Last updated: 08/24/2014

RV Electrical and Solar

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Copyright © 2002-2013 John Mayer. All rights reserved. For reuse policy see Reuse Policy

Warning:
 
In this section I describe various wiring techniques and electrical designs. These generally conform to the national electrical code, but it is up to YOU to determine their suitability to your situation. DO NOT take this as electrical advice, only as possible design considerations. If you do not understand basic residential wiring and 12-volt automotive wiring then you should not undertake any of these implementations without further help and advice. If in doubt be sure to get help. Electricity is dangerous. The high amperage DC electricity obtained from the large battery banks described here is suitable for welding and can easily kill you. Do not underestimate the danger involved in working with DC power!!

The information I present here is intended to get you started - it is not intended to give you detailed designs that you can implement directly! Every RV implementation is different, and will require specific design goals to be addressed. However, most of the major issues and considerations are discussed here. If you understand most of what is presented here then you will likely end up with a good system - even if you have someone else implement all or part of it.

In this Section:

Installers
Presentations
Introduction to Solar
Determining Your Needs
A Phased Approach
Why Many Systems Do Not Work Well
The Golden Rules of RV Solar and Electric
Equipment Recommendations
Residential Refrigerators

Solar Panels and Solar Controllers

Inverters, Chargers, Converters

Batteries and Charging


Wiring

  • Rooftop and Solar Controller Wiring
  • Solar Array Wiring Considerations
  • Cables and Battery Connections
  • Hints on Cable Building
  • Solder or Crimp?
  • Batter to Inverter Wiring
  • Interfacing to Your Loadcenter
  • AC Wire Types
  • Grounding
  • Neutral Bonding 
  • Installing a Sub Panel
  • Powering the Entire Loadcenter
  • "Splitting" a 50-amphere Loadcenter
  • Monitoring and Control
  • Recommendations

Installing a 30-Amphere Inverter in a 50-Amphere RV
AC Circuit Protection
Sample Systems

 


I'm assuming that you have a basic understanding of both 12-volt and 120-volt power. There are many excellent tutorials and books on both subjects. I won't repeat the information here, but leave it to you to explore on your own if you don't understand the basics. For basic 12-volt electrical info, try Mark Nemeth Electrical Info which is Mark Nemeth's article on 12-volt power. For wiring techniques and parts check the The Truck Electrical Center section of this site. The information there is oriented to upgrading an HDT truck, but is generally applicable to RV's.
 
For an understanding of various RV and house connectors, and proper wiring, check out http://www.myrv.us. This will give you an understanding of basic RV electrical service, and how it differs from residential electric.

If you have a basic understanding of AC/DC electricity then you should be able to design a reasonable system following the recommendations in the sections below. The system designs and components used are only examples, and need to be modified to meet your needs. You need to complete the entire design before you start implementation or you might find your system unable to meet your future expansion needs.
 

For parts and design help from the residential solar market try (first) Northern Arizona Wind and Sun. They have an excellent forum with true experts posting on it, and their store has reasonable prices. Do not underestimate what you will learn from reading their forum. Every time I go there I learn something new! After them try http://www.backwoodssolar.com. I'm also willing to answer questions and help in design if you contact me directly - see the About Us section for our email address.
 
A complete implementation of anything but the smallest RV solar system, including an inverter, and batteries (from scratch) can cost in excess of $3000, depending on sizing and components selected. Time spent in the design phase is time well invested. Mistakes can be expensive. If you have the system installed instead of doing it yourself make sure you find a good installer. You want someone who will charge by the hour - not a flat rate. You are more likely to get a good job if the installer is not rushed, or losing money on the work.

Installers

If you need help with system design you can work with a single vendor for most of your system components and they should be able to provide design help. The best thing is to work with someone who understands the special needs of RV's. Although for many years I did solar/electrical installations, I no longer do installations. I still do designs.

For installation, one of my top choices in the West would be AM Solar (Greg Holder). Their business is RV solar, they can supply almost all the required solar parts, their prices (for the most part) are reasonable, and their preconfigured systems are sufficient; AM Solar.

John Palmer (Palmer Energy Systems, Palmer Energy) also specializes in RV solar systems. He is located in Florida.

If you need an installer in the Phoenix area then check out D&R Family RV, Glendale, AZ, 623-842-1265.

If you are looking for an independent installer that travels around (mostly in the West) then check on "Handy Bob" (Bob Shearer). You might also be interested in his blog. We agree on most installation issues and techniques - although he is generally more opposed to generators than I am. One thing we do agree on, and always have - there are really a lot of bad solar installations out there. It is very difficult to find a good installer - although in my opinion things have improved in the last ten years. If you want a good evaluation of your existing system done, Bob can do it. If he was near me then I'd use him first.

As far as installers in Quartzsite go, I find it hard to recommend any of them. But if I HAD to use one I'd use Discount Solar.


Presentations

My presentation on RV Solar and Electrical from the 2011 HDT Rally can be downloaded from here. (809 KB PDF) If you use this presentation you don't need the previous years ones.

My presentation on RV Electrical and Solar from the 2010 HDT Rally can be downloaded from Files/Presentation HDT RV Electrical 10_13_2010.pdf  (421KB PDF file).

My solar and electrical presentations from the 2009 HDT Rally can be downloaded from RV Electrical Presentation - HDT Rally 2009.  This is a PDF file (434KB). It is similar to the 2010 presentation, but not the same. Robb Finch's presentation on Wind Power can be downloaded from Wind Turbines - HDT Rally 2009 (PDF, 1.2 MB).

 

Introduction to Solar

The ability to dry camp, or boondock, is inherently part of the capabilities of all RV’s. The amount of time one can live effectively “off-grid” is dependent on your water storage capabilities, and the size of your battery bank (or how much you want to run your generator). Most RV manufacturers do not provide advanced boondocking technology as a standard part of their RV’s, so you are usually limited to 2-4 days without hookups. Enhancing the standard RV’s capabilities can allow you to live indefinitely without hookups.

So what do you need to effectively live off grid indefinitely? The heart of your system is the battery bank. You will need enough battery capacity to supply your energy needs. That means translating some of the DC battery power to AC, so it can be used by your normal RV appliances. You do this with an inverter.

Next, you need a way to replenish the battery power you use. That can be either a generator in combination with a modern battery charger, or solar panels in combination with a solar controller. Or a little of both, which is what many people use. Solar is really an option here. You can live effectively off grid with just a generator, a proper charger and a reasonably sized battery bank; but for long term use you will find it most convenient to combine this with some solar panels.

You also need a way to monitor the status of the system. Without monitoring the system you will not know how much energy is available for use, or when to use the generator to help recharge the battery bank. If the battery bank is the "heart" of your electrical system, then the monitors are the "brains". You need them both.
 

To live effectively off grid you also need a way to remove waste water, restore fresh water, and efficiently heat the RV (when required). These last three items are not covered here. This article concentrates on energy-related items.

 
Side Note: typically a "blue boy" is used to remove waste water, either gravity fed or in combination with a macerator pump. The simplest way to restore fresh water is with a plastic water bladder (check Camping World for a nice 45 gallon one that works well). The bladder folds down to a very small size when not in use. Heat is efficiently supplied with a catalytic heater. This uses no power to run, saving your battery power for better uses than running the furnace. It is also nearly 100% efficient in its use of propane. Your furnace is only about 60-70% efficient. For more on these topics see Boondocking Made Easier.
 
I've tried to convey what to look for in each of the areas covered. Although I have made some specific recommendations, you should not assume that these are the best available choices at the time you read this. Electrical and solar components change fast. Manufacturers continually upgrade their products, and introduce new products.  The intent of the information provided here is to help you to identify and select the products that will work for your particular implementation. There are many tradeoffs that need to be made when implementing an alternative energy system for your RV. There is no "right answer" in many of the areas - it is a personal choice with tradeoffs only you can make. The sample systems work well together and should satisfy the needs they are sized for, but they are only samples and there may be better components at the time you read this.
 

Determining Your Needs

First, you need to be realistic with your expectations. If you expect to install a solar system and use power just as you did when hooked to shore power, then you will be disappointed. Despite what some may tell you, living with an alternative energy system in an RV requires conservation. This is because, unlike off-grid home applications, most RV’s cannot store enough batteries to allow a large enough system for unregulated energy consumption. You need to learn to minimize use of high-power-consumption devices, supplement your existing RV systems with more efficient devices (such as using a catalytic heater instead of your RV furnace, which uses great amounts of 12-volt power), and monitor your energy use so you know when you are in trouble. Running out of power when you really need it is not fun. Killing your battery bank because you drew it down too far is even less fun – batteries are expensive.

You also need to examine your motivations for wanting solar. Solar use, and living "off-grid", is a lifestyle decision. Adding an effective solar system to an RV will rarely pay back the costs of installing it. Nor will you recoup your investment when selling the rig. The best (and really only) reason to add solar is so you have the option of boondocking for long periods of time without hookups. If you do not enjoy doing this, then you should reflect on why you want to install a solar system. One or two days of boondocking between sessions of hooking up to shore power does not require  solar, and its auxiliary systems. You can get by for a couple of days on a reasonable size battery bank. If you need 120-volt power, consider adding an inverter/charger. If you then find you need to recharge the batteries without shore power, you can consider adding a generator – either a small portable one, like a Honda 2000, or a genset that is permanently installed. If you have a motor home, you likely have a genset already and probably even an inverter. Notice, there is no solar system here. You really don’t need one if you are just overnighting occasionally.

Need to run your air conditioning? Well, a solar system is not going to help you here. It is not realistic to expect to run an air conditioner on a battery bank. You need a properly sized generator to run air conditioning “off-grid”. (Note: small window units and "mini-split" AC systems could be run for short periods of time off a large battery bank, but from a practical view, this is just not feasible for long periods. Large residential systems can have air conditioners run off them - but we are focusing on RV systems here.)


OK, so you like to boondock for long periods of time. You’ve decided that you can afford to invest $3000+ dollars  to make your life more pleasant when boondocking. How big of a system do you need? Only you can answer that. You need to examine your lifestyle while boondocking (or your anticipated lifestyle – you don’t actually have to boondock) and figure out how much power you use. Figuring out power usage while connected to shore power won’t give you your answer, because you are using lots of electric devices you won’t use when you boondock. For example: electric hot water heater, RV refrigerator on electric, battery chargers plugged in, converter on, lots of lights on, cooking turkeys in the microwave (just kidding).

A side note on system cost. Some would argue that $3K is way too high, and that you can implement a system for far less. While this is true if you implement a very small system, a complete system that will run most of the major items in your RV, and has the convenience of remote panels and a whole-house inverter/charger is going to cost in this ballpark and up.
 

So, how do you figure your power use? Think about what you have to use and add it all up. You can figure in watts, or in amphours. Watts is probably easier, but ultimately you will need to convert to amphours so I suggest you do your figuring in amps to start with. Look on the electric plate on the various devices and it will tell you what the device uses power-wise. Add them all up for the amount of time you run them. Don’t count any 120-volt lights, because you will only use 12-volt lighting while boondocking. Remember, you can figure watts by knowing the voltage and the amperage that the device is rated at – both are on the electrical plate (and if you are lucky, the wattage is there) watts=volts x amps. Sometimes electric plates on devices list ratings as xxVA (e.g. 40 VA) – this is watts (VA means Volts x Amps; actually there is a little more involved with VA because it accounts for power factor, but we will ignore all that for this discussion).

Here are the magic formulas that you learned in high school physics class and forgot.

watts=amps x volts
volts=watts/amps
amps=watts/volts

And for some shortcuts: if you know the AC amps just multiply by ten. Four amps AC is 40 amps DC.

When you work with solar it is best to figure everything in DC voltage, because your battery bank is DC – that usually means converting all your AC measurements to DC. In electrical stuff, watts is the universal measure. If you have a watt rating on a 12-volt appliance, it can be directly added to the watt rating of a 120-volt appliance to get the total watts consumed. Amperage ratings have to be converted, based on the voltage. Sounds complicated, but some simple math will allow you to get the total DC amps consumed from your battery.

Here are some 12 volt examples: 2 – 20 watt lights for 4 hrs= 40 x 4 = 160 watts, refrigerator 2 watts for 24 hrs = 48 watts. Now you have to figure your 120-volt loads: hairdryer 1500 watts for 12 minutes = 300 watts.  Microwave 1000 watts x 5 minutes = 83 watts. So all total we have (160+48+300+83) 591 watts in a 24 hr period. To convert to amps, divide by 12 or 120 – whichever voltage you are figuring for.  We did not count TV, satellite receiver, etc. You need to add up everything. Why did we count the refrigerator in our example when it is running on propane? Because, even when on propane, the refrigerator uses 12-volt power for its control circuits.

With an estimation of the number of watts you use on a daily basis you can calculate how many panels you need to supply that, and estimate how long you will have to run your generator to fill the “gap”, if generator use is part of your energy strategy. Don’t forget to add in “phantom” loads. For most smaller RVs, these average around 2-3 amps DC (per hour). (Note: larger motorhomes and large 5ers can have a phantom load of 12-18 amps DC per hour, depending on the RV.) These are loads that occur when it seems everything is “off”. They come from battery chargers, electronic boards in your propane appliances, propane and CO alarms, etc. You also need to factor in the inefficiencies of converting/using power. There is energy lost when inverting, and energy lost in wire runs. The rule of thumb is 30% lost when inverting, and 20% lost in direct 12-volt battery use. It generally will not be more than this – it may actually be less, depending on your system.

Don’t get obsessed with figuring exactly what you need. Just get close and then usage will allow you to adjust. As a rule of thumb, the average RVer uses between 75 and 125 amphours of DC per “cycle” (partial day and overnight). Remember, when you are using power during the day (while charging) your instrumentation is not giving you a true count because power is being supplied while you are using it. The nice thing about a properly designed solar system is that you can easily expand it by adding panels (as long as you buy a large enough solar controller initially, and wire everything for future expansion). For an excellent discussion of sizing your system take a look at Mac McClellan's website Electrical System Sizing. Throughout the discussion here I'll continually "harp" on building for future expansion. It costs little additional when you design/build the initial system, and is lots of additional expense later if you do not do it.

 

A Phased Approach

 
If you are not sure you will boondock a lot, or are overwhelmed by all that is required to implement a complete system for extended boondocking, consider using a phased approach. This will allow you to implement portions of the complete system, evaluate your use and needs, and then expand your system if you find it is beneficial to you. Here is my recommended approach: 
  1. Batteries. First I would augment my battery bank by upgrading to at least two 6-volt batteries. (I am assuming you have the typical RV with one 12-volt battery.) This should be able to be done to any RV without too much trouble. It will double the time you can boondock, and the 6-volt batteries will generally perform better than most 12-volt batteries. See the battery section for recommendations. Cost - $150+.
  2. Battery Monitor. Next, I would add a battery monitor - one with cumulative amp hours. This will tell you how much battery capacity is left, and will let you know when the bank is properly recharged. There is no other effective way to accomplish this that is convenient. Expect to pay around $160-$180 for a Trimetric RV2025 or RV 2030 with shunt.
  3. You will learn more about your use of power with the battery monitor than any other
    way. The single most important instrument in your RV is the battery monitor.
  4. Charging. You need a way to recharge your battery bank. It may be that you don't boondock long enough that you deplete the bank - but if you do you need a way to charge. Typically this is a generator of some sort. If you have a motorhome  you probably have one already. If not, look at the portable Honda's and Yamaha's in the 2000 watt range. They will not run an air conditioner, but they will very effectively recharge a battery bank and run a microwave. If you use your converter as the charging source, look into a charge wizard or upgraded charging capability for your converter. Most older converters (pre 2005) do not have an effective battery charger in them. Switching out converters is covered more at the end of the Inverter/Charger section. You will want a high output battery charger to take advantage of your generator. 
  5. Inverter. At this point you should have some experience boondocking and know what size inverter you need. Either you will need a large one to run the microwave, or you can get by with a smaller one that just runs your TV and other occasional small appliances. If you start with the small one and decide to add a larger one later you could use the small one for just your entertainment center, or you can sell it.  Most people who boondock for longer periods will want an inverter of some sort.
  6. Solar. If you boondock enough, and for long enough, you will eventually want to add solar to avoid running the generator. Solar is relatively expensive but has come down in price in recent years. Expect to pay about $1.00 to $1.20 per watt with shipping, although you can find panels in the sub- $1 range.

Back to Page Contents

Why Many Solar Systems Do Not Work Well

Many people complain that their systems do not provide them the time off-grid that they expected. I've been designing and installing systems since 2000, and I routinely hear these complaints. Almost always when you evaluate these systems it is an installation issue. Very few systems installed by RV manufacturers are done in an optimal fashion. Even dedicated "solar installers" often do not match components correctly or configure the system optimally. That is one reason I encourage people to implement their own systems, where they have the desire and the minimal necessary skills. Even if you do not do the installation yourself, designing the system will teach you enough to ensure a good installation by others.

The common problems/issues I encounter are:

  • The system is under-wired. The wire run from the solar panels to the controller, and then on to the battery bank, is sized too small. It should never be less than #6 cable, and I use #4 routinely on 12-volt nominal systems. Manufacturers commonly use #10. That is way too small for all but the smallest system. The only exceptions to this are with higher-voltage systems (more on that later). USE the wiring tables or online calculators to determine the correct size wire, and then go a little heavier. The wire size is not an "opinion" - it is simple physics. Use the calculators.
  • The solar panels are shaded at certain times of the day. Why an installer would place panels where they KNOW they will get shaded is a mystery. But it is not that uncommon. Even the shadow of the shaft of a TV antenna can kill the output of a panel. You want NO SHADOWS. More on this later....
  • The solar controller is too far from the battery bank. Put it as close as practical - but not in the same compartment. Do not use a controller that has an in-built display and place it in the RV so you can read it, instead use a controller with a remote display capability. Separately calculate the wire size needed from the controller at max output to the battery bank - this will likely be heavier than what is required from the panels to the controller.
  • The solar and charger settings are not optimal. On flooded cell batteries the absorption setpoint (the bulk charge rate) should be 14.8 volts UNLESS your battery manufacturer says otherwise. (Only pay attention to the battery manufacturer. Installers and even controller manufacturers will routinely provide you with bad information.) The default settings for wet-cell batteries in almost all controllers/chargers is 14.4-14.6 volts. That is not adequate to get a good charge on the bank. The other common issue is that the controller does not allow enough time during the absorption phase of the charge. Thus, the bank never approaches a "proper" charge.
  • Battery temperature sensors are not employed. To get a proper charge, both the inverter/charger and the solar controller should have a battery temperature sensor placed on the battery bank. The charge voltage varies depending on battery bank temperatures. It is difficult to get a good charge without the temperature sensors. If the inverter or solar controller offers a voltage sense line then that should be used as well.
  • Batteries are not checked and equalized when they should be. You need to check the battery bank water levels at least monthly until you learn your system. You need to check the batteries with a hydrometer at least two times a year and equalize if required.
  • Battery terminals are dirty and/or loose. You would not think this would be that common, but it is.
  • There is no instrumentation that records cumulative amphours drawn from the battery bank. Without this information it is difficult to evaluate the current battery condition. As a result, many battery banks are drawn down too far and their life is unnecessarily shortened.

The Golden Rules of RV Solar and Electric

This is a summary. Details are covered in the following sections. These are my opinions based on experience and education - you certainly do not have to follow these guidelines. But if you do, you will have a successful system if properly implemented.

Panels

  • Use high voltage (over 28 volts) on any but the smallest systems (small: under 400 watts)
  • Optimal input voltages for most MPPT controllers outputting to a 12-volt battery bank is in the 30-50 volt range.
  • Price panels on a per-watt basis. There is not much difference in panels unless you have special needs.
  • Use serial/parallel connection to get higher voltage, when required. Panels must be matched.

Solar Controller

  • Use an MPPT controller; high voltage; boost in the 10%+ range is realistic; price differential over PWM is not that great these days and for a larger system it allows many benefits ("larger system" = around 500-600+ watts)
  • Controller must allow adjustable voltage and charge times
  • Position close to the battery bank
  • Make SURE the wire size to the batteries is correct. It will be bigger than what comes from the roof in most cases.
  • Temperature compensation is NOT an option – use it. If a voltage sense line is available, use that too.
  • Fuses/breakers on input/output sides.

·    Batteries

  • Balance the system; have enough batteries for the amount of watts of panels you have (you can have more, but having less is wasteful)
  • Rule of thumb: 1 amp of storage for each watt of solar panel.
  • Flooded cell batteries charge at 14.8 volts NOT at 14.4/14.6 volts that you commonly see
  • Wire correctly: large enough wires, +/- connections on diagonal corners, equal length wire runs.
  • AGM batteries have advantages, but cost much more
  • Solar alone often will NOT bring a bank up to “full” state of charge because the system is continually in use. But if properly designed it can.
  • Use a battery monitor with a remote display (like a Trimetric, Link, or Magnum BMK)
  • With flooded cell batteries check specific gravity at least every 6 months. Equalize if required.
  • A desulfator “may” be helpful. Reports vary in RV use.

Inverter

  • Wiring is critical. Never less than 2/0 and usually 4/0. READ the book - there is no excuse to use a lighter wire than the manufacturer requires.
  • Short distance to the batteries. NEVER more than 10' max.
  • Catastrophe fuse
  • Remote display/control is important
  • Do not use too large an inverter for your needs. It is inefficient.
  • Charge section is critical if using AGM batteries. You want a LARGE charger with AGMs.
  • On flooded cells properly set the charge amperage…..C/20.
  • Wire through a subpanel. Wired in-line is OK for a 30-amp RV, but a subpanel is preferred. Do not wire 50-amp in-line unless the inverter has a 50-amp rated transfer switch (which is no longer available).
  • Temperature compensation is NOT an option – use it.
  • Build in provisions for removing inverter for service or upgrading your RV - AC wire length and junction box. If you have a converter leave it in place but disconnected from shore power. This can be used if the inverter/charger fails.

Wiring

  • Wire size is CRITICAL. It is the single-most common issue with installations. Use voltage/distance calculators. Then go heavier
  • Manufacturers almost never provide adequate wiring
  • Wire for 2% loss or less. I wire for 1% from the controller to the bank.
  • Use quality closed-end, coated lugs, and properly attach them; use dielectric grease and adhesive heat shrink
  • Fuse before/after controller; catastrophe fuse at battery bank
  • Use combiner on roof; I prefer a breaker box on larger systems. With high voltage systems the combiner can sometimes be in the main compartment and not on the roof, but calculate the loss on the #10 wires from the panels to see if this works.
  • Use distribution buss bar(s) near battery to tie loads together (if required)
  • Do not attach loads between shunt and battery.

Equipment Recommendations

I get asked often what I recommend, and that changes over time. The industry is constantly developing new products. What follows are my recommendations at the time I wrote this. Make sure you check these against your own needs, and against current technology. Although I try to keep this up to date, there is no guarantee. If you see something new that you think is better, feel free to write me about it, and why....

  • Magnum inverters. Also look at the BMK (battery monitor kit). Many people prefer the Trimetric - as do I.
  • Morningstar solar controllers. Personally, I like the MPPT 60 and its ability to directly network to your router. For larger installations, MidNite Solar has the Classic 150 which allows more panels to be used (otherwise you have to "stack" 60 amp controllers).
  • Solar panels:  Sun Electronics solar panels (lots of choice and reasonable prices, look at some of the blemmed products). AM Solar has a new 100 watt panel out - the GS100 (as of 4/14/2011). This is worth looking at. It has a high efficiency rating, and is narrow, so 4 fit across an RV roof, and it fits next to an airconditioner. But they are not cheap. Wholesalesolar.com has very good prices on a variety of panels. They "can" be cheaper than Sun, it just depends. Look at them both. I like the SolarWorld panels available at Wholesalesolar. USA made, excellent warranty, good efficiency and priced reasonably.
  • MidNite Solar breaker boxes, and combiner boxes. I like the ones with breakers in them, but there are other methods of protection that do not use breakers. AM Solar has a new combiner box that allows for larger wires.
  • Bogart Engineering Trimetric battery monitor RV2025 or RV 2030 is still my favorite. I had a Magnum BMK in my 2012 coach, and wished I had a Trimetric. My 2015 coach has a Trimetric TM-2030.
  • Look at the Magnum mini-panels (MPP) or the MidNite Solar E-Panel if you are doing a higher cost installation. They run about $600 but solve most of your wiring issues in one UL approved box. On a higher-end implementation you likely will be 75% of that with your own wiring. And there are extra advantages to these boxes. The MidNite E-Panel is probably best suited to most RV installations because of the dimensions (it mounts the inverter on the front of the panel), but in many cases neither of these will fit. This is for high-end systems only...otherwise the cost is not justified.

 

Residential Refrigerators

In the past few years I often get asked to design solar/electric systems for RV's with residential refrigerators. Since the late 2000's the energy efficiency of these refrigerators has improved enough that it is "possible" to both boondock and have your residential refrigerator. For avid boondockers having the electric refrigerator is likely too much of a compromise unless you have a very large solar/electrical system. But for people that do not boondock for months on end, it is now a viable alternative with a large solar system, or a combination of a medium system and an hour or so of generator time a day. As always, your usage habits and the compromises you are willing to make will factor into the decision to go with a residential refrigerator.

In general, these refrigerators add about 100 amp hours (DC) to your electrical burden (per 24 hrs). You need to replace both that, and whatever else you use for power. There are things you can do to minimize this usage some, but in general plan for 100 Ah.

I have a spreadsheet you can download with examples of generator runtime, various refrigerators, and some of the other planning factors involved with designing a system around a residential refrigerator. Take a look at it and see if this direction meets your needs. If you have suggestions or see errors in the spreadsheet let me know. Most of it has been validated with actual in-use systems.

 


 

Using a 30-Amphere Inverter in a 50-Amphere RV

Design Considerations for RV Genset and Inverter Installations 

 

Most modern, large 5'ers and motorhomes have 50 amp shore power (a 50 amp RV actually has 2 - 50 amp lines, each feeding one side of the loadcenter, for a total of 100 available amps). This section assumes the following issue, which is fairly common: If you have a 50 amp RV, how do you safely integrate an inverter, or inverter/charger that has an internal transfer switch rated at 30 amps? This design is specifically done to address the issue of an inverter/charger with a 30-amp transfer capability used in an RV with 50-amp service. The purpose of the design is to circumvent the limitations of the 30-amp transfer switch, and to avoid using a sub panel for the inverter-fed circuits. The best design is always one that isolates the inverter circuits to a sub panel, but that is not always practical in a retrofit implementation. Most people do not need to read this section.

 

Given a choice, I would always purchase an inverter/charger that has a 50 amp transfer switch. This would allow you to avoid the complexity of TS2 in this design and allow you to place the inverter directly in-line. Some manufacturers of high-powered inverter/chargers now offer a model with a 50 amp transfer switch. So if you are buying new, do yourself a favor and get one - it will simplify the installation.

 
Inverter with a Separate Battery Charger
 

Vehicle Electrical Center Sep charger.gif (11568 bytes)The simplest system is shown in the conceptual design drawing to the left. The major difference in this design is that you use an inverter, instead of an inverter/charger, and a separate battery charger.

 

The separate battery charger is required because you can't run 50 amps through the inverter pass thru relay - the original problem. This stops you from having  120 volt available to the battery charger, since the circuits inside the inverter for pass thru and battery charging both operate on the same 120-volt input.

 

 

 
Inverter/Charger with an External Transfer Switch
 

In the design below, we use an inverter/charger, but do not use the transfer function, protecting against over current.
 

Vehicle Electrical Center genset and inverter.gif (11887 bytes)This design utilizes the battery charger in an inverter/charger but does not use the power pass thru function. The input AC is fed directly from TS1, avoiding the RV loadcenter. This input AC to the inverter is ONLY used for battery charging, and is never passed on to the RV loadcenter. The reason the input is taken off of TS1 directly is to prevent a back feed situation from occurring if TS2 fails. (If power was obtained from the loadcenter and you were inverting then you would be in a circular input loop.)

 

In this scenario, the battery charger is supplying the battery bank, and power is passing through the pass thru relay, but it is "stopped" by the TS2 transfer relay, which is set to "prefer" the other input. This way no 50 amp load is ever placed on the 30 amp inverter transfer relay. Power only passes to the loadcenter from the inverter if there is NO power available from TS1 (no shore or genset). In that case, if the inverter is in invert mode, power will pass from the inverter to the RV loadcenter. 

 

 

The Preferred Design - All Charging Sources Integrated
 

 

Vehicle Electrical Center 1.gif (15683 bytes)This drawing provides an overview of the RV electrical system, and identifies major components used to support battery charging via: solar energy, the existing converter, and a new, high-powered battery charger contained in the inverter. It is a more detailed view of the design directly above.

 

Electrical input sources include a genset (either a portable, an RV mounted or a truck mounted), and shore power sources. Optionally, two main shore power sources are shown, controlled by a separate 50-amp transfer switch (TSO). These are intended to provide for a shore connection at the front of the 5er, and at the rear of the 5er. The existing converter is shown connected to an external power source (other than the RV) for optional use. This should never be plugged into the RV, but only to an external source via an extension cord.


Assumptions:

 

  1. The RV is wired for 50-amp shore power. This is actually 2-50 amp lines, for a total of 100 amps available at the loadcenter, on 2 legs. All shore power is assumed to be using 6ga wire, except where noted.
  2. All the transfer switches are 50 amps.
  3. The inverter is an inverter/charger with a high output battery charger that replaces the RV converter for normal use.  The inverter has a pass thru power capability controlled by a 30-amp transfer relay.
When inverting, the loadcenter is fully energized. It is up to the user to provide manual load management. In other words, don’t turn on the air conditioner, electric hot water heater, or other large loads. Turn the breakers off, if you are prone to forget.


A 400-amp catastrophe fuse is used to protect against an inverter short. It is placed either directly on the battery positive (if not placed in a fuse holder), or as close to the battery as possible, if a fuse holder is used. Use the size appropriate for your inverter. See the Truck Electrical Center page for additional details and sources for the fuse and other components.

 

The shunt is a 500-amp shunt. It must be placed “downstream” of all loads to get an accurate measure of amps/amp hours. Place it between the distribution hub and the battery negative.

 

Use appropriate size welding cable for the DC inverter runs. Consult the inverter installation instructions. Do not use less than 2/0. I prefer to use 4/0 in most situations if the inverter is 2000 watts or more. The inverter should not be more than 10 feet from the battery (cable run).


Note 1

 

Optionally, I show two main shore power cables. When using an external generator (either portable or truck mounted) it is often convenient to have a shore power cable at the front of the rig. You simply use another 50-amp transfer switch – that way you can’t have both “live” at once, or energize the other plug. This is obviously optional, but when wiring the transfer switches and deciding where to break into the main shore power cord you might consider leaving enough slack in the line to accommodate a future transfer switch if you decide not to do this right away.

 

Note 2

 

The line designated by Note 2 is the 120-volt AC input to the inverter. The inverter normally would pass this thru the transfer relay and on to the AC loadcenter. The issue is that the transfer switch is rated for 30-amps and the potential load on a single leg of the shore power line is 50 amps. The transfer switch built into the inverter can be overloaded. The purpose of TS1 is to circumvent this issue and still allow use of the high-powered battery charger in the inverter/charger. Thus, AC power needs to be supplied to the battery charger, but the power passing through the inverter must be stopped from reaching the loadcenter.  The inverter will pass power to TS2 when shore power is available, but since TS2 is already receiving shore power on the preferred input, the power from the inverter is blocked. Thus the relay in the inverter can never be overloaded, since no load is ever placed on it (when there is shore power available).  However, the battery charger is energized, and can charge the battery bank (assuming the inverter control is set to charge). Power is taken directly off the TS1 transfer switch output lugs. The line to the inverter from TS1 is a single 120-volt line, so only one of the hot terminals is tapped (along with ground and neutral). Since the only load on the AC lines into and out from the inverter are from the 1) battery charger and 2) the inverter, while inverting and passing power up to the loadcenter, these lines do not have to be sized the same as the main shore power lines. Depending on the size of the inverter, and the max "surge" of the inverter, you could use 12 ga. I recommend 10 ga., to cover any additional surge capacity various inverters might have. Each inverter will be different.

 

When wiring the input from the inverter to TS2 you need to jumper the hot lines. The inverter is only passing one hot line through, and you want to energize both of the lines going to the loadcenter. It is permissible to jumper between the two hot lines on  the input side of the TS2 inverter line to support this.

 

Note 3

 

Distribution hubs are used for DC power connections. The existing house DC wires that feed the DC loadcenter are not shown in the drawing, but they should be moved to the distribution hubs. Typically, a wire goes from the converter directly to the battery, and another from the converter to the DC loadcenter. If you are leaving the converter in place you can remove the converter-to-loadcenter wire, and splice a new wire into the line that goes from the battery charger output of the converter to the battery. (Your converter outputs may be different, but you get the idea...)
 
The solar input and conventional converter inputs attach directly to the distribution hubs. You should attach all DC power input/outputs here. Nothing should attach directly to the battery except some of the instrumentation and monitoring lines, and possibly the DC catastrophe fuse (if not in a holder). If you have additional DC loads you are adding, you may want to add a small DC fuse center, which would also attach to the distribution hubs. I usually add one to support fusing for the solar lines, and some of the instrumentation lines which otherwise require inline fusing (which is not as neat, and not centrally located).


Instrumentation

 

In the diagrams, the dotted lines denote instrumentation lines. These are not shown in detail – there are multiple connection points and lines for each instrument. Follow the instructions.

 

Sometimes the solar controller will have a remote display, and sometimes the entire controller will mount where the display can be seen – it depends on the controller you use. If you have a choice, acquire the remote monitor for the solar controller. It will make the wire run for the solar line shorter. The solar line should be as short as possible to minimize voltage drop. I prefer to use 6 ga for the drop from the roof to the battery bank. Sometimes that means you have to trim the wire where it goes into the terminals on the solar controller in order to make it fit. That is OK. On the roof, I interconnect the solar panels with a minimum of 10 ga.

 

If the inverter monitor panel has a running amp hour capability (also called cumulative amp hour) then you can eliminate the Trimetric amp hour meter, since it would be redundant. If not, you really need to know your accumulated amp hours (either positive or negative), since that is the best measure of the state-of-charge of your battery bank. You can buy a Trimetric meter, with shunt, for under $175 at www.solarseller.com. If you are using a Heart inverter, the Link 1000 or Link 2000 monitors contain an amp hour meter.

 

Again, most people do not need to be concerned with this section and it's complexities. This is NOT a preferred design!

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AC Circuit Protection

When revising your electrical system you should consider the addition of an AC power management system. These provide protection from miswired pedestals, high and low voltage conditions and surge suppression. They have a remote display that shows you line loading (so you can figure out exactly how much AC you are drawing on each leg of your box). It is best to use models that are hardwired, instead of external surge guards. Hardwired models are theft proof, and you won't forget to put them out. The time you forget to plug it in will be the time you really need it. They are available in 30-amp and 50-amp versions.

 

The Progressive Industries model 40240 (50-amp model, $494) is available at Camping World and other outlets. I highly recommend this capability – not only do you know what is going on with your AC loads, but you are protecting your coach AC system. From a design perspective, I prefer placing the device directly “next to” the loadcenter if you are using a sub panel. If wiring the inverter in-line then place the management system before the inverter. This will offer protection to the inverter from surges and spikes.

 

In my opinion, EVERY RV should have an electrical management system like the Progressive Industries version with the remote panel.

 

 

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Sample Systems

 

The sample systems I've configured here are just that - samples. You may not agree that they are the best combination of components for your particular situation. Everything is a tradeoff when it comes to RV's and this area is no different. However, these should give you a good place to start when you configure your own system. There are also some detailed sample systems (with pricing as of 5/2007) that are a little different in the downloadable Excel file Solar Bill of Materials.    (the formatting is messed up here - I'm getting to it.)


Refrigerator ONLY

 

This package supports a residential refrigerator, but does not supply other house circuits. It is intended to be paired with a residential refrigerator to support daily travel and a single night without shore power hookups or the requirement to run a genset. There is NO SOLAR in this package - thus, unless you choose to add a genset there is no ability to recharge the battery bank other than shore power. It must be stressed that this option ONLY supports the refrigerator - no other power outlets are on the inverter. There is no subpanel so house outlets cannot be easily added later. The pure sine wave inverter does have an automatic transfer switch to move from shore to battery power.


This configuration is intended for the customer that never boondocks but wants to ensure that a long travel day,  travel in hot weather, or a Park power outage does not affect the performance of the residential refrigerator.


While there are some slightly cheaper inverters than the Magnum specified, the advantage of the Magnum is that the same user interface for configuration is used for all the packages installed by production. Thus no additional training on various remote panels and inverters is required, and there is less chance of things “going wrong”. Plus customer training is the same as the “Medium” package.


This package minimizes the costs associated with supporting a residential refrigerator. While some additional savings could be achieved, this package cuts the costs pretty well.

 

Parts

  • Magnum MMS-1012 inverter with inbuilt transfer switch. Wholesale Solar $960.  Manual. Note: cheaper sine wave inverters are available - they are just that - CHEAP.  

  • ME-RC50 remote panel for the inverter. Wholesalesolar $150

  • Trimetric 2030RV battery monitor. 500 amp shunt. Solar Sellers 2030RV $142, shunt $26.  Manual.

  • Battery bank: 400 amphours of battery is the typical configuration. It can be any battery bank: Trojan wet cell T105 x 4 (450 AH); Lifeline AGM GPL-4CT 6 volt x 4 (440 AH); Lifeline AGM GPL-L16T  x 2 (400 AH); Fullriver AGM L16 x 2 (400 AH). I recommend that the standard package for this configuration be AGM. The typical target customer for this configuration is a “set it and forget it” type of person - having a no maintenance battery bank is beneficial for this customer category. While 200Ah of battery (half the sizes specified above) could be used and support the refrigerator during a travel day, this has the potential to stress the battery bank significantly if an overnight stop is included. The larger 400 Ah bank should be used - it will maximize battery bank life.


 

High-end System

 

This system is designed for the high energy consumer that boondocks in a variety of conditions, and wishes to ensure they always have the best power choices possible. It maximizes battery storage, charging sources and solar gain. It can easily support a residential refrigerator and minimal compromises on energy usage. The configuration will support 1200 watts of solar panels.

 

Load Sharing

 

This package provides for load sharing when hooked up to lower amperage shore power. Load sharing provides the ability to supplement shore power with battery power to ensure more coach electronics are usable on a 30 amp or smaller shorepower connection. This is handled by the inverter - power from the incoming shore source is synchronized and supplemented with inverter power from the battery bank. This is done automatically as loads demand power - the user only has to enable the feature.

 

Converter Supplement


This package also provides the ability to run off the inverter while simultaneously charging the battery bank on a low-powered shore circuit. This is typically used with a 15-20 amp circuit in a friends driveway, with a small portable generator charge source (like a Honda 1000), or a low power/bad power Rally hookup.

 

The typical inverter/charger is a singular function device - it is either charging the battery bank, or inverting power from the bank, but not both at the same time. In this package a 60 amp converter is added to the coach so that an independent charge source can be used to charge the battery bank WHILE the inverter is independently supplying coach power. This works in conjunction with solar to provide power to the coach battery bank while the coach’s house systems also consume power. The net result is the ability to support coach loads off the battery for longer periods of time - indefinitely if used judiciously.

 

The converter is sized such that a 15 amp circuit or Honda 1000 can drive it. This small, light, quiet portable generator is ideal for supplemental battery charging. Use of a converter also allows power that is low voltage to be used for battery charging - most converters accept power down into the 90 volt range and still perform to specifications. You would not be able to run coach systems directly off of 90 volt power.


Parts

  • Magnum MSH3012M pure sine wave hybrid inverter with 125 amp DC charge section. WholesaleSolar.  Note: does not show on their website but they have them.

  • ME-ARC  remote panel for the inverter. Wholesalesolar $240

  • Trimetric 2030RV battery monitor. 500 amp shunt. Solar Sellers 2030RV $142, shunt $26.  Manual.

  • Solar controller: MidNite Solar Classic 150. Wholesale Solar.  $618. Dummy display panel MNGP Dummy. The dummy panel is used when the display is removed from the Classic and remotely located. Alternatively, you can put in a second panel in the remote location. Panel.

  • Converter - standard 60 amp with with 3-stage charging. Wire into battery bank but do not plug into power outlet. Used for “driveway boondocking” or low shore power situations (described above). Coach is run off of inverter and converter charges bank independently.

  • Solar Panels:  5 x 275 watt SolarWorld panels. Total wattage is 1375. Array size is maxed out with the specified controller

  • Battery bank:  Lifeline AGM GPL-L16T  x 6 (1200 AH); Fullriver AGM L16 x 6 (1200 AH). Alternatively, 8 batteries of the same type would give you 1600 Ah.

 

Medium System

 

This system consists of solar panels,  a  medium size MPPT solar controller, and a pure sine wave 2000 or 2800 watt inverter with subpanel. It will run most house loads and the solar is adequate to keep the batteries charged under moderate load scenarios. The controller is maxed out with the three panels that are specified, so there is no room for expansion.

 

This configuration is intended to support moderate boondocking power requirements. Living offgrid for a week or more using moderate power should be easily achievable. It should be pointed out to all customers that offgrid living - unless one is an avid boondocker - requires support of a generator of some sort. Either a portable generator like a Honda 2000 used just for battery charging purposes, or an in built genset.

 

While this system is sized to support boondocking, it is not sized to support a residential refrigerator AND long term boondocking. With good solar conditions and/or running a generator some on a daily basis a residential refrigerator could easily be used. But it will require some compromise on energy usage.


Parts

  • Magnum MS2812 pure sinewave inverter with 125 amp DC charge section. Wholesale Solar. WholesaleSolar  $1985
    To slightly reduce costs the 2000 watt Magnum could be used. Wiring issues and remote panels are the same.

  • ME-ARC  remote panel for the inverter. Wholesalesolar $240

  • Trimetric 2030RV battery monitor. 500 amp shunt. Solar Sellers 2030RV $142, shunt $26.  Manual.

  • Solar controller: Morningstar Tristar MPPT60. Wholesalesolar. $505.  

  • Tristar Remote Meter 2. For solar controller. Wholesalesolar. $112

  • Battery bank:  Trojan wet cell T105 x 6 (675 AH); Lifeline AGM GPL-4CT 6 volt x 6 (660 AH); Lifeline AGM GPL-L16T  x 4 (800 AH); Fullriver AGM L16 x 4 (800 AH).

  • Solar: 3 x 275 watt SolarWorld panels. Total wattage is 825. Array size is maxed out with the specified controller.

 

Economy System

 

For those who want good performance, but price is the major consideration. The system is expandable, but uses lower-cost components.

 

  • Heart (Xantrex) 458 Modified Sine Wave Inverter 2000 watt/30 amp pass thru.

  • Trace C40 charge controller. PWM controller, not an MPPT. Can handle 24-volt input.

  • Trimetric TM-2030 battery  monitor. Has cumulative amp hours.

  • 3 - Grape 160-watt  Solar Panels (Home Depot). You can add two more panels with the C40 controller.

  • 4 – Sam’s Club 6 volt Golf Cart batteries (410 Ah rating). Expand to 6 if you need more reserve, but you will probably want to go with an extra solar panel if you have 6 batteries.

 

 

Our Systems (since 2005)

 

On Our 2010 New Horizons

  • Xantrex RS 3000 pure sine wave inverter/charger. 50-amp pass thru; wired to a subpanel. 150-amp charge section.

  • Xantrex XW 60-amp MPPT charge controller.

  • SCP networked to both the inverter and charge controller. This provides complete control and monitoring of both devices.

  • Trimetric 2025RV battery monitor.

  • 4 - Sun Electronics Sun SV-T-205 HV panels. Wired as a parallel array. These are the same as Evergreen Panels. They are not UL listed, which gives a far cheaper price. Imp=7.36 A at Vmp=27.90V. MC-4 connectors. Not presently on the rig but everything is set up for them.

  • AM Solar Large combiner box.

  • Midnite Solar "Baby Box" enclosure with 2 breakers to isolate the solar controller input/outputs.

  • 6 – Trojan T-105 6 volt batteries (675 Ah rating). In retrospect going with 4 - L16RE batteries would have given me 650 Ah and it is likely a better battery. But the deal on the T105s was too good to pass up. I'll likely replace with the L16s.

  • 5500 watt LP genset.

On Our 2012 New Horizons

  • Magnum MS2812  pure sine wave inverter charger. 2800 watts with a 125 ADC charge section. ME-RC remote display.

  • Magnum BMK battery monitor uses the same display as the inverter.

  • Morningstar Tristar MPPT 60 solar charge controller with remote panel.

  • 4 - Sun Electronics Sun SV-T-205 HV panels. Wired as a parallel array. These are the same as Evergreen Panels. They are not UL listed, which gives a far cheaper price. Imp=7.36 A at Vmp=27.90V. MC-4 connectors. Installed by New Horizons.

  • AM Solar Large combiner box.

  • Midnite Solar "Baby Box" enclosure with 2 breakers to isolate the solar controller input/outputs.

  • Four 8D Lifeline AGM batteries for 1020 Amphours of stored power. Half is usable.

  • 5500 watt LP genset.

The system I had in the Royals International is similar to the economy system, with a Trace C60 PWM charge controller and four KC-120 panels feeding 4 Sam's Club golf cart batteries.