Tow Vehicle Solar: Step By Step

[Les Izmore]

I believe we are now the official Unofficial Camp Inn Forum Guinea Pigs for charging the camper battery via a solar panel mounted on our tow vehicle. And the same system maintains the battery charge on our van during the day while it is parked. I don't think many Camp Inn owners will have much need or desire to do what we have done, but I suspect there are others outside the Forum who might want to do this and would appreciate knowing the details.

A good starting question would be why would we want to do this (at least that was our installer's first question)? The easy answer is that laziness is the Great Motivator - not having to stow and deploy a portable solar panel has plenty of appeal, plus we don't have to remember to re-position the panel throughout the day (and it frees up interior cargo space for us), Lana's lead doesn't get wrapped around the panel, and we don't have to worry about someone walking off with it while we are away. But there are other pieces to our puzzle, and a big one is our inability to override our van's desire to turn on all of the interior lights and the exterior running lights (including those of the camper, if the 7 pin is connected) every time any door is opened. And by solving that particular problem, it also allows us to power some equipment in the van during daylight hours (not the least of which is a fan to keep Lana cool while we are doing our grocery shopping during the summer).

The main disclaimer here is that this is an experimental set up. Since it is cobbled together with pieces from several manufacturers, nobody wants to warrant or even speculate on how well things will work together. When asking whether certain aspects of our system will perform as we expect, often we would be lucky to even get an "in theory, but we can't guarantee that" response. It seems to be working well now, and our fingers are crossed that it will continue to do so at least long enough to pay for itself. Anyone thinking of installing a similar setup might be wise to wait and see how ours fares over time before following suit...

Our installation is not as simple as running a line from the panel to the optional factory-installed controller on the camper. Power lines feed from our roof mounted solar panel through a cable entry plate to a dual battery charge controller. The dual battery controller allows us to charge two batteries simultaneously and (I hope) avoid any issues with mis-matched batteries (my understanding is that there is probably a blocking diode or similar device that prevents power from one battery to migrate through the controller to the other battery, and vice versa - at any rate it is clear that the typical use of this controller is for a vehicle battery and an RV battery, which would not be of the same type or size). The controller also allows us to determine how much of the available charge goes to each battery. For our needs, having 10% of power going to maintain the charge of the van's battery and 90% going to maintain the charge of the camper battery is likely to a good setting. It is possible to put more of a charge to the van battery, if it turns out that it needs more power.

The instructions for this cable entry plate didn't show where the MC4 connectors should be positioned.
In this configuration it is a bit difficult to disconnect them...​

The dual charge controller, with the charge indicator showing only the 10% charge going to the van's battery
(the camper was not connected to the van's 7-pin plug at this time).​

The wiring to the van battery is pretty straight forward - it can be wired directly (in our installation it is wired to the van battery side of the battery isolator). In fact, it is essential to wire this connection to the solar controller BEFORE connecting the solar panel. The controller needs a constant battery supply, and in our installation the van battery supplies this need. If the camper battery were the sole power source, switching on and off at the relay switch would likely short out the controller and/or panel.

The wiring for the camper's battery is where things get more complicated (at least to a layperson like myself). It gets wired into the charge line that goes from the van's battery isolator to the 7 pin connector. Wiring it directly to the charge line is a bad idea, since, with the ignition on, you would be adding the solar charge to the charge that is being supplied by the battery and alternator (making it possible, or even likely, to overcharge the camper battery). Cary supplied the solution for solving this dilemma: a simple and inexpensive automotive relay switch - with the ignition switched on, power from the solar panel is blocked and the charge comes from the alternator; with the ignition switched off, the alternator is not running and power is supplied from the solar panel.

Craig supplied this drawing of how the relay switch needs to be wired:

We relied upon Major Tire and Hitch in Boise to do the hard part of the install (which was their first solar install, but they are very talented guys). Things in our van are pretty cramped, especially in the engine compartment, so attempting this on my own was certain to have taxed my patience and probably busted a few of my knuckles. I managed to install the panels, cable entry plate and dual controller. And they wired from the controller to the battery, switch, battery isolator and charge line.

A traffic jam atop our van's battery box. That silver thing is our battery isolator.​

Ford is going to love us the next time we replace our battery!
That is the relay switch tucked in behind the battery isolator.​

So, what is going on at the dual controller now that all these gizmos are wired together?

With the the van's ignition on:

• The 10% line indicator flashes - this is because the alternator is providing sufficient charging, so the solar charge is on standby.
• The 90% line indicator is off. Solar power is blocked at the relay switch, so that only the alternator charge goes into the charge line.

With the van's ignition off:

• The 10% line indicator is on, and will go to flashing if the van's battery is fully charged.
• With the 7 pin disconnected, the 90% indicator is off - there is no battery to be charged.
• With the 7 pin connected, the 90% indicator is on, and will go to flashing if the van's battery is fully charged (this provides a charge to maintain our Dometic while we are parked).

The benefit of this setup for us is that, while we are leapfrogging our way from place to place (tagteam cycling), both batteries are being charged via the solar panel whenever we stop (assuming there is enough sunlight to provide adequate amperage). So the Dometic doesn't deplete the camper battery while we are parked, and the van's flashers and/or the lights activated by opening any door won't deplete the van battery. In theory, our two main power problems are solved, meaning we should be able to boondock more, and thus lower our travel expenses. Hopefully this will allow us to eventually recoup our investment.

Since there was some risk involved in cobbling our system together, we went with a cheap, flexible Chinese panel ($180 vs. up to $600 for a glass panel of similar output). It has mostly good reviews on Amazon.com, though it is only warranted for 5 years vs. 20 years for a glass panel. In addition to the cost savings, it is also 80% lighter and creates significantly less drag (that being said, it is probably less efficient than a typical glass panel). These were important considerations for us. And at the rate we are going, we may wear our van out before the solar panel warranty expires. But even if we end up replacing the $180 panel once, it is still a lot cheaper than going with the glass panel.

A fairly low profile installation...​

According to Cary, it probably isn't a good idea to leave the camper connected to the van's 7-pin plug when we are on shore power. While (at least in theory) both the dual battery charger and the camper's battery tender will each prevent overcharging the camper's battery, they could end up confusing one another, leading to unforeseen and undesired consequences. It is better to avoid that scenario, than to suffer the possible consequences.

Thanks again to Cary and Craig for their help in designing this system! Their free advice has saved me a lot of money and allowed me to find a way to solve multiple problems at the same time. And it allowed me to avoid the time and frustration of trying to find someone local who might have been capable of providing similar advice.

 

[Ken & Peggy]

Interesting, very interesting. I've got to re-read it a couple more times.

 

[rgupnorth]

Looks like a nightmare schematic problem - good thing the CI guys like a challenge.

 

[Sky bear]

To quote the late John Denver, "That's far out, man!".

 

[Les Izmore]

An update to our initial post: One thing that I forgot to mention is that our installation exceeds the maximum cable length recommended by Renogy. If my notoriously unreliable memory is correct, they recommend no more than 25 feet. By the time the cable gets from the van's roof to the battery it takes about 17 feet of cable (it is definitely not a straight run). Ditto from there to the 7-pin. And at least another 12 feet or so to the camper battery. So we are close to double the maximum recommended length. I suspect that the biggest issue is voltage loss across that distance - not so much that we will lose too much voltage going to the camper battery, but that the controller will sense less voltage in the camper's battery than is actually the case (which could cause it to overcharge the camper battery). That is perhaps our main long term concern with our setup, and perhaps the main reason that others should not follow suit too quickly.

The left half of the image below shows the voltage in the camper with the solar panel in full sun at around 1 pm on a cloudless day. The right half shows the voltage after we had been on shore power overnight, just before we plugged the panel in. I don't know if this a good thing or not, but it seems reassuring to me that the panel is capable or providing a higher voltage charge than the van's alternator (which measures 14.0v at the 7 pin connector).

NOTE: It is not possible to measure the solar panel voltage at the 7 pin connector, because no voltage will flow into the charge line until the solar controller senses a battery at the other end. Thus it was necessary to get the above reading at the galley 12v plug.

 

[Les Izmore]

We've been camping for about the past two weeks without having to connect to shore power, so the solar setup is definitely doing its job. We've mostly camped in pine forests, rather than in full sun situations, and the power generated from the panel seems capable of keeping up with the Dometic's load. I had hoped to provide some specifics about our experience, but there are far too many variables to do so. As Fernlane noted, his tri-metic meter is the best way of getting a clear idea of how the Dometic and solar interact with one another. I would recommend any new Camp Inn owners who will be extensively using their Dometic to consider having the factory install one for them.

Since the Dometic was the primary reason for installing the solar setup, it is worth commenting on our experiences thus far.

First, we have opted to store the Dometic in our van until evening. And we toss it back in the van before setting out in the morning. That way it gets charged via the alternator and allows the camper battery to get a full alternator charge without having the Dometic's load interfere with that. That way it spends the night attached to a fully charged camper battery. And since it relies upon a charge from the solar panel when the van is not running, we've changed the controller's charge profile to 30% van charging and 70% camper charging. But since there is virtually no load on the camper battery after it is initially recharged after a night of use, it should be fully charged most of the time, allowing 100% of the charge to go to the Dometic the majority of the time.

Second, we had been advised to use the Dometic's Med battery monitor setting to keep from drawing the charge on the camper's AGM battery down too low. What we found was, that on a three week old battery that had been on shore power most of those first three weeks, on the Med setting the Dometic would draw too much power and shut itself down every few seconds or so. So we are back to using the Lo setting, despite the negative affects that it could have on our battery's life. This was a primary reason for choosing to store the Dometic in our van during the day - the hope that it will extend the camper battery's life (and hopefully not significantly shorten the life of the van battery).

 

[Les Izmore]

Another update: we just spent an entire month without connecting to shore power and everything is working great. We use our generator maybe once or twice a week, generally to charge devices that can't be charged via USB or because we need supplemental heating. We could do the recharging via solar with our inverter, but thus far it has been more convenient to fire up the generator, since we already have those devices connected to the camper's shore power wiring. If we run the generator during cool weather, we will sometimes also watch a video while the generator is running, since that would otherwise add another significant load on the camper battery at a time when solar power is limited (at night.in the evening).

At this point it looks as though it would take a period of not driving and having limited access to solar (lots of clouds or too much shade) for this setup to not meet our needs. At least until the battery starts to wear down and lose its ability to hold a charge, or the panel loses its ability to provide a full charge. It seems we are the outliers on this issue: we probably run our Dometic off battery/solar more than anyone else on the forum, so once we reach the point where the battery is once again wearing out we will update this thread, so that others have a reasonable idea how long an AGM battery will last with near constant use, coupled with the heavy load imposed by the Dometic. I suspect we might be lucky to get a couple years use before that happens. If we do better than that, we will be thrilled.

As long as things keep working as planned, we won't provide any further updates to this thread until this winter. It is nice to have the solar working for us even when we haven't yet set up camp, and it is even nicer to not have to deploy a portable panel and worry about someone walking off with it. When we tell people we are running off of solar, most of them have no clue where the panel is located - they expect it to be a big bulky thing with sharp edges.

 

[AlCat]

Thanks for taking the leap on this.

I apologize if I missed this while reading. Is your van battery bigger than a normal car battery? I'm wondering how long the Dometic can safely sit inside your (sometimes hot) van, as I would expect that would cause the Dometic to cycle on quite often. (I'm wondering if the best daytime place for the Dometic is in the cabin of the Teardrop, sitting on a hard surface such as a collapsed folding table.)

 

[Les Izmore]

Battery size: our van battery is Ford standard equipment. We replaced it once (which is part of why we invested in the solar setup) and had requested a higher capacity battery when we had that done. We were told that no such battery existed for our vehicle. I suspect that is due to the space constraints where the battery is located.

Heat in the van: with a windowless van, heat build up is substantially less than, for instance, the typical SUV.

Dometic impact on the van battery: our original van battery lasted just 15 months, and that was before we started carrying to Dometic in the van vs. the camper. The reason for that short lifespan was due to two factors: 1) every time a door is opened on the van, the running lights and interior lights come one. If the 7 pin is connected, then the running lights also come on in the camper, 2) when we were tag-team cycling everywhere, there were some places where we used our emergency flashers a lot.

We subsequently learned how to turn off the lights once a door is opened (several calls to Ford and visits to local dealers were to no avail - a little over two years after the 2015+ TCs started production, someone on the Transit Connect forum discovered the fix - moving the light stalk forward or back after the door is opened). We also replaced our camper marker lights with LEDs.

Our current battery has lasted 5 months longer than the original battery and shows no signs of an impending demise, despite frequently carrying the Dometic in the van since having the solar panel installed. Of course when the Dometic is drawing the most power is also when the panel is producing the most power. I suspect that, with the power from the panel being delivered to the van's battery post, the Dometic would only draw power from the battery if the load is greater than what is being supplied by the panel, but I am way out of my depth on that subject.

Of course we very recently changed part of our solar setup, eliminating the battery isolator, relay switch and PWM dual battery solar controller in favor of a CTEK DC-to-DC battery charger installed in the van. We took our van in for a factory recall last November, and since that time the old setup stopped working properly. The new setup greatly simplifies diagnosing any potential problems, plus it has a more efficient MPPT solar controller, and is a much better match to the charging profile of our camper's AGM battery.