The outboard batteries on

[Rum_Pirate]

On my boat I have two 85hp outboard engines.

They are supposed to be completely independent installations.

However the two batteries have been connected by one wire. Why?

 

[tico]

Common Earth?

 

[markdj]

If u have any electronics and there is appositives connection as well, it is distributing the load though it also means u have no redundancy. Better to use one start, one domestic but this would require voltage sensitive relay to be installed.

 

[Rum_Pirate]

Common Earth?

Yes, but there is no earth point on the fibreglass boat.

 

[jfm]

Yes but joining the negatives ensures both engine casings are at the same elctrical potential. If you made them totally independent one could be an anode relative to the other, resulting in corrosion of the anodic engine. Much better to hard-connect the negatives

Anyway, conencting the negatives doesn't really mean they're not independent. you could if you wish hard connect the negatives but still keep the batteries independent, so that if one goes flat the other will start its engine

 

[Rum_Pirate]

Yes but joining the negatives ensures both engine casings are at the same elctrical potential. If you made them totally independent one could be an anode relative to the other, resulting in corrosion of the anodic engine. Much better to hard-connect the negatives

Anyway, conencting the negatives doesn't really mean they're not independent. you could if you wish hard connect the negatives but still keep the batteries independent, so that if one goes flat the other will start its engine

Ah! The mist of ignorance clears. Thanks.

 

[VicS]

Yes but joining the negatives ensures both engine casings are at the same elctrical potential. If you made them totally independent one could be an anode relative to the other, resulting in corrosion of the anodic engine. Much better to hard-connect the negatives

Anyway, conencting the negatives doesn't really mean they're not independent. you could if you wish hard connect the negatives but still keep the batteries independent, so that if one goes flat the other will start its engine

Ah but you can only get a current flow between them causing corrosion if they are connected!

If left isolated from each other there is no return path for the current.

No path = no current. No current = no corrosion!