
	Last updated: 12/24/2016

Inverters and Chargers

The Inverter/Charger

Checklist For Selection

What About My Converter?

Really Basic Stuff

Inverters and converters can be confusing to people not "steeped" in electronics. But they are pretty simple in concept. An inverter takes DC battery power (12, 24, or 48 volts) and "inverts" it to AC power. Typically 125 volt AC power, although you can also produce 240 volt power with the right setup. It really is as simple as that.

Inverters can be modified sine wave or pure sine wave. For casual use on non-sensitive electronics the modified sine wave inverter may be sufficient. But for any sensitive electronics you will want a sine wave inverter. A sine wave inverter produces a waveform that is as good or better than grid power. Use of a modified sine wave inverter on appliances that need a pure sine wave can result in overheating or damage to components. Residential refrigerators and any electronic appliance that has a transformer "brick" can be damaged from modified sine wave inverters.

Sine wave Modified sinewave

In RVs, inverters are typically used to power only part of the RV. Most RVs do not have enough battery capacity to allow powering of high current components like air conditioning units, or appliances that use resistive elements like spaceheaters, or electric hot water heaters. In RVs, propane is typically used for heating and hot water heaters when off the grid. The highest power item in an RV typically powered by the inverter is a microwave oven. All other inverter powered items usually have less power draw. With use of residential refrigerators becoming common in RVs they now use more total power than most other items in the RV. But they use this over a longer period of time, and do not have a large "peak" power draw.

To keep the inverter from being used to power items that are not suitable for inverter power, the inverter circuits are usually separated from the non-inverter circuits and placed on a separate electrical subpanel. If retrofitting an inverter into an RV this subpanel is required to be added, and can often represent the hardest part of the installation.

Most larger inverters used in RVs are not "just" inverters. They actually have three functions: inverter, charger, and transfer switch. The charge section of the inverter takes the place of the typical battery charger (converter) in the RV. It's function is to charge the battery bank when on shore power; these chargers typically have better components in them than the converter, and a more sophisticated charge algorithm. The transfer switch handles the automatic transition from shore power to inverted battery power. So, for example, if the inverter is in standby and shore power drops, the transfer switch will automatically transfer the power "inverted" from the battery bank to the RV. It does this fast enough that the inverter functions as a UPS, and almost all appliances and electronic components will not even know that shore power was dropped.

A "converter" is really just a battery charger. It takes 125 volt AC power and converts it to 12 volt DC. This is used to charge your battery, and in some cases to directly power your RV 12-volt load center. Basic converters are pretty dumb - they simply produce a single voltage and have no logic in them to account for the battery state of charge. More advanced converters have three stage battery chargers in them. These more advanced converters are what you want in your RV. The basic converters can overcharge your batteries.

I will assume that the inverters that you are interested in are all hardwire inverter/chargers capable of powering most of the appliances in your RV. I don’t recommend a separate battery charger and inverter. The combination inverter/chargers are easier to install, provide better battery charging, and result in much simpler control circuitry. (For advanced solar systems some might argue with my statements above. There are always exceptions to every generalization - but in RV use it is generally best to stick to an inverter/charger, in my opinion.)

This puts your choices in the category of higher-cost inverter/chargers. Typically these range in power from 1800 watts to 3000 watts. The “typical” RV is well served with a 2000 - 2800 watt sine wave inverter/charger, which usually has a 100-125 amp battery charger included with it. This will run almost all microwave ovens, which is the heaviest load most inverters in an RV see. If you have special needs that require more power, then inverters up to 3000+ watts are readily available. Expect to pay between $900-$2500 for a quality inverter/charger, depending on wattage and waveform. Pure sine wave inverters are more costly, and often not required. With inverter/chargers you usually get what you pay for – so beware the inexpensive high wattage inverters.

Microwaves are usually the highest load device you will run on the inverter. Microwaves are sensitive to peak voltage. The higher the peak voltage, the better they run. Both modified sine wave and pure sine wave inverters are dependent on battery voltage levels and load levels for peak power. Thus output voltage will drop a little if the battery is not at peak voltage, or if the load is heavy. That is why most microwaves do not cook as well on inverters as on shore/generator power. Some microwaves will not run on lower-cost modified sine wave inverters, but this is very rare. Unfortunately, there is no way for me to tell you if your microwave will perform acceptably on modified sine wave. The best I can do is to tell you that in dozens of cases I have personally been involved in I have only seen one microwave not perform well with modified sine wave - and that microwave was mid-90's vintage.

A standard strategy with microwave cooking on inverters is to increase the cooking time. Because of the high draw, microwaves are typically used only for reheating when running on inverter power. We have found it best to run microwaves only on high power when running on the inverter.

Some computer monitors show slight waves in them when on MSW inverter power. The modified sine wave inverter that we had in our Kountry Star and also our Royals International ran a Dell LCD monitor and a Viewsonic LCD monitor with no problems.

Most clocks will not run properly on modified sine wave – this is because the inverter output waveform will vary some, based on load. Use battery-powered clocks if you need to keep accurate time.

Battery chargers for small devices may work properly on MSW, or may fail. Check the charger for overheating. If the charger is excessively hot, do not use it on the inverter.

Lower Cost Inverters

There are a number of lower cost inverters commonly seen on the Internet or at the buyers club stores like Sam's Club or Costco. In general, with inverters you do get what you pay for, and I do not generally recommend these inverters. However, there are some lower cost pure sine wave inverters on the market that seem to be "OK". AM Solar and others have had very good luck with the KISAE Abso 2000 watt PSW inverter. This is much lower cost than a Magnuum or Xantrex PSW inverter and seems to be holding up well in use. I'd not hesitate to use it in an HDT conversion (truck conversion) or for other light use locations. I'd prefer to stick to the name brands for more demanding installations - but that is just my personal preference. The KISAE 2000has an internal transfer switch and a 55 amp charger; it costs under $650. It does have a hardwire capability, and the ability to remove and remotely mount the integrated display. Only you can decide if something like this meets your needs.

Load Sharing

A number of higher-end inverter models (Magnum, Victron, Xantrex) a have a feature that I'll call "load sharing". These are sometimes called "hybrid" inverters. They have the ability to supplement shore power with battery power if you are on a lower amperage shore power circuit and have a demand for excess power. Typically, these would come into play when a 50 amp coach is using 30 amp shore power and you want to run a (lets say) microwave while already close to the 30 amps available from the shore power circuit. The inverter will detect the extra power demand and automatically supply power from the battery bank to make up the deficit. It synchronizes power with the incoming shore power - it is all transparent to the end user. Of course, it can only supply this "extra" power on the circuits that the inverter can handle, e.g. the subpanel circuits. Nevertheless, this is a useful feature for supplementing shore power, or supplementing a smaller generator hooked to your shore power line.

The Victron inverters have had this feature for some time. The Magnum 3012 and the Xantrex Freedom SW inverters also have this feature. Xantrex calls it "generator support mode", and Magnum calls it "Load Support". Victron, who has very sophisticated components, calls this feature PowerAssist. Victron offers high end electrical equipment to the yachting industry and is typically not widely seen in the mobile RV environment. Some of the high end bus conversions use Victron, and it is fairly popular among the "bus nut" crowd that converts busses for RV use. For higher end systems Victron is worth a look, but most people will choose Magnum. Anyone that wants to discuss Victron instead of Magnum for a high end installation can feel free to discuss it with me after researching them. Victron has a lot going for them, but they are not cheap. I particularly like the Victron Battery Monitor. It has a great display, and with the addition of the Bluetooth module you can view results on your network. It is competitively priced with the Magnum BMK and the Trimetric - definately worth considering.

Charge Limiting

Most of the high end inverters can also dynamically manage the charger power being sent to the battery bank. Basically, when the charger is active they monitor the line and reduce the current going to the charger if a house load demands more power. You can also set maximum limits that the charger will not exceed (all within the proper charging algorithm of course). When load sharing is present they will shut the charger down automatically and start the load share process if required.

Feature Checklist

There are many inverters on the market that would work well in your RV. To some extent it is a personal choice. My personal preference is in the Equipment Recommendations section - but I greatly prefer the Magnum products for a whole-house inverter. Note, if you choose a Magnum inverter you might consider pairing it with a Magnum solar charge controller (the PT-100). They work together to manage your battery charging needs.

The sections that follow will help you narrow your inverter selection. I also include my opinion on a variety of inverters in the other sections. Here is my checklist for inverter selection:

Sine wave or modified sine wave? Some people feel they have to have pure sine wave. If you have special needs that you know can’t be handled by a modified sine wave inverter, then go ahead and pay the extra for the pure sine wave. Usually, this is not necessary. Oxygen generators, CPAP machines, residential refrigerators and laser printers often require pure sine wave. Almost all other devices do not. However, with the price of pure sine wave inverters much less than they were in past years it is probably best if you seriously consider them first. At this point in time I would not put a MSW inverter in my personal RV - but you may be able to use one.

You have to figure the size, in watts. Don’t plan on using everything in the RV at once like you do on shore power. Based on that, you should be able to figure your max draw. Often, 2000 watts is sufficient. Don’t worry about battery charging capability; all the inverter/chargers have sufficient charger output.

What is the transfer switch rating? Also, how are you going to interface to your load center (split box, sub panel, wired inline)? This will narrow your selection further. While there used to be inverters with 50 amp rated transfer switches that could handle two power legs, these are no longer available. So you are really in the situation of requiring a subpanel if you have a 50-amp RV.

What monitoring system is designed to interface to the inverter? Does it have a cumulative ampere-hour capability, or do you have to use a different meter for that? You have to balance monitor system costs – it may be cheaper to buy a monitor that is not part of the manufacturer’s package and use it in conjunction with a cheaper remote control offered by the manufacturer. Does the inverter have the features you need/want? Does the monitor package have the features you need or want (like generator management, if you need it).

Does the instrumentation for the inverter allow you to control all functions of the inverter individually? I like the battery charger to be separately controlled. I choose to use solar for charging almost all the time, even when on shore power. I only use the battery charger if we have many rainy days. Some inverters automatically charge the batteries if shore power is present; this function cannot be disabled.
Does the inverter have an equalization mode? You will want to equalize your batteries from time-to-time. Either the inverter needs this function, or your solar controller needs to have it. It is a little easier if the inverter has it, but either will work fine.
Does the inverter have battery temperature sensing? You definitely want this for most efficient battery charging. Most of the inverters in the price range you will look at have this as either a standard feature, or an option. If optional be sure to get it.
Can you change the charger voltage "set points"? This is useful for getting the batteries fully charged. In many cased flooded cell charging algorithms in the chargers do not bring the bulk-charge voltage high enough. Being able to tailor this allows you to adjust the bulk voltage so your batteries get fully charged. In particular, MANY inverters have the bulk charge set point at 14.4 volts (or around there). For most flooded cells you want a set point of 14.8 volts.

What About My Converter?

The problem with older converters is that they do not have a very good battery charger section, and some of them do not even put out regulated (clean) 12-volt power for the DC house systems. If you put in a full solar inverter/charger system then you can potentially eliminate the charge and supply functions of the converter and use it strictly as a "standby" power source. This is discussed below.

The key to acceptable performance from any converter is that it has a three-stage charging cycle. Without that, you run into all kinds of issues with battery charging. The major converter manufacturers now all make products that have three stage charging capability. Take a look at converters from Iota, WFCO, Progressive Dynamics, and Parallax. Just make sure that anything you buy has a three-stage charging capability.

If you are taking a phased approach to upgrading your RV electrical components and do not want to buy a large hardwired inverter with a superior battery charging capability, then you may want to upgrade your converter section. First you have to determine if you have the older style converter. A very popular converter, used in many RV's, is the Magnetek 63xx series of converters. They were inexpensive and many manufacturers installed them. Unfortunately, you get what you pay for - they have very low power output, unfiltered power, and single charging set points. They are basically incapable of recharging a battery fully without overheating it. If you have one of these, this is why you have to add water to your batteries often, and why your batteries do not last as long as they should.

If you decide not to upgrade to an inverter/charger, then you might consider replacing the older Magnetek with a modern Intellipower 91xx series with a Charge Wizard. The Charge Wizard converts the 9100 series from a 2-stage to a 3-stage charger. It only costs about $25, and is the best money you will ever spend. It will enable your batteries to fully charge when hooked to shore power, without overheating and boiling off excessive amounts of water. The 9100 series comes in various sizes from 30 amps to 80 amps. Choose the one that meets your needs, but I would not go lower than 60 amps. The advantage of using the 9100 series is that the charger section can use all of the rated power, minus what the RV DC systems are currently using. This is unlike the 6300 series that had a fixed charger section of around 5 (effective) amps. Thus, the 9100 series is effective when used with a generator to recharge your batteries.

If you have an older converter integrated with the 12-volt loadcenter, trying to replace it with upgraded electronics can be difficult. You can always add a newer separate converter and just disable the old converter. Usually, all that is required is pulling a fuse/flipping a breaker and re-routing the DC wires.

Some very good replacement articles have been written that will step you through replacing your converter. I'm not going to try to re-do them here. Do a search on the web and you will find a lot of info. Or look at Converter Upgrades for a good collection of articles. BestConverter also has a good selection of products for upgrading your converter.

Bottom line: replacing an older converter is an upgrade you should consider if you are not going to put in a large inverter/charger. You need an effective battery charger to use with a generator if you intend to boondock for any length of time, and this is the most cost effective way to do it, plus it benefits you when you are on shore power as well. However, if you intend to go to an inverter/charger you might consider skipping to that step now, and investing the $300 from the new converter into the inverter/charger.

When adding a high-powered battery charger many people throw the old converter out. Let me suggest that you keep it, and wire it into the system by connecting its output to the distribution hubs you have added. However, you will leave it unplugged. If the converter was previously hardwired, install a pigtail on it so you can plug it into a standard outlet.

The purpose of doing this is twofold. First, if you have an inverter failure of some sort, you can fall back on the converter while the inverter is being repaired. Secondly, and most important, if you are in a situation where the shore power is of low quality, or of low amperage (say a 15 amp outlet at a friends house, or a rally), then you can not plug into the main shore power to supply your coach - it is simply not enough power to be convenient. Instead, run your coach on the inverter. Then, you can plug in the converter to the 15 amp external circuit and simultaneously charge your battery bank. (Remember, you can’t use the inverter function and the battery charge function of your inverter/charger at the same time). This allows you to have a clean source of power, and recharge the bank at a reasonable rate.

You can’t plug the converter in anywhere except to an external source of power if running on the inverter (as described above). If you plugged it into your RV outlets then when you inverted power you would set up a feedback loop and drain your battery bank, and potentially damage equipment.

Note: The above applies to a separate converter that plugs into a receptacle - which is fairly typical in larger rigs. If you have an integrated converter/charger/12-volt loadcenter then you will have to figure out the wiring on it to accomplish the above. They are all a little different. If you choose not to modify this type of converter, you can just turn off the breaker that feeds power to it. Everything should then work as if it was never there.

Xantrex Inverters

Note (9/3/2014): Some of this inverter info is dated. I'm in the process of rewriting this section.....

The purpose of this section is not to push Xantrex products - although they make some decent stuff. It is to help you differentiate their many models of inverters. There are many other brands of inverters available that are as good, or better, than the Xantrex inverters. Take a look at the Magnum and Outback inverters - both of which have an excellent reputation.

Xantrex sells Trace, Heart, and Statpower inverters and associated components - as well as their own lines. They bought all these companies years ago. It can be very confusing trying to figure out the differences in the Xantrex inverters. There are so many that initially it can be overwhelming.

Many of the Xantrex products do not feature monitors with cumulative amp hours, which I (and most experts) consider a requirement. You will have to augment the instrumentation for this function if you use one of these Xantrex inverter lines. All of the inverters discussed here have equalization. Here is my opinion on their various products.

The Prosine 2.0 Inverter/charger is pure sine wave, has separate battery charger controls, has equalization, battery temperature sensing, and comes with a remote control panel. The transfer switch is 30 amp only, so it will require a sub panel if installed in a 50 amp RV. They retail for $2000, but are easy to find cheaper. I would combine it with a Trimetric 2020 meter. If I was considering this inverter, I would look carefully at the RS series as a better alternative.

The RV series (RV2012) is a modified sine wave inverter with a split-phase 50-amp transfer switch. You can use it with a 50 amp RV. It does have equalization and a temperature compensation capability. However, it does not have the ability to turn the battery charger off. As long as AC power is available the charger is in operation. Personally, I don’t like this “feature”; I prefer to have control over charging. Use it with the RC6 remote, which provides basic monitoring and “On/Off” control. Add a Trimetric for advanced monitoring. Retail is $1700.

The DR series of inverters are modified sine wave with a 30-amp transfer switch. The 2412 has a 2400-watt inverter with a 120 amp charger. Like the RV series, the battery charger is always “On”. Use it with the basic RC8 remote, and augment with a Trimetric. Retail runs around $1100. If you are considering this inverter, look at the Freedom 458 2.0 as a better alternative (cheaper, and with a Link 1000 monitor does not require the Trimetric).

The SW series is 24-volt and 48-volt only. Not suitable for most RV applications.

The Freedom 458 series (Heart) is a modified sine wave inverter with a 30-amp transfer switch. It has temperature compensation, equalization and a battery charger that is controllable (on/off). Use it with the Link 1000 monitor (or the newer LinkLITE or LinkPRO) for full system control and monitoring, including cumulative amp hours. This is a nice combination if it’s specifications work for you. Retail is $1225, but they are commonly available for under $900; the Link 1000 runs around $250. This combination is the best value of all the Xantrex inverters in this size range, and works well. I've used it in two of my personal RV's and installed it in others. If you want pure sine wave this won't work for you, however.

The RS series is a pure sine wave inverter available with a 30-amp transfer switch (RS2000) or a split-phase 50 amp transfer switch (RS3000). It has selectable charger control, equalization, temperature compensation and uses the SCP monitor (System Control Panel). The SCP allows control of multiple Xantrex devices from a single control panel. The most likely device you would add would be a generator remote start, or the XW MPPT solar controller. These can all co-exist on a single control network, and be monitored/controlled with a single SCP. Personally, I like this series the most. Although it does not have cumulative amp hours (you still have to add the Trimetric) it has great features, and is moderately priced for what you get. If retrofitting a 50-amp RV I would use the RS3000 since it can handle two legs of 50-amp, thus avoiding adding a sub-panel if you choose.. The RS2000 list price is $1600; the RS3000 is $2000, but you can find the RS2000 for $1125 and the RS3000 for $1395 if you look hard. The SCP sells for around $205. Note: as of 2010 the RS Series is no longer available.