Battery install in my CT and a question

[CoventryKid]

I would really appreciate some assistance!

When I converted my CT last year, the plan was to go all-electric. I figured we would always stay where we could plug into shore power. Fridge, cooktop, heater, lights, etc. all run off 110v via 30A - 4 circuit panel, etc.

My MaxxAir fan and Sureflo water pump are 12v. They run off a RoadPro 6A converter into a BlueSea fuse block. I cut off the cigarette plug and wired 1 lead to the bottom and the other lead to the top of the fuse block.



Life was good but my wife and I found that during our 5 month tour last fall that sometimes we wanted to stay where there was no shore power.

We return home unexpectedly last October, so I figured I'd use the time to add a 12v battery. I installed a SPDT switch to direct the power from either the RoadPro 12v or the battery 12v. The Roadpro 12v side of things works fine, but the battery side doesn't. Nothing, nada.

I think the reason the battery side doesn't work is because there is no ground. The switch controls where the power (+) comes from. But the "ground" from both the fan and the pump run back to the fuse block. But there is no (-) back to the battery (or ground).

I think I need a DPDT switch rather than a SPDT. With a DPDT switch, I can switch both the power (+) and the ground (-) appropriately.

Writing this entry, I think I have answered my question. But I'd still like to ask: Will a DPDT switch solve my problem? Or is there another, perhaps better way to do this?

Thanks for any and all guidance!

[MtnDon]

You don't really need to switch the negative. The negative of each can be combined, mixed, connected to the same common negative terminal block, however you want to look at it. Separate the positives using that switch and select the one you wish to draw from.

[troubleScottie]

You probably should add a charger. Obviously it will need shore power. However you might want to be able to continue traveling and recharge the battery between boondocking stops. You can also think about charging from the TV. There is information about this on the site.

[OverTheTopCargoTrailer]

Doug

Once you start with a battery....
Soon you will be on the DARK SIDE , solar & Lifep04

Walmart boondocking & despersed camping

[CoventryKid]

MtnDon: Thank you! I'm on the right track with the switch switching the positives but....I'm not sure I understand re the negatives:

"The negative of each can be combined, mixed, connected to the same common negative terminal block, however you want to look at it. Separate the positives using that switch and select the one you wish to draw from."

As it is right now, the negative on the converter is part of the 2-wire that connects thru the converter to the 110v plug. If the converter is not on (running off the battery as I would like to do), will the negative of the converter still act as negative??

Or (thinking and writing at the same time)....should I take the wire I am using as the negative to/from the converter and make that a common ground and connect everything to it, as you suggest?

More thinking....should I just ignore the 2nd wire of the converter and ground my fuse panel to the trailer? That might work - the converter is only putting out 12v on 1 of the 2 wires, right?

Michael: Thanks. Yes I do have a smart charger. Genius I think. Not me, the charger. So I can charge when plugged in then be free roam for a few days without plugging in.

ottct: Thanks for the smile!! No, not Walmart, just the freedom to stop for lunch and get water from the tank, etc. If I was a few years younger, I definitely do solar, etc.

[OverTheTopCargoTrailer]

Doug

You can always connect all the negatives of the 12 volt together.

But don't connect negative from 12v to the 120 ac volt side, that's seperate system.

How can you be too old for solar ?

Cheers ottct

But I do need to say everytime I look at your trailer, again & again I am amazed at how you really knocked it out of the ballpark with your design.

[MtnDon]

I don't have a diagram showing your wiring so when you refer to " the negative on the converter is part of the 2-wire that connects thru the converter to the 110v plug" I am not clear on what is being talked about.

Let's see if this can help.... An RV manufactured to RVIA standards will have 120 VAC wiring with black (hot), white or grey (neutral) and green or bare (ground) and DC wiring that will have a positive and a negative (colors can vary). No ground wires.

The 120 VAC ground (green, bare) connected to the frame.
The 12 VDC battery Negative connected to the frame.
12 VDC switches all on positive wires only.
12 VDC devices all wired with both a positive and a negative wire from source to device.
NO AC bond connection between neutral and ground.
Any devices like converters or inverters that come with a separate ground lug on the case will have that lug connected to the RV frame/chassis. Via the ground buss bar is okay.
Those are the RVIA standards.

You can have two separate battery systems, using a common negative but keeping the positives separated. You can even have two or more DC systems, with one being 12 VDC and another that could be 24 VDC and have both of those negatives connected to the frame and/or the same negative buss bar (common point) and everything would be okay as the positives would be completely separate. So keep the DC positive wires from either battery separated and you can forget about the negative wires. Depending on the DC loads that could require a HD switch. They do make those battery switches in versions specifically aimed at switching from one battery bank to another. And be sure your DC switches are DC rated.

Use breakers or fuses as close to the battery + as possible to protect all positive DC wires, even those skinny ones used for things like a simple voltmeter.

Does that help?

[CoventryKid]

MtnDon: THANK YOU! I really do appreciate you taking your time to detail all of this information for me. Hopefully others will find it of interest too.

Saturday of a long weekend here, so I have printed a copy of your explanation to study over the weekend.

In the meantime, here is a picture with explanations of what I did - hopefully it will explain what I meant about "the negative on the converter is part of the 2-wire that connects thru the converter to the 110v plug".



Thanks again for your detailed explanation.

[MtnDon]

Sorry, but I really can't easily tell what is going on from the photograph. A schematic wiring diagram would be useful if it showed all the wires and their connections and was labeled.

[CoventryKid]

OTTCT: Apologies, I just noticed your entry from Sat.

MtnDon has been very helpful. I understand 120v wiring - did a lot of it during my home reno days, and 12v is easy too. But what I'm having trouble with is where the Roadpro converter supplies 12v to my fuse panel. The two wires (12v side) were originally attached to the female cigarette lighter plug. I cut the plug off and connected the 2 wires to opposite ends of the fuse panel.

Your comment, and MtnDon's, about connecting all the 12v negatives together makes sense. I think that is where I am going wrong in my thinking. I will give that a try the next tme I am at the trailer.

Finally, thank you ottct for your kind comments about my trailer.

[wanabxtrm]

Either a dpdt or common ground should work. I'd recommend the later. If you are wiring like most your frame will be a common ground point if nothing else, though if wired with a dedicated (-) circuit to each item it shouldn't actually be passing much if any amperage unless you develop a short.

[CoventryKid]

Just to finish this topic off, in case others try some of the dumb things I've tried......

Turns out all that was needed was a ground from the ground terminal on the BlueSea panel to a ground screwed to the trailer frame. With that, the batteries have a ground and everything works as it should - "shore" power or "battery" power.

Thanks to all who helped with their suggestions.