Great discussion. I considered a prop shaft brush to protect the strut, essentially bonding it to the same zinc protecting my shaft & prop but a marine electrician talked me out of it. I installed a rudder style zinc to protect the strut. My 48 volt system is floating & isolated from the prop shaft with a flexible coupling.
My 12 volt house system, 120 AC are grounded to the same keel bolt as my lightening system. It has been suggested by the same electrician to bond my motor/drive drop pan to the same keel bolt. Not necessarily for "grounding" purposes but for protection from a lightening strick. I figure once I do that the 48 volt system will be "grounded" by default. Throw some solar into the mix, the case of the controller gets "grounded" also. Far as "bonding" thru hulls, people are getting away from doing so. My thru hulls are no longer "bonded".
My boat is on a mooring so I'm not plugged into marina shore power. Fact is that's where the majority of stray current issues originate. If I kept my boat in a slip then I would have a galvanic isolator on the ac side..
Funny thing about E-11, nothing in there really addresses electric drives.
Bob
--------------------------------------------
On Fri, 3/2/18, James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:
Subject: Re: [Electric Boats] Re: Electric motor Grounding locations
To: electricboats@yahoogroups.com
Date: Friday, March 2, 2018, 10:26 AM
If you use a shaft brush as your only
ground point on a boat then how is that going to affect your
electronics grounds? I don't think they would like
it.
There is an issue
with a lot of conversions pulling out the diesel and not
re-establishing the ground point and the whole boat grounds
become floating. That needs a solution.
But you can also ground right to the
body of the motor and make sure that if there is a flexible
non-conductive coupling in place that you put a wire between
the two faces of the coupling so you have continuity between
the motor and the shaft.
The issue with this is the ground
point then passes through the final drive bearing, which can
then become seized in a lightning strike.
To find a workable solution you need
to look at the entirety of the boats grounding
system.
The rudder
shaft should be bonded to the boats grounds. There is a
high likelihood the keel bolts may also be bonded to the
boats grounds. So really there should be three places
where the boats grounds touch water on a "normal"
sailboat.
If the
boat is a bonded boat, then all the through hulls are also
bonded and in the water. (My preference is marelon through
hulls unless you need additional grounding for an
SSB)
But my
preference is totally different from all this. And I
welcome any and all criticism to this as I have been
thinking about this a long time, and it would be nice to
have a grounding plan ratified at large by the members of
this group.
The grounding system has multiple
purposes on a boat.
1)
Redundant AC Ground
The boat's ground provide a
redundant AC ground - when there is no isolation
transformer - which I totally disagree with - but it is.
With an isolation
transformer you get rid of the ground loop between the shore
power green wire and the water. This prevents corrosion
in Salt Water and Electric Shock Drowning in Fresh or
Brackish Water. The idea of the boats grounds becoming
a redundant fault carrying grounding system for AC really
troubles me.
The problem with not using an
isolation transformer and making it the redundant AC ground
is you now have a ground loop. The boat is grounded
through the shore power ground and through the boat's
grounds. This causes corrosion problems which can be
mitigated by a galvanic isolator but never really properly
solved by a galvanic isolator - because the diodes are only
capable of stopping low voltage DC and cannot stop higher
potentials. Plus when a Galvanic Isolator Fails, it fails
closed so that AC current is not interrupted. So now
imagine you have an AC fault, and the green wire on your
shore power cord is compromised, then that AC fault is now
bleeding right into the water. If you are in fresh
water, and a swimmer passes between your boat and any other
grounded boat, the swimmer dies. No marks are left on the
swimmers body and the death is often misdiagnosed as
drowning.
Now
lets say your boat with AC ground is perfectly wired by E-11
standards, and another boat has an AC fault - then your
boat becomes the return path for the current from the boat
with a fault, a swimmer passes through the two boats, and
dies.
The only way to
stop this is with an isolation transformer. There
simply is no other way to completely stop the possibility of
Electric Shock Drowning in Fresh or Brackish
Water.
So rule number
one in my book is to install an isolation transformer on any
boat that is going to be navigating fresh
water.
This issue in
salt water is corrosion. And the only way to completely
eliminate corrosion is with an isolation
transformer.
If you
don't have an isolation transformer, and you are
following E-11 precisely, then I recommend that every
circuit on the boat be protected by a GFCI and the whole
boat be protected by an ELCI. Some boats, especially
race boats, do not want the weight of a transformer on
board. On these boats, AC should be limited as much as
possible and each circuit protected to the highest degree
with GFCI.
2) Lightning
Protection:
When a
sailboat gets hit by lightning there should be a low
resistant path to ground for the main strike down the mast.
This is ordinarily a 2 gage conductor from the mast to
the keel bolt or preferably an underwater strike plate.
The strike will also come down all the rigging so every
piece of rigging should also have a side conductor to
transfer lightning to the water. Side conductors can
simply be bolts through the hull. The best protection
is old school chain plates that go down to the water on the
outside of the hull. Modern yacht design doesn't
like this though because it doesn't allow the head sail
to be set in as tight.
If the propeller shaft is bonded
into the ground system of the boat, then it invites a
lightning path which goes through the engine block and
through the final drive bearing. The problem with this is
the engine or its final drive bearing can seize during a
lightning strike. Hence the recommendation is to run a
motor if navigating through lightning.
3)
Bonding System:
The
bonding system is also part of the grounding system. Its
purpose is to make sure that every conductive surface on a
boat is held at the same potential so you can't touch
two conductive objects and get a shock. Since this is
also lightning related, you often see lifelines and rigging
lines connected to the bonding system. I am an avid
supporter of a robust bonding system on a boat.
However I also would rather not have wires everywhere, so I
simply build everything I can in non-conductive PVC boxes
and use Marelon through hulls.
4)
Electrical System grounds. 12 volt DC and if you plan
to ground your 48 volt DC are all hooked together and kept
at the same potential. Sometimes there might be 4 or 5
electrical systems sharing the same ground. One boat I
worked on had 12, 24, 120, 240 and 3 phase 208 all sharing
the same ground. What is important here is that every
electrical system gets tied into the boats grounds at the
same point at one main ground busbar.
5)
Electronics Grounds: Many electronics need to be
grounded to prevent static electricity buildup or to provide
a counterpoise for radio transmission. Electronics
grounds need to be clean without any kind of EMI.
My
preference is to lay one conductor down the stem of the
boat, from bow pulpit to underwater dynaplate at base of
mast, to rudder shaft, which becomes the main ground trunk
to which everything can be grounded or bonded. The
dynaplate should be directly below the mast and the down
conductor cable should be straight without any kinks in it.
On my boat I
did not bond the propeller shaft into the grounding system,
but rather keep it as an independent system. It it is in
an area that you can't readily touch it.. It is
unlikely to get energized so does it really need to be
hooked into ground? If the prop shaft, propeller and zinc
is an independent system, then the zinc only has to protect
the stainless shaft / bronze propeller and not the rest of
the boat and the zinc will last longer. If the boat
gets struck by lightning, there is no direct path to ground
through the motor or final drive bearing. However, if
you choose this route then you need to have an underwater
dynaplate and underwater zinc to protect the underwater
metals of the boat. I welcome your comments and
conversation on whether the prop shaft really needs to be
bonded into the grounds of a boat and if it does - how.
James
Lambden
The Electric Propeller Company
625C East Haley Street,
Santa
Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
On Mar 1, 2018, at
10:21 PM, 'james@deny.org'
james@deny.org
[electricboats] wrote:
E-11
would have all three grounds connected, negative from each
DC bus and AC ground (green wire) would all be connected via
properly sized cables or straps and then connected to the
shaft via the brush. Your boat should already have the AC
and 12 volt systems bonded. That is normally close to the
most negative 12 volt bus. If you don't want to buy the
current ABYC E-11 PDF, you can probably google "ABYC
E-11 pdf" and find an older one some place of the web.
It is pretty easy to read through and will give lots of good
advise.
The above
is if you choose to have a common earth ground. If however
you want to float the traction battery pack (48 volt) then
don't connect that to the brush or the other two. But do
connect the 12volt and AC to the shaft brush. Again the
cable used should be sized to match the largest cable used
to carry current on the pack.
On Feb 27, 2018, at 12:04 PM, Matt mattkaine@hotmail.com
[electricboats] <electricboats@yahoogroups.com>
wrote:
I ordered the shaft brush you recommended. Just so I'm
clear, you are saying the 120AC ground should be isolated
from low voltage DC grounds and I should tie the 48vDC and
12vDC grounds together, then connect that to the Shaft
Brush? I was under the impression
the AC and DC grounds we're supposed to be tied
together, so any stray current goes to earth via the shore
power ground line for safety. I do have a galvanic isolater
on my system just after shore power plug, then ground runs
to AC panel ground bus bar, which
is connected to DC ground bus bar.
Sent from my Huawei Mobile
-------- Original Message --------
Subject: Re: [Electric Boats] Re: Electric motor Grounding
locations
From: "'james@deny.org'
james@deny.org
[electricboats]"
To: electricboats@yahoogroups.com
CC:
For 48 volts and less, I follow the ABYC E-11
recommendations and have a common ground between all
systems. At higher voltages ABYC TE-30 says keep them
separate.
I personally went with a 48 volt system because I
wanted to be able to have a common ground. I don't like
having different potentials between different systems that I
or a swimmer nearby could be a bridge path between.
More important then if you bridge the two DC grounds
together, make sure your old AC system still has earth
ground. Most marine systems used the engine block via the
shaft to ground to earth. If your boat does not have
another path, once you removed the
old engine your entire ground system may be isolated from
earth.
If so a cheap 35 dollar shaft brush will re-earth your
system. See my earth ground bellow:
http://www.deny.org/Escape_the_American_Dream/Project_Pictures/Pages/Work_In_Progress_old.html#19
On Feb 27, 2018, at 10:10 AM, king_of_neworleans <no_reply@yahoogroups.com>
wrote:
My 48v system is not
grounded. General consensus seems to be that this is best.
As for grounding the controller, I think tech support at
Sevcon can provide a better answer on whether it should be
grounded or not. My Kelly controller is not grounded. My
motor
casing and rotor shaft are incidentally grounded, of
course. However phase windings, power supply cables and 48v
bank are all floating. Some owners also use a flex coupling
to isolate the motor shaft and casing from ground as well,
though I don't think it
is necessary.
---In electricboats@yahoogroups.com,
<mattkaine@...> wrote :
So I
just installed a 10kw motor Kit from Trunderstruck EV on my
1976 Islander I-28. I am very happy with the install, works
awesome. I am however not sure on best method for grounding
new power system. So the current set up is this...I have 2x
12v
house batteries with a common ground bus, my 120vAC shore
power connects its ground to same ground bus. Now where I am
not sure...the 48v motor system consists of 8x 6vDC
batteries in series>Power relay>Sevcon Gen4
Controller>motor. Ground bypasses the relay
and goes straight to Sevcon. Should I connect 48v bank to
12v ground bus? Should I run a separate ground from motor
frame to ground bus?
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