Connecting portable solar panel to 7-pin connector

[levickms]

HI,

I have a Casita travel trailer. I use an Eco-Worthy 120 W solar panel to keep the battery topped up when I'm not using it, since my storage spot doesn't have access to AC.
My solar panel seemed to work perfectly as long as I was connecting it directly to the battery posts. However, I got tired of moving the battery every time I needed to connect the solar charger. I wired the solar panel to a truck-side 7-pin connector so that I could just plug it into the trailer's 7-pin connector. This seemed to work at first, but after a day in the sun, the solar panel charge controller began showing random voltages ranging from 10 to 20 volts that changed every few seconds. Now, the controller does the same thing when I connect it directly to the battery. It looks like connecting the solar controller via the 7-pin connector ruined it.

My theory is this:

1. There is a charge controller built into the trailer's wiring, so connecting via the wiring harness meant that there were two charge controller in the same circuit.
2. The trailer's built-in charge controller prevents over-charging while towing, so it should work the same way when connecting a solar panel to the 7-pin connector.
3. Once the battery neared full charge, the trailer's charge controller was switching the circuit on and off, disconnecting the solar panel charge controller from the battery.
4. The solar panel owner's manual says not to connect the panel to the charge controller without first connecting the battery
5. The switching on and off of the trailer charge controller while the solar panel was "hot" destroyed the solar charge controller.

I have two questions:

1. Does my theory above make sense??
2. If it does, would it be okay to just throw away the failed solar charge controller and connect the solar panel directly to the trailer 7-pin connector, relying on the trailer's built in charge controller to prevent overcharging of the battery?

Any help with these questions from those of you who understand RV wiring better than I do would be much appreciated

 

[Whinny]

7 pin harness is usually wired directly to the battery through a breaker, there is no controller or switch. Did you get the correct wiring in the 7 pin truck side plug? Positive should show as pin 4 with ground on pin 1. I find the panel can be connected before the battery if I shade it or turn it away from the sun-controller sometimes goes wonky if the panel is producing power, but hasn't failed yet.
I have been using an adapter like yours for years with no issues.....

 

[levickms]

Thanks for your reply; very helpful.

I just assumed there must be a charge controller between the tow vehicle and the trailer battery; what prevents overcharging on long drives?

If you are right, then maybe the solar panel charge controller just failed on it's own. I guess I can buy another one.

Michael

 

[HRTKD]

I just assumed there must be a charge controller between the tow vehicle and the trailer battery; what prevents overcharging on long drives?

If you are right, then maybe the solar panel charge controller just failed on it's own. I guess I can buy another one.

Nothing prevents the tow vehicle from overcharging the RV battery except that most tow vehicles don't produce a lot of amps. That's why many of us with LiFePO4 batteries in the RV either disconnect the 7 pin circuit from the LiFePO4 battery (lots of consequences there!), put in a DC-DC charger (still a few safety issues with that) or retain a small lead acid battery that does get charged by the 7 pin circuit and then disconnect the LiFePO4 from the 7 pin circuit. The latter is what I chose to do in my trailer.

I suspect that your solar charge controller simply went bad. I would guess that most solar charge controller aren't rated for outdoor deployment. If the solar charge controller has a temperature sensor then maybe it thought the battery was getting too hot?

For my ground deployed panels, I put in an outlet on the side of the trailer that I plug the PV into. That works well for my situation.

 

[Short_Shot]

What consequences would there be from simply disconnecting the 7 pin power in the trailer?

Especially with an auxiliary dc to dc connection.

 

[HRTKD]

What consequences would there be from simply disconnecting the 7 pin power in the trailer?

Especially with an auxiliary dc to dc connection.

No power to the breakaway brake system if you just disconnect the 7 pin circuit from the RV battery.

 

[Short_Shot]

No power to the breakaway brake system if you just disconnect the 7 pin circuit from the RV battery.

The brakes are activated by a mechanical breakaway cable are they not? So they don't need power from the 7 pin as long as they have power somehow.

And the regular brake function is a different pin so it should work fine.

 

[HRTKD]

The brakes are activated by a mechanical breakaway cable are they not? So they don't need power from the 7 pin as long as they have power somehow.

And the regular brake function is a different pin so it should work fine.

The pin for the breakaway may be mechanical, but the brakes will draw about 4 amps when the pin is pulled. The emergency braking has to come from the RV battery. The regular braking power is supplied through the 7 pin on a different wire.

 

[Short_Shot]

The pin for the breakaway may be mechanical, but the brakes will draw about 4 amps when the pin is pulled. The emergency braking has to come from the RV battery. The regular braking power is supplied through the 7 pin on a different wire.

Yes. That's what I said.

So there's no issue disconnecting the 7 pin power at all as long as the brakes are still connected to the lithium battery.

 

[HRTKD]

Yes, but I bring it up because many people don't remember about the breakaway brakes and realize that depending on how they disconnect the 7 pin circuit to the LiFePO4 battery they may also cut off power to the breakaway brakes.

 

[LVLAaron]

Yes, but I bring it up because many people don't remember about the breakaway brakes and realize that depending on how they disconnect the 7 pin circuit to the LiFePO4 battery they may also cut off power to the breakaway brakes.

If the trailer breaks away, I presume your 7 pin connector is also going to be disconnected.

 

[HRTKD]

If the trailer breaks away, I presume your 7 pin connector is also going to be disconnected.

The breakaway system is independent of the 7-pin cable. Leave your trailer unconnected from the tow vehicle and pull the breakaway pin. The brakes will engage.

 

[Short_Shot]

If the trailer breaks away, I presume your 7 pin connector is also going to be disconnected.

If the trailer breaks away that far you've got way bigger problems.

Safety chains should keep it close enough not to yank that connector out.

 

[Short_Shot]

The breakaway system is independent of the 7-pin cable. Leave your trailer unconnected from the tow vehicle and pull the breakaway pin. The brakes will engage.

But it does charge from that connector though.

Which is irrelevant if you've got an on-board or other alternative solution.

 

[12VoltInstalls]

what prevents overcharging on long drives?

USUALLY the breakaway battery is shared with the fla house batteries on a camper, OR an independent fla breakaway battery is in place. So same chemistry as tie rig, same nominal voltage. The vehicle should be ~14V from alternator which is a happy place for fla.
A) the brake battery won’t care, and
B) the long run from front to rear usually makes you lucky to even get 13.x volts from the 7pin. So in essence the 7-pin is undercharging anyways.