Electrical question

[timchapman]

Should the negatives of the house battery and the starter battery be commoned together or kept separate?

 

[Tranona]

If you want the engine start to be independent then no connection to the house bank except possibly through paralleling emergency switching.

 

[prv]

If you want the engine start to be independent then no connection to the house bank except possibly through paralleling emergency switching.

Surely a shared negative is perfectly normal though, and not a problem? If nothing else, any mains charger is likely to have only a single negative connection.

Pete

 

[VicMallows]

Unless the engine is designed so that the block is TOTALLY isolated from ALL electrical accessories (which would be very unusual) I think it would be most unwise NOT to connect the battery negatives.

 

[VicS]

Should the negatives of the house battery and the starter battery be commoned together or kept separate?

They will have to be common if the alternator, and other charging systems, are to charge both without switching.

Unless the engine is designed so that the block is TOTALLY isolated from ALL electrical accessories (which would be very unusual) I think it would be most unwise NOT to connect the battery negatives.

Isolation of the engine block from the negative is a different issue and can still be so even if the battery negs are common

 

[nimbusgb]

Common allthe negs

 

[halcyon]

Common allthe negs

Common earth point, avoids the risk of a difference in earths in various points of the boat and the associated risk of electrolysis.

Brian

 

[Ann-Marie]

Should the negatives of the house battery and the starter battery be commoned together or kept separate?

Typically the house battery will need to be charged while underway from the engine alternator by using a switch, an isolator, or a Combiner100. The negative terminals need to be connected together to provide a return path for this charging current. I like to see this common between the batteries at least as heavy gauge cable as your starter motor cables. That way if you jumper the positive terminals together in an emergency to start the engine, the negative connection will be able to carry the load and not catch fire.

 

[nigelmercier]

Agree with all above saying to have a common negative, but note that this may not mean connecting the battery negatives together, there may be shunts to consider. If so, consider the battery and associated shunt as a single unit, do not attach anything to the wire between.

 

[William_H]

Agree common all negatives togehter (unless there is a shunt) but do use heavy cable from domestic batteries in case they are needed to start the engine. olewill

 

[savageseadog]

It's better to use two negative cables from the battery negative, one for the starter and engine and one for everything else. If you use one cable make sure it's a thick one, 35mm square or more.