Wiring Fishing boat from scratch - Batteries, house loads

JackAndCoke

Recruit
Joined
Jun 20, 2008
Messages
4
After having spent my evening reading through different threads, taking notes, crossing out notes and giving myself a throbbing headache, I decided just to make my own thread. Basically I am wiring my boston whaler with a 90 hp outboard yamaha for a proper fishing boat. I'm new to boat wiring so please bare with me!

Although it may be overkill I would like to have 3 batteries in the boat that would all get charged by the alternator. I keep reading only about 3 batteries on a twin engine boat, is it even possible? I say 3 batteries because I will be doing fishing tournaments, thus spending the whole day on the water with the house loads of:
-trolling motor (which I would prefer to be running on 24 volt)
-aerator (for livewell)
-pump (for livewell)
-bilge pump
-fish finder
-lights


I understand that running the batteries in parallel (like this http://forums.iboats.com/attachment.php?attachmentid=201820&d=1373124988 ) will make one big battery, only as strong as the weakest one.

If I just use two batteries and a switch (like in this thread http://forums.iboats.com/electrical...tors/need-info-adding-2nd-battery-249593.html ), I am basically killing one battery with all my house loads and reserving the other battery for starting, however both are getting charged when I'm driving, right? Am I better off using an isolator (I admit I did less research on this).

Comments, diagrams, suggestions are all appreciated!
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,755
Re: Wiring Fishing boat from scratch - Batteries, house loads

Everything in your "likes" list including the two links are 12 volt related yet you want a 24 volt troller. The next issue is whether the outboard has enough alternator capacity to charge three batteries. Third issue is if you do end up with a 24 volt troller, you cannot charge those batteries from the engine unless you come up with a switching system that breaks the series connections between the two engines. You cannot have a common ground with a 12 volt charging system and a 24 volt series battery bank. There are some alternator DC chargers available but you will not likely appreciate the price. Just because you have an alternator, does not mean it has unlimited output. Troller batteries get deeply discharged and you would need to run wide open for hours to even get close to fully charging them. An on-board charger is needed that you plug into shore power at the dock.

You also need to understand how a dual battery switch (OFF-BAT1-BOTH-BAT2) works and is wired.. You also need to understand that you don't leave ONLY the engine on one battery. The instruments on your boat are also on that circuit. If you use a dual battery switch, then EVERYTHING, including the engine gets wired to the COM terminal on the switch. You then become the traffic cop for electricity so to speak. OFF is obviously off and all circuits are dead. BAT 1 powers everything and ONLY BAT 1 is charged. BOTH = selects both batteries for powering everything and both will be charged. BAT 2 = means ONLY battery #2 is selected and is being charged as well as running everything. How you use the switch depends on what you plan on doing that day. There is no need for constant fiddling if you THINK about it before leaving the dock. So - With a 12 volt troller you need three batteries. #1 is engine circuit, #2 is house loads, #3 is troller. You install the switch and/or ACR between the BAT 1 and BAT 2. The engine does not charge BAT 3 for reasons previously discussed. If you have a 24 volt troller, you need two batteries in SERIES to create 24 volts. So you now have FOUR batteries. Again, the two troller batteries are not charged by the engine. Use the search feature in this forum. This stuff has been discussed over and over and the results are always the same. No need to re-invent the wheel.
 

JackAndCoke

Recruit
Joined
Jun 20, 2008
Messages
4
Re: Wiring Fishing boat from scratch - Batteries, house loads

I really did try n search. My understanding is so minimal that without being able to ask a straight forward question, I seemed to confuse myself even more, sorry.

My trolling motor actually has a switch of either 12volt or 24 volt. If I understand correctly, this won't really be an issue though as my trolling motor will be in a circuit of it's own just with the battery #3. Meaning, if I had the extra fourth battery, I could easily add it into that circuit in series.

Alternator capacity as in the alternator amperage output? Can this be checked? An ammeter would have to be placed in series with the alternator, right? If I now only have two batteries in the circuit (the third will be with the trolling motor) is this still an issue?

Thanks for dumbing down the switch for me, got it now! All the instruments will be running off of which ever battery is selected. This way, is an ACR necessary, or just the switch is enough to control it? Will try n find a write up on the best way to go about using the switch once on the water!
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
Re: Wiring Fishing boat from scratch - Batteries, house loads

The specifications for your outboard should include the output of the alternator. If you don't have the manual, post in the Yamaha outboard forum section, or contact Yamaha.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Wiring Fishing boat from scratch - Batteries, house loads

A lot of people come to these forums asking electrical questions and most have no clue about electricity. So dumbing down the answer was not the intent. The intent was to get you to know the systems.
What you want, can't happen.
You can have a house battery and a starting battery on a system that can keep both systems separate and also charge both from the motor, but you CAN NOT include the 24V system in the 12 volt system and charge from a 12 volt alternator.

Forgetting the 24V system completely, here is how to set up the battery system to keep house and starting completely separate.
Add-A-Battery - 120A - Blue Sea Systems

Here is the kit needed to do that.
Blue Sea Systems Add A Battery 7650 - iboats

Once you have your battery plan, then you need a plan for wiring the house electrical.

Then you have to build the 24V system.

Lots to think about just with the 12V battery system, what motor will you have? What is the charging out put of the charging system?
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,755
Re: Wiring Fishing boat from scratch - Batteries, house loads

Assuming this 90 HP Yamaha is a two stroke, it would likely have a 10 amp alternator which is barely enough to keep ONE battery charged much less two or three. Forget that.

Don has a couple of nice diagrams in which an ACR and a switch are used so you don't need to muck with the switch. But if you elect to NOT have the ACR, using the switch is not rocket science. Most folks get all wrapped around the axle over this and there is no reason for that. The prime objective is to "protect" the starting battery. If an engine is properly tuned and you are using the proper starting procedure you could run half the summer without EVER charging the start battery so this paranoia is really unfounded unless one also runs a bunch of accessories (high power stereo for example) for long periods with the engine off. Therefore, THINK about your day and set the switch accordingly. If you will make a short run to an island or bar and why set the switch to BAT 1 (start) and then switch to BOTH or BAT 2. Starting the engine sucks so little out of the battery you could simply set the switch to BAT 2, start the engine and go do your thing. BAT 1 remains charged since you didn't use it. Or set the switch to BOTH, start the engine and go do your thing. Both batteries get charged (although no much due to the low output) then switch to BAT 2 at your destination. See -- that's just one scenario. Your the boss -- send the juice where it needs to go for the trip you are about to take.

You have a 12/24 volt motor so why not use the 24 volt capability? Yes you need two batteries for that but performance is better. Based on you list of accessories being powered, you really don't need a "house" battery. Using a large capacity START battery will be fine. Two deep cycles for the troller, forget the swtich and acr and go boating/fishing. A pair of jumper cables or a jump start box starts the engine should it ever run down. Besides, you have two other batteries to jump start the motor. Rational thought is a wonderful thing -- Not????????
 

JackAndCoke

Recruit
Joined
Jun 20, 2008
Messages
4
Re: Wiring Fishing boat from scratch - Batteries, house loads

Thanks guys, especially Silvertip, you just answered questions in my head that I hadn't even thought about asking yet. I'm all set for now!

I'm still leaning towards going with the switch.

Don, I don't mean to be a pain but I read in one thread that you draw up wiring diagrams as a hobby. Do you happen to have with about the same instruments that I'll be running. I have a general idea, but if I had something concrete with fuses or wire gauges it would be amazing.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,755
Re: Wiring Fishing boat from scratch - Batteries, house loads

The one "key" instrument not listed is a voltmeter. That little sucker tells you the health of the charging system with the engine running, and the health of the battery system with the key on but engine NOT running.
 

JackAndCoke

Recruit
Joined
Jun 20, 2008
Messages
4
Re: Wiring Fishing boat from scratch - Batteries, house loads

The one "key" instrument not listed is a voltmeter. That little sucker tells you the health of the charging system with the engine running, and the health of the battery system with the key on but engine NOT running.

Thanks for the information Silvertip, will definitely look into a voltmeter. Looks like I'll be ordering online, I can't find a store anywhere in my area that sell marine intruments, let alone marine grade wire.
 
Top