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The bilge pump should be hot regardless of the battery switch so that the float switch can kick on if needed. On mine, I have a hot lead going directly to one battery.

In a typical OEM installation, does the bilge get power even when the battery switch is in the off position? If no, do you leave the batter selector switch set to one of the batteries when the boat is slipped?
For any accessories that need to be hot with key off (i.e. bilge), will I have to change their wiring when installing the switch? I am not exactly sure how those accessories are wired to keep them hot all the time. Thanks in advance for your help.

schoolsOut wrote:

It normally does, but if I'm slipped, I will have a batt on. My thought is, if there is an elec fire (or performing any elec work) on the boat, that switch will shut EVERYTHING down. I can't think of any other reason to turn the switch to or leave OFF, thus you would always have power available to the bilge pump float switch.

The original factory dual battery set up on my 2004 Sundowner has the bilge pump +12V supply taken permanently from both batteries at the battery switch. It is taken via 2 diodes; that way, the batteries are not actually connected together with the switch set to "off" so one dead battery can't flatten the other. The voltage drop over the diodes is negligible as far as the operation of the bilge pump is concerned. The diodes chosen clearly must be capable of handling the current the bilge pump takes, on mine they are ASI 1N3208.

Still need to run the negative cable to the motor on the second battery. I have not yet found a location to connect it. I will work on that tomorrow.

Since I did not have a battery switch before,........... .

schoolsOut wrote:

Both battery negative cables on mine are connected to the same engine block stud; there are a couple near the starter ( very prone to corrosion due to the dissimilar metals used there !)

I'm surprised you didn't have a battery switch as standard on a 2005 boat, even with a single battery set up. My 1999 Sundowner had a single battery, but had a standard fit battery "on/ off" isolation switch. Maybe a battery switch for single battery is a requirement for CE ( European market) certification and in not required under USCG rules ?

There is a stud just like the one by the starter on the other side of the engine that you can use for a grounding point.

Author:	schoolsOut [ Sun Jul 21, 2013 4:35 pm ]
Post subject:	Installing Second Battery with switch
I am about to install a second battery and Perko switch. I believe I have all that I need. Here is a quick breakdown of my plan: Positive battery cable from each battery to the Perko. Positive battery cable from Perko to starter Negative battery cable from each battery to engine ground Now for my questions. In a typical OEM installation, does the bilge get power even when the battery switch is in the off position? If no, do you leave the batter selector switch set to one of the batteries when the boat is slipped? For any accessories that need to be hot with key off (i.e. bilge), will I have to change their wiring when installing the switch? I am not exactly sure how those accessories are wired to keep them hot all the time. Thanks in advance for your help.

Author:	EvilZ [ Sun Jul 21, 2013 6:56 pm ]
Post subject:	Re: Installing Second Battery with switch
The bilge pump should be hot regardless of the battery switch so that the float switch can kick on if needed. On mine, I have a hot lead going directly to one battery.

Author:	schoolsOut [ Sun Jul 21, 2013 7:49 pm ]
Post subject:	Re: Installing Second Battery with switch
EvilZ wrote: The bilge pump should be hot regardless of the battery switch so that the float switch can kick on if needed. On mine, I have a hot lead going directly to one battery. That's kind of what I thought. I do not have a hot wire running to my single battery at this point. Would it be run directly to the starter at this point? The bilge is hot with the key off currently. If so, I guess I can just reroute it to the nearest battery, in this case the starboard battery.

Author:	Walt [ Sun Jul 21, 2013 8:49 pm ]
Post subject:	Re: Installing Second Battery with switch
schoolsOut wrote: In a typical OEM installation, does the bilge get power even when the battery switch is in the off position? If no, do you leave the batter selector switch set to one of the batteries when the boat is slipped? For any accessories that need to be hot with key off (i.e. bilge), will I have to change their wiring when installing the switch? I am not exactly sure how those accessories are wired to keep them hot all the time. Thanks in advance for your help. It normally does, but if I'm slipped, I will have a batt on. My thought is, if there is an elec fire (or performing any elec work) on the boat, that switch will shut EVERYTHING down. I can't think of any other reason to turn the switch to or leave OFF, thus you would always have power available to the bilge pump float switch.

Author:	Paul I. [ Sun Jul 21, 2013 9:20 pm ]
Post subject:	Re: Installing Second Battery with switch
Walt wrote: schoolsOut wrote: In a typical OEM installation, does the bilge get power even when the battery switch is in the off position? If no, do you leave the batter selector switch set to one of the batteries when the boat is slipped? For any accessories that need to be hot with key off (i.e. bilge), will I have to change their wiring when installing the switch? I am not exactly sure how those accessories are wired to keep them hot all the time. Thanks in advance for your help. It normally does, but if I'm slipped, I will have a batt on. My thought is, if there is an elec fire (or performing any elec work) on the boat, that switch will shut EVERYTHING down. I can't think of any other reason to turn the switch to or leave OFF, thus you would always have power available to the bilge pump float switch. I always turn my 12V/batteries off. You may leave something on that you may not want on. As in your fresh water pump and than it burns out. Now as too " that switch will shut EVERYTHING down." That switch only shuts off/down 12V, not 120V A.C. So I don't understand what you are tiring to say? To get back on track: I would fuse anything that I connect to the battery as in this bilge pump. I would also add a battery combiner so both batteries are being charged no matter how the battery switch is set.

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Author:	LouC [ Sun Jul 21, 2013 9:36 pm ]
Post subject:	Re: Installing Second Battery with switch
There are different schools of thought on this point, many will say that the bilge pump auto switch and the pump should not be switched off by the battery. I was concerned that in the event of a fuel leak I could not shut off the bilge pump if I wired it that way. So I always leave the batt switch on with the boat on the mooring but I am careful to shut off anything than can drain the batt. You can do it either way, but the idea of a fuel leak and a bilge pump pumping gas out did not sit well with me...... If you do wire it the way I did, put a tag on the batt switch "do not shut off batteries if in the water" to remind anyone who uses the boat to leave it ON.

Author:	Graham R [ Mon Jul 22, 2013 7:51 am ]
Post subject:	Re: Installing Second Battery with switch
The original factory dual battery set up on my 2004 Sundowner has the bilge pump +12V supply taken permanently from both batteries at the battery switch. It is taken via 2 diodes; that way, the batteries are not actually connected together with the switch set to "off" so one dead battery can't flatten the other. The voltage drop over the diodes is negligible as far as the operation of the bilge pump is concerned. The diodes chosen clearly must be capable of handling the current the bilge pump takes, on mine they are ASI 1N3208.

Author:	Paul I. [ Mon Jul 22, 2013 1:41 pm ]
Post subject:	Re: Installing Second Battery with switch
Graham R wrote: The original factory dual battery set up on my 2004 Sundowner has the bilge pump +12V supply taken permanently from both batteries at the battery switch. It is taken via 2 diodes; that way, the batteries are not actually connected together with the switch set to "off" so one dead battery can't flatten the other. The voltage drop over the diodes is negligible as far as the operation of the bilge pump is concerned. The diodes chosen clearly must be capable of handling the current the bilge pump takes, on mine they are ASI 1N3208. I like that!! You can pull power from both and as you put it "not actually connected together".

Author:	schoolsOut [ Mon Jul 22, 2013 4:13 pm ]
Post subject:	Re: Installing Second Battery with switch
At this point, I have the batteries wired up and switch installed. Still need to run the negative cable to the motor on the second battery. I have not yet found a location to connect it. I will work on that tomorrow. I am assuming that since I have not altered the wiring of the bilge, it will only run with the battery selector switch set to something other than "Off". I was taking a look at the bilge and float wiring and it appears that they are wired up to the starter to keep them hot all the time. Since I did not have a battery switch before, I am not terribly concerned about keeping the selector switch set to "1" or "2" when the boat is left in the water. It is really no different than now. I do not regularly leave the boat in the water overnight except for a couple of vacations a summer. With the added battery I have gained the security of a back-up battery and the ability to cut all power when the boat is on the trailer. I will look into running the float switch to a battery in the off-season. Headed to Smith Mountain Lake in VA for a week so at least I have the back-up battery installed. The boat will be kept in the water for the week, so I will leave the battery selector switch set to one of the batteries. Thanks for all the feedback.

Author:	Graham R [ Mon Jul 22, 2013 4:30 pm ]
Post subject:	Re: Installing Second Battery with switch
schoolsOut wrote: Still need to run the negative cable to the motor on the second battery. I have not yet found a location to connect it. I will work on that tomorrow. Since I did not have a battery switch before,........... . Both battery negative cables on mine are connected to the same engine block stud; there are a couple near the starter ( very prone to corrosion due to the dissimilar metals used there !) I'm surprised you didn't have a battery switch as standard on a 2005 boat, even with a single battery set up. My 1999 Sundowner had a single battery, but had a standard fit battery "on/ off" isolation switch. Maybe a battery switch for single battery is a requirement for CE ( European market) certification and in not required under USCG rules ?

Author:	schoolsOut [ Mon Jul 22, 2013 4:49 pm ]
Post subject:	Re: Installing Second Battery with switch
Graham R wrote: schoolsOut wrote: Still need to run the negative cable to the motor on the second battery. I have not yet found a location to connect it. I will work on that tomorrow. Since I did not have a battery switch before,........... . Both battery negative cables on mine are connected to the same engine block stud; there are a couple near the starter ( very prone to corrosion due to the dissimilar metals used there !) I'm surprised you didn't have a battery switch as standard on a 2005 boat, even with a single battery set up. My 1999 Sundowner had a single battery, but had a standard fit battery "on/ off" isolation switch. Maybe a battery switch for single battery is a requirement for CE ( European market) certification and in not required under USCG rules ? I thought about using the same stud, but I installed my second battery on the other side of the boat to keep things balanced and I figured I would not run another 8" battery cable if I don't need to. My pops is an auto mech. He will give me some guidance tomorrow. I was also surprised that my boat didn't have a second battery or at least an on/off switch, but sure enough, it didn't. Must have been an option. It was really not difficult to install. I used the suggestion from a previous thread to install the second battery under the port side rear hatch since there was not a nice flat location to install inside the engine compartment.

Author:	LouC [ Mon Jul 22, 2013 5:33 pm ]
Post subject:	Re: Installing Second Battery with switch
There is a stud just like the one by the starter on the other side of the engine that you can use for a grounding point.

Author:	schoolsOut [ Tue Jul 23, 2013 6:39 pm ]
Post subject:	Re: Installing Second Battery with switch
LouC wrote: There is a stud just like the one by the starter on the other side of the engine that you can use for a grounding point. Yep, found it. The stud diameter was slightly larger than the hole diameter in the battery cable, so I drilled it out to fit. Second battery is installed and working. Feeling really good about having a back-up battery and the ability to cut all power when on the trailer. Ready to drop anchor and crank the tunes without a worry in the world!

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