

in this cat-

egory also include diesel engine pre-heaters or glow-plugs, the

anchor windlass,

electric

winches, electric thrusters and electric

The starting type battery is normally used for these applications. The battery rating should allow for worst case scenarios, toilets.

such as very cold temperatures. In cold temperatures the battery efficiency

is

lowered and engine starting requires greater power

due to increased

When

oil viscosity.

are batteries connected

in

series?

Batteries are connected in series to increase the voltage. Batteries

and

8V and 12V can be connected 36V or 48V. Six-

with ratings of 1.2V, 6V,

cells

in series to

make up banks

of 12V, 24V, 32V,

volt batteries are frequently used in 12-

they are easier to install and remove. in series, the batteries

and

age. If

is

When

as

connecting batteries

should be of the same make, rating, model

one battery requires replacement, the other should

also be replaced. In

relay

and 24-volt systems

some

installations a series-parallel switch or

used to connect batteries for 24 or 48 volts to power

thrusters

and

trolling motors.

Series Connection

12 + 12 = 24 Volts

Positive -i

Ne 9 atl ve oo + 1 00 = 100 Ah

3

Batteries

When

are batteries connected

in parallel?

Batteries are connected in parallel to increase the rating or amphour power capacity for the same voltage. Batteries up to around 115Ah are a popular arrangement. They are usually installed in parallel banks of up to three. It is common to have

large traction or truck batteries of very large dimensions such as

the

8D

size installed.

As they are physically very

large

and heavy,

servicing can be difficult although manufacturers are trying to

solve this problem.

Parallel Connection

+

100 + 100 = 200 Ah

Negative

4

Understanding Boat Batteries and Battery Charging

About connecting batteries

When

connecting batteries, quality battery terminals must be The wing nuts type should not be used as they are hard to tension up without breaking the ears or wings off. Always use a bolt- or clamp-type connector. The clamp type does not require a terminal lug. It is also good protection to install a terminal used.

cover over the connection to prevent accidental contact.

Battery Terminals

Battery Terminal Covers

2.

How does When two

LEAD ACID BATTERIES

a flooded or wet cell lead acid battery work? electrodes of different metal are placed in an elec-

trolyte, they

form

a galvanic cell.

takes place within each ical

flooded lead-acid

volts per cell. In a loss will

occur

cell

cell

it is

electrochemical process a voltage. In the typ-

the generated voltage

normal flooded

when

An

which generates cell

electrically

is

nominally 2.1

lead-acid battery, water

broken

down

and hydrogen near the end of charging. In normal

into

oxygen

batteries, the

gases disperse to the atmosphere, resulting in electrolyte loss.

These are the bubbles seen in the

What The

cells

during charging.

are the components of a battery cell?

which are internally connected in series to make up the battery. The battery cell is made up of several basic components. typical 12-volt battery consists of 6 cells,

Lead dioxide (Pb02), which and is brown in color.

is

the positive plate active

ma-

Lead peroxide

the negative plate material

and

terial

is

(Pb),

which

is

grey in color.

Sulfuric acid

(H2S04), which

is

the electrolyte in a diluted

solution with water.

The

grids,

which are used

to hold the lead dioxide

and lead

peroxide plate material.

The

separators,

which are used to hold or space the

plates

apart.

The

battery casing, which

The

terminals,

is

used to contain each

which are used to connect the

cell.

cells.

5

Understanding Boat Batteries and Battery Charging

6

What The

cell electrolyte is

is

Specific Gravity?

the battery acid. This

and water.

is

a dilute solution of

measurement

Specific Gravity (SG)

is

the

used to define electrolyte acid concentration.

A

fully

sulfuric acid

has an

SG

charged

cell

typically in the range 1.240 to 1.280, corrected for

an approximate volume ratio of acid to water of 1:3. Pure sulfuric acid has an SG of 1.835, and water has a nominal 1.0. The SG of a battery also indicates charge temperature. This

is

level.

Lead Acid Battery

State of

Charge Table

S.G.

Voltage

Charge Level

1250

12.75

100%

1235

12.65

1220

12.55

1160

12.10

1145

11.95

1130

11.85

1115

11.75

90% 80% 70% 60% 50% 40% 30% 20% 10%

1100

11.65

0

1205

12.45

1190

12.35

1175

12.25

Lead Acid Batteries

7

What happens when a When

an external load such as a

positive is

and

cell light

discharges? is

connected across the

negative terminals, the cell will discharge.

a potential or voltage difference

As there

between the two poles,

elec-

trons will flow from the negative pole to the positive pole.

A

chemical reaction then takes place between the two plate materials

and the

electrolyte.

During the discharge reaction, the plates form lead sulfate and water. This

interact with the electrolyte to

reaction dilutes the electrolyte, reducing the density. plates

become

As both the

similar in composition, the cell loses the ability to

generate a voltage.

Lead Acid Discharge and Recharge Reaction

Charged

Cell

Nominal Voltage

2V per

Cell

Positive

Negative

Plate

Plate

H

1°°' 77

«

(--

«

d

80

'

Lead

Electrolyte

Peroxide

Sulfuric Acid

PbO

SG

12.80

Pb Sponge Lead

Understanding Boat Batteries and Battery Charging

8

How The charging process decomposes to

a cell recharged?

is

The water hydrogen and oxygen. The two plate

reverses the discharge reaction.

release the

materials are then restored to the original material. plates are fully restored

nominal

and the

density, the battery

is

electrolyte

is

When

completely recharged.

Lead Acid Charge and Discharge Reaction

Discharged Cell

+

•

Positive

Negative

Plate

Plate

Electrolyte

Lead Sulfate Sulfuric Acid

PbS04

SG

11.20

the

returned to the

Lead Sulfate

PbS04

9

Lead Acid Batteries

How does For accuracy,

all

temperature affect the readings?

hydrometer readings should be corrected for

temperature. Ideally, actual

cell

temperatures should be used, but

ambient battery temperatures are sufficient. Hydrometer floats usually have the reference temperature printed on them and this should be used for calculations. For every 2.7°F (1.5°C) the

cell

above the reference value, add 1 point (0.001) to the hydrometer reading. For every 2.7°F (1.5°C) the cell temperature is below the reference value, subtract 1 point (0.001) from the hydrometer reading. For example if the reference temperature is 68°F (20°C), at a temperature of 77°F (25°C) add 0.004 to the temperature

reading.

If

is

the temperature

is

near freezing at 41 °F (5°C), deduct

0.012 from the reading.

How When

important

topping up the

is

battery water? always use

cell electrolyte,

ionized water. Rainwater

is

distilled or de-

acceptable, but under no circum-

stances use water out of the galley tap or faucet, as this water

generally has an excessive mineral content or other impurities that pollute cell will

and damage the

cells.

Impurities introduced into the

remain, and concentrations will accumulate at each top

up and reduce

service

life.

What Plate sulfation

is

When

is

a battery

the

is

most

plate sulfation?

common

cause of battery failure.

discharged the chemical reaction converts both

plates to lead sulfate.

If

recharging

lead sulfate starts to harden

and

is

not carried out quickly, the

crystallize.

This

is

characterized

by white crystals on the brown plates and is almost non-reversible. The immediate effect of sulfation is partial and permanent loss of capacity as the active plate materials are reduced. Electrolyte density also partially decreases, as the chemical reaction during charging terial

cannot be

fully reversed.

This sulfated ma-

introduces higher resistances within the

charging.

As the

cell

and

inhibits

level of sulfated material increases, the cell loses

the capability to retain a charge

and the battery

fails.

Understanding Boat Batteries and Battery Charging

10

How Battery efficiency

is

more

but

efficient,

commissioned

At 32°F (0°C), the

affected by temperature.

by 60%. Batteries

efficiency will fall

are

efficient is a battery?

in

may have reduced

in tropical areas often

warm life

tropical climates

spans, and batteries

have lower acid

densities.

Batteries in cold climates have increased operating lives, but are less efficient.

What

is

self

discharge?

During charging, small particles of the antimony used in the plates and other impurities dissolve out of the positive plates and deposit on to the negative ones. Other impurities from the topping up water also deposit on the plates. A localized chemical reaction then takes place, slowly discharging the

cell.

Self-discharge

by temperature. At 32°F (0°C), the self-discharge rates are small. At 86°F (30°C), the self-discharge rates are very high and the specific gravity can decrease by as much as 0.002 per day, typically up to 4% per month. rates are affected

What do the group numbers mean? These are standard

sizes

used in the United States. The following

are for 12-volt batteries that are typically used in boats

vary according to battery type. Large ier to

handle with Rolls having

cell

8D

batteries are

based units.

Group

Capacity

24

Ah 80-90 Ah 105 Ah 160 Ah 225 Ah 160-200 Ah 220-245 Ah

27 31

904D 908D

4D 8D

65-75

and

will

now

eas-

Lead Acid Batteries

What

11

is

a dual purpose battery?

These batteries are a combination of deep cycle and starting battery. They have both the high cranking capacity with good cy-

They are used in many smaller boats where smaller house loads do not require a separate deep cycle battery and a

cling ability.

start battery.

When A

should a battery be recharged?

deep cycle battery should be recharged

falls

to a

maximum

of

50%. A

when

recharged immediately after each use and level of

10%

cycled, the

of

life

maximum

the charge level

starting battery should always be

charge

maximum

level. If a start

of the battery will be severely reduced.

Rolls

Red Battery

Courtesy Rolls

Mastervolt Battery Courtesy Mastervolt

allowable

battery

is

deep

AGM

3.

BATTERIES

What are Absorbed Glass Mat (AGM) or Valve Regulated Lead Acid (VRLA) batteries? These are new generation battery types. The electrolyte

is

held

within a very fine microporous, boron-silicate glass matting that is

placed between the plates. This absorbs and immobilizes the

acid while

still

allowing plate interaction. They are also called

starved electrolyte batteries, as the

mat

is

only

95%

soaked

in

electrolyte.

AGM

Battery Principles

DC

i

G-n

DC

Current

Source

13

Understanding Boat Batteries and Battery Charging

14

How does

an AGSVS battery work?

These batteries use a principle called Recombinant Gas Absorption. The plates and separators are held under pressure. During charging, the evolved oxygen

is

only able to

move through

the

separator pores from positive to negative, reacting with the lead plate.

The negative

plate charge

is

then effectively maintained

below 90%, which stops hydrogen generation.

How

are

AGM

batteries charged?

Typical charge voltages are in the range 14.4 to 14.6 volts at

68°F (20°C). The batteries have a very low internal resistance, which results in minimal heating effects during heavy charge and discharge. They can be bulk charged at very high currents, typically by a factor of five over flooded cells, and a factor of 10 over gel batteries. They also allow 30% deeper discharges and recharge 20% faster than gel batteries, and have good recovery from full discharge conditions. Self-discharge rates are only 1%-

3%.

100%

Typical charge voltage levels are:

75%

is

volts

is flat.

12.6 volts,

50%

is

12.3 volts,

At high temperatures both

25%

is

is

12.8-12.9 volts,

12 volts and 11.8

AGM and gel cells are un-

able to dissipate the heat generated by oxygen and hydrogen re-

combination and to gassing

this

can create thermal runaway. This

and the drying out of

pacity can occur

when

cells.

A

the positive plate

to higher operating temperatures caused

process and higher charge currents.

premature

will lead

loss of ca-

and grids degrade due by the recombination

GEL BATTERIES

4.

What The

is

a gel battery?

gel cell has a solidified gel as

an

electrolyte,

which

is

locked

During charging the gel liquefies due to its thixotropic properties, and solidification after charging can exceed an hour as thixotropic gels have a reduced viscosity under stress. The newer battery types use phosphoric acid in the gel to into each

group of

plates.

retard the sulfation hardening rates.

How The

is

a gel battery constructed?

lead plates in a gel cell are reinforced with calcium, rather than

the antimony used in flooded cells. This reduces self-discharge rates,

and they are

This also helps gel diffusion and

relatively thin.

improves the charge acceptance rate as diffusion problems are

re-

duced. The separator provides electrical and mechanical isolation of the plates. Each sure

if

cell

has a safety valve to relieve the excess pres-

the set internal pressure

close tightly to prevent

is

exceeded.

The

valve will then re-

oxygen from entering the

cell.

Gel Cell Battery Principles

Vented Gas Valve

Pb

Gel electrolyte

—

Pb02

Separator

15

Understanding Boat Batteries and Battery Charging

16

How The

are gel cell batteries charged?

gel battery has a higher charge acceptance rate

flooded

cell battery.

typical rate

than the

This allows a more rapid charge rate and the

50% of Ah capacity. A gel cell battery cannot tolany equalizing charge applied; this over charge conseriously damage them. During charging the current is

erate having

dition will

causes the decomposition of the water and the generation of oxy-

The oxygen diffuses through the unfilled mat separator pores to the negative plate, and reacts chemically to form lead oxide, lead sulfate and water. The charge current then reduces and does not evolve hydrogen gas. If gen

at the positive plate.

glass

recombination of hydrogen ditions, the gases

accept

will

teries

may

is

incomplete during overcharge con-

vent to the battery locker. While these bat-

some 30-40%

current than

greater

an

equivalent lead acid battery they are restricted in the voltage levels

allowed, so you cannot use any fast charging system. Typical

open

circuit voltages are:

75%

is

volts

is

units

is

12.65 volts,

50%

is

100%

charge

12.35 volts,

is

25%

12.85-12.95 volts, is

12 volts and 11.8

The normal optimum voltage tolerance on Dryfit 14.4 volts. There are some minimal heating effects durflat.

ing charging caused by the recombination reaction. Continuous over- or undercharging of gel cells

premature

failure. In

many

automotive type chargers.

is

the

cases this

is

most common cause of due to use of imprecise

5.

GENERAL INFORMATION ON BATTERY TYPES

What

an alkaline

is

Alkaline cells are also

cell

battery?

commonly known

(NiCad) and Nickel Iron (NiFe) batteries.

as Nickel

The

Cadmium

principal factors

500% more), greater weight and physical size, and they are normally only be found in larger boats. The batteries use an alkaline electrolyte and not an acid. Unlike lead-acid cells, plates undergo changes in their oxidation state, and do not alter physically. As the active materials do not dissolve in the are cost (typically

electrolyte, the plate life

is

very long.

The

positive plate

of Nickel-Hydroxide, and the negative plate of droxide.

The

electrolyte

is

is

made

Cadmium Hy-

a potassium hydroxide solution with

a specific gravity of 1.3. Unlike lead-acid cells, the density does

not significantly alter during charge and discharge and hydro-

meter readings cannot be used to determine the state of charge. Electrolyte loss

is

relatively

low

in operation.

Lead-acid and

NiCad batteries should never be located in the same compartment as the cells will become contaminated by acid fumes causing permanent damage.

What

are the advantages and disadvantages of battery types? Flooded

more

cell batteries

resilient to

that maintenance erated,

cost less, they are lighter in weight,

and are

overcharge conditions. The disadvantages are is

required, acid can be spilled, gases are gen-

and they have

relatively high self-discharge rates.

AGM batteries don't require maintenance, and don't spill acid or generate gas in normal operation.

They

also have

low

self-

discharge rates, have good deep-cycle ability and maintain a

rel-

The disadvantages

are

atively constant voltage during discharge.

and if overcharged they are permanently damaged, and they are heavy. that they are expensive,

17

Understanding Boat Batteries and Battery Charging

18

Gel batteries don't require maintenance, don't

spill

acid or

generate gas in normal operation. They also have low self-dis-

charge rates, and some have good deep-cycle vantages are that they are expensive, and

if

ability.

The

disad-

overcharged they are

permanently damaged.

Can

I

mix the battery types?

Battery types must not be mixed. Each battery type has a different charging voltage and discharge characteristic, so the battery types

must be the same. Also never mix old

batteries with

new

batteries.

What

are the

Numbers ity

life

expectancies of each battery type?

are usually based

on the manufacturer's

deep-cycle lead acid traction battery can have a

data. life

A

qual-

exceeding

and discharge to 50%. A gel cell has a life 500-800 cycles depending on the make. An of approximately AGM battery has a cycle life of 350 to 2200 depending on the

2500

cycles of charge

type.

What happens when

a battery

is

completely flattened?

Deep-cycle batteries are permanently damaged within days by sulfation of plates. Gel batteries can survive

up

to a

month, while

AGM can survive also about a month. All can be recharged however

damage occurs and

cycle

life is

reduced.

6.

BATTERY RATINGS AND SELECTION What

is

The Amp-hour

the Amp-hour rating of a battery?

rating (Ah) of a battery refers to the available cur-

rent a battery can deliver over a final voltage

nominal period

amps per

reached, or

is

hour.

normally specified at the 10- or 20-hour

until a specified

Amp-hour

rate.

rates are

This rating

is

nor-

mally only applied to deep-cycle batteries. For example, a battery is

rated at 105

Ah

10-hour

at

This means that the battery

10 hours, when a

cell

is

rate, final voltage 1.7 volts per cell.

capable of delivering 10.5 amps for

voltage of 1.7 volts will be reached. At this

point the battery volts will be at 10.2 volts.

What

is

the Reserve Capacity rating of a battery?

The Reserve Capacity

rating specifies the

number

of minutes a

battery can supply a nominal current at a nominal temperature

without the voltage dropping below a certain the

power

available

when an

able to operate ignition

and

alternator fails

level. It indicates

and the power

avail-

auxiliaries. Typically, the rating

specified for a 30-minute period at

77°F (25°C) with

is

a final volt-

age of 10.2 volts.

What

is

the Cold Cranking

The Cold Cranking

Amp

Amps (CCA)

rating?

rating specifies the current available at

0°F (-18°C) for a period of 30 seconds, while being able to maintain a cell voltage exceeding 1.2 volts per cell. This rating

applicable for engine starting.

more power

The higher

available, especially in cold

is

only

the battery rating, the

weather conditions.

19

20

Understanding Boat Batteries and Battery Charging

What

the Marine Cranking

is

The Marine Cranking

Amp

rating

Amps (MCA) is

a relatively

rating?

new

rating

which defines the current available at 32°F (0°C) for a period of 30 seconds, while being able to maintain a cell voltage exceeding 1.2 volts per ing. If

cell.

you are

This rating

United States or Canada, the

Why Many

is

only applicable for engine start-

in cold climate area

CCA

rating

The more

is

more

relevant.

are plate numbers quoted?

battery data sheets specify the

fined as the

such as the UK, Europe,

number

number of plates. This

is

of positive and negative plates within a

de-

cell.

plates installed, the greater the plate material surface

area. This increases the current during high current rate dis-

charges and the cranking capacity and cold weather performance are improved.

What This

is

is

a marine battery?

a sales or marketing description for certain constructional

The plates may be thicker than normal or there may be more of them. The internal plate supports may be able to absorb vibration. The battery cases may be manufactured with a resilient rubber compound. The cell filling caps may be of an anti-spill defeatures.

sign. In general, batteries are of a similar design

with very

little

to distinguish the automotive types, except the label.

What

is

a deep-cycle battery?

Service loads require a battery that can withstand cycles of long

continuous discharge, and repeated recharging. This deep cycling requires the use of the suitably are available in

all

named

deep-cycle battery. These

battery chemistry types.

21

Battery Ratings and Selection

How The

is

the deep-cycle battery constructed?

lead acid deep-cycle battery

is

typified

by the use of

thick,

high-density flat-pasted plates, or a combination of flat and tu-

The plate materials may also contain small proportions of antimony to help stiffen them. Porous, insulating separators are used between the plates and glass matting is used to assist in retaining active material on the plates that may break away as they expand and contract during charge and recharge bular plates.

cycles. If material

may

accumulates at the

occur, although this

material

is lost,

is

less

cell

common

base, a cell short circuit in

modern

batteries. If

the plates will have reduced capacity or insuffi-

cient active material to sustain the chemical reaction with result-

ant cell failure. Much has been done to develop stronger and more efficient plates. Rolls have their Rezistox positive plates. The grid design has fewer heavier sections to hold the high density active material. This is due to the dynamic forces that normally cause expansion and contraction with subsequent warping

and cracking. Separator design has also evolved; Rolls use double insulated thick glass tive plate

retains cuits.

woven ones

that totally encase the posi-

along with a microporous polyethylene envelope. This

any material shed from the plates than cause

cell

short

cir-

22

Understanding Boat Batteries and Battery Charging

How many deep

cycles are available?

The number of available deep cycles varies between the different battery makes and models. Typically it is within the range of 8001500 cycles of discharge to 50% of nominal capacity and then complete recharging. Battery cycles

and the depth of

of capacity will last

charged to discharge

40%

is

life is

a function of the

number

cycling. Batteries discharged to only

much

of

70%

longer than batteries that are dis-

of capacity. In practice, plan your system so that

limited to

50%

of battery capacity.

The

typical

life

of batteries where batteries are properly recharged and cycle capabilities

maximized can be up

to 5-10 years.

Deep Cycles Courtesy Surrette

DEPTH OF DISCHARGE

23

Battery Ratings and Selection

How

is

a deep cycle battery selected?

Many onboard power

problems

result

from improperly

selected

batteries. Battery bank capacities can be seriously underrated, which causes power shortages. If batteries are overrated the

charging system cannot properly recharge them, and sulfation of the plates can occur with premature failure. All the electrical

equipment on board

is

listed

along with the power consumption

ratings.

What happens

if

the battery

is

discharged

faster than the nominal rate?

The which

faster a battery is

is

either the 10- or

discharged over the nominal rating,

20-hour

rate, the less the real

capacity the battery has. This effect tion,

which has

is

amp-hour

defined by Peukerts Equa-

a logarithmic characteristic. This

equation

is

based on the high and low discharge rates and discharge times for each to derive the Peukert coefficient

V. Average

values are

around 1.10 to 1.20. If we discharge a 250 amp-hour battery bank, which has nominal battery discharge rates for each identical battery of 12 amps per hour at a rate of 16 amps, we will actually have approximately 10-15% less capacity. Battery discharge meters such as the E-Meter incorporate this coefficient into the monitoring and calculation process.

What happens when the The slower

the battery

is

battery

is

slowly discharged?

discharged over the nominal rate, the

If we discharge our 240 amphour battery bank at 6 amps per hour we will actually have approximately 10-15% more capacity. The disadvantage here is

greater the real battery capacity.

that slowly discharged batteries are harder to charge cled

below 50%.

if

deep cy-

Understanding Boat Batteries and Battery Charging

24

Can

all

the battery capacity be used?

For a deep-cycle battery the discharge capacity should be kept at 50% of nominal battery capacity to maximize life. We can as-

sume

that a battery capacity of

imum

level.

frightening realities

The

240 amp-hours

is

the basic min-

minimum requirement, but certain must now be introduced into the equation.

This should be a

below typify

figures

a

common system, with alternator Maximum charge deficiency

charging and a standard regulator. is

based on the assumption that boat batteries are rarely above

70% tors.

a

charge and cannot be fully recharged with normal regula-

There

minimum

is

reduced capacity due to sulfation, which

of

10%

of capacity.

The key

timum power

levels

of numbers

the charging system.

is

and avoiding

this

surprising set

240 Ah

Cycling Level (50%)

Max. Charge

Deficiency (30%)

Lost Capacity (10%)

Deduct 120 Ah

is

Ah

Deduct

72

Deduct

24 Ah 24 Ah

Available Battery Capacity

What

typically

to maintaining the op-

common and

Nominal Capacity

Maximum

is

a discharge requirement?

240 Ah has been calculated as that required to supply 10 amps per hour over 12 hours to 50% of battery capacity. In most cases, the discharge requirements are worst for the night period, and this is the 12-hour

The nominal required

battery capacity of

period that should be used in calculations.

What

is

required

is

a

bank with similar discharge rates as the current consumption rate. This will maximize the capacity of the battery bank with respect to the effect defined in Peukerts coefficient. battery

25

Battery Ratings and Selection

What

is

battery load matching?

The main aim is to match the discharge characteristics of the battery bank to that of our calculated load of 10 amps per hour over 12 hours. Calculations assume that the charging system recharge batteries to virtually factors affecting

100%

is

able to

of nominal capacity.

The

matching are the discharge and battery capacity

requirements.

About battery capacity requirements As the consumption rate is based on a 12-hour period, a battery bank that is similarly rated at the 10-hour rate is required. In practice you will not match the precise required capacity, therefore you should go to the next battery size up. This is important also as the battery will be discharged longer and faster over 12 hours, so a margin is required. If you choose a battery that has 240 amp-hours at the 20-hour rate, in effect you will actually be installing a battery that in the calculated service has

10-15%

less

capacity than that stated on the label, which will then be ap-

proximately 215 Ah, so you are below capacity. This

is

not the

fault of the supplier, but simply a failure to correctly calculate

and specify the

The

right battery to

ratings can usually be

meet system requirements.

found on the equipment nameplates

The ratings are given in amps (A) recommended that where watts are used, this rating is converted to current in amps. To do this, divide the power rating in watts by the operating voltage, 12 or 24 volts. or in the equipment manuals. or watts (W).

It is

Watts (W)

Amps

6 watts

0.5

12 watts

1.0

18 watts

24 watts 36 watts

48 watts 60 watts 72 watts

(A)

amp amp

amps amps 3.0 amps 4.0 amps 5.0 amps 6.0 amps 1.5

2.0

Understanding Boat Batteries and Battery Charging

26

What time in

periods should be used

the power consumption calculation?

For sailing or power boats, calculate the power consumption for a 12-hour period while in port or at anchor. The calculation should assume that the engine will not be operated, and that no generator or shore power with battery charger will be opera-

When a boat is motoring, all the power is being supplied from the engine alternators, and when the batteries are fully

tional.

charged, the alternator effectively supplies

What

is

all

power.

a Load Calculation Table?

A

Load Calculation Table is used to list and carry out calculaTo calculate the total boat electrical system loading, multiply the total current values by the number of operating hours to get the amp-hour rating. If equipment uses a current of 1 amp over a 24-hour period, then it consumes 24 amp-hours (Ah). The table shows many typical power consumptions. There is space tions.

and calculation of your own boat

for insertion

How

electrical data.

to perform a load calculation

equipment on the boat must be listed along with the power consumption ratings. Ratings are found on the equipment nameplates and in equipment manuals. Insert your own values into the current column, typical values are in brackets. Calculate the power used over 12 hours. To convert power in watts to the curAll

rent in amps, divide the

power value by

the system voltage.

Add

and multiply by hours (12) to determine the average amp-hour consumption rate. Most equipment will be on when sailing, anchored or moored. Equipment used when motoring or when shore power is connected is not relevant. Depending on the frequency between

up

all

the current figures relevant to your vessel

charging periods select the column that suits your boat

The most

typical scenario

chor and the

lights,

is

where the boat

entertainment systems,

activity.

moored or at ansome radio or naviis

gation equipment and an electric refrigerator are used. Eg. Total consumption

is

120

Ah over

12 hours

=10 amps/hour

27

Battery Ratings and Selection

Load Table Equipment k orlof — IvclLlclI

-

11

Rpppivp lYcLcivc

\WCctLUCI X / POt"nPf

vil

m

1

1~

OLdiiuuy

IVciClcll

VHF VI

1

DC

Load Calculation

Current (A)

rone lldllMIlll 1

1 -

v dA

SA\

(4 (0

SA)

(0

SA)

(0

SA)

(0 SA) -TV ) \J J

>3

\

Mo lMdv\rtf*v LCX

.

(0

^A\

ff)

^A^

hicnrinnpr UlllClllS

J LCI CU

Tnvprfpr 111VC1LC1

^fnv JLUy

A nrnnr xvllCllVJi

lant T -LlgllL

R pfricrprofinn

n da^ /4

OA)

llllCIlVJl l_/lglllc)

(4

0A^

iom l"pr V_>U1 nn ULCl

5A)

Tp|pvicir>n 1C1CV151U11

O O

0A\

Video

(1

5 A)

1 1 vj

Trolling

Motor

(15.0 A)

Consumption (Ah)

Understanding Boat Batteries and Battery Charging

28

How Some

should intermittent loads be calculated?

come on and off periodically such as water pumps, using battery power for short periods. It is difficult to quantify actual real current demands with intermittent loads. I use a baseloads

minutes per hour, which

line of 6

Load Table 2 Equipment

Intermittent

(3.5A)

Water Pump

(3.5A)

Shower Pump

(2.5A)

(15.0A)

Toilet

Cabin Fans

VHF

(1.0A)

Transmit

Spot Light

(4.0A)

(3.0A)

(40.0A)

Inverter

Cabin Lights

Load Table

DC

Current (A)

Pump

Bilge

-

is .1

1

Load Table 2

TOTAL LOAD

(4.0A)

of an hour.

Load Calculation Consumption (Ah)

29

Battery Ratings and Selection

How The

to select start batteries?

must be capable of delivering the engine motor with sufficient current to crank over and start the

starting battery

starter

engine. This starting load can be increased by engine compression, oil viscosity

and engine driven loads. Loads such

thruster or anchor windlass under

full

as a

load also require similar

amounts of current. The starting battery is normally seon the basis of the engine manufacturer's recommendations and the table shows recommended battery ratings for various diesel ratings as well as typical starter motor currents. It

large

lected

is

good

practice to allow for a multi-start capability as a safety

margin. Allowances should be

made

for the decreased efficiency

of engines in cold climates as a greater engine starting current

is

required, and therefore larger battery ratings.

Battery Ratings Table

Current Load

Engine Rating

kW kW 15 kW 22 kW 30 kW 37 kW

Hp Hp 20 Hp 30 Hp 40 Hp 50 Hp

Battery

10

7.5

59 amps

375

15

11

67 amps

420

67 amps

420

75 amps

450

85 amps

500

115 amps

500

100

115/60 amps

500

150

150/75 amps

600

120 amps

800

Hp Hp 200 Hp

How The

a starting battery

is

CCA

CCA CCA CCA CCA CCA CCA CCA CCA CCA

constructed

starting battery contains relatively thin, closely spaced

porous

plates,

which gives

maximum

exposure of active plate

material to the electrolyte with minimal internal resistance. This

enables

maximum

rent availability.

chemical reaction rates, and

maximum

cur-

Understanding Boat Batteries and Battery Charging

30

Can

start batteries be

deep cycled?

Starting batteries cannot withstand cycling, flattened have

an extremely short service

be maintained within as

25-50

95%

of

if

deep cycled or

Ideally they should

charge. Cycle

full

cycles. Start batteries

and

life.

life

can be as low

not fully recharged will suffer

if

from sulfation. If improperly used under charged they will sulfate.

for deep cycle applications

and

Will start batteries self discharge? Starting batteries have very

low

self-discharge rates

and

this is

generally not a problem in normal engine installations.

How

efficient are start batteries?

Cold temperatures dramatically gine lubricating tures,

oil viscosities

and further increase the

affect battery

performance. En-

low temperaon the battery.

are also affected by starting loads

Battery Power Table

Temperature

Battery Level

Power Required

80°F (+27°C)

32°F (0°C)

100% 65%

0°F (-18°C)

40%

100% 155% 210%

How

should start batteries be recharged?

The discharged current must be restored quickly to avoid damage, and charge voltages should compensate for temperature. Normally after a high current discharge of relatively short duration, there is no appreciable decrease in electrolyte density. The battery is quickly recharged, as the counter voltage phenomenon does not have time to build up and has a negligible effect on the charging.

7.

SAFETY, INSTALLATION

AND MAINTENANCE How The

hazardous are batteries?

lead-acid battery

is

potentially hazardous

and proper

handling procedures should be followed. Battery

cells

explosive mixture of hydrogen and oxygen gas at

safe

contain an

all

times.

An

naked flames, sparks or cigaexplosion rettes are introduced into the immediate vicinity. Always use insulated tools. Cover the terminals with an insulating material to prevent accidental short circuit. Watchbands, bracelets and neck risk exists at all times

if

chains can accidentally cause a short circuit. Sulfuric acid

is

highly corrosive and must be handled with extreme caution. Al-

ways ted,

lift

lift

the battery with carriers

if fitted. If

no

carriers are

using opposite corners to prevent case distortion

electrolyte spills. If a fast charging device

the ventilation remains sufficient to

is

fit-

and

installed, ensure that

remove any generated

gasses,

and prevent them from accumulating.

Where should

batteries be installed?

Batteries should be installed within a separate space or

ment

that

is

located above the

maximum

protected from mechanical damage.

The

bilge

water

compartlevel,

and

batteries should be in-

box protected from temperature extremes, alcommonly used. The preferred temperature range is 50°-80°F (10°C-27°C). Always allow sufficient vertical clearance to install and remove batteries, as well as access and allow hydrometer testing. The batteries should never be installed close to any source of ignition, such as fuel tanks and system parts such as fuel filters, separators and valves. Any leak or accumulation of fuel represents a serious hazard and so any stalled in a lined

though

plastic containers are

source of ignition should be removed.

31

Understanding Boat Batteries and Battery Charging

32

What about The

battery

battery boxes?

box should be made of any acid spills coming

lined to prevent

plastic, fiberglass or lead

into contact with

wood

or

water. Boxes should be at least the full height of the battery so that any spills will be contained at

all

times.

are acceptable alternatives. Battery boxes

down and ies

PVC

must

battery boxes

also be fastened

tie-down straps are available. Physically secure batter-

with either straps or a removable restraining rod across the

top to prevent any movement. Insert rubber spacers around the

any minor movements and vibrations. Battery all times and secured. PVC or other connection covers should be installed where accidental contact by tools or other items can cause a short circuit across the termibatteries to stop

box

lids

nals.

should be in place at

Terminals should be coated to limit the corrosive effects of

acid.

Battery boxes Courtesy Blue Sea Systems

Safety, Installation

How

33

and Maintenance

should battery negatives be interconnected?

When two

or

more

batteries are connected in parallel, all the bat-

tery negatives are also connected together.

bank and

When

a house battery

from the same source, connected. The polarizing ground is then

a starting battery are charged

the negatives are also

connected to one of the battery negatives. In dual battery systems the cables connecting each battery negative or positive should be

rated the same.

How The

should battery positives be connected?

positive cables

start battery

must be connected

in

such a

way

that the

cannot not be accidentally discharged. Where

lenoid system

is

used to parallel the batteries for charging,

it

a so-

must

always open when the charging stops. Where high current equip-

ment can cause system disturbances such

as large load surges

and

voltage droops, consideration should be given to installing a separate battery

bank with the required

characteristics to

equipment.

Parallel Connection Unit Courtesy Blue Sea Systems

power

the

Understanding Boat Batteries and Battery Charging

34

What

battery maintenance

Check the density of

the electrolyte but

after charging or discharging. cells stabilize, as

it

takes

Wait

required?

is

do not

at least half

test

immediately

an hour

until the

some time for the pockets of varying Never test immediately after top-

electrolyte densities to equalize.

ping up the electrolyte. Wait until after a charging period, as

it

mix evenly. Check the elecAlways top up electrolyte levels with de-

similarly takes times for the water to trolyte level in each cell.

ionized or distilled water to the correct levels. Ensure that the

terminal posts are clean and tight. Coat the terminals with pe-

troleum

jelly.

Clean the battery surfaces with a clean,

damp

cloth.

and other surface contamination can cause surface leakage between the positive and negative terminals across the battery casing top. This can slowly discharge the battery and is a common cause of flat batteries, and mysterious but untraceable Moisture,

salt

system leaks.

What

A

fully

is

charged battery has a load connected along with a

voltmeter. Typically the load

value and onds.

a load test?

is

often around

is

digital

rated at about half the rated

300 amps. This

is

CCA

connected for 15 sec-

The voltage at the end of this period is an indicator of conand the capability to sustain the electrical chemical

dition

reaction. still

A

reading of over 9.6 volts indicates that the battery

is

under 9.6 volts indicates the battery

is

serviceable; a rating

failing.

8.

CHARGING, ALTERNATORS

AND REGULATORS About charging efficiency Manufacturers specify nominal capacities of batteries, and the total capacity of the bank must be taken into consideration. Older batteries have reduced capacities due to normal in-service aging,

and plate

sulfation,

which increases

also inhibits the charging process.

dependent, and the temperature

is

The

internal resistance

electrolyte

and

temperature

is

maximum

a factor in setting

charging voltages. The state of charge at charging commence-

ment can be checked using the open circuit voltage test and electrolyte density. The level of charge will affect the charging rate.

What Charging voltage

is is

the correct charging voltage? defined as the battery voltage plus the

cell

voltage drops. Cell volt drops are due to internal resistance, plate sulfation, electrolyte impurities

and gas bubble formation that

occurs on the plates during charging. These resistances oppose the charging

and must be exceeded to

effectively recharge the

charged state

battery. Resistance to charging increases as a fully is

reached and decreases with discharge.

ing in terms of the current

it

A

battery

is

self-regulat-

can accept under charge. Over-cur-

rent charging at excessive voltages simply generates heat

damages the

What does The bulk charge phase

is

bulk charge

mean?

the initial charging period

ing takes place until the gassing point in the

is

where charg-

reached. This

is

typically

range 14.4 to 14.6 volts, corrected for temperature. The

bulk charge rate can be anywhere between rated

and

plates.

amp-hour capacity

at the

20-hour

25%

and

40%

of

rate as long as tempera-

ture rises are limited.

35

Understanding Boat Batteries and Battery Charging

36

What does

absorption charge

mean?

After attaining the gassing voltage, the charge level should be

maintained at 14.4 volts until the charge current battery capacity. This level ical

300 amp-hour bank,

What The

is

normally

this is

85%

falls to

5%

15 amps.

a float charge?

is

battery charge rate should be reduced to a float voltage of

approximately 13.2 to 13.8 volts to maintain the battery at charge.

Charge Cycles

V A 15 10 14

Bulk

Absorption

9

Float

Charge

N

Voltage (V)

13 8 12 7 11

of

of capacity. In a typ-

6

10 5