Battery amperage?

[Sanguinius]

Before someone kicks this to electrical, It IS an engine as well as an electrical question. I feel it fits better here though.

My boat has twin inboard 318's. I have no battery and am looking to find out the Amp rating required for a cabin cruiser with the twins. I'm looking at a 75 Amp right now but I'm not used to deep cycle ratings I'm used to CCA ratings since cars don't need the constant power.

Also does the battery run the electronics in the boat while running (AC and DC or only DC available out to sea?). Thanks.

 

[roscoe]

Re: Battery amperage?

You should not be using a deep cycle battery.
Deep cycle batteries are for trolling motors.

You need a starting battery, Something in the 600cca or 800mca range, or bigger.

Your engines should be equipped with an alternator to run the accessories and charge the battery.

On a boat that size, you likely have one or two deep cycle batteries also, to run any high draw accessories.

If you have only one battery, get the largest "dual purpose" battery you can find, like a series 31.

No way of us knowing how your particular boat is wired up.

 

[Sanguinius]

Re: Battery amperage?

Yeah I'm not even sure how my boat is wired up. I'm about to redo the wiring myself here shortly since most of it was fairly well thrashed from seawater exposure.

So now my question is this: Do the alternators run the 120 AC as well as the 12 V DC? and what are recommendations for the wiring setup for this boat? It's a 1965 Owens Cabin Cruiser. That's all that the title tells me at least.

 

[JB]

Re: Battery amperage?

You may think it is an engine/electrical question, but it sure as heck isn't an outboard question.

I think it is a boat question.

 

[Sorrento 25]

Re: Battery amperage?

You really need to determine what the original setup was and how the house loads are wired. What do you have for a switch and how many batteries did the boat have? How much do you want to spend upgrading the electrical system?

I think the best setup for twins is two small cranking batteries and a separate house bank as big as you need it to be. Spend some time researching the Blue Sea and Jack Rabbit Marine sites for good info on electrical systems. I love the Blue Sea isolation concept that protects your start battery and eliminates the evil 1-2-both-off switches. A/C underway requires an inverter or generator. You probably need a new onboard charger too so if you decide to try an inverter look at inverter/chargers.

 

[mattttt25]

Re: Battery amperage?

You're asking some simple, yet involved questions. For the simple ones...

Like others said you want cranking batteries, minimum of 2 going through a series of switches. You want to be able to isolate 1 battery to 1 engine, but also cross them when needed. Look around here and on google to find wiring diagrams and a better explanation. With this set up, you also probably want a large deep cycle for your 'house' power.

As for house power, the batteries and your engines only generate DC. You can run your DC items no problem. If you have a 120 V system installed, then you need either a battery running to an inverter or a separate generator to provide the AC.