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Old June 18th 06, 10:02 PM posted to rec.boats.electronics
Russell
 
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Default Isolation Transformer and DC corrosion

Since my post a few days ago, spoke to our marine electrician and the
on-staff electrical expert retained by the Harbor office. We are going
to have to install an isolation transformer in our dock box. This will
cost about $1,000 after parts, labor and some mods to the box. All 90
boats in our harbor that got the notices have to do this, move, or
unplug or disconnect the AC ground from the DC, not a good option.
So, now I see the West Advisor says that apparently solves the marina's
issue with the AC, but unless we separate all the underwater stuff,
like the through hulls, we still are subject to DC corrosion. Can this
be true? What is the real solution to the AC, the DC, the safety and
the corrosion problem? Is there one? We are one of 90 modest boats from
about 28-48 feet, mostly 1970's through 1990's vintage. We all have to
get these transformers now, but the issue is what else do we need to do
once we are on the transformer?


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Old June 18th 06, 10:48 PM posted to rec.boats.electronics
Glenn Ashmore
 
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Default Isolation Transformer and DC corrosion

If you have 90 boats in the marina with the same problem then the problem is
with the marina and not the boats. The marina operator is just trying to
pawn it off on the boat owners. Trusting what the "electrician" say doesn't
cut it because it is very likely that he caused the problem in the first
place. I would get everyone together and chip in maybe $50 each and hire a
real EE to figure out what the problem is and force the marina operator to
fix it. $4K for a couple of days investigation by someone who knows what he
is doing is certainly better than covering the marina operator's ass by
spending over $100K to cover up the symptoms.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Russell" wrote in message
oups.com...
Since my post a few days ago, spoke to our marine electrician and the
on-staff electrical expert retained by the Harbor office. We are going
to have to install an isolation transformer in our dock box. This will
cost about $1,000 after parts, labor and some mods to the box. All 90
boats in our harbor that got the notices have to do this, move, or
unplug or disconnect the AC ground from the DC, not a good option.
So, now I see the West Advisor says that apparently solves the marina's
issue with the AC, but unless we separate all the underwater stuff,
like the through hulls, we still are subject to DC corrosion. Can this
be true? What is the real solution to the AC, the DC, the safety and
the corrosion problem? Is there one? We are one of 90 modest boats from
about 28-48 feet, mostly 1970's through 1990's vintage. We all have to
get these transformers now, but the issue is what else do we need to do
once we are on the transformer?



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Old June 18th 06, 11:05 PM posted to rec.boats.electronics
chuck
 
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Default Isolation Transformer and DC corrosion

Russell wrote:
Since my post a few days ago, spoke to our marine electrician and the
on-staff electrical expert retained by the Harbor office. We are going
to have to install an isolation transformer in our dock box. This will
cost about $1,000 after parts, labor and some mods to the box. All 90
boats in our harbor that got the notices have to do this, move, or
unplug or disconnect the AC ground from the DC, not a good option.
So, now I see the West Advisor says that apparently solves the marina's
issue with the AC, but unless we separate all the underwater stuff,
like the through hulls, we still are subject to DC corrosion. Can this
be true? What is the real solution to the AC, the DC, the safety and
the corrosion problem? Is there one? We are one of 90 modest boats from
about 28-48 feet, mostly 1970's through 1990's vintage. We all have to
get these transformers now, but the issue is what else do we need to do
once we are on the transformer?


Well, the way this has happened concerns
me, as I said before. That you are
required to purchase the transformer
makes the situation even worse (except
for whoever is making a $90,000 sale). I
know of no precedent for an action of
this sort by a marina.

It is really too bad, because it is
fairly easy for an unskilled technician
to determine which boat(s) are causing
the problem.

Regardless, the transformer will solve
the corrosion problem ONLY if the
secondary hot and neutral are connected
to nothing on land. No grounding on land
whatever. You then will use the neutral
wire onboard as both neutral and ground.

The corrosion problem I'm referring to
is one in which an unprotected vessel
near yours obtains protection from your
zinc using the AC grounding conductor as
the return path. There are obviously
other corrosion problems, some quite
serious, but the isolation transformer
will do nothing to protect against those.

You will still need a zinc to protect
underwater props, etc., but that is
almost always under your complete
control. Except in very unusual
circumstances, if you install proper
sized zincs and check them from time to
time, you should have no further
corrosion problems. A technician can
even show you how to make simple
measurements to check on whether your
protection system is working.

To summarize: yes the transformer will
completely eliminate what it appears is
causing your corrosion problem based on
what you have described. I don't believe
the isolation transformer will introduce
any new problems at all, other than the
cost.

Hope this helps, Russell.

Good luck.

Chuck

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Old June 18th 06, 11:07 PM posted to rec.boats.electronics
chuck
 
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Default Isolation Transformer and DC corrosion

Glenn Ashmore wrote:
If you have 90 boats in the marina with the same problem then the problem is
with the marina and not the boats. The marina operator is just trying to
pawn it off on the boat owners. Trusting what the "electrician" say doesn't
cut it because it is very likely that he caused the problem in the first
place. I would get everyone together and chip in maybe $50 each and hire a
real EE to figure out what the problem is and force the marina operator to
fix it. $4K for a couple of days investigation by someone who knows what he
is doing is certainly better than covering the marina operator's ass by
spending over $100K to cover up the symptoms.


I second Glenn's suggestion!

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Old June 19th 06, 01:03 AM posted to rec.boats.electronics
David&Joan
 
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Default Isolation Transformer and DC corrosion

Whatever you do, don't install the isolation transformer at the dock box,
install it in your boat. That way you can easily take it with you. And BTW a
30 amp Charles River isolation transformer is less than $500 bucks and will
take less than an hour to install it on your boat.

David




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Old June 19th 06, 02:35 AM posted to rec.boats.electronics
Glenn Ashmore
 
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Default Isolation Transformer and DC corrosion

Definitely mount it on the boat. Once you make a place for it to mount
wiring it up is simple but I wish I could find a Charles transformer for
less than $500. I need two and the best price I have found is $670 each.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"David&Joan" wrote in message
news:[email protected]
Whatever you do, don't install the isolation transformer at the dock box,
install it in your boat. That way you can easily take it with you. And BTW
a 30 amp Charles River isolation transformer is less than $500 bucks and
will take less than an hour to install it on your boat.

David



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Old June 19th 06, 03:00 AM posted to rec.boats.electronics
Larry
 
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Default Isolation Transformer and DC corrosion

"Russell" wrote in news:1150664559.195111.128480
@h76g2000cwa.googlegroups.com:

Since my post a few days ago, spoke to our marine electrician and the
on-staff electrical expert retained by the Harbor office. We are going
to have to install an isolation transformer in our dock box. This will
cost about $1,000 after parts, labor and some mods to the box. All 90
boats in our harbor that got the notices have to do this, move, or
unplug or disconnect the AC ground from the DC, not a good option.
So, now I see the West Advisor says that apparently solves the marina's
issue with the AC, but unless we separate all the underwater stuff,
like the through hulls, we still are subject to DC corrosion. Can this
be true? What is the real solution to the AC, the DC, the safety and
the corrosion problem? Is there one? We are one of 90 modest boats from
about 28-48 feet, mostly 1970's through 1990's vintage. We all have to
get these transformers now, but the issue is what else do we need to do
once we are on the transformer?



As long as the AC ground on the dock is connected to the DC ground, and
therefore all the underwater metal parts of the boat, the electrolysis
problems caused by your boat being connected to the earth and all the
other boats so connected WILL CONTINUE UNABATED, isolation transformers
or no isolation transformers! It's a BATTERY made up of your metal
parts, the seawater as electrolyte and the marina metal parts, including
the bottom of the harbor the marina is grounded to! You have, by
shorting your plate of the battery to the marina plate of the battery,
SHORTED OUT THE ELECTROLYSIS BATTERY and its plate is going to be EATEN
in the process. AC power is not required to accomplish this, only
CHEMISTRY, basic battery chemistry.

Now, the secondary winding of the isolation transformer HAS NO GROUND
WHATSOEVER, if it is an isolation transformer it isolates its AC power
from GROUND. So, you may touch ANY grounded anything, including the AC
power ground wire of the power company itself, from EITHER side of the AC
output winding of the isolation transformer and you WON'T GET SHOCKED!
That's why we call it an ISOLATION transformer....it isolates the AC
power going to the boat from GROUND.

Once the AC power supply to the boat has no ground connection,
whatsoever, you can fully disconnect the boat from shore ground,
altogether, and noone will get a shock UNLESS THEY CONNECT THEMSELVES
STRAIGHT ACROSS THE TWO OUTPUT WIRES OF THE ISOLATION TRANSFORMER WHERE
THE POWER HAPPENS. There are NO other circuits for current to flow
through!

The only connection from the primary side to the secondary side of an
isolation transformer is MAGNETISM IN THE CORE. There are special
insulating tapes put between the core of the transformer and the windings
to PREVENT any path between them.

Geez....this ISN'T ROCKET SCIENCE! Disconnect the damned shore ground
from the boat and install the isolation transformer with no secondary
ground and it'll be JUST FINE FOR ALL!

Once the isolation transformer is between the boat and the power company,
the boat only needs TWO WIRES!..the ones to the secondary 120VAC winding!

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Old June 19th 06, 03:13 AM posted to rec.boats.electronics
Larry
 
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Default Isolation Transformer and DC corrosion

"Glenn Ashmore" wrote in news:tbnlg.112499$Ce1.112216
@dukeread01:

Definitely mount it on the boat. Once you make a place for it to mount
wiring it up is simple but I wish I could find a Charles transformer

for
less than $500. I need two and the best price I have found is $670

each.



Hmm....50A service at 120VAC = 6 KVA.

http://www.charlesindustries.com/main/ma_iso_bost.html
16" x 15" x 12" and weighs 155 lbs....about as much as one passenger.

Can't put it in the bilge where it'll rot in the wet, but try to keep it
as low as possible and near centerline so you don't lean over too far.

Here....justification!:

http://www.charlesindustries.com/main/ma_iso_bost.html

"The Isolation Transformer
The ABYC defines an Isolation Transformer as a
transformer installed in the shore power supply circuit on a
boat to electrically isolate all AC system conductors, including
the AC green grounding conductor on the boat from the
AC system conductors of the shore power supply.
If we are bringing AC shore power aboard to an
electrical panel on a boat, a marine grade Isolation
Transformer should always be used in the shore power
circuit where it comes aboard, and before it reaches the
AC distribution panel or any other device aboard.
The AC shore power current passes through the
transformer's primary windings only, and induces a
current in the secondary windings, which supply the
boat. Primary and secondary windings are insulated
from each other, and a ground fault on the shore side
will not involve our boat.
At its simplest form, a transformer consists of two
coils of wire in close proximity but electrically isolated
from each other, usually wrapped around a common
metal core to contain the magnetic fields produced. If an
alternating current is applied to one of the coils, it will
induce a similar current in the other coil.
Most transformers are designed to step voltage up
or down by having differing numbers of turns in the
two coils. An isolation transformer has the same number
of turns in each coil, serving only to isolate the boat
from the shoreside power, but to give the same voltage.
An Isolation Transformer is used because the shoreside
AC power is referenced to ground. If you are connected
to the earth and you touch the "hot" lead of a normal
shoreside AC service, you will get shocked.
The isolation transformer removes the ground
reference from the ship's service. Neither of the two
sides of an AC circuit on the boat is at ground potential.
Therefore you must contact both sides of the onboard
supply to shock yourself."
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Old June 19th 06, 05:11 AM posted to rec.boats.electronics
 
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Default Isolation Transformer and DC corrosion


Larry wrote:

Once the isolation transformer is between the boat and the power company,
the boat only needs TWO WIRES!..the ones to the secondary 120VAC winding!


The boat still needs 3 wires just like before. One side of the
secondary of the isolation transformer will now go to the BOATS ground
system, including the green ground wire on the boat. The secondary of
the isolation transformer is treated the same way as your generator
system when feeding the boat.

Regards
Gary

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Old June 19th 06, 05:17 AM posted to rec.boats.electronics
 
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Default Isolation Transformer and DC corrosion


Russell wrote:
Since my post a few days ago, spoke to our marine electrician and the
on-staff electrical expert retained by the Harbor office. We are going
to have to install an isolation transformer in our dock box. This will
cost about $1,000 after parts, labor and some mods to the box. All 90
boats in our harbor that got the notices have to do this, move, or
unplug or disconnect the AC ground from the DC, not a good option.
So, now I see the West Advisor says that apparently solves the marina's
issue with the AC, but unless we separate all the underwater stuff,
like the through hulls, we still are subject to DC corrosion. Can this
be true? What is the real solution to the AC, the DC, the safety and
the corrosion problem? Is there one? We are one of 90 modest boats from
about 28-48 feet, mostly 1970's through 1990's vintage. We all have to
get these transformers now, but the issue is what else do we need to do
once we are on the transformer?


You should also be able to install an isolator on your boat, if it does
not already have one, and be in compliance of isolating the ground to
electrolysis.

If an isolator will not function properly in the marina then there is a
problem with the marinas wiring, which sounds highly suspect to start
with.

Ask for the details of how the hired electrician has determined that
your boat is causing problems and let us know what he says. What kind
of measurements did he do?

Regards
Gary



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