Battery Switch, 12vt

[Josh00333]

Ok Q: should a battery disconnect switch be on the positive or neg side?

We used to do them on the positive leg in the marine power boat world, but I'm under the impression neg is more widely practiced?

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[ScottBeach]

I really don't understand how a hot line is ever a good idea. Every bypass sold is for the hot (+) side.

 

[Lost1wing]

It would make sense on the positive side for a negative potential chassis where short circuits are possible. The switch should be on the Negative when the their is positive potential on the chassis. It depends on the design.

 

[Deleted member 52902]

In the case of a winch, you might see for example, the logic of having a cut off switch on the positive line. Located at the power source end (the battery) of the positive cable going to the winch. If you have some sort of front end crash where a steel or aluminum bumper is crumpled such that it makes contact through the insulation with the positive line, this could turn the crash into a melt down fire. Potentially a crash that wasn't deadly, may now have made a turn for the worse. If the negative line was shorted in a similar fashion, it doesn't matter because it already goes to chassis ground at both ends anyway.

A high amperage capable, ideally also waterproof switch under the hood, connected to the winch positive cable as close as possible to the positive battery terminal is a good idea. Accomplishing that in the narrow confines of our underhood area, depending on your powerplant and possibly other add-ons can be problematic.

I have a switch I purchased for this purpose but instead got re-purposed to be used on the exterior wall of my barn to "kill" my solar panel system. Battery runs overhead 12 volt lights and battery charger/maintainers for vehicles that more or less are stored in the barn during Winter months. I need to get another such switch for my JEEP, with the idea of a bracket that raises the switch above the already crowded mass. I believe such an elevated switch will still clear the closed hood while also being "in your face" when the hood is opened. The best place for it would be the switch mounted near the battery, but externally on the cowl I suppose. Except not exactly aesthetically desirable there. Anyway, the positive line disconnect for any device I can think of is the only line necessary to be disconnected. Short of (not a pun), a double throw, double pole switch that disconnects positive and negative terminals, if the negative line to a device is not also physically grounded.

 

[Reddog]

Ok Q: should a battery disconnect switch be on the positive or neg side?

We used to do them on the positive leg in the marine power boat world, but I'm under the impression neg is more widely practiced?

Positive side, always.

 

[djthumper]

Positive side

 

[Josh00333]

Ok update and against the grain I went negative.

No reason other than the way the factory lines laid out it made most sense.

Programed a custom charge profile and all set.

This was in my trailer replaced the 3 100 amp hr amg with a 300 amp hr lithium.
Added a cut off switch to isolate 100% when in storage.

 

[Jaxmax]

Going against the grain on a 12 volt negative ground system is not really a great idea, you received good advice. Everything in your camper is negative ground, the frame any metal part of lights, and just about everything your positive cable might touch including the bracket holding the batteries down. The battery is isolated though.
Also really nice camper!….Jack

 

[Zachanadandy]

Going against the grain on a 12 volt negative ground system is not really a great idea, you received good advice. Everything in your camper is negative ground, the frame any metal part of lights, and just about everything your positive cable might touch including the bracket holding the batteries down. The battery is isolated though…..Jack

If the battery negative is isolated those negative grounds don't exist. You could bolt the positive lead from the battery to the chassis and nothing would happen... until you ground the chassis to the battery.

 

[sharpsicle]

If the battery negative is isolated those negative grounds don't exist. You could bolt the positive lead from the battery to the chassis and nothing would happen... until you ground the chassis to the battery.

If it's isolated from everything with a charge, yes. That's the reason you go positive: they all route back. Negatives don't, so you can introduce a ground through something else holding charge without knowing it. Might not be likely, but it's the reason you go positive.

Same reason that if you had an old British car that used positive chassis electronics, you'd put the shutoff on the negative side.

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