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4 batteries, twin outboards

Old 03-14-2018, 12:05 PM
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Default 4 batteries, twin outboards

I'm trying to optimize my setup. I'm currently running (4) Group 34 AGM batteries set up as shown below. I've never thought twice about it since I really don't use much power. I assumed having two batteries for each motor would provide the redundancy I need.

WRONG!!! I learned this lesson the easy way when I went to my boat the first time this spring after the off season - all 4 batteries were dead.

Now, I'm looking to optimize my wiring with the following in mind:

1. Entire boat is 12V system.
2. I want to be able to start either motor from either of the two batteries on that side of the boat (cat, so batteries are physically separated.
3. I want to have cabling on hand to tie motor to opposite battery in the event of power loss on either bank.
4. I'm adding a 1000W wetsounds amp - most likely to use about 500W when cruising. Much less at idle/off - not a sandbar boat.

My thoughts:

Remove all tie wires between batteries. Use the Perko switches (typically leave on BOTH). In an emergency, tie negatives and positives together from one side to the other to create parallel system. Install amp wiring (4 gauge, 25' run) on one of the batteries on the right in order to avoid drawing from same bank as house.
Old 03-14-2018, 12:08 PM
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Old 03-14-2018, 12:28 PM
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I am considering the same setup though not a Cat. Not really anything wrong with your setup but I'd suggest the following.


1. Tie all grounds together. There is no reason not to do so and you'll need it to tie one bank to the other.
2. If you have A/B switch for each side, add a third On/Off to tie port to starboard in that emergency.
3. The house should be tied to the common on the switch for that side so you can select either battery.
4. Most would say the "modern" setup is to have the #1 battery on each side connected to the engine on that side and install ACRs on each side to charge a separate house battery, that should like be the two #2 batteries in parallel. You then have an On/Off for the house and another to parallel all in an emergency.
Old 03-14-2018, 12:50 PM
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Originally Posted by Catspearos View Post
Remove all tie wires between batteries.
what are "tie wires" ? and what's this:

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Originally Posted by chris.817 View Post
Not really anything wrong with your setup
I'm not so sure.

what IS "optimal" ? IMO:

One starting battery per motor - with a switch to use the other if necessary.
and a separate house battery - kept charged by one or both motors -
either by their built-in isolated charging leads - or an ACR - or Yandina.
Old 03-14-2018, 12:59 PM
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Thanks for the feedback guys.

By tie wires, I am referring to the wire that interconnect the batteries. As for your "whats this", its simply a connection between the two positives on those batteries.
Old 03-14-2018, 01:11 PM
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Originally Posted by Catspearos View Post
Thanks for the feedback guys.

By tie wires, I am referring to the wire that interconnect the batteries. As for your "whats this", its simply a connection between the two positives on those batteries.
well, as chris mentions, the negative of every battery must be connected to ground.

but when you parallel two batteries - connecting the positives -
if a charging voltage is applied, they charge together
if you are drawing a load, they discharge together

and if you leave them sitting that way,
they alternately try to "charge each other" - until they are both dead

which may be how you managed to kill the last 4 AGMs
Old 03-14-2018, 01:13 PM
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Iím about to do the same thing, twin motors, four batteries, but only three banks.

Each motor will have dedicated battery, then two batteries will be wired in parallel for the house. Will have charging relies between them.

This way house canít ever draw down the starting.

Below is a diagram from Blue Seas.


Last edited by phigamfsu; 03-14-2018 at 01:21 PM.
Old 03-14-2018, 01:15 PM
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Agreed!

So by tying the negatives together, I have a common ground. And I can either add the jumper between the positive wires in the two banks to draw power from all 4 (both switches on BOTH) or add an off/on switch that effectively does the same thing.

Right?
Old 03-14-2018, 01:36 PM
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Another vote to not tie the whole mess together except for grounds of course.

One bat dedicated to each motor w/ an emergency parallel switch to tie them together.

Two batts paralleled for the house bank w/ a switch to feed the distribution fuses.

Either the charging lead from each motor to the house bank -or- an ACR from each start batt to the house bank.

If using the ACR, it is connected between the motor-side of the starting batt switch and the batt side of the house batt switch (might seem odd but consider what can happen if that is not the connection scheme.)

I suppose you could add another switch to connect the house bank to either of the starting batts if you wanted.

I'd not want to ever have all 4 batts tied together. Can't think of a reason to do that and lots of reasons not to.
Old 03-14-2018, 03:29 PM
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Why not just go w/ a BEP cluster, & wire your 2 house batteries in parallel as suggested? Easy, easy - let's you connect the house batteries if one goes down, & keeps the house isolated.

Battery Distribution Cluster for Twin Outboard Engine with Three Battery Banks | BEP
Old 03-14-2018, 05:20 PM
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Originally Posted by Fwpratt View Post
what are "tie wires" ? and what's this:

Attachment 1065519



I'm not so sure.

what IS "optimal" ? IMO:

One starting battery per motor - with a switch to use the other if necessary.
and a separate house battery - kept charged by one or both motors -
either by their built-in isolated charging leads - or an ACR - or Yandina.

If the "tie wire" were cut and had a "parallel start" solenoid installed controlled with a dash mounted toggle switch I believe you would accomplish your objective. Am I wrong?
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Old 03-14-2018, 06:10 PM
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Originally Posted by NEBassMan View Post
Two batts paralleled for the house bank w/ a switch to feed the distribution fuses.

Either the charging lead from each motor to the house bank
-or- an ACR from each start batt to the house bank.
If he has that capability, I give a vote for it. I'm about to rewire mine and add an addt'l battery for the house and will be connected that way. My question for you, however, is why connect both motors to the bank? "could" that cause problems as you have (basically) two separate alternators charging the same bank? I'm planning on only hooking into one of mine but curious as to what your reasoning is..I may change it up.
Old 03-15-2018, 02:48 AM
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By far, the optimal set up is 2 start batteries and 1 house battery.
Use an ACR to keep all fully charged, protected against draining and all available if necessary.
Old 03-15-2018, 09:35 AM
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Originally Posted by HLastrapes View Post
If he has that capability, I give a vote for it. I'm about to rewire mine and add an addt'l battery for the house and will be connected that way. My question for you, however, is why connect both motors to the bank? "could" that cause problems as you have (basically) two separate alternators charging the same bank? I'm planning on only hooking into one of mine but curious as to what your reasoning is..I may change it up.
The 2ndary alternator output (on Yamis that have it anyway) is isolated so hooking the output from both motors together is not an issue. Yamaha shows that configuration as a rigging option as well. I'm not a real fan of connecting things together unless there is a good reason though. For example, I currently only have one motor connected to my house bank as that seems to be doing the job. When I add 3 batts for my Rhodan trolling motor, I will add the 2nd motor's output to the house bank which will also feed charging current to the trolling batts via a Yardina combiner.
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Old 03-15-2018, 09:57 AM
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Ah, i got ya. My Evinrudes have the secondary charging output as well. I'll have to do some more research to see if connecting them in the future would cause any issues.
Old 03-16-2018, 10:35 AM
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Originally Posted by NEBassMan View Post
The 2ndary alternator output (on Yamis that have it anyway) is isolated so hooking the output from both motors together is not an issue. Yamaha shows that configuration as a rigging option as well. I'm not a real fan of connecting things together unless there is a good reason though. For example, I currently only have one motor connected to my house bank as that seems to be doing the job. When I add 3 batts for my Rhodan trolling motor, I will add the 2nd motor's output to the house bank which will also feed charging current to the trolling batts via a Yardina combiner.
If the dual output alternator is an option (i.e. if this is going on your boat with the twin Yammy 250's), here's the layout I went with. Some people won't like it, but it's what I prefer. 2 switches, no ACR and ability to parallel your house batteries and your starting batteries, and all this is running with every battery isolated unless you put one switch or the other to 'both'. Each outboard is charging it's starter battery and 1 house battery (which can be combined to make a house bank out of the two...or just switch from one to the other if you draw one down).


Last edited by Mixed Nuts; 03-16-2018 at 10:42 AM.
Old 03-16-2018, 05:48 PM
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The simplest would be to just tie three of the batteries together in parallel for your house bank. Keep the 4th battery as a backup. Run everything off the house bank (1) and turn the switch to both occasionally while running to make sure the backup is charged. If you accidently run the house bank down switch to the backup (2) to start.

Your ground is also tied from one of the battery posts to both engines and your "house power", usually through a buss bar. This is not shown in the picture.
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Old 03-16-2018, 06:45 PM
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https://www.thehulltruth.com/boating-forum/914395-people-who-post-bad-advice-why.html
Old 03-16-2018, 06:57 PM
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Default Battery setup

I have 2 outboards and 4 batteries and this thread explains how I set my system up. I used a BEP cluster. Itís pretty bulletproof and seems to work perfectly.

New BEP cluster installation
Old 03-16-2018, 07:02 PM
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Originally Posted by Scott D View Post
I have 2 outboards and 4 batteries and this thread explains how I set my system up. I used a BEP cluster. Itís pretty bulletproof and seems to work perfectly.

New BEP cluster installation
x3 on BEP

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