Linking just the negatives of two batteries in series

[Tmacmi]

I am trying to clean up the spider web of cables around my battery bank. I'm building a battery box as part of the process.

The neatest way to do this is to run the outside negative through the box across the inside battery and then have 2 negative cables running to the ground on the transmission housing.

However that got me to thinking. Can't I just run the two negative terminals in series creating just one cable to ground.

I'd have two positives back to the main switch as always.

The batteries are 27 DC with 750 CCA

[Spot]

Negatives are linked for parallel, not series...

[Shrew]

I see batteries in neither Series or Parallel. I see two battery banks each with a single battery.

[The Way]

Originally Posted by Tmacmi

I am trying to clean up the spider web of cables around my battery bank. I'm building a battery box as part of the process.

The neatest way to do this is to run the outside negative through the box across the inside battery and then have 2 negative cables running to the ground on the transmission housing.

However that got me to thinking. Can't I just run the two negative terminals in series creating just one cable to ground.

I'd have two positives back to the main switch as always.

The batteries are 27 DC with 750 CCA

Yes. Mine have been that way for years. It makes sense since there is a common ground somewhere anyway. One is the start battery, the other a deep-cycle house battery. I connect the 2 negatives with a cable, and one of the 2 to the ground with another cable.

Fair winds,
Jack

[Tmacmi]

Originally Posted by Shrew

I see batteries in neither Series or Parallel. I see two battery banks each with a single battery.

Yes. Exactly. That is the starting point.

The question is can I run the negative from terminal to terminal (parallel, thank you) and thence on to the ground connection.

It appears the answer is yes.

Follow up question, do I have to increase the gauge of the negative ground wire because it is now carrying increased load?

[PirateGuy]

Originally Posted by Tmacmi

Yes. Exactly. That is the starting point.

The question is can I run the negative from terminal to terminal (parallel, thank you) and thence on to the ground connection.

It appears the answer is yes.

Follow up question, do I have to increase the gauge of the negative ground wire because it is now carrying increased load?

Depends on the length of cable. Check the tables, for a very short cable, there might not be any significant voltage drop with your existing cabling, assuming re-use.

[Tmacmi]

Originally Posted by PirateGuy

Depends on the length of cable. Check the tables, for a very short cable, there might not be any significant voltage drop with your existing cabling, assuming re-use.

I'm having all new cables made that's part of why I'm asking. The length is about 4'

[oldjags]

If the batteries aren't part of the same bank, I think it's probably OK to 'daisy-chain' the negatives together and then run only one wire to the ground buss. Just make sure the cable is a large enough gauge.

Batteries on the same bank though should all have identical-length cables run to the busses.

[zstine]

Originally Posted by Tmacmi

I'm having all new cables made that's part of why I'm asking. The length is about 4'

we also need to know the existing AWG wire size and highest amperage expected to tell if the existing cable is okay... wire size charts are also easy to look up yourself, btw.

[guyrj33]

There is no harm in oversizing the common ground cable. Your highest current draw is probably starting your engine, and that's a time where minimizing voltage drop can make a noticeable difference.
I once made oversize battery cables for a car I owned (the parts were free) and the engine cranked noticeably faster.
With your current battery arrangement, you do not need to keep cable lengths the same.
There is a lot that can be learned from a good book on 12v systems.

[Montanan]

I see several opposite polarity wires crossing and laying in direct contact with each other which wires are NOT fuse protected such that if they short to each other there will be huge and unprotected circuit of power.

Never have opposite polarity wiring or cabling come in contact, or potential contact with each other, if such portion of the positive polarity wire or cable is not protected by circuit breaking devices, [a fuse or a circuit breaker] to the source of the power, be that source the terminal of a battery or a bus connection.

The wiring in the image is hazardous and amateurish. Makes me wonder what the rest of the wiring is like.

Question:

Is this bank of batteries:
1) two completely separate battery banks;
or are they
2) two batteries in parallel circuitry?

Answer the above question, then and only then can forum members provide guidance.

Awaiting your response.

[Montanan]

Originally Posted by Tmacmi

I'm having all new cables made that's part of why I'm asking. The length is about 4'

The "length" of a circuit is its complete pathway from the positive power source and back to the negative of the power supply.

Do not calculate your gauge size based on just the length from the source to the load, or to a component within the circuit, e.g., to a common bus.

One needs to calculate the resistance and voltage drop across the entirety of the electrical circuit and each component thereof needs to have adequacy of ampacity.

THINK CIRCUIT, not partials of circuits.

[RigBig]

I see a number of circuits coming from those batteries that don't have a fuse at the battery. Bad idea. Plus neither battery seems to have a battery tie-down strap. Again, bad idea.

To answer your question you can connect both negatives together at the batteries and run one ground to the engine if thats where your common ground is located. It isn't parallel or series. Just a common connection.

[19thol]

Geez, everyone is getting their panties in a bunch over your picture of batteries, good thing they can't see mine!! There would be a rush on the emergency room.

[Spot]

Originally Posted by RigBig

I see a number of circuits coming from those batteries that don't have a fuse at the battery. Bad idea. Plus neither battery seems to have a battery tie-down strap. Again, bad idea.

To answer your question you can connect both negatives together at the batteries and run one ground to the engine if thats where your common ground is located. It isn't parallel or series. Just a common connection.

Not series, not parallel, common connection for ground