Over Current Protection On Pos Battery Connection - Page 4 - 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 > General Interest > General Discussion (sailing related)
 Not a Member? 


Like Tree5Likes
Reply
 
LinkBack Thread Tools
  #31  
Old 03-04-2012
JSG JSG is offline
Junior Member
 
Join Date: Mar 2012
Posts: 4
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
JSG is on a distinguished road
I have an 87 Hunter 28.5 with 3 batteries. One stands alone and the other 2 are in parallel. I also have the usual battery switch (1, 2, both, off). None of the batteries are fused. I want to protect myself from a dead short and I was thinking about installing a heavy breaker between the starter and the battery switch. My thinking is that way I would be protected no matter which bank I was using.

I have a Yanmar 2GM20F diesel which I figure draws near 80 amps.

Does anyone have any thoughts on this?

Thanks
Reply With Quote Share with Facebook
  #32  
Old 03-04-2012
hellosailor's Avatar
Plausible Deniability
 
Join Date: Apr 2006
Posts: 10,442
Thanks: 1
Thanked 76 Times in 74 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Fuse the batteries AT the battery terminal, not at the starter. Thtsa protects the entrie wire run instead of just most of it.

And FUSE them. A battery can easily arc and weld an ordinary breaker with over 3000Amps in a dead short. The next step up are better breakers, rated +5000 amps, at over $100 each. Fuses win.
Reply With Quote Share with Facebook
  #33  
Old 03-04-2012
JSG JSG is offline
Junior Member
 
Join Date: Mar 2012
Posts: 4
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
JSG is on a distinguished road
I probably did not make myself clear. I was thinking add placing the breaker just at the point where my battery cable leaves the battery switch.
Reply With Quote Share with Facebook
  #34  
Old 03-04-2012
hellosailor's Avatar
Plausible Deniability
 
Join Date: Apr 2006
Posts: 10,442
Thanks: 1
Thanked 76 Times in 74 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
"placing the breaker just at the point where my battery cable leaves the battery switch.
Like "

Still only two things wrong with that:
1-Breaker should be a fuse.
2-At the switch, still leaves some length of cable unprotected and able to start a fire or battery explosion.

Ain't my logic, that's the way insurers and regulators and manufacturers see it. Your way is better than nothing, but it still does not meet current standards. It exceeds 1960's standards but why not go whole hog?
Reply With Quote Share with Facebook
  #35  
Old 03-04-2012
JSG JSG is offline
Junior Member
 
Join Date: Mar 2012
Posts: 4
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
JSG is on a distinguished road
Your point is well taken concerning the use of fuses rather than a breaker and the placement of the fuses.

Thanks for your help, it sounds like a better plan than mine.
Reply With Quote Share with Facebook
  #36  
Old 03-04-2012
JSG JSG is offline
Junior Member
 
Join Date: Mar 2012
Posts: 4
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
JSG is on a distinguished road
Does anyone have any thoughts concerning ANL fuses vs MEGA fuses for fusing a battery?
Reply With Quote Share with Facebook
  #37  
Old 03-04-2012
Senior Member
 
Join Date: Mar 2008
Posts: 885
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
GaryHLucas is on a distinguished road
Re: Over Current Protection On Pos Battery Connection

I can't believe Sailnet just dumped my whole post and I need to type it again!

I usually don't get involved with electrical threads, too many boat electrical experts here already. However I decided this one needed comment. I have an extensive electrical background, growing up in the business with my dad. He was great teacher, and taught me why as well as how. In the early years house wiring was knob & tube and you'd often hear "This house is a fire trap, it still has that old knob and tube wiring! We need to replace it all." Yet nothing could be further from the truth. The conductors were spaced 12" apart, supported by ceramic insulators, with soldered connections, how could any of that short out or start a fire? My younger brother though managed to burn out his first apartment when he fastened up a piece of loose paneling with a large nail, driving it right through a modern cable.

A boat has low voltage wiring, the wires are often spaced far apart, so how do we get a short circuit to start a fire? Same as in house wiring, short circuits are not the most likely source of ignition. A high resistance connection is the real hazard. A connection dropping a couple of volts at a couple of amps can produce a whole lot of heat, just like a 25 watt soldering iron can. The problem is, that a fuse can't protect your house or your boat against a high resistance connection causing a fire. The bad connection is actually limiting the current in the circuit, often to far less than the fuse rating. Fuses have time/current curves too. A 30 amp fuse will never trip with a 30 amp load. It might take several MINUTES to trip at 40 amps, and even some very long seconds at 100 amps!

A fuse right at the battery can protect you against that errant wrench that somehow finds its way directly across the main buss connections. However the fact is that with both wires insulated, low voltages, and wires running though insulators like wood and fiberglass, the chances of a short that would be cleared by a fuse is very low.

Boat wiring is low voltage, so currents are quite high to get the watts needed. Voltage drop is therefore a problem, so very large wires are the rule rather than the exception. To get the best protection you should therefore size the fuses for the load, not the wire size. A short on a 30 amp rated wire with a 30 amp fuse might not ever blow a 30 amp fuse. However it could generate a whole lot of heat at that bad connection you didn't even know about, which kept the current from blowing the fuse. So fuse should be sized for the total load, not the wire size. It wouldn't be unusual to have a five amp load at the bow of your boat that had a #10 wire nominally rated at 30 amps, to keep the voltage up for that long run. However a 6 amp fuse would keep the load working reliably, and limit to a great extent the possibility that a bad connection could overheat, especially if a short occurred.

You need to be alert for high resistance connections that lead to fires. Keep flammable materials away from electrical connections. Watch for poor performance on radios, winches, lights, windlasses, that signal a poor connection when you already know the wire sizes are okay. Check connections using a volt meter, while the load is turned on, you need current to test. A good connection should show nearly 0 volts when the probes are touched across a connection over a distance of an inch or two. A bad connection may show a fraction of a volt, and possibly many volts across the connection.

Hope this helps,

Gary H. Lucas
jimjazzdad likes this.
Reply With Quote Share with Facebook
  #38  
Old 03-05-2012
casey1999's Avatar
Senior Member
 
Join Date: Oct 2010
Location: HI
Posts: 2,785
Thanks: 3
Thanked 16 Times in 16 Posts
Rep Power: 4
casey1999 is on a distinguished road
Re: Over Current Protection On Pos Battery Connection

Thanks all for your expert advice. Hopefully this will save at least one boat from fire.
Regards
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
internet connection mfsykes Gear & Maintenance 9 12-07-2011 02:22 PM
Internet connection eitan Gear & Maintenance 4 12-15-2009 02:58 AM
Cable TV connection watom Electrical Systems 9 04-27-2009 05:22 PM
Battery Switch: Field Disconnect Protection SEMIJim Gear & Maintenance 9 08-10-2008 10:56 PM
Propane Connection TheStorm Gear & Maintenance 0 05-15-2007 02:01 PM


All times are GMT -4. The time now is 11:28 AM.

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

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.