Engine Starting Video / Real World Amp Load Data

Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
If the alternator output is NOT routed through

the 1-2-B switch, and is run directly to the house bank, then the 1-2-B switch is not part of the charging circuit, and it is used ONLY to determine FROM which bank power is selected (i.e., to the distribution panel and to the starter), then this issue becomes irrelevant.

Too many boats still have the alternator output run to the "C" post of the 1-2-B switch. That's where the problem comes from, because the switch is then the determinant of where the alternator output goes. That's why people had to start their engines on BOTH, because moving the switch could cause fried diodes.

Each skipper needs to figure out how their boat is actually wired, and then make a decision as to how he runs his electrical system. While most have 1-2-B switch, what's behind the panel and how the wiring is run (or how YOU design your system) makes all the difference in the world.

In order to keep the 1-2-B switch if you want to, and to make life simpler, run the alternator output away from the switch, directly to the house bank, and decide how you want to charge your reserve bank (i.e., combiner, echo charger, another switch), and then keep the battery bank outputs going to the switch, and the outputs of the switch go to the starter and the panel.

Yes, I know echo chargers are better than combiners for start banks, but you can put a simple toggle switch on a combiner (ground leg) and control its output, too.

We use our house bank to start the engine, too. Our reserve emergency (start) bank is kept fully charged and is only used periodically to check it's working, and is left as a true backup. That's why I agree that we should stop calling it a start bank and begin using the term emergency or reserve bank. It's like one of those jump start packs, but it's always there, ready to be used.

Here's a wiring diagram of our boat. I worked with Jim Moe on editing his excellent article that Don's Reply #19 linked to on our C34 website. These are two different wiring diagrams with two different approaches to the issue, but both get the alternator output to the house bank. I deliberately chose to leave the 1-2-B switch and make it work correctly for me.

Many variations on the theme, but the MOST important thing is to get the alternator OFF the 1-2-B switch. It'll save you headaches, and make understanding what you have much easier, because UNLESS it's moved, think about it, you have incoming and outgoing power running through the switch when the engine is running -- the switch serves two purpose then.

KISS. Many ways to do that. And many thanks to Maine Sail for bringing up this fun topic in a thoughtful and helpful way. (I finally got this wiring diagram scanned in as a jpg for help in answering a lot of questions folks have been asking for years. The only odd thing you may notice is that I paralleled a new #4 ground to the existing ground from the NDP back to the engine - that was only for access reasons. Based on amperage and distance the new #2 wire alternator output is oversized, as are the paralled #4s, but they work!)
 

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