Setting up a remote negative buss

[Tmacmi]

All my negatives return to the panel via spade connectors as you can see in the attached. I am going to build a remote negative buss. I have two questions.

1) Does there need to be a negative line run from the buss back to the panel?

2) The negative wire (perhaps 2) run from the panel down to the transmission bell housing at the same spot as the negative cables from the batteries. Is that acceptable to replicate? Or should they go directly to the battery negatives.

Thanks,

TMAC

[smac999]

Nothing is attached. But if the panel has indicator lights it needs a ground

Do not use the engine as ground. Go to battery. Or ideally a main bus bar near battery. (Which would connect all battery banks, engine , panel. Ac ground, bonding system. Etc)

[Manateeman]

Smac999 is on the money.
Victron has a nice tutorial on basic electrical. Try marine how too as well.
Sorry I’m to old to know how to post links so maybe somebody here can throw up a few more to read under the tree.
My manatees drank all the eggnog are sleeping and thus of no help.
Happy trails to you.
Mark

[Dsanduril]

The other two have it pretty much covered, some details to deal with but in principle create your negative bus and take it back to the battery/bus without going to the panel.

Caveat - this will create unbalanced DC circuits in your boat. Unbalanced DC circuits generate magnetic fields, the magnitude of which depends on the current in the circuit. If you run the positive and negative cables together they come close to cancelling each other (not perfectly since, with the exception of coax, they don't occupy the exact same space). Unbalanced DC circuits will affect nearby compasses (don't forget an autopilot compass that may be buried somewhere) and other magnetically sensitive gear. So give some thought to where the unbalanced wires run, how much current they carry, and how close they are to any compass unit.

[guyrj33]

Originally Posted by Dsanduril

The other two have it pretty much covered, some details to deal with but in principle create your negative bus and take it back to the battery/bus without going to the panel.

Caveat - this will create unbalanced DC circuits in your boat. Unbalanced DC circuits generate magnetic fields, the magnitude of which depends on the current in the circuit. If you run the positive and negative cables together they come close to cancelling each other (not perfectly since, with the exception of coax, they don't occupy the exact same space). Unbalanced DC circuits will affect nearby compasses (don't forget an autopilot compass that may be buried somewhere) and other magnetically sensitive gear. So give some thought to where the unbalanced wires run, how much current they carry, and how close they are to any compass unit.

Hogwash.

[Dsanduril]

Originally Posted by guyrj33

Hogwash.

Really? And on what do you base that statement?

Here’s just one short article Effects of static fields on compasses.

And a brief excerpt:

Note that these calculations are for a typical underground cable. For subsea cables, the two cores are usually further apart, widening the zone in which magnetic fields may be significant.

Yes, that article is about larger DC circuits, but the core physics is the same.

Or perhaps this video will convince:

https://m.youtube.com/watch?v=HcPDc23ZLEs

Or maybe just the ABYC standard for DC wiring:

11.14.4.2.1 Wiring shall be installed in a manner that will avoid magnetic loops in the area of the compass and magnetically sensitive devices. Wires that may create magnetic fields in this area shall run in twisted pairs.

Or back up your statement with some science.

[guyrj33]

Originally Posted by Dsanduril

Really? And on what do you base that statement?

Or back up your statement with some science.

In your poorly constructed reply to the original post Dsanduril wrote
"...
Caveat - this will create unbalanced DC circuits in your boat. Unbalanced DC circuits generate magnetic fields, the magnitude of which depends on the current in the circuit. If you run the positive and negative cables together they come close to cancelling each other (not perfectly since, with the exception of coax, they don't occupy the exact same space). Unbalanced DC circuits will affect nearby compasses (don't forget an autopilot compass that may be buried somewhere) and other magnetically sensitive gear. So give some thought to where the unbalanced wires run, how much current they carry, and how close they are to any compass unit."

Ok let's start with the false concept of an unbalanced DC circuit; the same current is flowing at all points in the circuit it's not unbalanced. You might be confused by reference to equal length wiring for multiple batteries joined together to form a battery bank. I don't know.
If by unbalanced you are referring to different length supply and ground paths that's not how magnetic fields are created so you statement "Unbalanced DC circuits will affect nearby compasses" is pure conjecture a.k.a. HOGWASH.
DC current in a conductor will produce a magnetic field. DC current in a conductor will produce a magnetic field. DC wiring with the supply and return running parallel to each other will produce magnetic fields in both conductors and they will reinforce each other (see right hand rule for magnetic fields). SCIENCE
"If you run the positive and negative cables together they come close to cancelling each other" again HOGWASH. If you want to mitigate the magnet field caused by parallel supply and return currents in a DC circuit twist the wires along their length. SCIENCE
COAX is used to shield HF signals not for DC. SCIENCE

[bcboomer]

guyrj33

You are right but perhaps you could be a little more diplomatic in your post. "hogwash" is just plain insulting and doesn't add to the conversation.
This forum has lost some really good contributors over the past 2 years and this type of attitude may be part of the reason.

[LostDog88]

Originally Posted by guyrj33

In your poorly constructed reply to the original post Dsanduril wrote
"...


"If you run the positive and negative cables together they come close to cancelling each other" again HOGWASH. If you want to mitigate the magnet field caused by parallel supply and return currents in a DC circuit twist the wires along their length. SCIENCE
COAX is used to shield HF signals not for DC. SCIENCE

Can't remember the law, but basically it goes like this:

Wires running in parallel create capacitance. The opposite of capacitance is inductance. Twist the wires around each other and the capacitance is balanced, or equaled.

That is why telephone/data lines are twisted around each other. Other wise you'd hear loud pops on the line every now and then. And computers just simply wouldn't be able to transmit their magic.

At least that is what I remember from "School." Which was a very long time ago.

[Dsanduril]

When I wrote “unbalanced” I was trying to describe a circuit in which the positive and negative currents follow a significantly different path. Certainly they carry the same current, but not possibly in generally the same location.

Coax can be, and sometimes is used for DC power distribution. It is not common, but it is the best way to minimize magnetic fields from the power flow. Having concentric positive and negative flow results in the least external disturbance. Your laptop computer power adapter most likely has a coax power cable on the DC/output side (as an example).

A twisted pair is next up, but the twists are not perfect cancellation and more external effects will be noticed. The effectiveness depends on the degree of twist.

After that, the standard twin lead, or two single wires run in parallel. The magnetic field around a parallel pair is very non-homogeneous, it will depend on the spacing of the pair and whether you are “above” the pair or off to the “side” of the pair.

Lastly, what I was trying to to describe with the word “unbalanced”, with a magnetic field generated by an un-paired conductor there is nothing nearby that even remotely balances/cancels the field. It is this I was presenting to the OP. This can easily be seen on boats if you look around things like the alternator field wire from an external regulator (uni-directional current) or other similar installations. These present the most risk to compasses and other magnetically sensitive equipment.

[hzcruiser]

Originally Posted by Tmacmi

All my negatives return to the panel via spade connectors as you can see in the attached. I am going to build a remote negative buss. I have two questions.

1) Does there need to be a negative line run from the buss back to the panel?

2) The negative wire (perhaps 2) run from the panel down to the transmission bell housing at the same spot as the negative cables from the batteries. Is that acceptable to replicate? Or should they go directly to the battery negatives.

Thanks,

TMAC

I'd say your questions have been answered already, until the thread drifted into magnetism (and other black magic ).


But yes, your panel (likely) needs a wire to the negative bus if the panel itself needs to power something, like indicator lights, LEDs, backlight for night mode, or a voltmeter to show you the panel voltage. Since it's already been set up that way by the sounds of it, why would you want to change that anyway, if I may ask?

In terms of "unbalanced" wires, as in running only the positive leads to the panel and the negative leads go somewhere else and eventually to the batteries, it's something I would avoid if possible as it can make toubleshooting much harder.
You can still have more than one place with bus bars, but I would still keep the positive and negative wires and bars close together, then run e.g. figure-8 wiring to each consumer. For larger wires I cable-tie or shrink-tube the two corresponding wires together every half metre or so.

[goboatingnow]

Just to say to the OP. You can run your negative wire back as required to a common point typically at the battery

There is no practical drawback , as usual keep current carrying wires away from magnetic sensitive devices as best as possible

[Tmacmi]

Now that the holiday's have past I'd like to pick this back up. Its probably worthwhile to go backwards. I apologize for any confusion or lack of clarity this created.

The reason I want to create a remote negative busbar is that the panel's existing negative buss (which uses bayonet connections) is more than full, most connections are now doubled up. See attached photo which I was supposed to attach with the original post.

There is no room immediately behind the panel to put a new negative busbar, the closest accessible spot to install a negative busbar is approximately 24" from the main panel. That means that there will be a 24" long area were 18 different negative leads of varying gauges will not be be in close proximity to their matching positive lines. The binnacle is approximately 48" from this area. There is a back up compass approximately 18" above this area on a bulkhead. Do you believe there will be magnetic interference given these details? I have attached a very rudimentary drawing of what it will look like upon completion.

I also want to ask about running the ground from the negative bussbar to the battery. I am not arguing, but as I said the current grounds from the panel go to the same place the batteries ground on the transmission bell. Doesn't this achieve the same result? Or is there something more I'm missing?

[Frankly]

If I am understanding your configuration correctly, if you run the negative back to the engine then it is essentially the same as the battery until you hit the starter. Then the starter current will produce a voltage drop along this common path and the panel circuits will experience this difference. Might work OK but a better practice would be directly back to the battery negative.


Frankly

[HeinSdL]

Thread drift again - while you're at it, you may want to think about putting everything into a wiring schematic (if this doesn't already exist) and number the wires. I am lucky to have all my wires numbered + I recently received a wiring diagram from the yard where my boat was built. It's remarkable how quickly the electrical system becomes highly complex and hence difficult to troubleshoot, hence the benefit of having a schematic to work from.