Wiring Gauge from Battery

DABWCA

I'm getting ready to have my tow vehicle wired to deliver power to a brake controller (possibly the Tekonsha RF that mounts to the frame but needs a charge wire) and to keep the T@B battery charged. My dealer would do it for me but it seemed like a good idea to see what a reputable shop that specializes in hitches and installations would do. I'm not talking about u-Haul but a shop that's supposed to really know how to do this stuff right. 

Wiring a charge wire seemed straightforward enough and the price was right, but I was surprised to be told that they would use 12 gauge wire and that if I wanted 10 gauge then I'd need to supply it myself.  These guys install a lot of hitches and wiring for all sorts of vehicles. 

I'm thinking that 12 gauge wire could cause issues, especially if appliances like the 3-way fridge are drawing power.  

Any thoughts about whether or not I should avoid a 12 gauge connection?

source3

There are many charts showing the proper gauge wire depending current (amps) draw.  One nice explanation with chart is at http://www.crutchfield.com/S-EDCCR2IXz9C/learn/learningcenter/car/cable_gauge_chart.html 

It is also convenient to have the battery charge wire ran through a relay.  I use a fused relay (http://www.hella.co.nz/en/products/relays-flashers/mini-relays-normally-open/12v-4-pin-normally-open-mini-relay-25a-fused.html). You can also buy a socket for the relay to plug into.  I have it mounted to the engine side firewall.

In simple terms-
The relay is closed (switch on) when your TV is running - send current to you trailer plug.  When the TV is not running, the relay opens (switch off) and no power to the trailer plug.  This avoids accidentally running down your TV battery because you forgot to unplug the trailer from the TV.  

I have the relay switched through the "charge" fuse of the TV.  The switch wire can be smaller gauge as the charge fuse is only drawing at most 7.5amps.  The input/output wires that will be carrying the current to the trailer plug is a larger gauge as the current will be ~20 amps. Limited by the Hella 25A fuse.

Read up on automotive relays until you can wrap your head around the idea.  It can be confusing.  Most automotive relays discussed on the internet are for headlights, but the concept is the same.

And here is a simple diagram.  Terminal #87 will be going out to your trailer battery charge plug.  http://www.mp3car.com/imagehosting/12527647e9129233622.bmp

Nomad

Just as an FYI, the Zamp Solar cable is 12 gauge according to the factory.

source3

Another item to consider when running 10 Ga. wire is the connection from the plug on the trailer to the trailer battery.  Does the T@B run 10 Ga. or 12 Ga?  If 12 Ga., then no reason to run 10 Ga. on the TV unless you plan to upgrade the wiring on the T@B.  As for powering the fridge, the power is coming from the trailer battery, being recharged by the TV when all plugged in and vehicle is running (if wired this way; see my previous post).  A 10 Ga. charge wire will recharge the trailer battery faster (more current flow).  How much faster I do not know? Have not done the calculations.  Charging time is also dependent on the power consumption of the trailer while receiving a charge from the TV.   Another factor is the amps that the TV alternator can put out.  If you are running a lot of gadgets on the TV and are charging the trailer at the same time, the TV alternator might not be able to handle the load sufficiently (just trying to complete things a little).  

mawebb

The wire guage from the converter to the battery is 10 guage and is fused at 30 amps at both the converter and at the battery (2 fuses). I would run 10 guage from your alternator / battery of the TV. As mentioned use a relay or a solid state isolator such as used for boats. The solid state isolators are more expensive but can be more reliable in the long run. 

DABWCA

Martin - Thanks for the specific insight into the T@B 10 guage setup. That's what I wanted to know. I suppose the charge wire should also be fused at the tow vehicle battery with 30 amps.

I'm not familiar with isolators and relays. Can you recommend any and describe where in the network they might be installed? 

Michigan_Mike

DABWCA said:

I'm not familiar with isolators and relays. Can you recommend any and describe where in the network they might be installed? 

Battery isolators are typically located in the vehicle engine compartment and in closer proximity to the vehicle starter and battery.   There are many different models out there and you might look on Amazon, etc. and read some reviews and select an isolator that meets your specifications or needs.   

Here is a YouTube video that will help out some too (discusses isolator operation) and there are many videos on the site that also discuss installation.   Good luck!

https://youtu.be/RlNTqEqRF0Q

mawebb

The solid state automatic charging relay I was referencing would be like the Blue Sea Systems m-acr 7601. 

http://www.amazon.com/Blue-Sea-Systems-Automatic-Charging/dp/B00BFVHL2I/ref=sr_1_1?ie=UTF8&qid=1430799828&sr=8-1&keywords=blue+sea+7601


I know it may seem complicated, but it is quite simple. The ACR sits in series between the TV and the T@B. It would be located near the battery of the TV. You would fuse the line to the ACR with a 30 amp fuse. The connection to the starter is optional, and is used to disconnect the load (T@B) when starting, to ensure the T@B cannot prevent your vehicle from starting, should there be a heavy load coming from the T@B. So the simple and easy installation is to go from battery, through a fuse, through the ACR (terminals can be interchanged) and then back to the 7 pin connector at the rear of the TV.

The way these devices work is they only allow current to flow from a good battery to a weaker battery. When the good battery starts to deplete, they no longer allow the flow of current, ensuring the TV battery has enough capacity to start the vehicle.

The older mechanical relays such as the Tekonsha 7000 12 Volt 3 Terminal Battery Isolator, simply switch off the connection between the TV and the T@B when the TV is not running.

An added benefit of the ACR, is your T@B will keep your TV battery charged, as long as the 7 pin connector is connected and the T@B is plugged in to 110 VAC.

mawebb

I should also mention that there are solid state devices that must be connected to your alternator. These are more complex to install and I do have concerns that if they fail, they could impact the TV electrical charging system. The ACR is newer and more sophisticated technology that makes the installation so much simpler and less subject to failure. Note that they are engineered for marine use, where you simply can't call for AAA, so they are engineered for high reliability.