Battery disconnect

[rollexx]

Picked up a battery disconnect for our fifth wheel. It's the paddle type that connects to
the negative battery post. Our trailer has two 12V batteries wired together.
I asked the guy at camping world if by installing this switch on one battery would it cut both batteries off. He said yes.
Well after installing I still get 12V power to 12V systems. Can only get power off by disconnecting a wire on second battery. Do I really need a switch for both batteries or am I doing something wrong? Thanks

[Harvey51]

A battery has 6 cells connected together in series with only two external posts.

Similarly, Think of two batteries connected together in parallel as a single battery or box. One wire coming out to ground, another wire to positive. A switch on either wire would isolate the whole double battery. One of the wires will come directly from a battery post so the aforementioned disconnect could be attached to that post.

However, that post will have a second wire on it, going to the same polarity post on the other battery. Could be tricky getting the wire and the switch on the same post.

[BFL13]

If the two batteries are connected by a positive to positive wire and then a neg to frame and a neg to frame, so that the frame is part of the neg path paralleling the batts, AND then, you have the rig's "load" wires on the pos and neg of one of the batteries (leaving the other batt as the "downstream battery" )--- then, if you put a disconnect switch on the neg post of the battery with the load wires on it, that will leave the other battery running the rig's 12v.

It has the positive path connected, and it has its own neg path to the frame. The rig's neg side of its DC panel is connected to the frame making the neg path complete.

You can fix that and use a neg side disconnect switch if you run a wire neg to neg battery, not using the frame, so that one only one battery is connected to the frame AND you arrange the rig's load wires so that the neg load wire(s) go to that same neg post AND put your neg side disconnect switch there.

[RoyB]

I placed my main battery switch in the positive cables coming from my 12V Distribution Panel...

This is a quick diagram of my setup....

Roy's Image

I originally started out with four batteries but lost one right away from boiling out the battery fluids so have been running three batteries every since... I originally had extended angle sections under the batteries extending them out both sides of my trailer tongue area. You can see my Blue Sea four postion switch on the corss member in the photo...


Roy's image

One of the reasons for me using the positive lead connection was i wanted to have my Breakaway Switch wiring and a coupe of other 'switched' 12VDC connections always hot especially when being towed...

ALot of folks like to have their battery disconnect in the NEGATIVE cable so that the battery is completely out of the circuit when disconnected.

Both places Positive or Negative terminals will allow you to Disconnect from the battery source.

It all depends on what you want to do with your batteries...

In the automotive world the folks liked to always pull the negative terminal first so that it would not create a place to short out anything like touching a ground with the wrench taking off the positive terminal...

A downside on using cheap battery switches is they will arc over when making contact and eventually become non-usable... Using a company like BLUE SEA which primarily deals with Boats and all have a great designed switch to prevent arcing between contacts... The BLue Sea 9001E cost $38 I think is on Amazon...

Roy Ken

[rollexx]

Thanks all

[Sam_Spade]

CA Traveler wrote:
Here is the correct wiring for parallel batteries,

Alas, that picture probably causes more confusion than it solves.

It doesn't show the cables from/to the OTHER battery.....which is what the original question WAS.

[CA_Traveler]

Here is the correct wiring for parallel batteries, just ignore the shunt.

Here's my battery monitor shunt and battery switch. Flattened 3/4" copper pipe makes a nice buss bar. Note: These are AGM batteries and locating a shunt near flooded batteries should be avoided due to the corrosive battery fumes. The copper buss bar color is due to battery protective spray.

The switch is a full battery disconnect located on the negative terminal. The large cable on the switch is the chassis ground. The smaller cable on the battery post is for a parallel connected battery. The small wires are for the battery monitor.



Click For Full-Size Image.

[naturist]

Correct response from the RV guy would have been a bit more detailed than a simple yes. It depends on how the batteries are wired. If wired correctly AND you install the switch correctly, the answer is yes. But if they are not wired correctly, OR you don't install the switch correctly, then no. As you discovered.

[K_Charles]

Both battery grounds need to go thru a disconnect.

[Sam_Spade]

rollexx wrote:

I asked the guy at camping world if by installing this switch on one battery would it cut both batteries off. He said yes.

Do I really need a switch for both batteries or am I doing something wrong? Thanks

Obviously the guy at CW is wrong.

IF....the cable from each battery negative goes to a connection on the frame.....then YES you need two switches.

If those two cables come together somewhere before they go to the chassis, then the switch needs to be put in that one common cable.

P.S. When you have more than one 12 V battery, they are wired in PARALLEL. That knowledge may be useful in the future.

[2oldman]

Depends on which battery you put it on
.

[DrewE]

Assuming you have a jumper between the batteries, and then a wire from one of the batteries to the trailer ground (which would be the most common setup), you'd put the switch on the battery with two connections with the ground connection to the trailer on one side and the battery post and the jumper to the other battery on the other side. The connection between the batteries remains connected all the time, but the connection between them and the trailer is switched.