Negative battery switch

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prroots

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Dec 10, 2010
254
None NA Stuart, FL
I'm purchasing a 2001 Beneteau 411. There are 3 battery switches corresponding to start, house, and negative. The negative switch allows one to disconnect the common negative to both start and house batteries. Can anyone explain how this switch is used? Thanks
Pete
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
I've never heard a practical reason for the switch. The only logical reason was just for safety if working on the electric system. After all, the shore power ground is connected to the engine block, and thus the battery negs.

I replaced the ground switch with a second positive battery switch to control the second house battery i am adding. I merely let the neg switch (with wires attached) lay on the hull. I was figuring to get (and will receive on Wednesday) a Victron battery monitor system. The shunt for that goes on the neg batt cables, so is a good time to revamp the neg buss block and cables.
 
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Rob2435

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Jun 4, 2004
287
Beneteau Oceanis 352 NYC
Like Ron said, I use it when working on the boat's electrical system. Other than that, it doesn't have much use.
 
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JohnShannon

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Jan 4, 2010
1,037
Farr 30 San Francisco
In my experience when you have a bunch of kids on board and someone fools with that switch the entire electrical system blows up!

I don't like that switch.
 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
That is what happens if you shut off the ground while the positive is still energized. Flat rule on our boat, "nobody messes with the ship's systems unless they know what they are doing, and have permission from the skipper".
 
Ron M

Ron M

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Mar 21, 2010
67
Beneteau 331 Rock Hall, MD
I was wondering the same thing. Called Beneteau Tech Support today.... his reason was to isolate the DC system from any stray currents while not being used. I'm designing a DC system which will allow the House and Start banks to be separate. Combining them would only occur with a Start battery failure. My thought was to use the two red handles as the On/Off for each bank and change the black handle (to be painted blue) to a Combine switch for the paralleling wire.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
TO COMBINE WHAT? TO ASSUME YOUR 331 IS LIKE MY 323, IF YOU TURN ON BOTH REDS AT THE SAME TIME, THEY ARE PARALLEL-CONNECTED VIA THE (12-volt BUSS) WIRE ACROSS THE BACK OF THE SWITCHES. I GET THE SAME RESULT IF I TURN ON ALL THREE REDS: PARALLEL-CONNECTED BATTERIES.

Also, if you have a nav station volt meter, it may be wired to the engine battery switch (wire 'T1"?). It only reads one battery. Move that T1 (or whatever it's called on your boat) onto the 12v buss wire on the back of the red switches and you can read the voltage on whichever battery is turned on.
 
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prroots

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Dec 10, 2010
254
None NA Stuart, FL
Thanks for all the feedback. I will be modifying the existing system in several ways. First the battery charger will be connected just to the house battery whereas now it's connected to both batteries via separate outputs. Also the alternator output will be connected directly to house battery whereas now it's connected to both batteries on the other side of the switches. An Echo Charge combiner will connect the Start battery to the House battery to keep the Start battery charged without risk of either inadvertent discharge or overcharge. I'll also replace the single 4D house battery with four 6 Volt golf cart batteries and add a Victron BMV-600 battery monitor to house bank. Basically, I'm following the recommendations espoused in the following thread:
http://www.sailnet.com/forums/electrical-systems/70350-battery-bank-design-recommendations.html
Pete
 
Ron M

Ron M

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Mar 21, 2010
67
Beneteau 331 Rock Hall, MD
Refine DC system answer

Currently with the "normal" three handles for battery switches the two reds are automatically paralleled. Aside from constant fiddling with the switches House and Start are not separate. I've decided to abandon the three switches and use as Blue Sea Dual Circuit Plus switch (and find some means of patching the two sets of holes in the bulkhead). This is much simpler switching. "ON" means House bank goes to House and Start battery to Starter... completely separated. It also has a "Combine" position which will parallel the two... normally for the situation where the Start battery has failed.
 
Vegas

Vegas

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Feb 12, 2009
137
Beneteau 37 JBM, St. Clair Shores, MI
Some people fully charge their batteries at the end of the season then disconnect the negative posts so the batteries don't lose their charge. They then leave the batteries aboard and in position. Could that just be a convenient way to "disconnect" the negative posts?????
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
ProfRon said:
Currently with the "normal" three handles for battery switches the two reds are automatically paralleled. Aside from constant fiddling with the switches House and Start are not separate. I've decided to abandon the three switches and use as Blue Sea Dual Circuit Plus switch (and find some means of patching the two sets of holes in the bulkhead). This is much simpler switching. "ON" means House bank goes to House and Start battery to Starter... completely separated. It also has a "Combine" position which will parallel the two... normally for the situation where the Start battery has failed.
Click to expand
I'm not into the 331 like I am my 323, but it seems you could accomplish the same thing (and save $$$) by deleting the 12-volt buss connection between the two red switches. (You'd have the one battery per one switch.) Different strokes for different skippers, buit if you need to 'combine' both batteries, you are joining a dead battery with a fully charged one- and maybe not have ANY juice left. I'm not sure why "constant fiddling" with the switches is necessary, but IMHO, the switch setup the Beneteaus have is the better way to go.
 
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