Battery switch question

[Mycroft]

My new-to-me 43 foot cutter has two main battery switches.

A. is a standard 1-Both-2-Off switch
B. is an On-Off switch that appears to be connected to bank 2

So if B is off, then switching A to bank 2 from Both turns power off.

It seems that B is some kind of redundant since you can easily disconnect from bank 2 by moving A to bank 1.

What might be the purpose for this configuration?

Thanks,
Bob

[Maine Sail]

Originally Posted by Mycroft

My new-to-me 43 foot cutter has two main battery switches.

A. is a standard 1-Both-2-Off switch
B. is an On-Off switch that appears to be connected to bank 2

So if B is off, then switching A to bank 2 from Both turns power off.

It seems that B is some kind of redundant since you can easily disconnect from bank 2 by moving A to bank 1.

What might be the purpose for this configuration?

Thanks,
Bob

Pretty common configuration if one wants a dedicated starting battery and yet still retain all the redundancy of the 1/2/ALL..

Wiring can look similar to this:

[Mycroft]

Thanks!

So how should the switches be set for these ops:

1. Starting the engine.
2. Underway with engine running
3. Underway/anchored without the engine running
4. Berthed and hooked to shore power

I'm guessing:

1. A-1, B-On unless the starter bank 2 is dead in which case A would be switched to Both?

2. A-Both, B-On so both banks can charge?

3. A-1, B-Off so the starter bank is reserved for starting

4. A-Both, B-On so both banks can charge?

Thanks again.

Bob

[smac999]

you would have to figure out the whole system to answer that question. first would be to confirm if the above picture is what you have. you'll have to look at the back of the switches and follow all the wires.

next you need to figure out what you have for a charging system. both from a shore charger and the alternator. like if you have a diode block, acr etc. and a multi bank charger.

if it's set up properly you'd never move the switches unless you had a problem or a dead battery.

if it's not set up well you'd probably have to switch to both to charge.

[h the boat]

Originally Posted by Mycroft

Thanks!

So how should the switches be set for these ops:

1. Starting the engine.
2. Underway with engine running
3. Underway/anchored without the engine running
4. Berthed and hooked to shore power

I'm guessing:

1. A-1, B-On unless the starter bank 2 is dead in which case A would be switched to Both?

2. A-Both, B-On so both banks can charge?

3. A-1, B-Off so the starter bank is reserved for starting

4. A-Both, B-On so both banks can charge?

Thanks again.

Bob

Main Sail is quite correct, it dosent matter if you have a diode splitter or not, his configuration is correct, however if the start battery is totally flat for any reason, it is always better not to switch it in, as it will draw a lot of current from your service battery, and may not be enough to start your engine. Good tip, always check your batteries regularly and keep them clean and dry on the outside and topped up with Distilled water on the inside. Unless they are of the permanently sealed type... H the Boat.

[Maine Sail]

Originally Posted by Mycroft

Thanks!

So how should the switches be set for these ops:

1. Starting the engine.
2. Underway with engine running
3. Underway/anchored without the engine running
4. Berthed and hooked to shore power

I'm guessing:

1. A-1, B-On unless the starter bank 2 is dead in which case A would be switched to Both?

2. A-Both, B-On so both banks can charge?

3. A-1, B-Off so the starter bank is reserved for starting

4. A-Both, B-On so both banks can charge?

Thanks again.

Bob

Bob,

We have no way to know how your system is physically wired. If you can tell us what is connected to what & where including starter, house loads, alternator and the switches we can then help. Best to draw it out.....

The drawing I showed you is pretty generic and people mess up that wiring often so it's very hard to say how your system works without physically seeing it...

[Mycroft]

Thanks guys! Looks like I need to do some more wire tracing.