Battery cut-off switch - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
 Not a Member? 
  #1  
Old 05-28-2011
Junior Member
 
Join Date: May 2011
Posts: 1
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
SothernDragon is on a distinguished road
Battery cut-off switch

I've bought a used boat that had for 20 years the cut-off batteries switch isolating the ground (negative) batt cables.
Shouldn´t be on the positive cables ?
What´s the problem if I leave it as is ? (If worked 20 years..... )
Thanks in advance for your replies.
Reply With Quote Share with Facebook
  #2  
Old 05-29-2011
mitiempo's Avatar
Senior Member
 
Join Date: Sep 2008
Location: Victoria B.C. Canada
Posts: 6,980
Thanks: 0
Thanked 61 Times in 52 Posts
Rep Power: 7
mitiempo will become famous soon enough mitiempo will become famous soon enough
Normally the switch is in the positive wire as you thought. I would change it, even though it has worked for a long time. But that is just my opinion.

Maybe someone like Maine Sail will add theirs.
__________________
Brian
Living aboard in Victoria Harbour
Reply With Quote Share with Facebook
  #3  
Old 05-29-2011
Junior Member
 
Join Date: Oct 2010
Posts: 18
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
captiantim68 is on a distinguished road
Send a message via Skype™ to captiantim68
you get less of an arc when you disconnect the negative first, basic electricity.

Is it a gas boat?
__________________
Tim & Crew S/V Euroclydon
Stop dreaming and start doing. Its a much better way of life

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #4  
Old 05-29-2011
Senior Member
 
Join Date: Jun 2007
Posts: 2,710
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
SEMIJim will become famous soon enough SEMIJim will become famous soon enough
Quote:
Originally Posted by captiantim68 View Post
you get less of an arc when you disconnect the negative first, basic electricity.
Which bit of basic electricity would that be?

The "disconnect the negative first" rule applies to removing the cables. (Primarily in a car.) If you're loosening the positive cable clamp with a wrench and the wrench hits some other metal object in the engine compartment, it could be welded in place and the resulting high current flow can well result in serious damage. Thus: Disconnect negative first.

Otherwise: Flowing electricity doesn't know the difference: In each case: One side of the connection has positive potential in relation to the other.

To the OP: Without giving it a lot of thought, and w/o having actually seen your wiring, I don't know as it makes any difference. I'd switch it, tho, purely because it's non-standard and unexpected.

Jim
Reply With Quote Share with Facebook
  #5  
Old 05-29-2011
peikenberry's Avatar
Senior Member
 
Join Date: Apr 2000
Location: Seattle/Tacoma
Posts: 188
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 15
peikenberry is on a distinguished road
40 or more years ago it was quite common to find boats (and cars) with positive grounds. In other words everything was reversed. But today polarity is a very important issue. In other words maintaining positive and negative are hooked up correctly. So, now all boats are negative ground and switches and fuses are in the positive wire. I would switch it, but before I did, I would make sure polarity is maintained throughout the system. In other words positive is hooked to positive throughout.

to learn about DC systems see DC Electricity New Boatbuilders Home Page - Everything Boat Building - Basic Electricity DC Page 1
__________________
Ike
My Boat building Web Site

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

My Boating Safety Blog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Dont Tell Me that I can't. Tell me how I can!
Reply With Quote Share with Facebook
  #6  
Old 05-30-2011
Classic30's Avatar
Once known as Hartley18
 
Join Date: Aug 2007
Location: Melbourne, Australia
Posts: 4,404
Thanks: 23
Thanked 30 Times in 30 Posts
Rep Power: 8
Classic30 will become famous soon enough Classic30 will become famous soon enough
Quote:
Originally Posted by peikenberry View Post
40 or more years ago it was quite common to find boats (and cars) with positive grounds. In other words everything was reversed. But today polarity is a very important issue. In other words maintaining positive and negative are hooked up correctly. So, now all boats are negative ground and switches and fuses are in the positive wire. I would switch it, but before I did, I would make sure polarity is maintained throughout the system. In other words positive is hooked to positive throughout.
FWIW, the main reason cars and boats were once wired for "positive grounding" (really "negative switching") and about its only advantage was that, wired in this way, it was possible to use a cute little 12V test-bulb to test for continuity at all points in the circuit up to the point of the final switch, making fault-finding relatively easy in the days before cheap Chinese-made multimeters.

Nowadays, the disadvantages outweight the advantages. If it were me, I'd change it.
__________________
-
"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"

Last edited by Classic30; 05-30-2011 at 01:13 AM.
Reply With Quote Share with Facebook
  #7  
Old 05-30-2011
Senior Member
 
Join Date: Jun 2007
Posts: 2,710
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
SEMIJim will become famous soon enough SEMIJim will become famous soon enough
Quote:
Originally Posted by Hartley18 View Post
FWIW, the main reason cars and boats were once wired for "positive grounding" (really "negative switching") and about its only advantage was that, wired in this way, it was possible to use a cute little 12V test-bulb to test for continuity at all points in the circuit up to the point of the final switch, making fault-finding relatively easy ...
I've only been out of bed for about (looks...) 15-20 minutes, and haven't had any coffee, yet, so maybe I'm missing something Really Obvious: But please explain why positive grounding vs. negative grounding (or "negative switched" vs. "positive switched," as you'd have it) is any easier to troubleshoot with a simple incandescent test lamp

Jim
Reply With Quote Share with Facebook
  #8  
Old 05-30-2011
mitiempo's Avatar
Senior Member
 
Join Date: Sep 2008
Location: Victoria B.C. Canada
Posts: 6,980
Thanks: 0
Thanked 61 Times in 52 Posts
Rep Power: 7
mitiempo will become famous soon enough mitiempo will become famous soon enough
I don't understand the troubleshooting being easier either.
__________________
Brian
Living aboard in Victoria Harbour
Reply With Quote Share with Facebook
  #9  
Old 05-30-2011
Senior Member
 
Join Date: Aug 2006
Location: Arlington, VA
Posts: 1,807
Thanks: 0
Thanked 4 Times in 4 Posts
Rep Power: 9
btrayfors will become famous soon enough btrayfors will become famous soon enough
He's talking about things Down Under. They work differently down there:

Toilets flush the wrong way, rivers run North, you can't see the North Star at night, shrimp is cooked "on the Barbie" (instead of Barbie cooking the shrimp as she does up our way).

And, apparently, electricity acts differently, too.

Give the guy a break :-)

Bill
Reply With Quote Share with Facebook
  #10  
Old 05-30-2011
Classic30's Avatar
Once known as Hartley18
 
Join Date: Aug 2007
Location: Melbourne, Australia
Posts: 4,404
Thanks: 23
Thanked 30 Times in 30 Posts
Rep Power: 8
Classic30 will become famous soon enough Classic30 will become famous soon enough


Quote:
Originally Posted by SEMIJim View Post
I've only been out of bed for about (looks...) 15-20 minutes, and haven't had any coffee, yet, so maybe I'm missing something Really Obvious: But please explain why positive grounding vs. negative grounding (or "negative switched" vs. "positive switched," as you'd have it) is any easier to troubleshoot with a simple incandescent test lamp

Jim
Ok. Assume you are living in an age when multimeters aren't for your average layman. All you have in your test kit is:
(a) a piece of wire with bare ends.
(b) a 12VDC light bulb.

Let us take a mast light for example: It isn't working. Okay. If the switch is in the negative lead, with the switch 'off' you should have +12VDC all the way from the battery, through the light and back to the switch. Test procedure is then:

1. Connect test bulb between +ve & -ve at panel: If it lights up, we have volts.
2. Connect test bulb across switch contacts: If it lights up, the mast bulb and all wiring is good.
3. Use piece of wire across switch contacts: If mast light lights up, switch is faulty.
4. At the top of the mast, connecting your test bulb from either side of the mast light to a known ground (eg. the stays), completing the circuit the test bulb should light. If it only lights one side, the mast bulb is blown; if neither side, the feed wire is open circuit.

With the "positive switched" system we have now, there is no +12VDC available at any point in the system downstream of the switch, so the only way to test the circuit for continuity is to use a multimeter set to "ohms" (effectively a battery and an ampmeter in a box) - or hook a test bulb up to +12VDC and have it light up on everything it touches, working or not... but there is no doubt that this system is safer.

Does that make sense now??


EDIT: The above assumes the system is still negative grounded. Perhaps the confusion (I'm confusing myself here!!) is coming from the idea of changing from negative to positive grounding. IIRC, positive grounding was used to minimise arcing - not to assist with fault-finding.

My bad..
__________________
-
"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"

Last edited by Classic30; 05-30-2011 at 08:36 PM.
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Battery switch Patbarbeau Gear & Maintenance 20 04-22-2012 09:31 PM
battery switch wireing MiVelero Electrical Systems 7 04-11-2010 08:28 PM
Battery switch confusion... advice jg91604 Beneteau 1 02-26-2008 07:03 PM
Battery Switch johar Gear & Maintenance 4 04-08-2003 04:28 PM
Wiring set-up for battery switch. pehrst Gear & Maintenance 6 06-18-2002 05:51 PM


All times are GMT -4. The time now is 09:27 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012