Two Banks Connected at Negative Terminals

[NOLA_sailing]

Good morning, everyone. I am gradually getting to know the systems on my newly purchased 1980 Catalina 30, one weekend at a time. I am well researched in 12V systems but am quite the novice in application. This weekend I was changing out the batteries (The boat has what I thought was two single battery banks). When I was replacing the batteries I noticed that although each battery's positive cable led to their respective post on the 1/2/both/off switch, battery two's negative cable was wired to battery one's negative terminal. Is this just a shortcut to closing each battery's circuit as the positives are independently wired to the switch? That is my first instinct but wanted to defer to the 12V sages here. Thanks!

[GordMay]

Yes, all Negatives connect together (then to engine).

See ➥ Basic DC Wiring Diagram - Figure 1b,From ABYC Section E-9 showing basic DC System Wiring Cruisers & Sailing Photo Gallery

And ➥ Basic DC Neg & Gnd Wiring - Figure 15, ABYC Section E-9 - DC Negative & Grounding Wiring Diagram Cruisers & Sailing Photo Gallery

[NOLA_sailing]

Thank you! My assumption was that with only two batteries in total, it was wired this way in lieu of using a neg bus bar. When it comes to electronics (as with anything I can't see or touch) I only minimally trust my own assumptions.

[ryon]

I suspect that there is a cable connecting those two negative terminals to a common ground.

[NOLA_sailing]

Originally Posted by ryon

I suspect that there is a cable connecting those two negative terminals to a common ground.

There is!

[Draikhyan]

Originally Posted by NOLA_sailing

Is this just a shortcut to closing each battery's circuit as the positives are independently wired to the switch?

Yes it is.

[bsurvey]

totally correct installation, battery negatives wire together then you have one lead to the ground on the hull, engine block, zinc ect all part if the bonding system,

[Cadence]

Originally Posted by NOLA_sailing

Good morning, everyone. I am gradually getting to know the systems on my newly purchased 1980 Catalina 30, one weekend at a time. I am well researched in 12V systems but am quite the novice in application. This weekend I was changing out the batteries (The boat has what I thought was two single battery banks). When I was replacing the batteries I noticed that although each battery's positive cable led to their respective post on the 1/2/both/off switch, battery two's negative cable was wired to battery one's negative terminal. Is this just a shortcut to closing each battery's circuit as the positives are independently wired to the switch? That is my first instinct but wanted to defer to the 12V sages here. Thanks!

Your good if I understand you. Neg. to neg. terminal and one wire to the neg. buss. If I did? A book on DC fundamentals would be a great investment. Nothing is as a frustration as DC in a saltwater environment.

[Old Swampy]

It might help to think about when the battery switch is on "both". The switch connects the positive terminals, but there has also got to be a negative connection of the two batteries, if they are to work together in parallel.

[Stu Jackson]

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 - SailboatOwners.com

Yes, the negatives are connected and go back to the engine ground.

These links are to show the the positive side options. You need to understand both of them.

Good luck. Happy learning.

[glenn.225]

NOLA

I have found these two links most helpful.

Electrical Systems 101

1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

Have a read through each of these, they are gold when it comes to understanding electrical systems in small boats. I had a very good understanding of automotive electrical systems but ran into issues when I tried to apply them to a boat. I gained quite a bit more insight about marine electrical systems from these posts and other marine electrical literature.

Also you will find lots of more helpful posts here from these two generous people and many others.

[glenn.225]

Stu your very helpful and quick too.

[NOLA_sailing]

Originally Posted by Stu Jackson

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 - SailboatOwners.com

Yes, the negatives are connected and go back to the engine ground.

These links are to show the the positive side options. You need to understand both of them.

Good luck. Happy learning.

Thank you, Stu! I have seen (and bookmarked) this and other Main Sails musings that are very informative. The real world wiring just threw me off as most diagrams show negative leads from separate banks joining at a neg bus. After thinking about it, and with confirmation from the CF brain trust, I now understand that the neg terminal is acting as a neg bus.

[NOLA_sailing]

Thanks, Glenn and Swampy!

[jeepbluetj]

I don't know the age of your C30, but catalina definitely didn't put any busses at all in mine. The factory wiring was poor, then the siliconehead POs seemed to have no idea at all how to hook wires together. My "neg buss" at the panel was about 20 wires crimped, soldered, and taped together.

Needless to say when I rewired I put in bussbars - one for the negs up in the panel, and a large one under the chart table for the batteries. I have 3 batteries (one under the starboard settee) and it cleaned up the wiring quite a bit.