2nd Battery hook-up.......

Boat of Us · Apr 22, 2003

Hello I have a little 21ft Maine Lobster Style boat. I do not have shore power installed. Like many people, my concern is draining out my battery. My question is, should I hook-up a 2nd battery and if so, is it a simple installation. I do intend to have a battery switch. Also, what should I have hooked up on each battery. I more or less just have the basic's. Nav lights, Bilge pump, dome lights, VHF, Radio etc... Thanks for the advice Debbie

golfer · Apr 22, 2003

Re: 2nd Battery hook-up.......

Very easy. Worth the time to do it...See the post about ? for dual battery, posted today as well...But basically, you run the starter cables to the starting battery/#1 switch. You run all other wiring to the #2 battery/#2 switch. Start the boat with #1 only, and switch to both after your started and running. While at rest, engine off, use #2, so you leave the charged starting battery (#1) alone, and ready to do it's sole purpose job of starting your boat.

Boat of Us · Apr 22, 2003

Re: 2nd Battery hook-up.......

Thanks alot for the info Golfer. When buying two battery's, is it best to buy one Starting battery, and one Deep cycle?? or 2 Deep cycle would be alright? Debbie

Trent · Apr 22, 2003

Re: 2nd Battery hook-up.......

Dont be switching the switch while running unless you have the proper field disconnect type switch!!! You will blow the diodes in the alternator!! Just switch to both for starting and running. When you shut the engine down, Then switch to single battery operation. Either #1 or #2

golfer · Apr 22, 2003

Re: 2nd Battery hook-up.......

1 starter, 1 deep cycle. I am going to disagree with trent. The alternater feeds the batteries after starting, not batteries feeding the alternater. Switching while running simply directs the charge to both batteries. On the other hand, starting with both batteries will feed the alternater/starter with 2 batteries, giving 24 volts, rather than 12. Field disconnect will help prevent damage from starting with 2 batteries. And, I should mention, never switch to off while running, this is another action the field disconnect will protect you from. The field disconnect switch is about 3x the cost of the regular Perko. I have the regular $19.99 Perko switch, and am just very careful about where I start, stop, etc. on the switch. I have been using this method for years, and different boats. Never had a problem, and been told/warned, not to start with 2 batteries because of the dual voltage (12 x 2 = 24). I may be wrong, I may be right, I may be crazy, but think I am right on....

Boatist · Apr 23, 2003

Re: 2nd Battery hook-up.......

Boat of Us Buy the switch with the field disconnect they are only about $10 more. You can blow your arternator diodes very easy it you do not. What happends is when you turn switch on some unit can find a point where have no battery load and with no load and alternator charging voltage will go so high it will blow all your output diodes and regulator. If the switch you buy makes the second battery before breaking the first battery then will be ok. But if you turn thru off and no field diaconect with engine running expect to be buying or repairing your alternator. West marine switch $4 difference. Check link to I/o section about the same thing. Also go to west marine on line catalog and put in page 537 at the upper left. Have many brand switches. I always use a battery isolator to charge both batteries and leave switch to the battery I want to start with. This way never have to turn switch unless you have a dead battery. http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=001778 http://wmarine.mobular.net/wmarine/5/5/2/index.jsp

Trent · Apr 23, 2003

Re: 2nd Battery hook-up.......

I respectfully and HIGHLY dissagree golfer and you have been missinformed and I will tell you why. Look at the diagram at the bottom and you will see how a switch is wired and its in parallel. You would be correct if the battery was wired in series. You would get 24 volts but it would last just a few min or less. 24 volts would fry the alternator, all the lights and voltage sensitive electronics and the starter and solinoids. Battery switches provide two 12volt batteries in parallel to the starter. (Like hooking up jumper cables to a car). Also it does take 12volts from the battery to "excite" the alternator field for charging to begin. The reason I say to get a good switch is one that is make before break. If its not a make before break switch it will we like turning off the switch. Turning off the switch without a field disconnect will fry the diodes in the alternator. You must have a good switch on your boat if you have never had a problem switching while running. Switch to both for starting and running so to charge the batteries. After shut down switch to one battery operation so you will not run down both batteries. If you run that battery down and cannot start you can switch to both and start (just like jummping off a car with jumper cables). Golfer switch your battery switch to both and measure the voltage at the starter and you will see 12 volts not 24. web page

Boat of Us · Apr 23, 2003

Re: 2nd Battery hook-up.......

Hi guys God, I really rattled up this topic didn't I!

It is abit confusing, but I'm starting to get the picture. I forgot to mention my motor is an outboard, Evinrude 100hp 1989, and not an inboard. I don't think this makes a difference...does it?? My Battery Switch is a Guest model 2100 with AFD. What is your opinion of Battery charger Solar panels. 5watts,350m Amps Thanks again for all the info Debbie

Trent · Apr 23, 2003

Re: 2nd Battery hook-up.......

Does not make a difference. Switching an outboard while runnning to off will fry the regulator/rectfier.

MrBill · Apr 23, 2003

Re: 2nd Battery hook-up.......

Trent is right on about the wiring and the advise about starting on "both" and charging "both". I recently installed a dual battery set-up, if done right only 12 volts will be delivered. I plan to switch to my #2 battery while on the mooring to run down only one battery while stopped (bilge pump, mooring lamp). Perko has an easy to follow diagram which Trent placed in another post...

SlugBug · Apr 24, 2003

Re: 2nd Battery hook-up.......

My understanding is that the switch CAN be turned from 1 to 2 or vice versa while the boat is running IF the switch has a make before break design (see PERKO home page). I thought that the only time the field disconnect came into play was to protect the alternator from being damaged if the switch was accidently turned to off while the motor was running. (Which I was told to never do) My switch as a make before break design - I have been switching between batteries while running and have not damaged the system.

Boatist · Apr 25, 2003

Re: 2nd Battery hook-up.......

SlugBug What you said is Correct with a make before break type switch. Most brand name switches are today but a lot of older switches are not. If switch is not make before break then when turn has a point where no battery connected and if field connected will blow alternator output diodes and or regulator. So little difference in price for switches with a alternator field disconnect I would never buy one without. Even with a make before break type switch can be hard on switch if turn while running. Lets say you have been running boat all night on battery 2 and battery is very low. Now before you start up you switch to battery 1 and start. After get motor warmed up a little you go back and switch to battery 2 to charge battery. Since battery 1 is now at 13.8 volts and battery 2 is at 8 to 10 volts when the second battery makes will get very high current flow from battery 1 to battery 2 and also from alternator to battery 2. With a good high amps switch should work ok but with low amp switches could cause switch to weld contacts or open a leg. For sure I would make this Switch at idle. This just like hooking up jumper cables from a car with a good battery and motor running to one with a dead battery but since the cables are shorter and bigger get even more current flow. Many car even with 100 amp alternator do not survive this task. I always connect the jumper cables with the engine off then start back up. Still what you said is correct and if have a good switch and battery near same charge very little chance of failure. Just make sure do not turn to off with out a field disconnect circuit.

Boat of Us · Apr 25, 2003

Re: 2nd Battery hook-up.......

Thanks a lot guys

SlugBug · Apr 25, 2003

Re: 2nd Battery hook-up.......

Boatist- What you said makes complete sense - I have always switched at an idle as you suggested. However, I have a question - in the scenario that you outlined, with battery 2 lo from overnight drain, would it be better to start in the "Both" position and THEN switch to the "2" position after the boat is warmed up? Your scenario is exactly how I use my battery - low from overnight then switch back after starting to charge for the next night etc. Would starting in both then switching to 2 take the stress off the system?

2nd Battery hook-up.......

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