MARINE ELECTRICAL SYSTEMS SEMINAR, PART 2
Cameron
By Cameron Clarke "S/V JUPITER"
First short intro:
While cruising the Pacific Coast, Mexico, Central America, and the
Caribbean, I conducted several hands-on seminars for cruising sailors
to learn about and improve their electrical systems. I now wish to
present this same material to others, via a multi-part
posting of articles to help you understand and troubleshoot your boat's
electrical system. This self-directed seminar aims to help you
understand the material without diagrams or graphics. If you feel you
need the specific diagrams and graphics, you may request them. Send
mailto:cam...@unix.infoserve.net and request "diagrams for marine seminar".
For a more complete introduction, see posting titled "MARINE
ELECTRICAL SYSTEMS SEMINAR, INTRODUCTION".
Copyright notice (C) 1995: All rights reserved. No material presented
herein may be copied in whole or part without the express and prior
written consent of the author, myself outside this particular news
group "rec.boats". This will attempt to defeat revised or incomplete
information from being distributed.
If you or your group would like to reprint or forward copies, please
mailto:cam...@unix.infoserve.net and request prior permission. And
withstanding any other matters we continue:
Part 2: GROUNDS
Most cruising sailors recharge their house batteries at anchor by
running their engine. Sometimes they run their mechanical refrigeration
at the same time. Some sailors recharge once per day, some twice per
day and others every second or third day. We will discuss ideal times
to charge in Part 3, so wait for that. Typically an alternator
is used to charge the batteries. How is the alternator connected
to your battery? Well there is most likely a wire on the back that
disappears into your wiring harness. This wire goes to an ammeter,
through which all the charging current flows, then routed back to the
engine and connected to the starter solenoid, where it connects to
the battery via a heavier gauge wire, probably through a battery switch
too. It is a long route with many connections. Oh "connections", do
we remember about those in Part 1? Yes, we must check these connections
too, but this is only half of the path. What about the ground? Remember
our sample circuit for the bilge pump? We cannot have a complete circuit
unless we connect to both the positive and negative of the battery.
How does the negative side of the alternator connect to the battery?
This is usually done via the case of the alternator. Yes the case of
most alternators is part of the circuit which is usually the negative
terminal. When the alternator is producing current and thereby charging
the battery, electrons are flowing out the alternator's case, through
the mounting bracket and bolts, the timing gear cover (on many engines
this is an aluminum casting), the engine block (cast iron), the
transmission bell housing (aluminum or cast iron?), the starter
motor adapter (aluminum), many bolts, into a large gauge wire from the
starter to the battery's negative post. Yes this is true! How many
connections is that? How many dissimilar metals? How much voltage
drop is created through all the connections? With just 35 amps of
charge current, I have measured as much as 2.5 volts between the
case of the alternator and the negative post of the battery. It is
not uncommon to find 1.0 volts drop with 35 amps current. We are
talking about just the negative side, the alternator "ground".
This is a good place for you to check your system. Carefully, so as
not to damage any of your personal parts while the engine is running and
the ammeter showing a good rate of charge, place the negative lead of
your voltmeter on the alternator case (because it is more negative than
the battery during charging) and the positive lead on the negative post
of the battery being charged. You may have to use a piece of wire to
extend the length of your voltmeter leads. What you measure in volts
times the charge current in amps is the loss in watts. Assume 35 amps
charging current and you measure 1.2 volts drop. The power loss is
35 times 1.2, or 42 watts.
Now measure the positive lead loss. Again carefully place the positive
voltmeter lead on the alternator's + output (be very careful not to short
the lead to the case, OK? I place an insulated alligator clip lead on
this terminal with engine off, then start), and negative lead on battery
positive terminal (we are measuring the voltage drop in the positive
side and the alternator is more positive than battery during charge). Due
to the greater number of connections and wire length, you may find this
value two or three times as great as the ground path loss. Let's assume
you measure 2.4 volts at 35 amps charge. That is 84 watts loss.
Now the battery is probably about 13.5 volts at this point, so 472.5
watts (35 times 13.5) are applied to it. The alternator is producing
598.5 watts (42 plus 84 plus 472.5) of which only 472.5 watts (about 79%)
charge the battery. That's a loss of 21%. Think now, if we did not have
this loss, we could save some fuel and running time! For those who have
installed large capacity alternators, 100 to 300 amp capable units, extra
care must be taken to insure a low voltage drop through the mounting
and positive output wiring. We will discuss this more in Part 4.
It is easy to reduce the loss in the ground path for the alternator,
simply by attaching a large ga wire (consult our wire table from part 1)
directly between the alternator case (there is usually an unused threaded
hole for this on the case) and the point the large negative battery cable
attaches to the engine. I think a starter mounting bolt best, unless you
have a starter (Lucas) with a designated negative post, use it. When
cranking the engine, the starter will draw 200 to 600 amps. The fewer
number and better quality of connections, the quicker the engine will
start. The starter and its brushes will last longer.
What other reasons are there to make a proper ground for the alternator?
When electrons move between dissimilar metals, they make little pits in
the metal they leave from. This is known as electrolysis. When you allow
current to flow through all those parts on your engine while charging
your batteries, you are slowly damaging those parts. You might also
find it difficult to remove some bolts too.
If you have an "internal" regulator, or even an "external" one that senses
voltage at the alternator or if the regulator takes its ground reference
from the alternator case, it will not charge the batteries properly, unless
the alternator has a low loss "ground" connection. More on this in Part 5
on Regulators.
You can reduce or eliminate the alternator whine in your HAM or VHF
radios and possibly eliminate the noise that affects some of your other
navigation electronics by using a low loss ground from the alternator.
There are really many benefits for this simple, easy to install piece
of wire, but mainly you will run your engine for less time, use less
fuel at anchor, and keep your cabin cooler in tropical climes as well
as prevent some electrolysis in the engine.
There are other types of "grounds" to talk about. In the U.S. our
household wiring is 120 Volts AC and we use 3 conductor cords. The
conductors are named "Hot", "Neutral", and "Protective Ground" (for
those with my drawings, please note size and shape of outlet's
conductors). Just like DC wiring on boats, AC also needs two wires to
make a circuit. If you have ever gotten a shock from 120, then you
became one of the wires, at least partially, to make the circuit. The
circuit is made between "Hot" and "Neutral". All the current flowing
through the load, the device consuming power, is supposed to flow through
these two conductors. The "protective ground" is there to help prevent
accidental electric shock. In power tools with metal cases, it connects
the case of the tool to "earth", a term expressed as grounded, via a pipe
driven into the earth near the electrical service panel (refer to
next two drawings). Land based electrical code (which is carried into
boats for the most part) states the "Neutral" shall be "earthed" via
a wire to a metal pipe driven into the earth and that the "protective
grounds" brought to the same point within the breaker or service panel.
This also applies to dock wiring. How many salt water marinas do you
know that don't have wiring problems? Perhaps many fresh water marinas
have their problems too.
Let's go back to our discussion in Part 1. Recall our bilge pump
circuit and all its connections (refer to first drawing). With a
battery voltage of 12.5 volts, the bilge pump received only 9.26 volts
because of the voltage drop in the wiring network. Right? We can measure
the voltage drop in any piece of wire or series of connections directly
with a voltmeter. This is a handy way to identify problem areas. If
you have not already done so, I urge you to measure a similar circuit
on your boat. Take the time to understand this. It is important. We
will refer to wiring losses, or voltage drop, many more times. By
understanding this, you will be able to handle 95% or more of your
wiring problems. You will save time, money, and aggravation.
The same applies to AC wiring. There will be a voltage drop in any
conductors under load. What does this mean for boaters? I was discussing
dock wiring and the electrical code regarding "Neutral" and "Protective
ground". "Protective ground" is for safety and is not to be used as
a current carrying conductor. "Neutral" on the other hand, is the
compliment for "Hot". It is used to carry the load current. As such,
over the course of wire length, a voltage drop will occur, increasing
in direct proportion with length of run and current load. Follow that?
Ok, now consider marina dock wiring. Power comes from the utility
company to a breaker or service panel. A ground reference is established
at that point via a pipe into the earth. "Neutral" and "Protective
ground" are connected together and to the pipe. The power then runs
to a series of dock boxes, and if each is wired to the code, new
ground reference points are established in the dock boxes. You then
run a cord from you vessel to the dock box and plug in. The "Protective
ground" on your vessel is then connected to you bonding system if
again done to code. Are all the grounds connected to the same
reference point? Yes and no. When current is flowing, the "Neutral"
conductor will produce a voltage drop, forcing the "Protective
grounds" at your boat, the dock box, and shore, to be at differing
voltage potentials (refer to dock electrical wiring). This produces
a leakage current flowing between the dock and shore, resulting in
some dock electrolysis. There will current flowing between your
vessel's bonded parts, the dock and shore, causing a little more
electrolysis. If any of the "Neutral" conductor's connections are
a bit loose or corroded, the problem will become much more severe.
What can be done? No, do not disconnect your safety grounds! First
make sure all connections are made to the proper places, are tight
and free from corrosion. You could use an isolation transformer for
your vessel's shore power. The Transformer's job is to isolate your
"Hot", "Neutral" and "grounds" from the sources. Done properly, this
works very well. But beware, you can pick up the shore's ground
from TV antenna wiring. You must connect the transformer case to
shore "Protective ground", but could then connect the vessel's
"protective ground" through your bonding system. You could also
benefit from being able to step up or down the shore voltage to
meet your needs in foreign ports, as many isolation transformers
have multiple taps for this purpose. They are heavy. I used one
that weighed some 80 pounds!
Could you use just the "Hot" and "Neutral" from shore and establish
"Protective ground" within your vessel? This can be very risky. You
must know what you are doing and therefore I cannot and will not
recommend it. In fact all shore power wiring is dangerous around
boats. If you do not feel competent in this area, please hire a
qualified electrician to help you. I have known people who were
electrocuted for swimming near a boat at dock that had severe
electrical faults. Please be careful. Have any doubts? Place one
voltmeter lead into the water near your vessel and the other lead
on the dock. If you can measure anything, you have a problem to
correct.
You might want to use a GFI (Ground Fault Interrupter) type circuit
breaker for your vessel's shore power mains breaker. This would trip
and disconnect power should it detect current flowing in the "Protective
ground". Remember, the cause could be from a faulty dock box down the
way, or even a neighbor's vessel. Should the GFI breaker detect current
flowing through your vessel's ground, it would disconnect all circuits
to your boat, protecting your boat from your's or neighbor's problems.
In any event, you can measure these problems by measuring voltage
drop between "ground" points, but be careful! Shore power is very
dangerous around water. Maybe you should leave this to a qualified
electrician. Just be forewarned, shore power down island is much
different than back home. You can find some very strange things!
Bonding is an attempt to bring all the vessel's submerged metallic
objects to the same voltage potential, and thereby reduce electrolytic
action between the parts when electrons leave into the water. There
are three common methods, series connection, common point, and copper
sheeting.
Series connection bonding is just what its name implies (please
refer to bonding examples in the drawings). Think of a rudder post
connected (by a wire) to the shaft strut. The shaft strut connected
to a thru-hull, connected to the battery, connected to the engine,
connected to a couple more thru-hulls, and finally to the head stay.
The wires are short and few, but a large voltage difference between
the rudder post and forestay can exist due to the number of connections.
This is considered poor bonding practice and provides little
protection. In many cases it may even be more harmful than no
bonding at all. It is the common technique of older Taiwan made
boats. If you have this type, then I suggest you change it
to common point method.
Common point bonding has one point that all the wires from metallic
fittings, one wire per fitting, come to and is attached via one wire
to the engine at the same point the battery negative cable is attached.
Should current flow in any one object, it will not affect the others
like the series connections will. You may find you have something
like this, but a couple objects are tied in series, or the common
point is not tied to the engine in the correct point. You can
easily correct those errors. This method provides good bonding
and is more than adequate for almost all boats. Any electrolysis
problem can be easily offset with a sacrificial zinc anode, i.e.
shaft zinc, or other zincs. This is common technique in U.S. built
boats.
Copper sheeting, about 6" wide provides a very low resistance between
any two points. The sheet is laid along the length of the hull and
very short pieces of wire connect objects to the sheet. The sheet
in turn is ideally connected to the engine at the same point the
battery negative cable is attached. Although it looks more like a
series connection, the inherently low resistance of the sheet provides
the lowest possible voltage drop any where in the circuit. Some
variations use copper screening which also makes a very effective
ground plane for HAM radios. The drawback is that a little slat water
on the copper sheet, will cause corrosion and possible electrical
breaks in the sheet where the sheet is completely eroded away. If
you have this type, make sure it stays dry. You can repair breaks
by soldering in overlapping pieces. It is very difficult to make
this type of bonding system after the boat is built. Keep all sheet
out of the bilge. You can run it under the floorboards along the
centerline.
By connecting your bonding system to your sacrificial zinc anodes,
you can protect those metal objects from electrolysis. I will talk
more about electrolysis and its causes in Part 6.
My vessel uses the common point method. It works well as long as I
keep the connections to the objects clean and tight. Remember,
CONNECTIONS! Keep 'em clean and tight!
What are the differences between alternator ground, protective
ground, neutral conductor, and bonding? What are the similarities?
Proper uses? They are similar in that they all try to establish a
stable voltage reference point within each system. They are different
because they have different functions. Both the Alternator ground
and neutral conductors carry the load current for their respective
loads. The Bonding ground is to prevent current flow by eliminating
possible voltage potential difference between objects. The effectiveness
of any of these grounds be measured and simple improvements made to
decrease charge time, add safety, and reduce electrolysis.
Submissions:
If you have a specific problem you wish to have addressed, please
send it in. Include your vessel type and size, what area you sail in,
as well as any pertinent information to the problem.
To obtain related graphics for all parts, or submit comments, send
mailto:cam...@unix.infoserve.net
End "MARINE ELECTRICAL SYSTEMS SEMINAR, PART 2"
Learn about Batteries in Part 3