wiring 2 batteries and two engines

[zanati]

hi , i'm just rebuliding and old 1975 24ft long, chrysler boat. it has 2 volvos aq 145A engines and sterndrives, and i need to know wich is the right wiring for the batteries. i have 2 12v 75amps batteries and 1 battery selector (pos 1 , 2 , both and off). the engines has the original instruments and wiring.

thanks

juan cruz

 

[tashasdaddy]

Re: wiring 2 batteries and two engines

i think you will get a quicker response in the electrical/electronics forum. moving.

 

[Silvertip]

Re: wiring 2 batteries and two engines

You are the second person with that configuration and for the life of me I can't imagine why or how a switch would be needed or used i that situation unless it was a "special switch". You have one battery for each engine. A single battery switch has a terminal for each battery (BAT 1 and BAT 2) but only one common (COM) terminal. So which engine would the COM terminal feed? It doesn't make sense. The only plausable connection would be to wire the batteries in parallel, feed the COM terminal and then run what would normally be the BAT 1 and BAT 2 inputs to the respective engine. That however leaves a very dangerous situation in that switching to BAT 1 or BAT 2 would kill the charging system on the opposite engine. If anyone can clarify why and how a single battery switch would be used on a dual engine, dual battery setup I'd sure like to see a diagram.

 

[PondTunes]

Re: wiring 2 batteries and two engines

Typically in dual engine setups each engine has its own battery (and should have its own disconnect) then there may be a third battery (the house battery) for running accessories.

That being said:
The only way I can see that this would work is if only one engine had an alternator. So do both engines have alternators? If so are they both wired up? If not then wire the switch/batteries up to the engine with the alternator.

The way the above setup would work is say battery #1 serves to crank both engines one at the time. The second is probably intended for accessory loads and would function just like in a single engine setup.

 

[burroak]

Re: wiring 2 batteries and two engines

Take a peek at this schematic. It cleans up your circuitry and provides a stable, elegant solution to your situation. You can ignore the third battery if you wish since it is designed to isolate the boat electrical system.

"www.cmsquick.com/schematic-f.jpg" "" added per site rules. Remove the and click.

 

[Nova II 260]

Re: wiring 2 batteries and two engines

Single switch is not the ideal setup IMHO.

 

[PondTunes]

Re: wiring 2 batteries and two engines

Agreed the single switch setup probably isn't the best solution and Fox's wiring diagram is another way yours might be set-up. In his diagram the starboard and port engines both have a battery to crank them..

They are also hooked to the accessory circuitry via the disconnect switch. This means you either run your accessories off #1 or #2 (you pick) it also gives you the option of connecting the batteries together to crank an engine in the event of a dead battery or battery failure.

NOTE: Leaving the switch in the Both setting would cause both batteries to act like a single battery and could result in two dead batteries with no backup.

 

[SuperNova]

Re: wiring 2 batteries and two engines

Let me chime in here. I and my BIL have two Novas. Both with twin 260's. Both with two Batteries. Mine is wired with a single selector switch. His is wired with two selector switches. We will be re-wiring his to a single selector switch.

When this is done properly, Both batteries ground all the time. The positive of both batteries is wired to the switch #1 and #2. Both positive wires from the starters go to the common pole of the switch.

This setup allows you to use either battery or both to crank either engine and also allows you to isolate one battery without isolating one engine. Having two alternators then becomes a backup and allows charging even if one engine fails.
After having boats wired both ways, he and I agree the single switch is the better way to go. When you are on anchor, you can switch to just one battery and be assured you'll have the other to start both engines.
--
Stan

 

[PondTunes]

Re: wiring 2 batteries and two engines

The more that I look at this setup, the single switch setup isn't bad at all and it also has the advantage of keeping the end user from turning the switch to off killing the charging system. The way the above diagram is set up the charging system wouldn't be affected if the user switched the selector to OFF; only the house systems would be disconnected.

The only way I see to improve on the single OFF-1-Both-2 switch setup above would be a third battery isolated from the common post to run house circuits.

The big disadvantage to A dual switch setup with on/off switches could allow you to disconnect the battery from the alternator causing charging system damage.

 

[zanati]

Re: wiring 2 batteries and two engines

ok . i was planning to use the wiring sugested by nova 260 (sames as whaler boats) . my question is : if i wire bat 1 positive to the Left switch terminal(on the battery key) the bat 2 positive to the right switch terminal . but using the original volvo wires(the coded and coloured from factory for the aq145A )requires the big positive wire direct to the crank and the red to the alternator. so . always even switching the batteries selector to off . i will have energy to crank and use the engines.
just have the advantage to use BOTH position to engine start , and during the navigation either Left or Right. , just both only to eng start.

am'i clear?

so i don't know how to fully isolate the batteries when in OFF position.
thanks

juan cruz

 

[PondTunes]

Re: wiring 2 batteries and two engines

With Nova's setup you wont be able to disconnect the batteries from the engine short of removing the battery cables. Switching the OFF-1-Both-2 switch to the OFF position will disconnect your house loads (typically radio/fish finder/livewell pump) preventing them from draining either battery.

If you are wanting a way to disconnect the batteries from the engine (preventing accidental starting, preventing your kids from cranking it etc.) you could wire a simple OFF-ON perko/guest style switch in the positive lead going to each battery. They make these with a key that you can lock out so they can't be switched on.

 

[SuperNova]

Re: wiring 2 batteries and two engines

If you wire one switch, your house feed is connected to the same terminal on the switch as your starter feeds, thereby putting the whole boat's electrical load in control of the switch.

 

[PondTunes]

Re: wiring 2 batteries and two engines

SuperNova If your boat is wired like the above image (the one I was talking about) Then switching the switch to OFF only disconnects the house load from battery 1 or battery 2. If you notice the + and - of battery #1 & #2 are connected to the engine directly, not through the OFF-1-2-Both switch. The switch has nothing to do with disconnecting the engine from the battery. So if you go and pull your starter without disconnecting the battery terminals you could easily cause a short because the red wire to the starter would be hot while you were working on it.

The above situation should prevent any load on the batteries while in the OFF setting but it won't disconnect power at the engines.. A screwdriver across the solenoid terminals would still cause the engine to turn over or the possible short as described above. Again not saying anything is wrong with the setup in any way just be aware that you still need to remove battery cables or add in a ON-OFF disconnect for servicing the engine!

 

[SuperNova]

Re: wiring 2 batteries and two engines

Yes, you are absolutely correct,pond. But that is not how my boat is wired. In my boat the house load and the engines are all wired to the common terminal. So I start both engines with both batteries and I run with both batteries. When I sit on anchor, I switch to one of the batteries so I know I have a good battery in reserve for when I restart. It's very simple and works phenominally well.
--
Stan

 

[PondTunes]

Re: wiring 2 batteries and two engines

(EDIT sorry stupid picture isnt showing up its the attachment below)

Is this the way your boat is wired supernova? I've seen this setup on several boats too it's simple and effective but you are forced to operate the switch all the time. You have to remember to switch it while anchored then remember to switch it to charge. Once we get to this setup I would have to say an automatic battery isolation/charging relay would be the solution I would recommend. It never forgets to charge and prevents both batteries being drained.

This design does have one advantage as both batteries are charged via the alternators on both engines. I would really consider adding master disconnects to it to allow the engines to be serviced with no danger of short circuits. Other than that this setup will require no remembering to switch unless there is a problem.

 

[Nova II 260]

Re: wiring 2 batteries and two engines

The way my Nova is wired

 

[SuperNova]

Re: wiring 2 batteries and two engines

Once again, No that is not the way my boat is wired. Both of my engines go through the switch as does the house panel feed. I can switch the house and both engines to either battery, both or off. In the OFF position, the switch kills the whole boat, except the radio memory b/c that is wired directly to the port battery. So to summarize, use your diagram. but put the house and Both engine feeds on the common (C) post.
--
Stan

 

[SuperNova]

Re: wiring 2 batteries and two engines

The way my Nova is wired

That is just unecessarily complicated. What is the point of having two switches? One is totally redundant and unneeded. It just overcomplicates what should be a simple circuit, in my opinion.
--
Stan

 

[PondTunes]

Re: wiring 2 batteries and two engines

Once again, No that is not the way my boat is wired. Both of my engines go through the switch as does the house panel feed. I can switch the house and both engines to either battery, both or off. In the OFF position, the switch kills the whole boat, except the radio memory b/c that is wired directly to the port battery. So to summarize, use your diagram. but put the house and Both engine feeds on the common (C) post.
--
Stan

Sorry the image wasn't showing up:

That is just unecessarily complicated. What is the point of having two switches? One is totally redundant and unneeded. It just overcomplicates what should be a simple circuit, in my opinion.
--
Stan

The point of having the two switches for one thing is that the two charging systems are isolated from one another.. What happens if a short takes them both out? A Two switch or the NovaII's single switch would prevent that from happening. Secondly no switching is required unless there is a problem, set switch engine 1 to battery 1, then engine 2 to battery 2. The house load is connected to battery 1 and everything takes care of itself unless there is a problem. Then either battery or both can be used for starting & either engine can be used to charge the batteries.

 

[SuperNova]

Re: wiring 2 batteries and two engines

Yes, ponds now that is how my boat is wired. My BIL is with the two switches, and he is not at all happy with it.....it is much more of a PITA than mine is. You are correct though that the switch needs to be mounted somewhere fairly accessible, but you don't switch it as much as you think. And I did have a charging failure on the starboard engine....the port engine still charged both batteries just fine, however I see your point that I can't isolate the engines independently, so if I had a short in the battery cable on one engine, I'd be screwed. Thanks for your patience.
--

Stan