What gauge wire should I use? - Fiberglass RV


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Old 09-27-2007, 05:35 PM   #1
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What gage wire should I run from my truck battery to the trailer plug connector.______________________________I want to supply 12 Volts to the Scamp for the Frig. when driving down the road. I do not want to buy a extra 12 volt battery for the trailer, when I have one in my truck that I can use and also keep charged as I'am driving.
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Old 09-27-2007, 08:26 PM   #2
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What gage wire should I run from my truck battery to the trailer plug connector.______________________________I want to supply 12 Volts to the Scamp for the Frig. when driving down the road. I do not want to buy a extra 12 volt battery for the trailer, when I have one in my truck that I can use and also keep charged as I'am driving.
10 Gauge for 30 amps (http://en.wikipedia.org/wiki/American_wire_gauge), BUT I wouldn't use my car battery over a battery in the trailer. Car batteries are designed to provide a lot of power for a short period of time, then get recharged before too much of their charge is drained. Using them to provide a little power for a long time draws their power levels down more quickly than you'd expect, and damages the battery if you do it too often. You'd be much better off buying a deep-cycle or marine battery that's designed to do the job.

--Peter
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Old 09-27-2007, 09:23 PM   #3
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I would only use this set up when driving. I would hook up 120 shore line when at camp. I will have to test this out to see how much of a draw the frig takes off the car battery.
I had three tent trailers before the Scamp and I ran the lights off the car battery with no problem using a extension cord for the power line from the battery to the tent trailer but I never ran a frig.
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Old 09-28-2007, 10:42 AM   #4
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Be sure to use a 30amp circuit breaker type fuse at the battery.
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Old 09-28-2007, 12:56 PM   #5
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With no battery in the trailer I would consider connecting the power line from the tug to just the refrigerator circuit. In that case, there is no need to allow as much as 30A, with typical small refrigerators drawing no more than 10A (maybe allow 20A just in case).

The wire should be reasonably thick to minimize voltage loss so that the refrigerator gets enough voltage and can perform well, and of course it must be thick enough to safely carry whatever current the fuse allows (such as 10 ga for 30A as Peter mentioned).

You might want a relay in the power line, controlled by an ignition-switched circuit, so that you don't accidentally run down the tug's battery when stopped along the way. This is the same method normally used with a trailer battery, and for essentially the same reason.

If you always camp with power, or are willing to use something other than built-in 12V lights when camped without power, this seems like a simple and workable approach to me.
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Old 09-29-2007, 04:43 PM   #6
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I have used #8 and even #6 stranded for on-vehicle cabling on the principle that the #10 is adequate for the load but may be imposing enough voltage drop that the charge will be reduced before it gets to the egg battery. I figured as long as I was running the wiring, it might as well be more than adequate.

However, I was usually relying on the TV as my primary method of charging the egg. Had I been in the practice of having shore power for converter or battery-charger use, I might have felt differently.

As recommend by Darwin, I used a 30A circuit breaker, of the auto-reset type, mounted at the TV battery. Since I wasn't running either a furnace fan or a fridge, I didn't bother with an isolation device, but they are a very good idea if there is any 12VDC load that may inadvertantly drain both batteries.
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Old 09-29-2007, 07:35 PM   #7
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Hello Kevin,
I would suggest adding a deep cycle battery to the trailer. This will add a cushion for voltage drop in addition to the other benefits.
You can do it inexpensively. A battery box is $10 and a deep cycle battery is $70-200.
We just stepped up to the $200 Trojan deep cycle. I was tempted to go with two 6 volt batteries but decided on a large single for weight/space savings. I will add solar soon to supplement the car alternator and a 3 stage charger.

Here are some good reading links that will fill in the rest of the picture:
http://www.neon-john.com/RV/Electrical/rv_...tion_relays.htm
http://www.eham.net/articles/13130

An Isolator will help you not kill your car battery if you shut off the engine.
I am torn between these two Isolators:
www.powerstream.com/battery-isolator.htm
http://www.hellroaring.com/bic75150.htm


This week I sent emails to both of the above companies and got really nice and well thought out replies from both. That was a pleasant surprise. I can say that both can be recommended for their customer service.

While thinking about chargers, I found that the Xantrex 3 stage, 40 amp charger is the cheapest when I follow the links from their web site to buy.com .
http://www.xantrex.com/web/id/147/p/.../7/product.asp
Following this route, shipping is free and Google offered a $10 discount for using their system. The total ended up being $86 for a very nice ( and light) 3 stage charger.

well, this has gotten long and definitely more than you asked for, so good luck with your project.

Best regards,
Nolan
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Old 09-29-2007, 08:08 PM   #8
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Kevin,

Back when I was building my teardrop trailer, I got hooked up with a Brit who designs batteries for the British Government's military equipment. We're talking deep-cycle, massive storage devices here. Anyway, I wanted to charge the trailer's battery from the auto as I traveled, and it took many weeks of arguments with him before he convinced me that (and I'm still not sure I understand why), even though it's been done that way almost since hooking up the first trailer to an automobile, it is actually very hard on both the auto battery and it's charging system. (was that a long sentence, or what?) He finally convinced me it would be best to use a generator and a regular 3-stage Microprocessor Charger to charge my two Group 27 batteries. Second best would be to use a solar charging panel. (only "second best" because it takes so much longer.) He said the Group 27 batteries will last much longer.............several lifetimes longer were his exact words.
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Old 09-30-2007, 07:11 PM   #9
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Charging the egg battery with the TV charging system is less than perfect, esp considering the two batteries are of dissimilar ages and types (starter vs deep cycle), plus one is right where it was designed to be and the other is at the end of a long wire. Additionally, they are being discharged at different rates and times and finally, the TV charging system sees some composite of both of them and delivers a compromise charge that isn't really right for either.

However, all that said, there's just no way to beat the convenience of just getting into the TV and charging batteries while one is driving to where ever! I, for one, will pay the price of reduced battery life for that convenience. Solar would be nice....
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Old 10-01-2007, 05:21 PM   #10
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...He said the Group 27 batteries will last much longer...
With all due respect to the battery expert... I think there has been some misunderstanding, or information taken out of context. "Group 27" is simply is specification of dimensions according to standards published by BCI, which defines a large number of "groups". All Group 27 batteries are the same size, and many are the deep-cycle type which we want for RV use, but other batteries in this same size could be starting batteries, entirely unsuited to the purpose. The battery group doesn't matter (except that as always, size matters and in batteries bigger is better) but the type (deep cycle) does.

For instance, Trojan sells proper deep cycle batteries in Group 27 size... but they also sell dual purpose and marine starting batteries in that same size.

Even if the Group 27 size were only available in deep cycle types, that would not mean they were superior - batteries of the same construction in other sizes of similar total capacity would be just as good.
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Old 10-05-2007, 08:05 PM   #11
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Perhaps he meant that a Group 27 battery would last longer than a Group 24 of the same type, merely because it is bigger and usually has more capacity.
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Old 10-06-2007, 10:20 AM   #12
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Perhaps he meant that a Group 27 battery would last longer than a Group 24 of the same type, merely because it is bigger and usually has more capacity.
This is a valid point: higher capacity means both a lower % discharge and a lower discharge rate relative to capacity, both of which are good for life.

On the other hand, I doubt that the size difference between group 24 and group 27 would make this much difference:
Quote:
....several lifetimes longer were his exact words.
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Old 10-06-2007, 06:51 PM   #13
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I recall many Casita and Scamp owners replacing their original Group 24 batts with Group 27 to get that extra capacity when replacement time came.
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Old 10-14-2007, 02:43 PM   #14
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Even if the Group 27 size were only available in deep cycle types, that would not mean they were superior - batteries of the same construction in other sizes of similar total capacity would be just as good.
I don't think Chris C. was quoting the battery expert as saying that the group 27 batteries would be better than any other battery type. I believe he was saying that the group 27 batteries would last "several lifetimes longer" if they were charged via a standalone generator and a 3 stage charger rather than via the TV alternator.

Eamon
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