Upgrading my charging /starting circuit

[tsl]

I have a cranking battery (875 MC 700 CC)plus a house bank with two 115 amp hour 180 reserve deep cycle batteries. I intend to replace my 50 amp alternator with a 75 amp from Arco. Still a bit undersized but I also have a low output wind generator.
I intend to use the attached layout since the battery switch on my boat is 15 ft (cable route distance) from my batteries and starter (which are 2 feet apart). The existing cables are #2 AWG which I believe are well under sized for a round trip using the standard layout. (running all cables to the switch and then back)
I will replace the battery switch with a HD Dual combiner switch with AFD.

With the previous layout (30 ft round trip) and #2 AWG and battery the cranking battery often could not get the engine started. The glow plugs nearly overwhelmed it. This layout will also allow me to eliminate the battery isolation diodes.
My questions:
Is this going to help? Solve the problem? or waist money?
Should I replace the existing #2 cable between the house batteries, switch and starter with 00 awg? or will the location of the cranking battery help the surge amperage should I have to combine both banks to start the engine.
How do I use the AFD? I will use an internally regulated alternator Arco 65108 with a lead that is marked S +sense that goes to the battery and EXC that goes to the ignition.
The boat is an Oday 39 with a Universal (Kubota) 44 hp diesel.

[GordMay]

The AFD is a second switch inside the battery switch, yet electrically isolated from it. The AFD switch closes before the battery switch contacts close and opens before they open.
It is connected in the field wire between the voltage regulator and the alternator, preventing the alternator from producing power when the AFD switch is open. Its purpose is to protect the alternator diodes, which can be damaged if the alternator is producing power and the battery switch is suddenly turned off.
See ➥ http://bluesea.com/files/resources/i...eb_version.pdf
And ➥ Using Blue Sea Systems' Battery Switch AFD Terminals to Indicate Switch Position - Resources - Blue Sea Systems

[tsl]

Thanks Gord,
Unfortunately,, my choice ($200 VS $1200) of alternator has an internal regulator so I was hoping I could use the AFD portion of the switch to break the ignition lead or the Sense lead that goes to the battery. Breaking either lead should stop any output and therefore save the diodes. That's my theory, I'm posting to get a bit of reality.

[GordMay]

If connected in series with the Alternator Field wires, the AFD auxiliary switch will interrupt the connection to the alternator’s field, preventing damaging transients.
Accordingly, the AFD auxiliary switch will only work when you have access to the Alternator Field Wires.
This is the typical situation with Externally Regulated Alternators; but an Internally Regulated Alt’ can have the Field Wires brought out (<$50 at an Alt Shop).

[motion30]

before you purchase a alt check ebay there are some good deals there

[btrayfors]

tsl,

With your house battery bank of only 230AH total, I would not bother upgrading the alternator just yet. Assuming these are flooded batteries, they'll only take a maximum of about 55A when they're discharged to 50% anyway, and even a larger alternator will scale back quite a bit after a few minutes.

Your proposed wiring is fine as far as it goes, but I'd add three things:

1. a simple on/off battery switch (like the Blue Sea Systems #6006) on the start battery;

2. an ANL or Class-T fuse in the starting circuit, located close to the start battery; and

3. an EchoCharge between the house and start batteries; this would automatically maintain the start battery without any intervention on your part.

The ON-OFF switch would be for the engine starter only. Leave it OFF when the engine isn't in use.

The 1-2-BOTH-OFF switch would remain in the number 2 position (house battery bank) or OFF.

JMO,

Bill