Components Used:

Renogy Rover 20 Amp MPPT Charge Controller

BT-1 Bluetooth Module

Renogy 15 amp MC4 inline fuse holder

12V Battery Disconnect Switch

Mighty Max 150 watt monocrystalline solar panel

14" MC4 - SAE Adapter

Windynation solar extension wires

Tools Used:

Wire stripper
Wire cutters
Digital Multimeter
Screw Drivers






First off, this is provided for general information purposes and is not meant to provide instruction for your particular application.  If you are not 100% confident and capable of working on your RV then leave that work to a certified professional.  Making improper modifications to your RV can cause serious injury to yourself or your RV.

With that said, we recently decided to add a solar charging system to our travel trailer.  We did this for two primary reasons.  First, the on board converter/charger which is integrated into the power center is pretty much junk.  If you consider how most travel trailers are used (occasional trips lasting only a few days) it does a decent enough job of keeping a charge on the batteries in the odd event you actually need to use them.  It is not designed to properly charge and maintain a battery over an extended period of time.  We spend a lot of time in our trailer, most of which is spent hooked to shore power.  Our converter ruins the battery about every 12 months.  Solar charge controllers (or dedicated AC chargers) are designed to properly charge and maintain your batteries over the long haul.

Next, we travel a lot in our travel trailer and we're always looking for ways to save a little money or have a new experience.  One thing we have not done much of is boondocking.  In fact, you can make the argument that we've never really done it at all.  We've stayed at campsites with no hookups, but usually just for a night while traveling and always in an official "campground".  We've never done an extended back country stay on BML land for example.  One reason we have not, is our inability to generate our own power.  Yes, we have an inverter generator but it is still relatively noisy and we have no backup should it fail.  The addition of a solar charging system adds that extra source of power with the added benefit of silent operation.

Determining what we needed:

After deciding to add the solar charging system the obvious question is: What do we need?  This is where things get tricky and potentially expensive.  As a starting point we considered these facts...

  1. We have a 2107 travel trailer which is "prewired for a Zamp solar system".
  2. Most of our time is spent on shore power at RV parks.
  3. Even when on shore power we want to charge the batteries using the solar charger.
  4. We will likely only boondock 5 days or less every 3 months or so.
  5. We stay all over the country so the solar has to work in heavily treed areas.
  6. We wanted the system to be as efficient as possible.

From these parameters we determined that we really didn't need a high end system capable of sustaining us on Mars until the next resupply ship arrives.  A basic system capable of reliably charging the batteries everyday would suffice.

In actually designing that basic system, we really didn't want to tear up a new trailer to get it installed.  Since the trailer was "prewired for Zamp solar", the first thing we considered was the obvious choice of just adding a portable solar suitcase.  In going this route, one must first understand what "pre-wired" means in relation to a solar system.  To do that you have to understand what's needed in a solar charging system.  The best way to do that is to look at something you may already be familiar with - a battery charger.

With a standard battery charger you have the following:

110 A/C power -> battery charger -> battery.

In this case, the energy source is 110 A/C power from the wall socket, the battery charger converts the 110 A/C into the appropriate voltage and current to charge the battery.  It also monitors the battery to determine state of charge and includes safeguards to prevent damaging the battery.  And the battery stores the charge.

A solar charging system is essentially the same with the following components:

Sun -> Solar Panel -> Solar charge controller -> Battery.

In a solar system the sun and solar panel combine to be the equivalent of  a 110 A/C outlet - they provide the raw energy for the system.  The solar charge controller is the charger that converts the power from the panels into a form that properly charges the battery.  It also monitors the charging process and protects the battery from damage.

In most cases, an RV "prewired for solar" only has the wiring installed that connects the solar charge controller to the battery.  It usually includes a standard plugin port on the outside of the RV where the remainder of the system can be plugged in.  This is where the self contained solar suitcase systems come in.

Figure 1: Adding a solar suitcase to a prewired RV is simple. Just plug it in as long as your suitcase matches the plug. In our case, it was "pre-wired for Zamp" so any Zamp solar suitcase would plug right in. Other brands will require at least one adapter to match Zamp's proprietary plug polarity.

A self contained solar suitcase includes the panels, a solar charge controller, and the wires necessary to plug it into the "pre-wired for solar" port on the side of your RV.  When you do that, you have connected your solar charging system to your batteries and you're all set up to solar charge.  Going this route has several advantages.

  1. It's a premade system - plug and play.
  2. They generally fold up for easy storage.
  3. They can be moved around to where the sun is. If your RV is in the shade, the panel's can be in the sun.
  4. It's easy to set-up.
  5. You can keep it if you change RVs
  6. No modifications are needed to the RV.

It sounds like almost the ideal solution for our solar needs but there are a few negatives.

  1. They are expensive - you pay for the convenience.
  2. They are easily stolen.
  3. They tend to rely on cheaper, less efficient components (PWM vs MPPT charge controllers).
  4. They are not easily expanded.

The biggest factor is the expense.  A 200 watt Zamp solar suitcase runs in the $950 range.  While it is a highly rated, quality product that does what it's designed to do very well, we could match or surpass its performance for about 1/3 the cost with not too much extra effort.  We didn't see the value in the convenience it offered.  Other vendors offer solar suitcase solutions in the $300 - $700 range.  Renogy would probably be the best lower cost option out there.  They also have a waterproof controller now so their product would be functionally comparable to the Zamp system.

One thing to note on the Zamp pre-wire if your RV is so equipped.  The Zamp plug is a standard SAE solar plug with one caveat of marketing genius - it is wired with revered polarity.  So, you can only attached a Zamp solar suitcase to that plug and have it work properly.  Other solar suitcase will require adapters.  If your non-Zamp solar suitcase has an SAE connector you'll need a polarity reversing adapter.  If it has MC4 connectors then you'll need an SAE adapter and a polarity reversing adapter.

We liked the idea of the portability a suitcase provides which would allow us to place it where the sun was if we were parked under trees.  We also liked the idea of not having to drill or cut holes on the roof of our new trailer.  We didn't like the cost and felt we could achieve the benefits of the portable system, with greater efficiency and less cost without making it more complicated to use.

Figure 2: We decided to integrate the charge controller into the internal wiring. The solar panels use an adapter to plug directly into the Zamp port. This forces raw solar power over the internal wiring between the Zamp port and the controller. The panels have to be fused and run in series to keep the current over those wires below the maximum the wires can support.

What we decided do was integrate a more efficient MPPT charge controller into the pre-wired system and mount it inside the trailer.  Doing this would use the existing wiring, allow us to keep the panels portable (or roof mount them), and gain the greater efficiency of the MPPT controller.  All at a lower cost.

The MPPT controller is key to this design.  It provides about 20% greater efficiency then the cheaper PWM controllers included on most solar suitcase setups.  That's a nice perk, but the real necessity is the ability to handle panel input voltages which are different then your battery bank.  We run two 6V golf cart batteries in series for 12 volts.  With a PWM controller we would have to have 12V panel input.  The MPPT charge controller we chose can accept panel input voltages up to 100V, and convert that to charge our 12V battery bank.

This comes into play when you consider how power is transferred in a solar system and how that relates to the pre-wiring in your RV.  In a solar system there are two sets of voltages/amperages in play.  There is the voltage/amperage in the wires between the panels and the charge controller.  There are different voltages/amperages in the wires between the charge controller and the battery banks.  If you use the pre-wiring in the RV with a solar suitcase, the volts/amps traveling through the pre-wiring in the RV are those sent out by the charge controller.  Since these are typically low voltage systems, the important number to look at is amps.  A 20 amp charge controller (which is usually included in a portable system) will put out a maximum of 20 amps over the pre-wired wiring to charge the battery.  The manufacturer of your RV would have anticipated this as the "intended use" and used 12 or 10 gauge wire which is capable of handling 20 or 30 amps respectively.  The wires are much less sensitive to voltage.

If you connect solar panels directly to that wire so the raw solar panal power is transferred to the charge controller over it (which is what our set up will do) then you have to keep the current over that wire below the maximum current the wire can handle.  In order to get a usable amount of power and still have panels we can maneuver, we need to use multiple panels.  Just like a battery, how you connect those panels affect how the power is transferred over the wire to the controller.  If you wire them in parallel, the array voltage is the same as the individual panel voltage, but the array amps output is the sum of the panels.  If we wanted 400 watts from four 100 watt 12 volt solar panels generating 6 amps each we would have the following:  Wired in parallel the wiring to the controller would see 12 volts and 24 amps.  Which is well over our 20 amp max.  Wired in series, the wiring to the controller would see 48 volts and only 6 amps.  12 gauge wiring can easily handle this, however because the array voltage is at 48V, a PWM controller cannot be used.  An MPPT controller will handle it just fine.

Choosing the components

We decided we needed the following parts to complete the system.

  1. MPPT Solar charge controller
  2. Solar panel(s)
  3. MC4 fuse between panel and RV
  4. MC4 solar extension wires
  5. MC4 to SAE adapter
  6. 10 gauge wire to connect controller to 12V system.
  7.  Battery disconnect switch.

Most of these are standard items and choosing a specific brand/part is personal preference.  The MPPT controller has to meet specific requirements.  First, it has to take input voltage from the panels in your system.  Sending it voltages higher then it can accept can damage it or cause it to not function correctly.  It also has to be able to work with your battery voltage.  A controller that can only handle 24V batteries will not work when connected to a 12V battery bank.  Finally, the output has to be sized to both your wiring and the battery bank size.  We have 10 gauge wiring so the largest controller we could use was a 30 amp without making major wiring changes.  Fortunately, with 220 amp hours of battery a 20 amp controller is all that is required.

After doing some research we went with the Renogy Rover 20A MPPT controller.  It's highly rated, reliable, affordable, has an integrated display, a temperature sensor and has a bluetooth option (which we opted for) that allows you to monitor and control it over your phone.  It also handles lithium batteries, which the slightly more expensive Commander did not.   We don't use lithium batteries at the moment but we may upgrade at some point.  Since we purchased our 20 amp unit, Renogy introduced a 30 amp version.  Had that been available we would have gone that route.


Installation for us was very easy.  The hardest part was locating the ends of the pre-wired wires in the trailer.  The manufacturer (Venture-RV) stated they were "connected to converter", however repeated calls to their support line failed to reveal exactly how.  Inspection of the 12V fuses showed no fuse dedicated to the solar pre-wiring and there were no obvious tie ins anywhere else.  We also looked at all the connections at or near the battery on the outside in case it was run straight to the battery.  No luck there either.

The next step was to pull the converter out.  Behind it we located two sets of three wires grouped together with wire nuts.  One set tied to a 20amp fuse marked "slide motor".  The other set tied to the grounding bar screwed to the floor behind the converter.  The other ends made up two wire pairs, one went toward the back through the floor and the other went toward the roof.

Figure 3: After tracing wires, this is how we determined the Zamp pre-wiring was connected into our system.

We removed the wire nuts and separated the wires.  We then applied a voltage to the terminals in the Zamp plug (via a 9 volt battery) and tested the two wires.  The set coming from the roof turned out to be our Zamp pre-wire.  Using the wire nuts we reconnected the slide motor leads and moved on to installing the controller.

Figure 4: This is how we integrated the Rover MPPT charge controller into our Zamp pre-wiring. Note that we connected the wires from the Zamp plug to the PV terminals in the controller so that standard SAE plug polarity will work - no need for a polarity reversing adapter.

We connected the Zamp wires to the PV in ports on the Rover controller.  To the battery out ports we connected 10 gauge wire.  The negative went back to the grounding bar behind the converter.  The positive was run to a battery disconnect switch.  We used another 10 gauge wire to connected the disconnect switch back to an unused output terminal on the DC distribution block of the converter.  Adding a 20 amp fuse completed the connection and protects the system from any over current issues the charge controller may generate.

The battery disconnect switch was included to allow us to turn off the solar system and turn on the converter to charge the batteries should the solar not be able to keep up.  Having both running at the same time may damage one or the other.

For panels we're going with Mighty Max 150W monocrystalline.  They are 12V and operate at about 8 amps. We went this route because we knew we'd need more then 100 watts and maybe more then 200.  (The 20 Amp controller can handle up to 400 watts.)  If we went with 100 watt panels then we'd have to buy 2 to start off with and if we need to go to 300 then we'd need 3.  Even though they are smaller then the 150's, 3 panels are harder to move around then 2.  So we started with one 150 watt panel and will likely add a second soon to give us a total of 300 watts.

Total spent so far is about $350 and the 150 watt panel charges the batteries in October full sun on the Northern Olympic Peninsula.  We're getting about 50 - 60 amp hours per day of charge which is not the most we could get.  Once the batteries all full (which happens by 2pm) the amp hours stored drops off dramatically.

The Mighty Max 150 watt solar panel is on the larger side at 39" x 39" and 26 lbs.  It seems well built and we've seen output as high as 145 watts in the fall full sun here in the far pacific north west.  That's 145 watts with about 75 feet of 10 AWG wire between the panel and the controller.  This is excellent given the environment and could be improved by using heavier (8 AWG) and/or shorter extension wires to minimize DC power loss.

By comparison, the 200 watt Zamp solar suitcase uses a PWM controller which is about 20% less efficient then the Rover 20A MPPT.  20% at 200 watts is 40 watts.  That makes the Zamp the equivalent of 160 watts compared to the 150 watt system we set up.  So the actual charging capacity difference between the much larger, heavier and expensive Zamp 2 panel suitcase and our single panel system is negligible.

Overall I am extremely happy with this setup. It was affordable, works great for our needs and offers lots of flexibility for the future. For example, if I decided to mount the panels on the roof, I have room to do that and I can just hang the cable off the back and plug it in - no need to feed the wire through the a hole in the roof.  In fact, I could keep a couple portable and a couple mounted and just plug in the ones what will work best for where we are parked. Additionally, if I wanted to upgrade the controller I think I could do it in about 15 minutes.

If I were to do this on a bigger budget, where would I have spent the money? I would have bought a better charge controller. Don't get me wrong the Rover is great for what we need it to do, but if we lived off grid all the time, had a larger battery bank or a large inverter then a more capable controller may be in order. Even with the current setup I would have spent the few bucks more for a 30 amp controller if it were available at the time.

The big thing that a better controller will provide is better control over the charging process. Your charge controller will usually be three stage - bulk, boost and float. More money may add more stages, but the important part is how the controller knows when to switch stages. In the case of wet cell batteries like ours, the boost phase and how it ends is important. In the boost phase, the controller switches into constant voltage mode. In this mode, a pre-specified voltage is held (usually 14.4-14.8V) and the current drops over time as the battery completes its charge. The Rover has this mode, which is good, but leaving this mode and going to float is triggered by time, not a target current. So in the setting you specify that it will boost for X minutes – whether it needs or not. At the end of X minutes it will switch out and go to float mode, whether it's fully charged or not. More expensive controllers will allow you to specify a target current – which is a good indicator that the battery has reached full charge. This ensures that it leaves bulk charge mode when the battery is full and prevents under or over charging.

Future Expansion

This system just keeps the batteries happy and the batteries of course only run the 12V systems. In our trailer that gives us the basic necessities including: lights, fans, propane fridge, propane water heater, water pump and furnace. At some point we'll be adding an inverter for AC devices like hair driers, coffee makers and the microwave. Inverters draw a lot more current so that install will require heavy wires to the battery which will in turn require a pretty significant rewiring of the circuits feeding and drawing from the batteries. I'll put together another post when I cross that bridge.

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