Battery Disconnect Wiring - Fiberglass RV


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Old 05-24-2020, 08:20 AM   #1
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Battery Disconnect Wiring

I'm finally getting around to installing a disconnect I bought last fall. Aside from being too small to actually show the instructions, I'm not sure whether to follow these.

I was planning to simply run the + and - wires from the battery through the disconnect before they connect to anything else in the camper. What are the benefits to that versus a more "complicated" install like the instructions would show if I could actually read them?

One thing I do want to consider is my solar panel. My current charge controller says the panels should be disconnected before the battery is disconnected. Not sure if there's an easy way for this disconnect to also cut off solar charging so I don't need to remember to do that first.

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Old 05-24-2020, 09:44 AM   #2
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My disconnect switch had two terminals. I connected it between the - negative battery post and its ground cable.
that takes to battery out of the circuit.
In order to charge the battery, or run and appliances or lights you have to close the switch.
The switch is opened just for storage, so the little parasitic loads, don't drain the battery. Be sure it is fully charged before storage.
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Old 05-24-2020, 09:46 AM   #3
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Disconnect options

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Originally Posted by ZachO View Post
One thing I do want to consider is my solar panel. My current charge controller says the panels should be disconnected before the battery is disconnected. Not sure if there's an easy way for this disconnect to also cut off solar charging so I don't need to remember to do that first.
Attachment 134920
I found the diagram hard to view. (Old age eye sight). It looked overly complicated.
If you can find a switch that will independently open and close two different circuits, you could operate both the battery disconnect AND the solar panel disconnect in one operation. The challenge will be finding a switch with the necessary current rating. One other solution is to have two identical switches mounted next to each other and physically connecting the two switch actuators together so that BOTH switches would turn on/off in one operation. I think that mounting the two switches one above the other would be the easiest way to make this happen.
As an afterthought, household electrical systems frequently mechanically link multiple breakers together when switching several phases on and off.
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Old 05-24-2020, 09:59 AM   #4
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The diagram is hard to read no matter young your eyes are.

Thanks, that's a good idea. I have a disconnect for the solar panels already, and mounting the battery disconnect just underneath it seems like the most sensible, simple solution. I may even mount some instructions on the wall next to them. A basic "disconnect this first" would do.

Even with a magnifying glass, you can't really read the instructions, but I don't think it matters. The point it to disconnect power. It shouldn't matter whether I splice it into the + or - side, right? Wayne you used -, what I can read of this diagram shows splicing into the + side.

But if I just took the positive or negative cable where it came into the camper, cut it and added this switch, that would work, right?
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Old 05-24-2020, 10:39 AM   #5
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Which cable

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Originally Posted by ZachO View Post
I'm finally getting around to installing a disconnect I bought last fall. Aside from being too small to actually show the instructions, I'm not sure whether to follow these.

I was planning to simply run the + and - wires from the battery through the disconnect before they connect to anything else in the camper. What are the benefits to that versus a more "complicated" install like the instructions would show if I could actually read them?

One thing I do want to consider is my solar panel. My current charge controller says the panels should be disconnected before the battery is disconnected. Not sure if there's an easy way for this disconnect to also cut off solar charging so I don't need to remember to do that first.

Attachment 134920
Something is telling me you should put the switch on the positive side of the battery. All of the Mercedes used to come in with a battery cut switch on the + side and that diagram also showed it on the + side. Will it work on the negative side, sure but there is something wrong with that and I can't seem to drag it out of my head now.

This site has some of the nicest wiring diagrams I have seen.

https://www.explorist.life/200-amp-h...van-solar-kit/

They are a little complex but you should be able to pick out the pieces you need. You should have a switch on the panels also and set it up so you can disconnect the battery and still have the solar charging. Then flip that solar switch to completely shut it down.
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Old 05-24-2020, 11:44 AM   #6
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What kind of switch is this? (Manufacturer?)

Taking your photo offline and enlarging it shows that the switch is, in fact, on the positive ( + ) side of the battery. There is a small + sign just below the left battery terminal and a small – sign below the right battery terminal.

I’m not sure what the symbol just to the right of the battery represents. My guess is that it might be intended to be a bus bar for the negative ( - ) connections to the battery.

Does this switch have some sort of remote? The diagram seems to depict that just to the right & below the “HEAVY DUTY LOADS” which connects to a plug (probably) on the switch which also shows a connection to the negative side of the battery.

There is a note pointing to the positive battery connection on the back of the switch. If the switch does have a remote, then you will need to insure that the battery connection goes to the correct connection on the back of the switch since that would most likely be a feed into the plug/socket that goes to the remote switch.
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Old 05-24-2020, 11:53 AM   #7
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If you wire that switch as the picture shows, it completely disconnects the battery.

there is no remote function to the switch.
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Old 05-24-2020, 11:54 AM   #8
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answer

If you wire that switch as the picture shows, it completely disconnects the battery.

there is no remote function to the switch.
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Old 05-24-2020, 05:10 PM   #9
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I wired my disconnect switch on the negative side of things in my Boler.
Why? Same principle as to why you should remove negative terminal first when disconnecting a battery.
https://www.hotrod.com/articles/kill...e-or-negative/
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Old 05-25-2020, 07:52 AM   #10
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Thanks everyone. I'm 99% sure I've asked this type question before and got similar answers, but I don't work with this stuff often enough for it to stick. It seems like no matter where you cut the circuit, + or -, it cuts the circuit. The negative battery terminal first thing makes sense.

I know I'm making this more complicated than I should, but is there any reason they show it on the + side because of the "complicated" way they're instructing me to wire it? And if all I'm going to do is leave my system as-is (a positive and negative wire running into the camper) and cut one of those wires and put this switch there, that negative would be "better"?

It's really a terrible diagram. It's shrunken down so far that it looks pixilated when I use a magnifying glass. No matter how much I enlarge it, it's still blurry. The diagram shows a "remote key switch", not sure why. It also shows a plug, socket, second on/off switch and mentions something that looks to me like "deutsch plug", and, yes it shows a ground bus.

I can read a somewhat basic wiring diagram to show how something is wired. But reading diagrams telling me how I should wire something that hasn't been wired yet always confuses the heck out of me, even when I thought I knew how to do it before reading the instructions.

Seems like they had a vehicle in mind when they made this diagram? "Ignition Protected" and "Cranking Rating".

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Old 05-25-2020, 09:12 AM   #11
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After excessive reading about this it seems everyone everywhere argues about this.

What was bothering me but I couldn't put my finger on it is if you put the switch on a vehicle negative cable you can disconnect the battery while the engine is running. The bad part is the engine will keep running with no battery in the circuit and you could destroy every solid state device in the vehicle.

On an RV it doesn't matter as much as long as you do not disable the emergency brake function in case of a trailer disconnect.
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Old 05-25-2020, 09:19 AM   #12
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It appears that the diagram is simply implying that if you were to use something with a remote sensor, you'd need to be sure to wire that into the disconnect switch as well so as to not cause any problems.

Ignition protected means that it is hermetically sealed or designed to not release sparks when used.

Cranking amps are the numbers of amperes a lead-acid battery at 32 degrees F (0 degrees C) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery).
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Old 05-25-2020, 11:44 AM   #13
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Alright, thanks.

I'll mount it in my trailer, up front near the battery, right under my solar panel disconnect switch. On the - cable.
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Old 05-25-2020, 12:37 PM   #14
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The reason you disconnect the negative terminal on the battery first is to prevent arcing if you accidentally touch your wrench to a metal part of the vehicle chassis. For a battery disconnect it really doesn't matter however I would follow the NEC wiring codes for 115 VAC systems and disconnect the hot or positive terminal. Don't forget your solar system when disconnecting the battery. I used 2 disconnects on my camper, one for the solar panel and a second 2 circuit version which disconnects the battery and the solar panel at the same time. I have since found a 2 pole knife switch which I modified so the battery blade closes prior to the solar panel blade. I am using it in my battery system at my camp. Here are links to the 2 pole switch. I posted about the 2 pole knife switch under 'Battery/solar panel disconnect'.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 07-06-2020, 07:27 PM   #15
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Finally just about to do this, and I notice the main battery fuse on the positive wire coming into the camper, right where I plan to mount the switch. Which got me thinking...is there a compelling reason not to just pull the main fuse to cut power, rather than install another disconnect to do the same thing?

I assume there is, but I don’t know that reason.
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Old 07-06-2020, 08:44 PM   #16
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Use a fuse as a switch?

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Originally Posted by ZachO View Post
Which got me thinking...is there a compelling reason not to just pull the main fuse to cut power, rather than install another disconnect to do the same thing?

I assume there is, but I don’t know that reason.
Fuses and circuit breakers are designed to be protection devices to prevent overloading current beyond the spec for the wiring and/or device behind them,

Will it work to use them as an off/on switch: (sort of) yes. But that isn't the intended design.
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Old 07-07-2020, 10:18 AM   #17
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I was thinking of whenever I work on my furnace or anything else, I always pull the fuse first. Maybe that isn't the right way and technically I should disconnect the entire system at the battery?

Seems like there are always a lot of opinions on this stuff. I'll still install the cutoff, if for no other reason than I've already bought all the stuff and don't plan on returning it.
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Old 07-07-2020, 04:15 PM   #18
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A lot of people make due with only pulling the main fuse vs. a proper switch. If you only do it on occasion it should be fine. But there are a few reasons to use a switch, most of them having to do with disconnecting the battery under load (even a small load). Repeatedly pulling the fuse when there is current running through it will cause some arcing. Repeated arcing will eventually damage the connection and create resistance. If the battery and fuse are in a closed environment, and with high current charging in process, the arcing can create an explosion risk, but its not really a concern with a battery and fuse in open air. Its more of a concern in vehicle engine compartments and boats that might have fuel vapor, which is why some battery switches are ignition proof. To me its more of a convenience issue. Its just easier to turn the switch. And if its not easy, I might not do it when I should. Plus, I dont have to worry about losing the fuse.
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Old 07-09-2020, 10:24 AM   #19
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Well it's in.

Thanks for the advice. As soon as I got it in, I found my new project...saw water dripping from a drain hole near the fridge vent outside. Hot water line to my kitchen faucet sprung a pretty nice leak. It never ends!
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Old 07-09-2020, 01:36 PM   #20
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Quote:
Originally Posted by ZachO View Post
One thing I do want to consider is my solar panel. My current charge controller says the panels should be disconnected before the battery is disconnected. Not sure if there's an easy way for this disconnect to also cut off solar charging so I don't need to remember to do that first.

Attachment 134920
I used one of these dual circuit switches that disconnects both solar panel and battery simultaneously.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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