One Starting Battery For Two Engines?

[nnyerges]

Hello all,

I am remodeling the entire electrical system of my boat and need advice to make my decision with respect to use two or one battery for starting the two Ditroit Diesel 310HP engines. I know that the most common is to use one battery for each engine and currently have two starting batteries (see DC-GENERAL-ORIGINAL.JPG)

Becouse space and weight problems, I need to remove one battery.

Obviously I can take out the HOUSE battery. Neither the GENSET battery, as it has its own alternator/battery charger and cannot be connected to the isolator. So I can only remove one of the engines starting battery (see DC-GENERAL-NEW.JPG)

The idea is to place the current HOUSE 1500A 8D battery, to start both engines, eliminating the 1200A. Place a new 8D DEEP CYCLE battery for the HOUSE. Switches A and B are used to draw a emergency parallel between any of the 3 batteries (including the GENSET battery). Switch C is for shutting the service when should start with the house battery. The two engine alternators are responsible for charging the starter and service battery through the isolator. Likewise, the AC / DC CHARGER is responsible for maintaining the 3 batteries charge, when the engines are stopped and AC is present.

I hear suggestions, criticisms and above all, I need the pros and cons that can give me, since if cannot remove the battery, I will have to do a big complicate job of remodeling the hull.

Thanks in advance,
Nicolas

EDITED: I mistake by placing AH on lead acid batteries, where A should say for cranking current of 1500A or 1200A. Deep Cycle 255AH data its ok

[RayThackeray]

Originally Posted by nnyerges

The idea is to place the current HOUSE 1500AH 8D battery, to start both engines, eliminating the 1200AH.
Nicolas

1200AH at 12 volts - isn't that like running at well over 10 kilowatts for an hour?!?! Damn, I wish I had one of them...

[CDK]

To me this sounds like someone has mixed up battery capacity and cranking current.

Give each engine a 120 or 160 Ah starter battery and keep the 1500 Ah house bank if you have the space for it and really need the power. Also remove the 1200 Ah genset battery.

You'll loose so much weight you should paint a new waterline on the hull.

[Frosty]

He means 120 amp, there no such thing as a 1200A.

Why would you care about wieght with 2x 310 Detroits.

Engines need a battery to start you cant reduce weight on that.

[nnyerges]

EDIT: I mistake by Placing on lead acid batteries AH, WHERE A Should say for cranking current of 1500A or 1200A. 255AH Deep Cycle dates its ok

When you specify a lead-acid battery, it is called by its cranking current or start current max. capacity and when you specify a Deep Cycle battery, it is called by reserve standby current in a hour. However, the fact that instead of writing A and not AH, does not mean you are unclear of what Im speaking here (I guess). Of course when I talk 1500 or 1200 I mean the cranking current. Now if you are so kind, can comment on the main reason of this post. Misspellings can be leave it for another topic. I just need to know if the new configuration its viable, not why i have to reduce weight. Thanks

[gonzo]

That is a very complicated system. Use one battery for starting and the rest for house.

[RayThackeray]

Originally Posted by gonzo

That is a very complicated system. Use one battery for starting and the rest for house.

What he said.

I'm in the process of installing two generators (that will power a DC motor drive each plus provide house power). I'm going to install a simple single cheap automotive starting battery for both, and will have a switch that allows the bridging of the house bank in case the starting battery gets low, for emergency starting. I can't imagine any need for anything more complicated.

[Frosty]

If both engines run of the same fuel supply I would not go this route.

[RayThackeray]

Originally Posted by Frosty

If both engines run of the same fuel supply I would not go this route.

This statement begs a question and an admonition:

To which route are you referring? And:
You can't make the statement without explaining your logic...

[Frosty]

If the engines run on the same fuel supply both engines will stop if fuel was contaminated. One battery is then all you have for re starting 2 troubled engines.

If one battery was exhausted niether engine could be started.

Unless-- you had a cross over to house.

[RayThackeray]

Originally Posted by Frosty

Unless-- you had a cross over to house.

But that was already stipulated. So the objection was already dealt with.

[Frosty]

Objection? from me? Just an opinion, but thank god almighty your here to keep me straight and word perfect.

You de man Ray.

Maybe he should just do what you say, yeah --I think that woulod be best, well I mean if thats ok with you Ray.

[FMS]

There appears to be a typo in the first post:

Originally Posted by nnyerges

Obviously I can take out the HOUSE battery. Neither the GENSET battery, as it has its own alternator/battery charger and cannot be connected to the isolator. So I can only remove one of the engines starting battery (see DC-GENERAL-NEW.JPG)

Looking at the diagram, I and I believe Ray assume this "can" was supposed to read "can't" whereas it seems Frosty assumed the house bank wouldn't be possible to bridge for emergency use.

[nnyerges]

Originally Posted by FMS

There appears to be a typo in the first post

Yes, it should say can't. Sorry

Originally Posted by Frosty

..Unless-- you had a cross over to house.

Thats switch "B" for. By the way, a question remains: I place the switch C, ostensibly to prevent any reverse current to the equipment of the ship, in the case i need to start the engines with the service battery. Is "C" necessary? I already have a master ship service breaker, do i have to turn it off when starting engines from house battery?

[tunnels]

Originally Posted by nnyerges

Yes, it should say can't. Sorry

Thats switch "B" for. By the way, a question remains: I place the switch C, ostensibly to prevent any reverse current to the equipment of the ship, in the case i need to start the engines with the service battery. Is "C" necessary? I already have a master ship service breaker, do i have to turn it off when starting engines from house battery?

Do you have trouble making up your mind what to have for breakfast in the morning ??