Charge Controller? - Fiberglass RV

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Old 05-17-2015, 03:23 PM   #1
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Name: Teri
Trailer: Trails West Campster
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Charge Controller?

Trying to understand what I need. Getting ready for a 4 week trip this summer in the Campster. I had 12v installed in my Campster and have done recharging with Solar panels so far. I have a CPAP so must maintain battery. I also have a 4 pin and no direct way to recharge from my TV.

My question, can I run a 12v extension cord from the 12v outlet in the back of my 07 Rav4 directly to the battery in my Campster? do I need any kind of controller to not overcharge the battery? and if so where, what, etc.?

Most of the power I use is for the CPAP, use a few lights otherwise.

Thanks for your input.

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Old 05-17-2015, 04:26 PM   #2
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No controller required. Just run 12v cord. I suggest to disconnect the cord when not moving to preserve Rav4 battery from discharging.

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Old 05-17-2015, 06:03 PM   #3
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Name: JD
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Why not add a 7 pin plug and socket and get the thing more correct?
You don't have to connect barkes for the 7 pin plug to do what you want.

Multi-Tow® 4 Wire Flat to 7 RV Blade & 4 Wire Flat
The 4 pin plug plugs nto you 4 pin existing connection and the other wires are connected as necessary for your 12 power etc.
Of course you would have to also install the 7 pin plug on yout trailer. You could parallel the two plugs so that it could be plugged int another tow vehicle that had only the 4 pin or 7 pin.
By the way this plug retains both the 4 pin and 7 pin connections at the same time.
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Old 05-18-2015, 10:53 PM   #4
Name: Fallon
Trailer: Shopping
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I just finished re-wiring (towing wires anyway, house 12v system still needs work) our new to us verry old Boler. I put a 7 pin & a 4 pin pigtail on it out of a breakout box. No brakes on it, but they will happen if we keep it & do the needed axle replacement. I figure the 7 pin is worth it just for the 12v power & the flexibility. This way anybody can tow it no mater what they have. My Tacoma has a 7 pin & brake controller. The wife's Escape only has a 4 pin, but I have something that looks like the above photo sitting on a shelf in my shop waiting to be installed as well. May or may not ever wire up brake controller stuff, but definitely will get 12v to a 7 pin socket on her Escape at some point.

Running something from the lighter outlet is ghetto, it will probably work. You might pop fuses though if the battery is low enough to pull higher amps. A safer way would be jumper cables or something heavier gauge directly between the batteries. Wiring up a 7 pin would be best though.

All of those options could drain your car battery though, if left hooked up while its not running.

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Old 05-19-2015, 06:32 AM   #5
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Lots of unknown information. Too much for me, anyhow, to offer much advice. How big, in terms of wattage are the solar panels. Many solar sites offer guidance with respect to at what size (wattage) you should have a controller.

Why is the poster running the 12v extension from tow to trailer. To charge the trailer battery or run the CPAP. Length reduces available current due to electrical resistance in the extension.

Converting to a 7 blade trailer connection is possible but since it has been my experience that running my tow vehicle to recharge the trailer battery just doesn’t do the job that would be low on my to-do list. (An argument for another day.) There are fairly simple marine recharging outlets that one could put on the outside of the trailer to make hooking up the solar panels easier. I like marine hardware because it tends to hold its appearance longer in the weather.

Don’t know the power requirements of the CPAP involved, don’t know the trailer battery size and how long it would power the CPAP in case of a couple overcast days.
Quando omni flunkus, moritati
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Old 05-20-2015, 09:22 PM   #6
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Charge Controller?

The devil is in the details with 12v, long wire runs and suspect connectors.

12v cigarette lighter plugs are about the worst way to connect the trailer battery to the car system. One I used to charge a model airplane battery at 5 amps got so hot it burned me when I pulled it out.

There will be too much voltage drop from the car battery to the trailer battery to have the car's alternator charge the trailer.

You need a thick wire, ten gage minimum, with a good connection to the car battery, terminated at a socket that will take high current without undue resistance, like a good seven pin connector or an Anderson type connector.

No charge controller needed.

You do need a charge controller for your solar panel however.

Denny Wolfe
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Old 05-20-2015, 10:58 PM   #7
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If you can get hold of a West Marine catalog they have ( or did the last time I looked) a dandy chart showing what size wire for what draw and distance. There can be a huge loss with a long run

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Old 05-21-2015, 12:08 AM   #8
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Originally Posted by Denece View Post
If you can get hold of a West Marine catalog they have ( or did the last time I looked) a dandy chart showing what size wire for what draw and distance. There can be a huge loss with a long run

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Ohm's Law... Losses depend on current. Charge current is high at first then gets lower as the battery gains charge. If the current is restricted by a smaller wire, it will just take a bit longer to charge. Again Mr. Ohm and his Law.
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Old 05-21-2015, 06:28 AM   #9
Name: Steve in NY
Trailer: Scamp
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You mean this:

Marine Wire Size and Ampacity | West Marine

I agree it is a really great resource.
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Old 05-21-2015, 06:43 AM   #10
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First, using the accessory outlet for charging the battery may not be a good idea because it is fused. We tried that with a Honda CRV by placing the RV's battery in the back of the CRV during the day while we drove around and it continually blew the fuse. And there is always the opportunity to run the TV's battery down if it is not disconnected. And last, running your TV to charge your coach battery is considered poor form in most campgrounds.

Next, many of the 7 pin plugs come pre-wired with a pigtail that connects to your existing flat-4 connector, all you have to add is the charging line.

You didn't mention how many watts your solar was rated at, but that should be your primary source of battery charging under the conditions mentioned.
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Old 05-21-2015, 08:28 AM   #11
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More to the point- where are you headed?
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Old 05-21-2015, 09:47 PM   #12
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Name: Teri
Trailer: Trails West Campster
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Bob, I do use the solar as the primary. I am looking to have the TV charge while moving as a supplement to when we are stationary. Sounds like the 7 pin is the best way to go. I need to have some work done before we leave so looks like I will add that to the list. Some things I can do, electrical, not so much. Don't know why but can't always wrap my head around it.

Bobbie, doing Yosemite, Lassen, Crater Lake, Glacier, Yellowstone, Grand Tetons and probably Craters of the Moon. The main focus is Glacier, Yellowstone and Tetons. That is where our time will be spent.

Gotta get finished with the school year and get working on the trailer.

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