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Open Roads Forum  >  Travel Trailers  >  Modifications and Accessories

 > 2 12v batteries---Mallard TT help

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bob213

Fresno, CA

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Posted: 11/29/19 11:17am Link  |  Quote  |  Print  |  Notify Moderator

If you want to add another 12v battery look at this. Scroll down for picture of wire connection for 2-12v.
12 volt side of life


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Posted: 11/29/19 11:47am Link  |  Quote  |  Print  |  Notify Moderator

The typical RV 6V deep cycle battery weighs 70 lbs and has 220 Ah capacity. So 110 Ah to 50% SOC. 2 12V would be about 160 Ah and less suited for house batteries. IF your car has a 12V charge line in the rear plug then it MAY charge the batteries. But likely the wiring is to small for anything but a minimum charge. In that case install heavy wires from car battery to trailer battery with connector and fuses.

Sounds like you should get some help with the wiring so that it's done correctly both electrically and mechanically.


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Bob


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Posted: 11/29/19 11:52am Link  |  Quote  |  Print  |  Notify Moderator

And some help understanding your energy requirements. A 1500W inverter implies your energy requirements are going up.

Grit dog

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Posted: 11/29/19 12:09pm Link  |  Quote  |  Print  |  Notify Moderator

Rusty, you can install 2 12v batteries in parallel and only run 1 set of leads to/from them or 2 6v golf cart type batteries in series and do the same.
Do some research on DC wiring before jumping in and possibly soending money on the wrong or unnecessary hardware.
Www.bcae1.com is a good tutorial on this type of stuff albeit not rv specific.

Vehicle charging, in order to get any good amperage from the alternator, a dedicated circuit needs to be installed much larger Than the 12v convienence circuit in the trailer plug. More like 4ga and the right connector.
I'm not well read on converter/inverters but like most things you get what you pay for and Harbor Freight is not a good example of long term quality in general.
Good luck with your project.
Also may I suggest tutorial videos or write ups on these types of projects or upgrades. I'm sure YouTube has a bunch that folks have posted.


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Krusty

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Posted: 11/29/19 12:55pm Link  |  Quote  |  Print  |  Notify Moderator

If you are planning on using that inverter to power up anything remotely close to its 1500 watt capacity, you will need much larger wire than 10 gauge


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2oldman

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Posted: 11/29/19 01:47pm Link  |  Quote  |  Print  |  Notify Moderator

RustyMacIntosh wrote:

But hooking up the lines to the trailer I need not to wire it in such a way it is 24v.
To do any kind of work like this you need a voltmeter. It's the #1 tool for not screwing things up.

naturist

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Posted: 11/29/19 02:38pm Link  |  Quote  |  Print  |  Notify Moderator

As things stand right now, you have two wires going to one battery. To avoid problems later with uneven charging, put the positive wire on the positive terminal on one battery, and the negative wire to the negative terminal on the other battery. Then to complete the circuit and insure you keep it to 12 volts and not 24 volts, you need TWO short jumpers to connect the two positive terminals together and the two negative terminals together.

If you put one short jumper in and connect a pos to a neg, that will cause the very problem you seek to avoid. Print this out, cut off this paragraph, and do what the other paragraph says. You will be golden.





opnspaces

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Posted: 11/29/19 03:54pm Link  |  Quote  |  Print  |  Notify Moderator

I have run a charge wire from the front of my 1996 Suburban to the rear. The wire was already there from the factory, I just had to hook it up. And I have checked many times and it does recharge the batteries from 50% charge to full in the two hours it takes me to drive home from the desert.

Hopefully you have a multimeter and know how to check voltage with it. If not I would probably go to Harbor Freight or Walmart and buy a cheap meter. If you have a meter but don't know how to use it try to give us a name and model number and we can look it up and tell you how.

First step is to use the meter to measure the voltage at the battery and write it down. This is important because you can't check the charge voltage at the rear plug if you don't know what your checking against. Next check voltage between the 12 volt power blade and ground blade of the 7 pin trailer connector on the Suburban and see if there is power there. If you find power there, is that power within .2 volts of the battery voltage? If yes, great. If no, not so great.

[image]
[image]Click For Full-Size Image.

If no voltage it's possible that everything is hooked up and you just have a blown fuse.

Try look under the hood on the drivers side by the brake booster of the Suburban. You are looking for a fuse and relay box. Inside that box you are looking for the AUX A or AUX B posts and fuses. See if you can find a wire hooked to one of these posts that goes down and back toward the rear of the Suburban. If so make sure that there is a corresponding fuse plugged in and that the fuse is not blown (ie post AUX A needs an AUX A fuse). If no fuse or a blown fuse put a new fuse in it's place. Now check for battery again at the rear of the Suburban.

[image]
[image]Click For Full-Size Image.


If you can't find a the wire in the relay box, you'll have to hook up a charge wire to one of these posts to charge the trailer while in tow. GM should have left a small wire harness with two disconnected wires behind this box that are for trailer charge and trailer brakes. The challenge is finding those two wires.

If you are lucky you can just look for and spot the wires, they will be folded over and taped to keep the ends clean. On my 1996 the wires are a blue wire and an orange wire. If you can't find them try looking under the dashboard at the trailer brake controller. There should be a wire (probably blue but not always) that goes froward from the brake controller. Try to follow that wire to where it comes out under the hood. Hopefully it goes into the small harness with the second wire.

If you find the second wire you can put a crimp on ring terminal on it and connect it to either Aux A or Aux B, it doesn't matter which you choose. Next make sure that there is a fuse plugged in to the slot that matches the post Aux A or Aux B that you hooked the wire to.

Once the wire is connected you have to find the other end near the trailer plug in the rear of the Suburban. Try tracing all the wires coming off the back of to connector, the wire will be there. Once you find the other end of the wire you can connect it to the trailer plug connector.

Now check again or battery voltage at the rear of the Suburban. If you now have voltage and it's within .2 volts of the battery voltage it's time to move forward.

plug the trailer in to the Suburban and then measure battery voltage at the trailer and write it down. Now start the Suburban and let it idle. Check the battery voltage on the Suburban and the battery voltage on the trailer. If the two battery voltages are within .2 volts of each other and are at least 13.5 volts then you are good to go. If the Suburban battery voltage jumps to 13.5 or more but the trailer battery still displays 12.x volts, then check for a blown fuse on the wore from the battery positive post to the 7 way plug.


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opnspaces

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Posted: 11/29/19 04:03pm Link  |  Quote  |  Print  |  Notify Moderator

To hook up two 12 volt batteries you need to simply put the batteries side by side. Reference the picture below.
  • Use a wire to connect the negative posts together
  • Use a second wire to connect the positive posts together.

Then:
  • Connect the positive wire from the trailer to the positive post on one battery.
  • Connect the negative wire from the trailer to the negative post on the second battery.


Ignore the disconnect in the picture if your trailer does not have one.
[image]

This will give you 2 twelve volt batteries wired as 12 volts.
As far as the hefty wire between the posts, I just use short battery wires with ring terminals at each end that I bought at Walmart next to the batteries. It's probably a bit overkill on wire size, but they were premade so it was easy.

opnspaces

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Posted: 11/29/19 04:17pm Link  |  Quote  |  Print  |  Notify Moderator

For 12 volt power I run some of these. I just tapped power off the overhead lights as they gave me the easiest route to where I wanted to install the ports. They were a bit expensive, but they were the only non illuminated outlets that I could find. I used a 1 1/16inch hole saw to make the hole in the side of the cabinet.
Amazon link

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