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Old 07-18-2014, 08:22 AM   #1
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Connections to 12v panel bus bars?

I'm just looking into solar power options at this point and know enough to be dangerous. What I'd like to do is get my existing 12 volt system pre-wired for easy hookup of panels in the future.

As I understand it, two heavy wires would be coming off of the charge controller and connect to the existing 12 volt system. What is the easiest and most common way to do this on a late 70's trailer?

Do you put extra terminals on the 12 volt panel bus bars? Perhaps splice into the heavy cables coming off the 12 volt power converter/battery charger? I'm interested in seeing any photos of this final connection to the trailer's existing 12 volt power distribution.

My trailer has two batteries as part of the original setup and I have added another two batteries in a vented enclosure under the front gaucho. Since the batteries are wired in parallel maybe hooking solar power to one battery would get the job done? See my blog for photos of the battery upgrade if you like.
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Old 07-18-2014, 08:27 AM   #2
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I'm no solar expert, but I would want the negative from the controller to one batterynegative terminal and the positive from the controller to the other battery positive terminal.
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Old 07-18-2014, 09:49 AM   #3
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Rich, your answer makes sense, but what is the best way to do this when you have a bank of four batteries? My concern is that all need to be charged evenly.

Assuming batteries are all in a row, 1 thru 4, and cable lengths between them are as short as possible, should I connect the positive to battery 1 and negative to battery 4?
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Old 07-18-2014, 09:56 AM   #4
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Yes. That's the way mine are. Go to AM Solar website. They have wiring schematics for trailer solar. You'll need circuit breakers and other stuff too that could be pre-wired.
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Old 07-18-2014, 09:59 AM   #5
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How is the coach wiring connected to the battery bank?
Both the + and - connected to battery 1?
It is difficult if not impossible to charge a battery bank evenly. No matter what type you use. You can get them close, but equal. No 2 batteries are EXACTLY identical. And since there is wiring and connections in a battery bank, there are minor amounts of resistance inherent in a battery bank when compared to a single battery.
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Old 07-18-2014, 10:19 AM   #6
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Depends on which solar company you are a fan of.

Many, like Airstream and Go Power insist that it is OK to connect the charge lines from the solar charge controller to your bus bars, using small wire gauges (generally 10AWG) for the wire runs. This method adds another layer of connections and will induce more voltage drop in you system, something that should be avoided whenever possible.

We (AM Solar) insist on a direct connection to the batteries from your solar charge controller using an appropriately sized fuse or circuit breaker on the solar positive charge line. In systems with multiple batteries, we also specify that the positive charge line be connected to the first battery and the negative connected to the last battery in the battery bank for more even charging.

PM me if you have any other specific questions.
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Old 07-18-2014, 11:01 AM   #7
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TG, since my trailer was originally equipped with two batteries, the bus bars have two positive and negative connections. The original battery boxes are in positions 1 and 4, with the new batteries being in positions 2 and 3.

One pair of + and - come off the bus bars in the panel and now connect to battery 2. These battery terminals have a second set of wiring connections for wires that connect battery 1 in parallel.

Likewise, battery 3 is connected to the bus bars, then connected in parallel to battery 4.

Yeah, I know that a perfectly even charge is next to impossible to get, but I want the system to be as good as it can be.
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Old 07-18-2014, 11:13 AM   #8
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Lewster handled it for me. This is a good practice for any charging system. Always get as close to the battery terminals as possible. Especially important where avoiding voltage drops are critical...like a solar system.
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Old 07-25-2014, 10:48 AM   #9
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Quote:
Originally Posted by lewster View Post
In systems with multiple batteries, we also specify that the positive charge line be connected to the first battery and the negative connected to the last battery in the battery bank for more even charging.
In my setup (which I didn't do), the solar wires simply connect to the bus bars. But so do the batteries - that is, all three batteries simply connect to the bus bars, too; they're not connected to a separate bus bar or anything. Is the idea behind what you do to ensure the charge voltage will flow through all batteries, even if they're hooked up as mine are?

My solar system uses the aforementioned 12 gauge wires before and after the controller, but a couple weeks ago I was working on something else and noticed what appeared to be two rather heavy (perhaps 8 gauge) wires behind the fridge. I didn't want to get distracted from what I was working on, so I didn't investigate them more closely, but I can't figure out what they'd be other than wires from the solar (which I know go through that area)...but then how do they get down to the 12 gauge wires? More investigation needed. (The controller is under an arm rest near the front of the camper, so it's not that.)

Someday I'm just going to start a thread documenting our electrical system...it's interesting. Like how the built-in voltmeter sometimes reads high, sometimes low, and sometimes right on...makes it hard to decide whether the batteries are charged or not.
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Old 08-12-2014, 10:19 PM   #10
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Bus Bar

The reason for a bus bar is so that all connections to that bar have equal access to battery voltage and current. There is no difference between the voltage anywhere along the bus bar. The only voltage drop would be due to the cable run from the battery to the bus bar. How much can that be on an Airstream where the bus bar is at the very front of the trailer? I'm guessing that is logic Airstream uses when the solar pre-wire travels to the bus bar from the controller.
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Old 08-12-2014, 11:24 PM   #11
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Every connection has inherent resistance....so does every wire. Use too small a cable and too many connections (many, I have found, are not even tight!) and you get significant voltage drop. Try a voltage test at the batteries with a quality volt meter. Then go along to the converter, DC outlets and other DC connections. You might be surprised at just how much your DC voltage decreases in the trailer.

What tolerance does Airstream have? Just look at the minimal gauge of the battery cables that are on new trailers and, of course, their insistence on using an antiquated, single stage constant voltage converter/charger on ALL of their new trailers that destroys batteries for your answer.

What's your tolerance level? 5%....8%....10%...? Ours is 2% or LESS. Quality solar is not an inexpensive addition to one's trailer. For the significant investment of a quality solar charging system, one would expect maximum return in charging amps to the batteries and longevity of that battery bank. 10AWG solar wire and multiple connections just don't cut it in our systems. YMMV!
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