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Request from Cary: Car-to-Camp-Inn wiring

W

Wendell Ann Hanks

Novice
Hello Cary-
Please again offer the diagnosis as to both why and the remedy for the pulling vehicle not charging the trailer when 12 volts is being transferred. Please include how to make the trailer charger modification to solve the problem without creating a new one when solar or 120 current is used. You explored this in a phone call and both your analysis and remedy would be helpful in print.
Many thanks!
Wendell
 
NOTE:
The reason I made the request of Cary on our site is because the problem, as he described on the phone, may be extensive to those of us who own Toyota pulling vehicles - and we would appreciate a diagnosis and how-to solve the problem in print.
Wendell
 
I have a Toyota FJ Cruiser, and when the key is in lock (vehicle turned off so key can be extracted) there is no voltage / current to any of the 12 volt plugs.

So when I had the seven pin connector wired (to include electric brakes and charging current to the trailer), these two wires come directly from the vehicle battery positive post with inline fuses.

When the trailer is connected and the vehicle engine is off, the battery on the trailer won't draw current to charge its battery because the voltage drops to the 12.6 range of the vehicle battery, whereas the alternator puts out 15-17.5 volts to charge the vehicle system. Also, the brakes on the trailer only work when the vehicle brakes are depressed. Therefore, leaving the trailer connected to the trailer over night will not drain the vehicle battery.

One side note, when parking the vehicle and connected trailer be sure not to be on a steep sloop, because the vehicle gear and parking brake have an extra 1500 pounds to manage in a stationary position. Or be sure to chock a wheel or two.
 
Ok, here ya go Wendell.

What Wendell is referring to is how to override the battery isolator option when using a tow vehicle that is wired with a factory regulated charge line in it’s 7 pin connector.

Let’s start with the basics of when and why this would happen. If your tow vehicle is wired with a factory 7 pin connector the optional trailer mounted battery isolator is not needed. This is because these factory towing packages will have a charge line relay in circuit that turns the charge line off when the ignition key is turned off.

So, step one to preventing possible charging voltage issues with factory regulated charge lines is to not order the optional battery isolator with your trailer if your vehicle is equipped with a factory installed (not necessarily dealer installed) 7 pin connector because it would be completely redundant.

Of course this is not always a solution if you change vehicles some day in the future, use multiple tow vehicles where the other vehicle does not have a factory installed 7 pin or as in Wendell’s case you bought your trailer second hand and did not get to configure it properly to your tow vehicle at time of order. For these scenarios there is some risk of compatibility problems with auto manufacturers who install voltage regulation into the 7 pin’s charge line. What that means is that rather than full alternator voltage being present at the 7 pin they regulate it down to a lower voltage. Why, we are not sure. Most trucks and larger SUVs that have factory 7 pins do no have this issue because they run power straight from the fuse block through a relay and back to the 7 pin. This is only regulated by the engine’s charging system of the tow vehicle. The Jeep Grand Cherokee Holly and I use as our family tow vehicle for example is wired this way. A couple manufacturers we have seen go with a regulated charge line outputs. The ones we are have seen have been Toyota, Range Rover and Lexus. This regulated charge line runs a lower voltage than the tow vehicle’s charging system.

How does this cause a problem? The optional battery isolator in the trailer is a solid state voltage sensing switch. When it detects the voltage on the charge line from the tow vehicle is high enough to indicate that the vehicle’s alternator is running and producing power it turns on and connects the camper’s battery to the tow vehicle’s charge line and therefore to the tow vehicle’s battery. The turn on voltage for the battery isolator is 13.4volts. Since a normal alternator charging voltage will see 13.8volts or higher back at the trailer this will turn on in short order. After you shut the engine off on the tow vehicle and the voltage falls back down to the nominal battery voltage of 12.2-12.3volts it turns the charge line off at 13.2volts disconnecting the camper from the tow vehicle’s battery preventing accidental tow vehicle battery discharges. The problem with the regulated charge lines is they typically will only get up to about 12.6-12.8volts back at the trailer and that does not turn on the battery isolator and therefore you are not charging your camper’s battery whilst driving.

How to bypass the voltage sensing function of the battery isolator? The battery isolator is located above the battery in the Camp-Inn trailer. It is the black metal box with the cooling fins on it. There are two large posts on it with the charge line wire and trailer positive power wire connected to them. Below these two large posts is one smaller post with a lead coming from it to one of the large posts. This smaller post is the voltage sensing connection and it is reading the voltage on the charge line through the wire that is connected to it. Below this single small post are three equally small posts that are evenly spaced horizontally across the bottom part of the isolator box. The right hand (rear of the trailer) most post is the remote manual turn-on post. This post is for turning on the battery isolator manually.

There are basically two ways to bypass this that we have done.

One way would be to wire a switch to the remote manual turn on post by connecting a lead to the large positive trailer power post to a toggle or rocker switch and then to the small remote manual turn-on post (the right most post on the lower line of three small posts). Locate the switch somewhere outside the battery compartment where you can access it. If you do it this way the isolator will still work as a battery sensing switch and provide starter battery discharge safety when connected to a vehicle without regulated charge line or a charge line relay when the switch is placed in the off position. Then when you connect to a vehicle with a factory regulated charge line like Wendell’s Toyota pickup you can flip the switch on and manually turn the isolator on full time allowing the tow vehicle to charge the camper’s battery when driving. Since the Toyota will have a charge line relay in it to turn off the charge line when the engine is not running, having the battery isolator switched on full time does not create a risk of accidental tow vehicle battery discharge.

The second way is quicker and easier. Take the small sense lead that is wired from the large post to the small voltage sense post on the isolator and disconnect it from the voltage sense post but leaving it connected to the large charge line post. Then connect the unhooked sense lead end of the wire to the remote manual turn-on post (the right most post on the lower line of three small posts). Doing this turns the isolator on anytime there is any voltage applied the charge line in the 7 pin connector. It will not provide any accidental discharge protection when connected to a vehicle without a built in charge line relay but will work fine with a tow vehicle that does have a built in charge line relay (like the Toyota pickup in question). This solution would be the way to go if you have a single tow vehicle with a known voltage regulation issue preventing the camper’s battery from charging when driving.

Sorry this is so long winded. There just is no way to do this without the putting forth the whole explanation to the what, why, where and when.

Cary
 
Yes, a big thank you to Cary.
Cary, considering the clarity and specificity of your explanation, you could be president of a major English-speaking nation.

Wendell
 
For what it's worth, I have the factory tow package and 7 pin in my 2014 Ram 1500 and the battery Isolator in my trailer and it charges just fine.

Randy
 
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