Connect alternator outputs of two motors to battery bank

[ironring1]

I have a Mercury 2-stroke 50HP outboard and a honda 4-stroke 8HP outboard on my boat. Do I need ti take any precautions before connecting the Honda's 12V output to my batteries so that it can charge them too?

That is, do I need to do anything special when connecting two different alternator outputs to a common battery bank?

 

[Earl Cordova]

Can't mix a 2 stroke alternator with a 4 stroke alternator.

 

[cyclops222]

Alternators do not care a bit if they are connected to a 2 or a 4 stroke motor.
Normally ...ONLY...1 alternator recharges the batteries. Do not connect 2 alternators together in any way at any time.

 

[tpenfield]

Might be a stator (on the small OB) vs. an alternator on the larger OB. It would be best to have a battery isolator in between.

 

[cyclops222]

There is a reason why many dual engined boats do not have 2 alternators.

 

[ironring1]

Alternators do not care a bit if they are connected to a 2 or a 4 stroke motor.
Normally ...ONLY...1 alternator recharges the batteries. Do not connect 2 alternators together in any way at any time.

Thanks. This was my thought, too. I've left the small motor's 12V output disconnected until I sort this all out. Of course, I want to be able to charge my batteries while the large engine is off, so I'll need to sort out what extra hardware I need to combine the two charging sources.

I realize the alternators don't really care what kind of engine is spinning them - I just included that info for additional context.

 

[Jeff J]

I think I would run them through a switch and select which alternator I wanted to be charging.

 

[cyclops222]

Be very difficult & dangerous for DIY guys.

 

[alldodge]

Might be a stator (on the small OB) vs. an alternator on the larger OB. It would be best to have a battery isolator in between.

I do like the isolator
But I'm thinking about the sense lead connection. The ALT needs to be able to read the voltage at the BAT so not to over or under charge. A Bat switch could be used but would need to switch

Without looking close at both Apps I'll assume neither puts out much in the way of Amps. The motors most likely can barely have enough more than just to keep the Bat charged. Could probably use a lawn mower Bat for the 8hp

 

[boscoe99]

Would both alternators be used at the same time or at only one at a time?

 

[kd4pbs]

Ever jump started a car? Ever notice how that when you jump start it successfully and both engines are running, nothing blows up, smokes, or fails even if you leave the jumper cables connected for quite some time to more rapidly charge the vehicle with the dead battery?
Nothing different here than that exact same setup.
Tie them together and don't stress.

 

[kd4pbs]

But I'm thinking about the sense lead connection. The ALT needs to be able to read the voltage at the BAT so not to over or under charge. A Bat switch could be used but would need to switch

Battery isolators supply a sense terminal for this exact reason.

 

[alldodge]

Battery isolators supply a sense terminal for this exact reason.

Not all do

 

[Scott Danforth]

use a large 50 amp diode to connect the honda to the battery. basically half a battery idolator.

the simple stator charge system will be fine.

 

[boscoe99]

Many twin engine airplanes have but one battery. To save weight. Both alternators (one from each motor) charge the battery at the same time.

 

[boscoe99]

Diagram from Yamaha showing two motors providing charge current to one battery.

 

[boscoe99]

Diagram from Evinrude showing two motors providing charge current to one battery.

 

[rolmops]

I presume that one is a kicker for trolling while the other is the main engine.
If you are not sure, the easy solution is to connect both alternators, but to run only one engine at a time.

 

[boscoe99]

All alternator regulators have diodes that prevent the flow of current from a battery to the alternator.

I don't see a problem running both motors at the same time connected to the one battery. Each battery will contribute a bit of current to the battery.

But as the man suggests, if there is any concern just run one motor at a time.