Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Dual Battery / Dual Engine

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Dual Battery / Dual Engine
jimh posted 02-10-2001 02:13 PM ET (US)   Profile for jimh   Send Email to jimh  
This message thread is for discussion and comments on the article in the Reference section on Dual Battery installations.


jimh posted 02-10-2001 02:21 PM ET (US)     Profile for jimh  Send Email to jimh     
I should add this disclaimer:

I have not actually tried either of these arrangements myself. I plan to re-wire my dual-battery/dual-engine boat this spring, as the current wiring seems to cause the charging coil on one engine or the other to burn out, probably due to some strange currents occuring from the prolonged connection of the two charging circuits to a single battery bank.

Although not as flexible, I may go with the easier to operate 3-switch arrangement. As long as the tie switch is not closed, the two engines and batteries are entirely separated and cannot be accidently connected by inappropriate setting of the other switches.

It is also a little simpler to wire.


triblet posted 02-10-2001 04:50 PM ET (US)     Profile for triblet  Send Email to triblet     
I believe that an alternator run with no
battery will blow diodes. The alternate
allows this.

I don't see how there's much difference in
how hard to wire they are.

Each has advantages. Original allows either
battery to start either engine. Get one
running, let run for a few minutes to charge
the battery back up, start the second.
Alternate does not allow this.

Alternate allows both batteries to start
either engine. But doesn't allow just the
other battery to start it. Primary doesn't
allow this.

I can see where you would want both of these.
I'd use the primary, and add a paralleling
switch. That would give you the best of
both worlds:
Impossible to have an engine that doesn't
have a battery.
Can start from the other battery.
Can start from both batteries.

I don't see where single battery, dual
engine is going to blow things. I'd look
elsewhere for the source of that problem.
A short?


jimh posted 02-10-2001 06:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Two responses:

1) The "Whaler-Factory" wiring does allow the paralleling of the batteries.

That happens when either of the OFF-1-2-ALL switches are in the ALL position. They suggest having them both in the ALL position.


2) As for my situation, I have scratched my head about it for some time, drawn diagrams, etc., trying to figure out what has happened, but the sad truth is that shortly after spending $300 getting the charging coil replaced on the PORT engine, the coil opened on the STBD engine. It might have been coincidence, but I think something is going in with two alternators charging one battery.

This is my best analysis: if the PORT engine charging system raises the battery voltage to a certain level, say 15.0 volts, and the STBD engine charging system is only producing 14.4 volts, then from the point of view of the STBD engine's charging system it is looking at an open circuit.

Current from the PORT engine's charging circuit would try to flow into the STBD engine charging circuit. Now, there are diodes which prevent this, but the effect of reverse biasing the diodes is to remove the load of the battery from the charging circuit. Then you are back to the forbidden case: operating the engine with no battery to absorb the charging current.

I think that is what is happening to my (over priced) charging stators.

Therefore--any theoretical objections aside--I plan to completely overhaul the wiring in the back of the boat to eliminate the present situation where both engines are paralleled to one (bank of) battery(s).


jimh posted 02-10-2001 06:12 PM ET (US)     Profile for jimh  Send Email to jimh     
Oh, a third topic:

I say that the "alternative" wiring is a bit simpler due to the fact that if one were to locate the OFF-1-2-ALL switches at opposite sides of the boat, then you have to run more wiring across to connect them.

I made the assumption that the batteries would be located one on each side of the boat. That is how they are in my 20-Revenge. There is a battery case in each extreme outboard end of the engine well, thus the batteries are located far apart. The OFF-1-2-ALL switches would likely be located on the cockpit bulkhead in front of the engine well. Thus you would need to run three pieces of 2-AWG cable across the boat to tie them together.

In the alternative arrangement, you only run two pieces of 2-AWG cable across the boat.

Now if you locate the batteries and the switches all close by, then there is not much difference.


DIVE 1 posted 02-10-2001 10:08 PM ET (US)     Profile for DIVE 1    
I have redone several dual outboard charging systems that were blowing charge coils. On every boat, 2 engines were trying to charge one battery or two batteries tied together at the same time. I can not explain what the problem is, but rewiring using the "alternative" has always prevented the problem from repeating itself. It is important to only use the "tie switch" for emergency starting and then turn it off. If you are worried about losing one battery because of a bad charge coil while underway, install an onboard battery conditioner. This will charge 2 isolated batteries at the same time with one engine. On DIVE 1 we installed 2 starting batteries and 1 house battery with the appropriate conditioner. All 3 batteries are charged from 1 or 2 engines while maintaining isolation from each other. We do not have a tie switch because we are afraid that someone would turn it on without realizing the destruction that could occur. We carry jumper cables.


jimh posted 02-11-2001 09:58 AM ET (US)     Profile for jimh  Send Email to jimh     

In a sense I am glad to hear that this has happened to someone else; I was beginning to think there was something weird going on in the boat wiring on my 20-Revenge. Sorry about those blown stator coils.

I would also like to ask if anyone can describe the wiring between the battery negative, the fuel tank, and the zinc anode.

My boat is in storage and not convenient to visit, so I can't refer to it for guidance.

Also, is there something installed in the ground/negative line on your boats? There is a small black plastic gizmo wired in the negative lead on my boat (I recall), and I am thinking it might be some type of noise filter for the electronics, or else it is a galvanic isolator. Anyone have a similar gizmo in their ground (green) wiring?


DIVE 1 posted 02-11-2001 10:26 AM ET (US)     Profile for DIVE 1    
You have the photo of the beautiful wiring that came on DIVE 1 - ha ha. The wiring was so corroded that it all went in the dumpster. We do not have a black plastic gizmo in our wiring harness.

Ground Wires: The first wire runs from the ground lug on the fuel tank directly to the anode on the transom. The second wire runs from the ground lug on the fuel tank to the negative side of the batteries. The third wire runs from the fuel tank ground lug to the fuel tank filler assembly. There should not be any splices in the fuel tank ground wires.


Ed Stone posted 02-14-2001 10:11 PM ET (US)     Profile for Ed Stone  Send Email to Ed Stone     
I've always thought you would run both
engines on the same battery and save the
other one for emergencys.
I'm going to mount a on board charger
to keep both batterys fully charged.
I've wondered about the solar charger
that goes directly to your 12 volt
Ed Stone
jimh posted 02-14-2001 11:48 PM ET (US)     Profile for jimh  Send Email to jimh     

Running two engines from one battery is exactly what you must avoid, otherwise you may damage the charging system of one of the engines.

The two chargers seem to buck each other until the strong one burns out the weaker one. Then things go just fine, but you have one engine with a burned out charger.

You don't necessarily even notice this because the good engine keeps the battery charged.

See Jim (DIVE-1)'s comments above.

jimh posted 02-15-2001 12:33 AM ET (US)     Profile for jimh  Send Email to jimh     
I revised the article to include some comments comparing the two techniques.

I also discovered while browsing the West Marine catalogue that they are fans of the alternative arrangement.


triblet posted 02-15-2001 09:45 AM ET (US)     Profile for triblet  Send Email to triblet     
>Notice that the alternate arrangement
>connects the circuit breaker panel to only
>the Starboard battery.

Provided the tie switch isn't thrown. If
you throw the tie switch you can flatten
both batteries.

I think I'd clearly label the normal position
of all switches.


Ed Stone posted 02-15-2001 10:13 PM ET (US)     Profile for Ed Stone  Send Email to Ed Stone     
Port position #1
Stbd position #2
Starting position All

I will look over the wiring to see which
method was used.
Thanks,Ed Stone

Lewis posted 02-19-2001 07:36 PM ET (US)     Profile for Lewis  Send Email to Lewis     
I have a 1984 25' outrage with two battery swithces, twin engines and three batteries. The third is under the center console. I know it isn't properly hooked up, you can't parallel start one engine. I want to get it all straight and could use some help. Do I need an isolater?
DIVE 1 posted 02-19-2001 09:44 PM ET (US)     Profile for DIVE 1    
I am personally not a fan of battery isolators because of the voltage drop that they cause. I prefer a battery combiner/conditioner. West Marine has several different models to fit almost every need. The instructions that come with the units are well detailed and easy to follow.
jimh posted 05-28-2001 07:59 PM ET (US)     Profile for jimh  Send Email to jimh     
I spent the weekend doing some electrical work on continuousWave (the boat), and in the process I "invented" a new wiring arrangement for use with dual engines and dual batteries.

I have added a schematic diagram to the REFERENCE article (see link above in first message) and some comments about the design.

One thing I like very much about the "new" arrangement is its extreme simplicity. It is being used, after all, on a small boat.

There is not that much room in the rear cockpit or motor well for multiple switches and multiple batteries. This wiring was very simple and yet it provides all the flexibility I think I will need.

Of course, after a season of use I may have a different idea. For the moment, we have the boat wired as shown and we'll see how it works!

Comments are invited, as always. A group discussion often produces new ideas and improves thinking.


Chap posted 08-02-2002 12:14 PM ET (US)     Profile for Chap  Send Email to Chap     
Hello jimh,
I've been looking at my non-switched dual battery/dual motor set up with a desire to add a switch. Had to jump a battery the other day.
Jimh I believe, I read somewhere recently that you now have removed your switch in favor of the set-up I currently am running. True? Are you switchless?
If so could you provide your reasoning? I assume simplicity and reliability but.....
On the learning curve.
jstachowiak posted 08-02-2002 03:16 PM ET (US)     Profile for jstachowiak  Send Email to jstachowiak     
For those who can get their hands on a copy of Florida Sportsman mag August 2002, this month, there is a good article about this topic. The article is specifically 4 batteries, two engines, but he talks about other set ups. Also, I just saw battery isolators at West Marine yesterday for about $70. An essential item when attempting this setup.
Capt_Tidy posted 08-02-2002 04:56 PM ET (US)     Profile for Capt_Tidy  Send Email to Capt_Tidy     
I have two set of batteries all managed by the Link 2000 system by Heart Interface... it's expensive ($450) but once installed, you will never leave the dock with it again... it has low battery alarms, digital battery readouts etc. If you have ever tried to figure out a short.. .this is the tool. I love it. I can charge via engine, charger, or solar without hassel.
Morocco posted 08-07-2002 05:01 PM ET (US)     Profile for Morocco  Send Email to Morocco     

In the 'new' schematic, since the batteries are each ALWAYS connected to the engine charging systems, you would never have to worry about burning out a coil because it's impossible to run either engine without being on line to a battery. Is that right?

In the normal operation section when both engines are running, the center switch can be OFF, 1 or 2? Anyplace but on Both, right? (on off you would have no house power, though?)

This battery stuff makes me batty...

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.