Galvanic ground isolation - SailNet Community
 
LinkBack Thread Tools
post #1 of 10 Old 12-20-2009 Thread Starter
2nd mate
 
Join Date: Aug 2009
Location: Belgium
Posts: 42
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Galvanic ground isolation

Hello,

I'm a student from belgium and I study at the nautical academy (last year now).
My boat is in antwerp and I use it as my student home (or dorm).

I've been reading around about galvanic corrosion trough the grounding cable from the shore power ( 230v 50Hz here).

I would like to stop this possible current flow, but standard galvanic isolators are to expensive for my studentbudget.

Therefore i would like to wire zenerdiodes in between, with a zenervoltage of about 3volts or so.
In this way 2 times (3 zdiodes in serie) in parallel:
The first 3 are installed in the other direction then the last.


z z
/ \ / \
to shore -- z -- z-----to boat
\ / \ /
z z
What do you guys think?
Will this hold if there is a serious power leak?

Last edited by bartvdv; 12-20-2009 at 07:28 AM.
bartvdv is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 10 Old 12-20-2009
Senior Member
 
nickmerc's Avatar
 
Join Date: Nov 2008
Location: O'Fallon, MO
Posts: 563
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
 
The galvanic isolator does more than just stopping stray current through the ground connection on shore power. It also needs to withstand a lightning strike that discharges into the water. And it needs to be safe so you do not get stray currents from your shore power line going into the water. This could be fatal to nearby swimmers. I installed one last winter and mine is a very simple device. It is just two diodes connected in series such that the current flow goes from the boat to the shore power. Since diodes have a small resistance in the "open" direction they still stop the galvanic currents. I believe these diodes have 1.5 ohms each. Two in series is 3 ohms and this is enough to stop the glavanic current while allowing the grounding system to work properly. These diodes are very hefty so they do not get fried the first time a significant current goes to ground.

I spent about $300 USD (with our economy this has to be about 200 euro). Here is a link to the one I used Home | DEI Marine
________
Live Sex

Last edited by nickmerc; 08-18-2011 at 05:39 AM.
nickmerc is offline  
Quote Quick Reply Share with Facebook
post #3 of 10 Old 12-20-2009
Senior Member
 
Join Date: May 2007
Posts: 551
Thanks: 3
Thanked 3 Times in 3 Posts
Rep Power: 9
 
The danger here is that a lightning strike will burn out the diodes leaving you with no ground on the AC system and you wont know it. The of-the-shelf products now have an indicator light that illuminates if the ground circuit is open so that you know that you have a problem. If you can add this feature to your setup you will be safe.
SteveInMD is offline  
Quote Quick Reply Share with Facebook
post #4 of 10 Old 12-20-2009
Senior Member
 
mitiempo's Avatar
 
Join Date: Sep 2008
Location: Victoria B.C. Canada
Posts: 7,487
Thanks: 0
Thanked 94 Times in 85 Posts
Rep Power: 8
   
The November issue of Practical Boat Owner (UK) has an article about building a galvanic isolator for less than 10 pounds. I don't have the details handy as I'm out of town at the moment.

Brian
Living aboard in Victoria Harbour
mitiempo is offline  
Quote Quick Reply Share with Facebook
post #5 of 10 Old 12-21-2009 Thread Starter
2nd mate
 
Join Date: Aug 2009
Location: Belgium
Posts: 42
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
I've just ordered my two diodebridges, as seen in that PBO isue.
Just € 10 !
What a difference with those €200 isolators!!!

Thank you!
bartvdv is offline  
Quote Quick Reply Share with Facebook
post #6 of 10 Old 01-14-2010
Panhandle Sailor
 
dreuge's Avatar
 
Join Date: Sep 2009
Location: Florida
Posts: 88
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
 
Hi,
Can you place a like to where you got these diodes.

Thanks.
dreuge is offline  
Quote Quick Reply Share with Facebook
post #7 of 10 Old 01-15-2010 Thread Starter
2nd mate
 
Join Date: Aug 2009
Location: Belgium
Posts: 42
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Conrad Electronic - Europa's grootste webwinkel in elektronica en techniek

Belgium site....
I bet you're sorry you're not from €urope


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
bartvdv is offline  
Quote Quick Reply Share with Facebook
post #8 of 10 Old 01-30-2010
Senior Member
 
Join Date: Sep 2009
Location: Kingston Washington
Posts: 527
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 6
 
I built my own with zener diodes. It's not a bridge just blocking in each AC direction. Key considerations: Each diode has to be able to handle the full load current of you AC source, that's what a ground is supposed to accomplish. Most electronic supply sources will have these. I doubled up to have back-up. Second you need to mount the dioeds in a manner that has the heat dissapation capability through the studs ahs the load current. I used a number of spaced flat aluminium bars. It's not a hard project and not costly.
One other issue is that you don't know if you have a blown diode unless you check it from time to time. There are multi-meters with a zener diode check function. If the diode's blown you've lost your ground protection.
Waltthesalt is offline  
Quote Quick Reply Share with Facebook
post #9 of 10 Old 01-30-2010
Senior Member
 
Join Date: Sep 2009
Location: Kingston Washington
Posts: 527
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 6
 
My previous comments may have been a bit cryptic. Here's the longer version as best as I recall:
You need 2 high current bridge rectifiers each capable of handling full shore power current. They are square devices with a bolt hole in the center and four spade connector terminals on the back 1 labeled +, one - and two usually labeled AC.
About 30 sq in of aluminium 1/8 inch thick for a heat sink.
Wire to make connections.
Stainess steel bolts and nuts to mount the rectiifers to the aluminium.

You're only ging to use the + and - terminals that are diagonally opposie eachother on the bridge recitfire, so cut off the other two terminals.
Mount the rectifiers on the heat sink with the bolts spacing the recitfiers at lest 4" apart. It helps to put heatsink grease in the cavity when mounting the recitfiers if you have it.
Hook one ground wire end to the + and the other to the - . Hook the second bridge in parallel. That way if one recitfer blows then the other will carry the load
Waltthesalt is offline  
Quote Quick Reply Share with Facebook
post #10 of 10 Old 01-31-2010 Thread Starter
2nd mate
 
Join Date: Aug 2009
Location: Belgium
Posts: 42
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
thats the exact same thing i did :-)


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
bartvdv is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
The Path to Lightning Protection Kathy Barron Gear and Maintenance Articles 0 08-13-2003 08:00 PM
The Path to Lightning Protection Kathy Barron Cruising Articles 0 08-13-2003 08:00 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome