Wireing the Positive alternator cable.

[Tree]

I've read many times here the advice to wire the alternator cables direct to the Battery Bank. But I wonder if there might be some circumstances where connecting at the far side of the battery switch might have an advantage.

Am I correct that the main reason why connecting to the far side of the battery switch is not a good idea is: that if the switch is turned (on or off) while the alternator is putting out power to the batteries, you run the high risk of damage to the diodes in the alternator?

The reason why I am considering wireing to the far side of the battery switch is that in my case, I am dealing with a fairly small sailboat and my motor is a Honda outboard. My single battery bank is a little over 200ah. The Honda is a pull start and only puts out 6 amps at best and really doesn't charge the batteries so much as keeps up with some of the electrical loads like the GPS, Auto pilot, VHF radio and lights. Deep recharging is done with shore power or portable generator. (these charging sources would be connected direct to the battery)

The problem is, that cable that runs from the outboard motor to the batteries is not "hard wired" onto the motor. It just plugs onto the outboard. I have had this cable "plug" fall into the water when the outboard was off the boat for service. Once, when reaching over the motor to adjust something, the cable caught on my arm and came almost unpluged and would have fallen into the water if I had not grabbed it.

Obviously, not a good situation.

What I am thinking:

I have a battery switch that is 1 - 2 - Both.

I would wire the switch backwards.

The battery bank would be connected to the "output"

The "house" would be connected to "1".

I would connect the alternator cable to the "2" Terminal.

I would re-label the switch.

The vast majority of the time, I would turn on my battery bank by turning to the "both" position. When I run the motor, I would be charging the batteries.

While at anchor or at the dock, I could power up the boat by using the "1" position. The outboard would be completely out of the power loop.

I can see some real advantages to knowing that the battery bank can be disconnected from the cable that runs to the outboard.

So, are there other reasons why I should not use the battery switch to make my alternator cable positive "dead" when not in use. Remembering to not fool with the battery switch while the motor is running might be safer than risking the cable falling in the water and shorting out the batteries ..... or having to disconnect the cable at the battery when working on the outboard.

Thoughts?

[btrayfors]

Wiring the 1-2-ALL switch "backwards" might get you in hot water.

An easy solution would be to buy a single OFF-ON battery switch like the Blue Sea Systems #6006 for the motor/alternator cable. You could then switch it into the circuit whenever you were running the motor, and out of the circuit when you weren't. Consider it an "engine switch".

BTW, this is a great little battery switch which costs about $20.

JMO,

Bill

[mitiempo]

Tree

Your boat, with an outboard instead of an inboard, doesn't have an engine ground like an inboard powered boat. The ground is the negative battery post. I don't think the positive falling in the water could short out the battery bank. The corrosion from water entering the cable sounds like the worst risk.

[Tree]

Originally Posted by btrayfors

Wiring the 1-2-ALL switch "backwards" might get you in hot water.

An easy solution would be to buy a single OFF-ON battery switch like the Blue Sea Systems #6006 for the motor/alternator cable. You could then switch it into the circuit whenever you were running the motor, and out of the circuit when you weren't. Consider it an "engine switch".

BTW, this is a great little battery switch which costs about $20.

JMO,

Bill

Hi.... thanks for the response.
Could you be more specific about how it would get me in trouble? Thanks

[Tree]

Originally Posted by mitiempo

Tree

Your boat, with an outboard instead of an inboard, doesn't have an engine ground like an inboard powered boat. The ground is the negative battery post. I don't think the positive falling in the water could short out the battery bank. The corrosion from water entering the cable sounds like the worst risk.

Mitiempo..... you have given great advice many many times here. Thank you for responding. I greatly respect your advice.

I am confused by your response. My outboard is connected to my battery with a cable that attaches to both hot and cold power sides. The plug is a 2 post plug with both pos and neg.
The darned thing has to be long enough so that I can turn the outboard when in tight maneuvering situations and it's just long enough to reach the water if not "plugged" in.

[btrayfors]

Originally Posted by Tree

Hi.... thanks for the response.
Could you be more specific about how it would get me in trouble? Thanks

You identified one thing yourself in the first post, i.e., you could put the switch in the wrong position while the engine was running -- or have it in the wrong position when you started the engine -- and risk blowing the diodes in the engine's alternator.

Of course, the same thing could happen with a simple ON-OFF switch since the engine is a pull-start (with an electric start the engine wouldn't start unless the switch were turned on).

Isn't there some solution which would eliminate the possibility of the battery wire coming loose from the engine and falling into the water? That might be the best way to go.

Bill

[Stu Jackson]

Originally Posted by Tree

I am confused by your response. My outboard is connected to my battery with a cable that attaches to both hot and cold power sides. The plug is a 2 post plug with both pos and neg.
The darned thing has to be long enough so that I can turn the outboard when in tight maneuvering situations and it's just long enough to reach the water if not "plugged" in.

Bill's got the right idea. Instead of fooling around with mis-wiring a simple 1/2/B switch, simply make the short connection at the motor a LONGER one, and move the plug to somewhere inside your cockpit. You could simply take the existing short connector and cut a new plug into the wire to the batteries, or hard wire it to a new plug in a better location. Address the issue directly instead of trying a complicated work-around.