Guidance needed to wire camper for on the road charging

WrongWayRex

We have ordered our camper with solar panels installed from the factory. But there are days we travel 6-12 hours before stopping. During that time, I would like to be charging the Tab battery with the tow vehicle. We currently do this with our Little Guy but it does not have solar. I have run a 8awg wire from the battery through a 30 amp fuse and to the 7 pin plug and to the hot side of the battery.

What will I need to do to make sure we can charge the battery of the Tab on the road but not damage my solar system?

All thoughts appreciated.

WrongWayRex

dragonsdofly

@WrongWayRex, not completely sure how every nuance works together, but if you have a built in solar charging system, my assumption (and you know the old adage), is that the solar system will have a charge controller which should be checking as long as is outputting power, not to overcharge your battery. Solar input should slow and stop as you top off the battery, whether from the charge line or from solar. What I'm not completely positive about is how the converter in the t@b works in conjunction with the charging line to keep your battery from overcharging.  Calling all electrical wizards to chime in here.......

Ratkity

Keep in mind that all charging are trickle charges, just like a separate stand-alone charger. That's what your solar is. It'll help top off the battery and help with phantom power draining your battery. That said, it won't charge a severely depleted battery. Keep an eye on your battery charge state (by meter, not by the SeeLevel). You'll be just fine! Don't worry too much if you meter during boondocking and don't hit that 12.2V state quickly (50% discharge). Then you'll need to re-evaluate what items you are using that are pulling a lot of volts and readjust your boondocking style accordingly. Everyone is different. Customize your camping to you! Happy camping It's supposed to be worry-free.

gregndeb

I pretty much did what you did.  10 ga wire through a circuit breaker.  I wired a relay so that the power to the 7-pin connector is only energized when the TV is switched On.  That way the TV battery is always full.  Our 2017 highlander allegedly has a smart charger that does vary charge voltage when we are on long trips.  As of now, we haven't used a lot of standalone battery power but haven't had issues either.
There are some DC-DC chargers that claim to charge the trailer battery better, but I suspect aren't needed unless you do more serious boondocking.  Any other opinions with the new DC-DC chargers?

johntreacy

In my walkthrough last week, I was told that both systems will charge the battery as I'm driving and that the TV would not drain if the TV wasn't running. I was a little surprised by the second point and asked again. I'm thinking a 7 pin breakout cable would be a good idea to run some tests with a multimeter. 

ScottG

Most (but not all) tow vehicles automatically disconnect the 12V charge line to the 7-pin when the vehicle is turned off. You need to figure out how your vehicle is configured before believing what you were told in your walkthrough!

Sharon_is_SAM

I agree with Scott.  Our Toyota Sienna after-market 7 pin charge line is still live when the ignition is off as the installer wanted no part of installing an isolation relay.  So, if running a refrigerator on DC while towing and then stopping for a longer time, it can deplete the Tab and van battery.  We disconnect when we stop for longer periods of time.  Does anyone know:  will the Tab battery discharge first and then the car battery? 

ScottG

Given that everything is wired together, I expect both batteries will be discharging if the T/V is not isolated. Which one wins the race to dead probably depends on several varying factors that are out of my pay grade!

sqrpeg

I’m also confused about how the various possible charging sources all work together.

Getting back to @WrongWayRex ’s original question - if you have roof-mounted solar that (I assume) remains connected and charging during transit, how does the solar controller handle the fact that there’s also 12V input coming from the TV?  And similarly, how would the smart(ish) charging system on a modern TV account for the additional input from the solar controller?

Seems like there's potential for battling charging algorithms - do things somehow "balance out", or can you only have one or the other connected at any given time?

WrongWayRex

I am a novice at this DC stuff, but it seems to me that if you have: a. solar 12vdc charging system sending power to the battery and b. a 12vdc tow vehicle charging system sending power to the battery, then there is the potential of a conflicting power amperage that can cause some problems. So if I was to put a blocking diode in the battery side of the solar input to the battery to stop the TV power from trickling to the solar equipment, and a blocking diode on the battery side of the TV input to keep the solar equipment from sending power to the TV, then they would be isolated from each other. The only way to keep the trailer load from bleeding the power from TV battery is to disconnect the connection to the battery. Either unplug the cord from the TV or put a switching relay in line that is controlled by the TV when engaged to drive down the road. Then and only then would battery power be available to charge the trailer. So a coupe of $2 diodes and a $10 40amp relay with a $5 fuse and holder should create a proper isolation and disconnect system. Keep in mind the relay control circuit will also need to be fused although it will be minimal, maybe two amps for the control circuit. Your main power from the TV battery should already be fused. If not, be aware of potential smoke loss from the wiring.

Keep in mind there is a third charging system in most of our units, when you are plugged into shore power, your inverter is automatically sending a charging signal to your battery. This will also need to be isolated from the other power sources.

FYI, to my knowledge, no one has figured out how to put the smoke back into the wires after it has been released.

Notice: Making an assumption that I know what I am talking about can be dangerous to your health and wallet.

Ratkity

The solar controller defers to all other power sources when the battery is charged. Since there is still electrical pull on the battery systems when pulling a camper due to phantom power inside (even without the frig on DC). The solar charger will still be doing a trickle charge as well as the trickle charge the battery will get from TV 12V source. Even together, there's a chance your frig set on DC will drain both batteries if you stop for a long lunch (possibly excluding the high efficiency, low amp draw frigs like the ARB on DC). 

A trickle charge is a trickle charge. Two trickle charges are still not going to equal a bulk charge that a battery charger gives to get a 50% depleted battery to 85-90% while driving 4 hours. Battery chargers take overnight to charge a battery fully. The last 10-15% is a slow trickle charge and takes the longest to complete.