Battery cut off switch

[ib516]

I just bought one like the one in the picture below. Should I install it on the positive terminal or the negative and why?



I run two 12V group 27s in parallel.

[MEXICOWANDERER]

Yep, garbage like that disconnect belongs right up there "With The Best Of Them"

[deleted-2]

69 Avion wrote:
As stated above, it is a sorry excuse for a cut off switch. Get a Blue Sea switch and be done with it.
BlueSea

I agree.
Put a BlueSea m series in our fiver.
Money well spent IMO.
Ordered it from Amazon.

[69_Avion]

As stated above, it is a sorry excuse for a cut off switch. Get a Blue Sea switch and be done with it.

http://www.bluesea.com/products/category/Manual_Battery_Switches

As far as what terminal it goes on, it all depends on what you are trying to do with it. To isolate a battery from the vehicle you would put it on the negative terminal (example-car battery). To isolate the battery from what it feeds, you would put it on the positive side of the battery (negative ground system). For a RV purpose most folks would want it on the positive side of the battery.

[DryCamper11]

I didn't watch the whole video, but I heard one reason for their recommendation to install on the negative was just that installation on the positive created a large chunk of pos-connnected metal that might inadvertently be shorted to the nearby neg-connected frame. When I have that situation, I use some 2" diameter flex hose and cut it about 6" long and split it lengthwise. It can then be spread open and placed over the positive components to protect them from inadvertent shorting to ground when working in the area with metal tools.

It is a bit safer to install in the negative if that's an option, but if you're going to install on the positive, connect the positive first and then connect the negative to the frame. It limits the risk of shorting with the wrench during install.

As to the trailer problem, you need to find out if you need a frame ground for your breakaway. I have a small generator trailer with a mechanical breakaway system and my toad breakaway uses an isolated ground, so either of those trailers could be installed with the switch in the negative. Those with large TTs probably don't have that option as they'll need the frame grounded.

[beemerphile1]

Brass plated pot metal, not brass.

They are using the negative post on a vehicle starting battery. Different factors are involved with a trailer battery as already hashed over.

[MEXICOWANDERER]

An Excellent Place To Put That Brass Battery Terminal...

[ib516]

beemerphile1 wrote:

Learjet wrote:

beemerphile1 wrote:

Why would there be a loose end anywhere? The topic is about where to locate a disconnect switch.

Doesn't the pictured battery discconnect in question come apart? If so, then there is your loose end and is on topic with the Op's post.

From the instructions on Amazon;
"...Turn black knob fully clockwise to connect battery power. To disconnect power, turn knob 1/4 turn counter clockwise...."

Reads to me like the device stays together.

Gama Electronics has an instruction video. They also say 1/4 turn to disconnect and they do not show separating the device. In the video they recommend the negative post but are thinking a starting battery, not the house battery of a trailer.

Frankly I think that device is a very poor excuse for a disconnect and is likely to provide unsatisfactory service but the OP didn't ask about that.

From that video, negative terminal it is, and they explain why. Thanks.

[beemerphile1]

Learjet wrote:

beemerphile1 wrote:

Why would there be a loose end anywhere? The topic is about where to locate a disconnect switch.

Doesn't the pictured battery discconnect in question come apart? If so, then there is your loose end and is on topic with the Op's post.

From the instructions on Amazon;
"...Turn black knob fully clockwise to connect battery power. To disconnect power, turn knob 1/4 turn counter clockwise...."

Reads to me like the device stays together.

Gama Electronics has an instruction video. They also say 1/4 turn to disconnect and they do not show separating the device. In the video they recommend the negative post but are thinking a starting battery, not the house battery of a trailer.

Frankly I think that device is a very poor excuse for a disconnect and is likely to provide unsatisfactory service but the OP didn't ask about that.

[time2roll]

I stick with the existing convention of all switches, fuses, breakers placed on the positive side(DC) or hot side(AC) of the circuit.

Only reason to place on the negative is to reduce risk of a short to ground when servicing the battery or other items close by.

When removing a battery cable for service it is best to remove the negative side first.

[Learjet]

beemerphile1 wrote:

Why would there be a loose end anywhere? The topic is about where to locate a disconnect switch.

Doesn't the pictured battery discconnect in question come apart? If so, then there is your loose end and is on topic with the Op's post.

[beemerphile1]

DryCamper11 wrote:
The breakaway needs to be wired directly to the battery to function. If it's wired after the switch - regardless of whether the switch is on the pos or neg, it won't work with the switch off. If the switch is on the neg, then the breakaway needs to go to the battery negative directly before the switch. The problem with that is where the negative is tied to the frame. If your breakaway uses the frame as its ground, then tying the breakaway negative to the battery negative before the switch will try to power anything else connected to the frame - regardless of whether the switch is on or off. I'd put the switch on the positive, but if your breakaway design used an isolated ground, it would be perfectly fine to run that ground before the switch and put the switch on the negative after that connection point.

A breakaway switch only switches the positive feed to the electric brakes. The brakes themselves are grounded and it is impossible for them to work in a breakaway situation if the battery ground is disconnected.

Electro-hydraulic brakes may be a different situation, I have no experience with them.

Some breakaway switches do have a ground connection but that is for an indicator light and has nothing to do with the braking function.

I already stated previously that the disconnect should be in the positive with the breakaway connected directly to the battery prior to the switch.

[DryCamper11]

beemerphile1 wrote:
If the switch is in the ground/negative, someday, someone, somewhere will tow the trailer with the switch open and the breakaway system will not be functional.

The breakaway needs to be wired directly to the battery to function. If it's wired after the switch - regardless of whether the switch is on the pos or neg, it won't work with the switch off. If the switch is on the neg, then the breakaway needs to go to the battery negative directly before the switch. The problem with that is where the negative is tied to the frame. If your breakaway uses the frame as its ground, then tying the breakaway negative to the battery negative before the switch will try to power anything else connected to the frame - regardless of whether the switch is on or off. I'd put the switch on the positive, but if your breakaway design used an isolated ground, it would be perfectly fine to run that ground before the switch and put the switch on the negative after that connection point.

[DryCamper11]

100ton wrote:
I guess the advantage of using it on the negative post would be not dealing with the potential "spark" issue when used on the positive side.

Sparking has to do with the current flowing and voltage across the switch. That's the same regardless of whether the switch is on the pos or neg. I can't see that it matters which side you switch, although convention is to switch the pos.

[beemerphile1]

If the switch is in the ground/negative, someday, someone, somewhere will tow the trailer with the switch open and the breakaway system will not be functional. That is a dangerous and illegal situation. There is no real benefit to switching the negative, so why take the risk of something that is almost inevitable to happen eventually.

Learjet wrote:
...If you have the battery disconnected and then plug in the trailer the disconnected end will be powered by the converter. If that loose end contacts the frame you can create a short....

Why would there be a loose end anywhere? The topic is about where to locate a disconnect switch.

[Learjet]

beemerphile1 wrote:
If this is for a trailer it MUST be in the positive side. .

Would like some facts to why it "MUST" be on the positive side.

Like others said either side...but...

With this type of device the Neg. would be better. If you have the battery disconnected and then plug in the trailer the disconnected end will be powered by the converter. If that loose end contacts the frame you can create a short.

The break-a-way switch is only a problem if you don't connect the battery before moving the trailer.