Trailer battery wiring questions?

[ExpoMike]

Hi everyone,

The wife and I received our Kamparoo trailer Friday and this thing is great. I so can't wait to get out for a trip. Still need to do the DMV thing as AAA does not title/register out of country vehicles.

I do have a question regarding the on board trailer battery. I understand the wiring for the plug part but what I am trying to understand is how to wire it on the vehicle.

Do I run a 12V + wire from the vehicle battery back to the trailer plug and that's it?

If that's the case, what prevents the vehicle from trying to pull current from the trailer battery when you start the vehicle?

Do I need some type of isolater under the hood?

If so, how does that effect things when I go to a dual, underhood battery setup (most likely using the National Luna relay setup)?

I just want to make sure I get things setup right since the Cherokee is currently at flat four plug and I need to add some wiring to setup for a 7 pin plug.

Thanks for the info! :26_7_2:

 

[Martyn]

Mike

Good news on the Kamperoo. Most vehicles have a 10 gauge wire run back to the trailer socket at the back of the vehicle. It is either fused or has a breaker in it.

To stop the vehicle drawing from the trailer battery unplug the trailer plug from the vehicle. I don't see a problem with starting your vehicle with the trailer plugged in. It can't draw much current from the trailer battery as the wire running to it is only 10 gauge. If you upgrade to a dedicated 6 gauge system then it would be a problem.

What does represent a problem is leaving the trailer plugged into the vehicle for an extended period of time if the vehicle has a major draw, or you leave the lights on. As a rule of thumb unplug the trailer from the vehicle overnight.

The 7 pin socket normally also has a wire from the in cab brake controller. The center terminal is an extra that can be used to function as a reverse light.

Most RV shops or a Midas that fits trailer hitches can do the work if you don't feel comfortable doing it.

 

[ExpoMike]

Thanks Martyn.

No issues with doing the work, just wanted to make sure I was going to do it correctly. I know the perfect curcuit breaker that allows me to manually open the curcuit versus having to disconnect the plug. I just wanted to make sure there was no issue with it pulling too much current during starting.

I guess one last question, what rating would you recommend for the curcuit breaker?

Thanks again!!!

 

[Martyn]

Thanks Martyn.

No issues with doing the work, just wanted to make sure I was going to do it correctly. I know the perfect curcuit breaker that allows me to manually open the curcuit versus having to disconnect the plug. I just wanted to make sure there was no issue with it pulling too much current during starting.

I guess one last question, what rating would you recommend for the curcuit breaker?

Thanks again!!!

Mike

On the trailer side we use a 20 amp fuse. I'd PM or e mail Mario to get his opinion on a breaker on the vehicle side, I'd be guessing.

 

[ExpoMike]

Cool. I am coming up to the shop on Saturday as I have arranged to meet Mario to pick up a Lock 'n Roll hitch. First mod to the trailer. :wings:

I'll ask him about it then, if he doesn't chime in before.

 

[Robert Bills]

On all of my tow rigs I use a constant duty solenoid to power an 8 ga. wire that runs through the connector to the trailer battery. (Also to my CJ battery when I flat tow it with my pickup.)

With the solenoid, the trailer battery is connected to the tow rig battery only when the tow rig ignition is "on." No need to disconnect the trailer to avoid running down either battery in camp or the risk from a "constant hot" 8 ga. wire running under the tow rig).

These are the same "Ford style" constant duty solenoids used on winches, lift gates, etc., available at any auto or trailer supply. For additional safety, the power leads are fused in the tow rigs and also in the trailer. (On my CJ I used a fusable link rather than a fuse on the wire from from the connector to the battery.)

 

[Joanne]

Here's how I hooked up the battery charging circuit on my little trailer.

To control the solenoid I have a toggle switch in series with the ignition switch. This automatically disconnects the connection whenever the ignition is turned off. When I am driving I can connect or disconnect from inside the truck.

It doesn't show on the diagram, but I also have an LED light that indicates when the connection to the trailer is active.

Joanne

 

[Robert Bills]

Please excuse my confusion, but isn't your solenoid already wired to be active only when the ignition is "on," such that the toggle to deactivate the solenoid when the ignition is "off" would be redundant? (Or is your solenoid triggered by a lead from the ignition that is always hot?)

That being said, I can see the value in having the toggle/led to deactivate the solenoid while the ignition is "on" for situations when there is no trailer in tow or one would not want a hot wire with engine running (for example, to prevent overcharging trailer battery, not diverting electricty from tow rig battery, safety issue, etc.).

 

[ExpoMike]

Cool! I like that idea of leaving things automatic or have a manual override should I need it.

Thanks a bunch guys! :jumping:

 

[robert j. yates]

That being said, I can see the value in having the toggle/led to deactivate the solenoid while the ignition is "on" for situations when there is no trailer in tow or one would not want a hot wire with engine running (for example, to prevent overcharging trailer battery, not diverting electricty from tow rig battery, safety issue, etc.).

That was my reasoning behind using the *switched* solenoid solution as well.

 

[Martyn]

Here's how I hooked up the battery charging circuit on my little trailer.

To control the solenoid I have a toggle switch in series with the ignition switch. This automatically disconnects the connection whenever the ignition is turned off. When I am driving I can connect or disconnect from inside the truck.

It doesn't show on the diagram, but I also have an LED light that indicates when the connection to the trailer is active.

Joanne

Make sure that the trailer is grounded to the vehicle though the 7 pin, rather than the just grounding the auxiliary to the trailer chassis. I'm sure we all know that, but it didn't show up in the electrical diagram.

 

[Joanne]

Please excuse my confusion, but isn't your solenoid already wired to be active only when the ignition is "on," such that the toggle to deactivate the solenoid when the ignition is "off" would be redundant? (Or is your solenoid triggered by a lead from the ignition that is always hot?)

That being said, I can see the value in having the toggle/led to deactivate the solenoid while the ignition is "on" for situations when there is no trailer in tow or one would not want a hot wire with engine running (for example, to prevent overcharging trailer battery, not diverting electricty from tow rig battery, safety issue, etc.).

You are on the right track. The toggle switch is intended to give me control when the ignition is "on" and I'm driving. Tying it to the ignition keeps me from stopping for the night and potentially draining both batteries.

In essence it's similar to your car radio. It can only be played when the ignition is ON and the radio is turned ON. Just because the ignition is on doesn't mean I want to be charging the trailer battery, but every time I shut off the ignition I want the trailer to be disconnected.

As always, the way I do things isn't necessarily the right way, just the way that makes sense to me at the time I'm doing it. I've had some really good mess-ups that seemed so logical at the time....

Joanne

 

[Joanne]

Make sure that the trailer is grounded to the vehicle though the 7 pin, rather than the just grounding the auxiliary to the trailer chassis. I'm sure we all know that, but it didn't show up in the electrical diagram.

Great point!! I think I'll modify the diagram to include that important connection.

Thanks!

Joanne

 

[Robert Bills]

Make sure that the trailer is grounded to the vehicle though the 7 pin, rather than the just grounding the auxiliary to the trailer chassis. I'm sure we all know that, but it didn't show up in the electrical diagram.

Perhaps you should explain why, since there are many of us who don't have a lot of experience designing electrical circuits. (Or who are like me and learn most things the hard way ). My trailer connections are grounded to the tow rig through the connectors, but for the life of me I don't know why I did that other than I was told to.

 

[Martyn]

Perhaps you should explain why, since there are many of us who don't have a lot of experience designing electrical circuits. (Or who are like me and learn most things the hard way ). My trailer connections are grounded to the tow rig through the connectors, but for the life of me I don't know why I did that other than I was told to.

In a standard trailer with no auxiliary battery all the power for the lights and brakes originates in the tow vehicle. On the trailer side anything 12 volt has a hot wire + and all negatives are run to the chassis.

With most trailer/vehicle connections a ground from the vehicle goes to the trailer. This ground in then connected to the trailer chassis. The result is the trailer is a continuation of the vehicle electrical circuit.

In some older trailers, and some trailers wired overseas there is no ground wire from the tow vehicle to the trailer. The ground is achieved through the coupler, usually a ball system. The problem with this is the ground can be intermittent causing electrical problems on the trailer side.

But the real reason you want to wire your trailer this way Robert is because...... I told you to.