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Old 07-26-2010, 07:57 PM   #1
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help adding 12 volt

Hello...proud papa of recently remodeled 1966 pathfinder 12 ft travel trailer. we gutted it, upgraded elec from 15 amp to 30, added 5000 btu window air conditioner.

now we are thinking about adding 12 volt power in the event we are somewhere w/o hookups....

consider myself fairly handy, but would like to find some advice on adding 12 volt power to the camper. it has no battery...nothing..
how is a battery wired to the trailer, what can we hope to power w/ just battery power....does the window air require too much power? i imagine i need a battery...another breaker box? converter? inverter?

thanks in advance....and i did search...all over the internet for a few hours....to no avail.


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Old 07-26-2010, 08:45 PM   #2
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Originally Posted by bfdbatt2 View Post
Hello...proud papa of recently remodeled 1966 pathfinder 12 ft travel trailer. we gutted it, upgraded elec from 15 amp to 30, added 5000 btu window air conditioner.

now we are thinking about adding 12 volt power in the event we are somewhere w/o hookups.....
bfdbatt2, Welcome to iRV2.com! What you are proposing is not impossible however I have to say it would probably be a lot of fun putting a system like this together from scratch.

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Old 07-26-2010, 09:22 PM   #3
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bfdbatt2 welcome to irv2.
Here is a thread about 12v side of life which should help you.
The neg- side of your batteries would connect to frame of trailer to make easy for wiring. You will need converter to charge batteries when hooked to shore power.
Your trailer also needs running lights when towing working off tow vehicle unless you already have take care of that. TRAILER TOW WIRING
You could also add solar panels for Battery charge on roof of trailer.
You need 110 for AC.
Draw everything out on paper than go to it, have fun.
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Old 07-27-2010, 05:54 AM   #4
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A fast rundown of what you'll need (I've done this before):

12 volt battery (duh!), preferably a deep cycle one, and a battery box to put it in
A short piece of plastic or vinyl sheathing like a piece of conduit
A 50' roll each of 14 gauge black and white multi strand wire
butt splice connectors (the blue ones)
a small fuse panel, no more than 4 fuse locations
Fuses, generally 20 amp or less
a way to charge the battery, either a small automatic charger or a small converter
a 30 amp self-resetting circuit breaker
A pair of ring terminals
a couple 12v of light fixtures
a 12v outlet (looks like a cigarette lighter plug), this is nice to have but not 100% needed

The best place to mount the battery would be on the tongue, if you have room. I've installed small pieces of angle iron to mount the box on, and I've run self-tapping screws through the plastic battery box into the tongue, both work.
The black wire should be positive, the white wire negative. That's how almost every RV is wired. Use the ring terminals to connect the wires to the battery, and connect the self-resetting breaker nearby, with all the power running through it. You can run the black wire into the trailer, and either run the white wire to ground on the tongue or run it inside to connect to the rest of the 12v stuff. It would be less wiring to ground it.
Mount your converter or battery charger near a 120v outlet, and mount the fuse panel near it. Some converters have fuse panels already on them.
Run a wire from each light fixture and the outlet to a fuse on the fuse panel, ground the lights and outlet, and ground the converter.
You're done, sit inside your trailer with the warm glow of 12v lighting washing over you, and enjoy the feeling of accomplishment.
Two wrongs don't make a right, but three rights make a left.

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Old 07-27-2010, 08:01 PM   #5
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2 wrongs don't make a right...but 3 lefts do...

If I recall correctly there are trailer connectors that have a 12 volt connection to keep the emergency battery for the electric brake battery charged.

This wire could be used to float charge the battery while in tow, just be sure to protect it from over-current from a deep charge as a dead battery will draw more energy than the wire can provide.

Take a trip to TSC, Walmart or a well stocked parts house and take a general look at the selection of batteries, avoid the wet type that have caps as these will gas explosive hydrogen, deep cycle maintenance free are better, best are AGM VRLA batteries that are safe enough to carry on an airplane, they are more expensive but are safe and will last 10 years or so.

Interstate has one that is MQ1800, Marquis series, not sure on the cost but they are 70 amp hour (20 hr rate) and are about the same size as a group 24 car battery.

Now that you see what you have to work with start hunting space in your project, under beds or behind things, a box could be built into the front near the hitch but 200 pounds of battry may cause tongue load concerns. More batteries is longer running time, just hook in parallel and insure all batteries are the exact same type ( buy them all same time and place), they do not need to all be in te same place, they can be seperated to help balance the load, if you do this make sure a large fuse is placed AT BOTH BATTERIES, any pinched wire could cause a fire so any connection to 12 volts needs to be fused near the 12 volt source.

Next determine your loads, a 70 amp hour battery is only good for about 8 amps of current to get the 70 amp hours, 8 amps will run for 8 hours, if you go up to 32 amps the battery will only run for about an hour or so. You need to properly engineer your system to build it to properly meed your needs otherwise you will not be happy.

The manufacturer can supply the rate sheet for the battery to assist, it is easy to determine after you know what your loads are.

To recharge your batteries if you have a 1 amp charger it will take double the capacity in hours to charge the battery, so 70 amp hours battery will need 140 hours at 1 amp to be fully charged, it actually is somewhat less but this is the simple math version to avoid short charging.

Best is to use the 1% rule, a float charge will give the longest lifespan of the battery without gassing the acid, take the full labeled capacity of the installed battery, calculate 1%, you may round up to the next amp as it is not that critical.

Locate a converter out of a motorhome, a local wrecking yard may have one or just order one, this will have the power distribution and charger built in.

Some also have the 120 volt AC load center built in.
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Old 07-28-2010, 09:29 AM   #6
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How much power does a battery contain.

First: Deep cycle batteries it is safe to use 1/2 of the stored power
Starting batteries and this includes Marine/Deep cycle, about 20 to 25 percent.

Next: When computing usable watts of power.. I normally consider the battery to be 10 volts, this allows for loss in an inverter or other conversion device, it also makes the math way easier.

A Group 24 battery is around 70-75 amp hours. that's 700-750 watt hours
G-27 is in the 90-100 range
G-29 is 100-105
G-31 is about 120
One pair GC-2 (Such as the Interstate U-2200) in series is 220 amp hours at 12 volts)

So the usable power, if drawn over a 20 hour period, is about 1100 watts

An air conditioner will draw 1100 watts in one hour in many cases

So a window A/C is not battery comparable unless you carry a whole bunch of batteries and that many would put your trailer overweight big time.

The window air should run on a Honda EU2000i though, with power to spare for battery re-charge
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Old 07-28-2010, 10:10 AM   #7
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I think if it were me I would start by locating a multi charge rate 12 volt fuse panel designed for a trailer. After you have that, it will provide you with multi stage converter that will keep your battery healthy and power the 12 volt system, a dc fuse panel, and a negative 12 volt buss. Buy yourself a battery or two and weld up the brakets to hold the batteries in boxes on the tounge. Next find some 6 gauge wire in both White and red or black and wire the feed from the batteries to the converter panel using a 30 amp resetting 12 volt breaker in the + line and run both the + and neg wires as stated in an ealier post in red or black from + and white being the 12 volt negative to the converter and negative buss Add a wire from Negative to the frame of the trailer and a bare #6 copper wire from the converter to to the frame. Those main feeds should be wrapped in split loom and tied securely to the frame. Now run all your circuits out of the breaker box using 12 gauge wires both white and red or black to all your 12 volt lights and appliances. Wire the positive side through the fuses on the panel using black or red and tie the white wire to your negative buss. Wire can be purchased as a red white combo or run separately and put in 1/4 inch split loom for your branch circuits. Resist the temptation to not wire the negative 12 volt and insted just return to the nearest ground. If a fault in the negative side develops, it's far easier to fix it if all the negative wires all run back to the negative buss and faults in the negative side will cause lots of noise in the electrical system weacuing havoc on sensitve electrical appliences like tv and radio.

Good luck and keep us posted.
-Paul R. Haller-
These prewired 12 volt load centers also will have 110 volt load ceter that can accomidate your 110 volt system also. make sure that your 120 volt drop cord is wired for 30 amp 110 and the 110 volt negative is also tied to the frame using a #6 bare copper wire.
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Old 07-29-2010, 09:46 AM   #8
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Exclamation Keep the wiring safe and in code

DO NOT connect the 110 negative to the chassis ground as this could be deadl if plugged into a miswired outlet.

THe negative/neutral/return depending on your language is the center point in a 240 VAC distributio center only for the return path of 120 volt loads, a miss-wire could have odd voltage to ground on this wire.

The GREEN wire is the SAFETY ground, it is the ONLY connection to the frame, and it should only be at ONE point, all 120 volt outlets need their green wire brought back to the ac load center
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Old 07-29-2010, 11:14 AM   #9
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Originally Posted by TQ60 View Post
DO NOT connect the 110 negative to the chassis ground as this could be deadl if plugged into a miswired outlet.

You are absolutely correct. Thank you for pointing out my error. The only place ground and neutral are connected is in the main panel. I meant to say connect ground to the frame.
-Paul R. Haller-

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