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Old 18-07-2005, 10:19   #1
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Alternator and Starter Isolation

Hi our starter motor died today and am replacing and upgrading the alternator at the same time. The boat is steel and therefore to my knowlege these should not be grounded as the boat should be running a floating ground system - ie. everything should be isolated from the hull. Does anyone have any brillient ideas of how to achieve this? It was previously not isolated.

Cheers

Southernman - now in Tonga.
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Old 18-07-2005, 13:18   #2
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The “short” (incomplete) answer to your question:
All (new ?) engine accessories should be Two-Wire (“Isolated Ground”) type, as opposed to “Automotive” 1-Wire Case Ground type. These will include the Starter, Alternator, Gauge Senders, etc.

BTW: I find the commonly used term “Isolated Ground” to be confusing when used to describe the "DC Negative Return conductor".
Although the DC Negative may be "Grounded" , it is not a "Groundiing" Cobductor.

Perhaps you could pose more specific questions after reviewing the following references:

ABYC Standards - Electrical AC & DC: http://www.cmsquick.com/tech_abyc_E.html
including “E-9" DC Systems: http://www.cmsquick.com/tech_abyc_E1.html

From Michael Kasten @ www.kastenmarine.com
“Corrosion, Zincs, & Bonding” http://www.kastenmarine.com/mbqCref.pdf
“Corrosion Prevention For Metal Boats” http://www.kastenmarine.com/corrosion.htm
“Metal Boats For Blue Water” http://www.kastenmarine.com/metalboats.htm
“Lightning & Boats“ http://www.kastenmarine.com/Lightning.htm

Tips on Electrical System Use and Maintenance ~ by David Pascoe
http://www.yachtsurvey.com/ElectricalSystems.htm

“Marine Grounding Systems” from West Marine West Advisors:
http://www.sailmail.com/grounds.htm

From Kevin Hughes @ ‘Sailnet’
“Understanding Grounding and Bonding”
http://www.sailnet.com/collections/a...eid=hughes0001

“Understanding Electrolysis”
http://www.sailnet.com/collections/a...eid=hughes0004

From my posting on another forum:

GROUNDING vs GROUNDED:

There are four main functions accomplished (on a boat) through GROUNDING:
1. Safety - prevent shock hazzard (AC green gnd wire)
2. Bonding - Interconnection of various items, often toprevent corrosion (tie all immersed metals together)
3. Lightning & Static Amelioration - provide a preferred path to ground for lightning.
4. Counterpoise - provide an RF ground, or zero reference for electronics.
None of these (4) GroundING wires are current-carrying, under NORMAL circumstances.
All of these Safety or Bonding ground cables are connected directly to the Main Ground Bus.

There are two main GROUNDED current-carrying conductors:
5. AC Neutral (White)
6. DC Negative Return (Yellow or Black)
Both the AC Neutral and the DC (negative) Return are ultimately connected to ground (hence groundED) , but are NOT GroundING wires.
The AC Neutral is connected to the (optional) Galvanic Isolator thence to the AC Neutral bus (at AC Panel), and finally the Main Ground Bus.,
The DC Negative Return is connected to the DC Negative Bus (at DC Panel), thence the Battery Negative Post, and finally to the Main Ground Bus.

The Main Ground Bus may be the Engine Block, or (preferably) a dedicated grounding terminal (bus or block) which is connected to an external ground plate.

To prevent confusion, I prefer to refer to groundED (current-carrying) conductors (numbers 5 & 6) by the term(s): AC “Neutral”, or DC “Negative” (return), and to the groundING cables as “Safety” or “Bonding” (RF Counterpoise, Lightning, or Corrosion) grounds.

See ABYC Section(s):
E-8 Alternating Current (AC) Systems
E-9 Direct Current (DC) Systems (Figures 15, 16 etc)
E-4 Lightning Protection


To bond or not?
http://cruisersforum.com/showthread....hlight=bonding
Lightning Protection

HTH,
Gord May
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Old 21-07-2005, 09:30   #3
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steel boat grounding

thanks for your reply GordMay. The interesting thing is that on a steel boat you want to avoid grounding to the hull hence in most new boats I see the whole electrical system is isolated from the boat. In most new applications in New Zealand, the motor is isolated from the hull using ceramic mounts and the prop shaft is also isolated using nylon type assemblies. Now my yacht has an exisiting engine installation that does not have isolated mounts or prop shaft. So my theory was to isolate the electrical connections to the engine hence my thinking of isolating the alternator and starter motor.

Am I right or wrong?
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Old 21-07-2005, 10:32   #4
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Seeing as the USA has a completly different electrical system to us, I explain in a Kiwi way.
The floating earth system, means yes, the negatives of Alternator and Starter and everything else, only ever meet back at the battery negative terminal post. I like to think of the system like this. It is a three wire system, just like our NZ MEN single phase AC. In our AC system, we have Phase(red/brown) and Neutral(black/blue) carying the hot stuff, but the Neutral is tied to Earth(green/green-yellow)back at the switchboard. The Earth, even though it is the same potential as the neutral, is on a seperate conductor and is used as the safety line.
With the floating earth principle on a boat, the Negative and positive are the hot lines and a bonding wire ties everything and anything metal together. That's if you follow the Bond everything principle. The bonding cable which is the earth, is still tied to the negative feed back at the battery negative post. The idea is that any/all potential stray current flows through one path only, thus sunk to "ground" and not possibly multiple paths, which would result in currents flowing. Err, that last part doesn't sound right, but I am tired, it's late, you get the jist, I'm off to bed.
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Old 21-07-2005, 11:23   #5
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southernman:

Yes, you are right.
Engine Isolation will require that all electrical be wired with two (2) wires (Positive and Negative).
This may require that you change out your starter, alternator, and all gauge senders to insulated/isolated two-wire type. Most engines are wired as “case ground” (Automitive style) systems, where the engine block is utilized as a common negative.

Gord
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Old 21-07-2005, 20:53   #6
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Living with a non-isolated engine

Gord and Wheels came through well on this one! There is one HUGE concept to grasp regardless of whether or not your engine (or anything else) is isolated.

Assuming that you have (or will have) an isolation transformer to remove any ac concerns (excepting fields external to your hull) you need to visualize all of your electrics in terms of loop currents.

Any time a source delivers current visualize the exact paths taken as the current passes through the conductors, through a load, through other conductors and back to the source. If you are fortunate enought to wire your vessel such that there is one and only one connection between the hull and all onboard electrical circuits then you will not have to be concerned about "ground loops" or "power loops" which are electrical paths which are shared between sources and/or loads that can cause differences in potential in the hull. More on this later, if you prefer.

I STRONGLY recommend that you buy a good quality digital volt-meter, such as a FLUKE (there are many good models). IN ADDITION buy a silver-silver chloride half cell for reference in measuring ANY and ALL places around the hull which might be susceptible to corrosion. One good model is: Stelth3 Model SRE-011-SPB and sell for about $200 US. See http://ns2.bhsg.net/farwest/fwst/refelect/borin03.htm

You drop the reference half-cell over the side (attached to an insulated wire, of course) and measure with the DVM voltages between the reference cell wire and points around the hull, including the engine, shaft, rudder post, etc. These readings remove all doubt as to whether or not these points are "protected" by your zincs.

Now, back to your original engine question. Even if you have isolated all of the engine electrics you still don't have isolated salt water cooling, do you? No one brings that fact up and currents CAN and DO pass from outside the hull through the engine to any ground loops that might exist via the cooling system. Consider this. You ought to be able to live with your existing engine electrics if you confine the engine electrical system to the block not allowing any connections to be made to your house dc electrical system other than one and only one connection to the engine starter negative attachment point. This is easiest to do if you can mount a house system alternator having isolated positive and negative terminals...easy to get with the large frame 165A-200A alternators. That leaves the stock alternator to only deal with the engine electrics and start battery. You might consider adding a discrete #4 AWG wire between the engine alternator frame and that starter negative attachment point on the block (necessarily on or very near the starter). This way you do not rely on the engine block to carry the alternator start battery charge current. The current will mostly preferentially pass through that discrete wire.

Does this help?
Regards,
Rick
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Old 22-07-2005, 12:27   #7
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Rick advises:
... “You drop the reference half-cell over the side (attached to an insulated wire, of course) and measure with the DVM voltages between the reference cell wire and points around the hull, including the engine, shaft, rudder post, etc. These readings remove all doubt as to whether or not these points are "protected" by your zincs ...”

Q: Do you have a list of appropriate millivolt readings for the various metals?

Gord
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Old 22-07-2005, 22:37   #8
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Reference half-cell readings

Here's what readings to expect:


Metal “Free” Protected Overprotected

Al 650 900 1050

Steel 550 800 1000

Bronze 300 550 800

Above readings in NEGATIVE milli-Volts relative to a silver-silver chloride half-cell reference. The "free" values are what you will get with no zinc protection present.

If all of your underwater exposed metals are bonded in the vessel then your readings should ALL be the same and be at least 200 mV greater than the least noble metal in your system. For example, if you have a fiberglass boat with bronze thru-hull fittings, a bronze prop and a stainless-steel shaft then the least noble metal is the steel and with proper zincs you should read at least -800 mV. Don't forget to bond and read your bronze raw water strainer which is "in circuit" with the sea water zinc-bonding system. Don't forget to bond bronze depth sounder transducers.

DO use a bonded shaft brush on your prop shaft. Do not think that just because your engine block is bonded that the shaft is bonded without a brush because internal oil films in the transmission bearings will prevent equal voltage readings
between the block and the shaft.

With aluminim you don't want to see readings at or above 1050 mV because the aluminum may suffer alkali corrosion from too much zinc ionic current. In addition, your anti-fouling paint will begin to suffer as well.

These measurements can show you just how much zinc to use in your bonding system. You can begin with no zinc and drop a zinc over the side (attached to a wire connected to your bonding system) of the size to use on your prop shaft, for exampe. In this case coat the surface which would normally contact the shaft with grease so that the test is representative of the actual surface area that the zinc will present to the water. Note the "protection" potential increase over that of the previous "free" reading. If you reach the protected value then that is the surface area of zinc that you need. Add more zincs if needed to reach a protected reading. Beyond that more zinc surface area will drive the readings towards the "overprotected" values. NOW you can imagine that if you want long lasting zinc you need increased THICKNESS of the existing zinc surface area and NOT more zincs added.

Note that the reference half-cell should be placed approximately at a depth and location somewhere where you are going to have the zincs mounted (within, say 6 feet or so) to obtain a measurement unaffected by metals away from the boat.

Make sense?
Regards,
Rick
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Old 23-07-2005, 01:53   #9
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Rick, while we are on the subject of isolation, just what exactly is inside a Galvanic isolator? I am presuming they are electronic, not an isolating transformer, correct?? But I also presume it isn't a simple diode either.
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Old 23-07-2005, 12:05   #10
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Galvanic Isolators

A Galvanic Isolator is a device installed in series with the (AC) grounding (green) conductor of the shore power cable, intended to block low voltage DC galvanic current flow, but permit the passage of alternating current (AC) normally associated with the (AC) grounding (green) conductor.

Typical Galvanic Isolators (small & inexpensive) are NOT Isolating Transformers (big/heavy & expensive). The common Isolator is a pair of High Power Diodes and a Capacitor installed in the AC Shore Power Ground Conductor.

In it’s simplest form, a Galvanic Isolator is 2 Diodes, Parallel wired in opposite polarities (back to back). Provides about 0.6 volts isolation between the AC Shore Ground and the boat's Ground Bus.
Better Isolators might have 4 diodes, 2 opposites pairs in series. Provides about 1.2 volts isolation between the AC Shore Ground and the boat's Ground Bus.
A capacitor is often added to improve AC conduction.
The new ABYC standards require a “Status Monitor” feature, requiring additional circuitry.

See also:
‘Galvanic Isolator Explained’:
http://www.yandina.com/galvanicIsolator.htm

‘Galvanic Isolators: Don't Plug-in Without One’: http://www.boatus.com/seaworthy/galvanic/default.asp

Isolator Installation Instructions (c/w Digrams):
http://www.yandina.com/acrobats/GalvOwnManual.pdf

TESTING A GALVANIC ISOLATOR:
Disconnect the shore power cable, and use a quality multi-meter having the diode test function.
Test the Galvanic Isolator in both directions.
Isolators with Capacitors should be shorted prior between test readings (to discharge the capacitor).
Each reading should be between approximately* 0.7 and 1.4 volts, with a difference between readings of less then 0.075 volts*.
*This reading is very dependent on the type Isolator and the multi-meter used. Refer to the Isolator Manufacturer’s instructions for readings specific to their product.
A lower or higher reading generally indicates the isolator has failed.

HTH,
Gord May
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Old 23-07-2005, 14:03   #11
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Corrosion Testing

I’ve noticed that different authorities recommend slightly differing millivolt potentials to protect immersed metals from corrosion.
ie: ”Yacht Corrosion Consultants”, Ca. recommends between 225 - 250mV, “Corrosion Labratories”, Au. recommends 200 mV
Note: A MilliVolt, mV = 0.001 Volts, or one-thousandth of a volt.

The recommendations generally range between 200 to 300 millivolts ~ Rick advises 250mV, which seems (to me) a good compromise.

Ideally (in a fully “Bonded” boat), all fittings should measure exactly the same voltage; but differentials of between 30 - 50mV are often deemed acceptable.

These recommendations are for Salt Water only. Fresh Water applications usually require Higher Voltages.

When a newly installed Zinc Anode begins to erode, the surface becomes pitted, creating a larger surface Area. This generates a slightly Increased voltage potential, which may result in a temporary “Overprotection” (causing accelerated Anode depletion, amphoteric attack on Aluminum, & Wood deterioration)

As the Zinc continues to erode, it’s Mass is decreased, generating a Decreased voltage, which results in “Underprotection”, and rapid corrosion of All immersed Metals. Replace Sacrificial Anodes immediately.

Newly installed Zincs initially generate some local hydrogen gas, and require about 24 hours to “stabilize”. Perhaps someone more expert than I can explain the chemistry (Rick?).
In any case, it’s often recommended that you wait 24 hours (or so) after installing new zincs. before testing.
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Old 23-07-2005, 19:43   #12
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Stabilized reference cell readings

Gord brings up a good point. When you first immerse either a zinc or a reference half-cell the readings will change and settle out with a varying reading with a stable average (assuming an adjacent boat or field near your boat is not affecting the reading over time). One phenomenon is called polarization potential which happens when any two dissimilar metals are placed into an electrolyte solution. It takes awhile for the positive free zinc ions to migrate through the salt water to cathodic metals which they are supposed to protect. As those ions contact and adhere to the cathodes a local capacitive effect takes place which affects the steady-state reading. In addition, during the "plating process" the half-cell potential at the zinc anode slightly drops due to the ionic flow which is a current not formed by electrons. The electrons flow through the bonding wires and back to the zinc.

Twenty or so hours is a good time for observing the steady-state protection values yet twenty minutes gives you a good idea. If you are chasing particular galvanic corrosion problems you definitely need to check at the 24 hour point to make sure of your protection potential of around 250mV. One vexing galvanic problem often found is with stainless or aluminum stern platform fittings which ride just in and out of the water. They are often not bonded well or are connected to a battery negative distribution point in the electrical system by mistake (or idnorance). and are often difficult to protect properly.

Visualize that the zinc ion migration will be affected by currents around the boat. In fact, most often you have essentially no protection when underway. Problems do not often occur due to this because even blue water sailers spend an aggrigate average time not moving over the course of a year.

Galvanic isolators need to be constructed with two diode pairs "back-to-back" which gives a diode "test" voltage drop reading of about 1.2V or so (depending upon the diode test current of your DVM as Gord points out as well as the die size of the diodes). The two diodes in series are necessary because with steel or aluminum in the water with protective zincs you exceed the "turn-on" value of one diode drop in a galvanic isolator. Now here's where you need to keep visualizing the big picture where somewhere back on shore is a ground rod connected to the "green" wire of your shore power. If you are attempting to protect a metal with a resulting potential around 600mV or more you will turn on the galvanic isolator slightly and reduce your ability to protect....you lose some galvanic isolation with good grounds (earths for Wheels).

You can make up your own galvanic isolator using "hockey puck" style diode bridge modules as long as they are rated at a continuous rms current rating greater than the breaker rating of your shore power. The reverse voltage rating should be 600V, in my opinion. You have to wire across the diode bridge to make it work for this application. When it comes to placing non-polarized capacitance across the isolator I have a difference of opinion with the ABYC recommendations. ABYC is concerned about developing ANY ac acrosss the isolator. I don't believe that anyone will get harmed with two Volts rms relative to the green wire should a short occur between the "hot" wire and the green wire before the shore breaker blows and I would rather have some ac galvanic isolation as well as dc.

Keep in mind that many appliances, like microwave ovens, reefers, and radios, have what are called "X" and "Y" filter capacitors between the hot and neutral and the green wire and between the hot and neutral. These capacitors cause a continuous small leakage ac current to the green wire all of the time and I prefer to not have that current pass throught the bonding system which it can with the ABYC recommended galvainc isolator configurations. Something to think about.

Regards,
Rick
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Old 25-07-2005, 02:04   #13
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steel boats and such...

As I recall, if my memory serves me correctly, on a steel boat the preferred method is to install the gear so that it is electrically isolated from the hull but connected together with a ground strap and then this strap is connected to the engine at one point.

Interesting for me to reply in this thread because my old steel sailboat Sara was 2 slips away from Gord on the Isle of Venice in Ft. Lauderdale many years ago!!!

As always, Gord, nice to read your very informative posts on the various BB’s.

p.s. – Maggie recently gave me Tim’s email address, we exchanged phone numbers and had a nice chat. He’s doing well for himself.
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Old 09-12-2010, 00:21   #14
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how to isolate case ground parts(alternator/starter..)

Quote:
Originally Posted by GordMay View Post
southernman:

Yes, you are right.
Engine Isolation will require that all electrical be wired with two (2) wires (Positive and Negative).
This may require that you change out your starter, alternator, and all gauge senders to insulated/isolated two-wire type. Most engines are wired as “case ground” (Automitive style) systems, where the engine block is utilized as a common negative.

Gord
I really wonder how to isolate case ground parts(alternator/starter..) in marine engine
I need to get information or sites substancially.
would you give me tips?
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Old 09-12-2010, 03:15   #15
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Southernman, in theory you are correct, it should all be above earth. In reality I doubt if it matters that much.
Our yacht is steel, and for 25 yrs we have had a starter and alternator that are earthed to the engine block, which in turn is connected to the battery negative with a heavy cable. We have never had a trace of electrolysis anywhere. Our anodes last for up to 5 years.
When the boat is unattended, the battery is disconnected at both poles.
When tested with a silver chloride reference electrode, it reads bang in the middle of the desirable zone.
If you are looking for a reference electrode, google "Rust Finder" which is an Australian made one at a reasonable price. I have found it to be an excellent product, and comes with good instructions for use. ( I have no connection with them at all .Pun intended)
Regards, Richard.
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