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post #5 of Old 05-14-2013
Stu Jackson
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Re: alternator questions

Originally Posted by SSBN506 View Post
I have a few questions about an alternator. I have a m25 on a 1986 Catalina 30
tall rig.

1. My first question is what is the amp output of that engine alternator?

2. My second question is about how it is wired. I have a clipper bm-1 battery
monitor I just installed. I have everything working for the most part as it is
monitoring my house bank and can pick up the drains of all the electrical stuff
and the change from solar. What I am wondering is how to get it to se the

3. My setup is as follows. I have the battery switch that has bank 1 and 2 all and
off. On bank on 1 have two batteries one is 85ah and 140ah connected together.
Bank 2 is the starting battery.

The bmr picks up everything from bank 1 just fine. I can but haven't wired it to
bank 2 yet.

4. My question is where will the alternator put it's charge? Does it
just put it back into the starting battery or is it wired to the electrical
panel so it will change all banks? Do I have to change the dale to all to charge
all battery's from the alternator?
1. The OEM alternator was 55A.
2. Seeing the alternator: most battery monitors measure NET charge. That means that if your fridge is on drawing 5A and your alternator is producing 20A, the monitor will see 15A. Same thing with your solar panel. If you want to see what the alternator is producing, turn everything else off, including the solar.
3. Don't understand "connecting to Bank 2, yet" bu I do not know what your monitor is capable of doing. If it does two banks for monitoring amp hours, that's great. Many monitors measure the house bank amp hours but only voltage from a second bank. Depends on what you have. I know I could look it up, but it's your monitor, right?
4. It all depends on how it's wired. Most OEM arrangements have the AO (alternator output) going through the C post of the 1-2-B switch. Here's some information that might interest you:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings -

Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

You migth also be interested in this:

Stu Jackson, Catalina 34, 1986, M25 engine, Rocna 10 (22#), Maple Bay, BC, Canada

Last edited by Stu Jackson; 05-14-2013 at 03:07 PM.
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