Should I parallel two engine batteries?

[Boater On Thames]

My boat has two engines and two separate engine starter battery. The port side engine battery also supply to the bow thruster. Should I parallel those two engine batteries so make a big one? Or just keep them separate?

What will you do? Thanks.

 

[peteK]

Keep them separate but link with a switch so you parallel if required.

 

[MapisM]

I'd rather join the batteries in a single bank, particularly since they are supposed to feed also the b/t.
And then install a switch to parallel the engine bank with the domestic bank in emergency.
That's the OEM setup in many boats, btw.

 

[Boater On Thames]

That is a smart idea! Thanks

 

[halcyon]

My boat has two engines and two separate engine starter battery. The port side engine battery also supply to the bow thruster. Should I parallel those two engine batteries so make a big one? Or just keep them separate?

What will you do? Thanks.

What is your system ? what method do you charge the service bank and bow batteries?

Brian

 

[Seastoke]

depending how good you are at wiring , its better to have a solenoid to link with a switch on the dash the switch being a hold on type ,then if one engine fails start the other then press button and start the other engine , this then does not mess with charging the batteries.

 

[simonfraser]

Does this not depend on the battery and engine size ?

 

[halcyon]

I'd rather join the batteries in a single bank, particularly since they are supposed to feed also the b/t.
And then install a switch to parallel the engine bank with the domestic bank in emergency.
That's the OEM setup in many boats, btw.

The problem with this set-up is you only have one alternator charging the service battery, the service load reduces available current from the one alternator and you can also get a reduction in max voltage due to service loading.

Brian

 

[MapisM]

There are ways round that, but I agree that what I previously suggested requires some re-thinking also of the charging arrangement.
Keeping the status quo with just a parallel switch between the two starting batteries is a simpler solution.

 

[Boater On Thames]

My system previously has a 3 output 70A charger. But now replaced to a 2 output 60A charger to charge all batteries. The output A connected to the house batteries bank. So I want to use the output B to charge the two engine batteries the same time without a battery isolator. Because I learned that the isolator will has around 1V drop.

The system also has two alternators (Engine is Volvo Penta TAMD61A, each engine has one) connected to an 2 in 3 out battery isolator to supply the turbo charge (I think so) and charge the house batteries bank.

 

[halcyon]

My system previously has a 3 output 70A charger. But now replaced to a 2 output 60A charger to charge all batteries. The output A connected to the house batteries bank. So I want to use the output B to charge the two engine batteries the same time without a battery isolator. Because I learned that the isolator will has around 1V drop.

The system also has two alternators (Engine is Volvo Penta TAMD61A, each engine has one) connected to an 2 in 3 out battery isolator to supply the turbo charge (I think so) and charge the house batteries bank.

Check alternator voltage and battery terminal voltage when charging at a high current, you may have a large volt drop from the splitter.

Join two batteries for engine start and connect one alt to them, then the other one to service bank will avoid the volt drop.

A VSR between them will allow the engine alternator to also charge the service bank as well, or the service alt to charge the engine batteries if alt fails. With link start on the VSR you also cover engine battery problems.

Brian

 

[Boater On Thames]

Thanks Brian. This sounds even better. So I can get rid of the existing splitter.

 

[Boater On Thames]

(deleted)

 

[PCUK]

I just have one starter battery for both engines as they do the least work of any batteries on-board.