Two engines and four batteries...How to Connect?

[dpb]

I am on my first twin diesel boat and just wanted to clarify a couple of things regarding the 12v electrics and charging arrangements.
First a few details (it is clear that the original configuration by the manufacturer has been tampered with and I havn’t worked out yet exactly how all is connected):
The boat has:
2 engines both, with alternators.
2 batteries the same size as 110amphour leisure batteries. These are currently designated as domestic only.
2 huge batteries, about the size of 4 or 5 80amphour batteries stuck side by side. One is a starter battery only, the other is linked to start and domestics.
All batteries have independant isolator switches.
One split diode,
One charger converter with three outputs
One shunt for joining two batteries.

What I am intending to do is:
Use small batteries as starter batteries (assuming adequate capacity) and large as domestics.
Connect both large batteries into one bank of domestics.
One alternator charging one starter battery only.
Other alternator charging other starter and domestic bank via split diode.
Charger out puts connected , (1) to starter battery (2) to other starter (3) to domestic bank.
Use shunt to connect starters if one is flat.

Does this sound right?....any comments?

 

[kashurst]

sounds about right, just check out your alternator and charger capacity re your battery capacities

 

[kashurst]

second thoughts check out the orientation of the diode splitter - is it for two alternators to charge one battery or one alternator charging two batteries. also does your alternator have remote voltage sensing so that the batteries after the diode splitter are charged correctly.

 

[pappaecho]

A bit worried about the old starter batteries, being used a domestics. Starter batteries deliver a lot of amps for a short period of time, with a fast recovery time.
Domestic batteries on the other hand are the converse, having much deeper discharge capabilities and deliver an even current for a long period of time, without damage to the battery.

 

[PCUK]

One battery to start both engines and the rest as domestics. Don't waste a second battery on engine starting as these are the least used on the boat. Include a solenoid between domestics and engine start for emergency starting.

 

[PaulGooch]

I'd use all 110ah leisure/marine batteries, all new if needs be.

One for the engine, the rest for domestics.

A single isolator like this : http://bluesea.com/products/5511e will mean one click of the switch enables/disables both circuits and the "combine" setting would allow the engines to be started from the domestic bank, in event of a starter battery failing.

Using an alternator to charge a single engine battery is a waste. The engine battery will be recharged very quickly and that alternator will be sitting idle, it would be better served charging the domestic bank. So, fit a diode pack for two alternators and two banks.

 

[dpb]

Thanks for the comments which I will take into consideration.....it seems that there may be more than one right answer!
I was suprised to find that even having spent a bit of time googling twin engine battery / circuit diagrams I only found single engine layouts, even checked MBM article search and found nothing showing twin engine wiring!

 

[halcyon]

I was suprised to find that even having spent a bit of time googling twin engine battery / circuit diagrams I only found single engine layouts, even checked MBM article search and found nothing showing twin engine wiring!

Using one battery for engine start and domestic can have a number of problems.
Volt drop and circuit noise can be a problem with electronics on engine starting.
Battery charging can be reduced due to the domestic load ( fridges, nav equip etc ) on the alternator, can reduce voltage and hence charge level.
Charging through the blocking diodes can / will reduce battery recharge level due to diode volt drop, so may well need alternator reg upgrade.

Connect both engine starter motors to one battery / battery bank, size as per engine maker spec, leave one alternator ( say port ) connected to this battery.

Connect starboard alternator to domestic bank direct.

Fit a suitable rated VSR between the two battery banks, this will allow port alternator to help charge a low domestic battery bank.

It also allows either alternator to automatically charge the other battery bank if it's alternator fails, and provides emergency link start from the domestic battery bank from the helm.

Brian

 

[PaulGooch]

Avoid VSR's.