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Jack & Danielle Mayer
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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.

 

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 watt modified sine wave inverter/charger, which usually has a 100 amp battery charger included with it. This will run almost all microwave ovens, which is the heaviest load most inverters see. If you have special needs that require more power, then inverters up to 3000 watts are readily available.  Expect to pay between $900-$2400 for a quality inverter/charger, depending on wattage and waveform. Pure sine wave inverters are more costly, and usually not required. With inverter/chargers you usually get what you pay for – so beware the inexpensive high wattage inverter.

 

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 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 inverter power. Our modified sine wave inverter runs a Dell LCD monitor and a Viewsonic LCD monitor with no problems.

 

Most clocks will also not run properly – 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, or may fail. Check the charger for overheating. If the charger is excessively hot, do not use it on the inverter.

 

There are many inverters on the market that would work well in your RV.  To some extent it is a personal choice. 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:

 

  1. 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 and laser printers often require pure sine wave. Almost all other devices do not.
  2. 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. Usually, 2000 watts is sufficient. Don’t worry about battery charging capability – all the inverter/chargers have plenty of charger output.
  3. 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. If you have a 50 amp RV you need to choose an inverter that has a 50 amp transfer switch unless you are using a sub panel. If you plan to remove the inverter when you sell the RV you might want to choose a 50 amp inverter now, even if your current RV is only 30 amps.
  4. 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).
  5. Does the instrumentation and 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 can not be disabled.
  6. 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 regulator needs to have it. It is a little easier if the inverter has it, but either will work fine.
  7. Does the inverter have battery temperature sensing? You definately 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.

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 elsewhere in these sections.
 
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 setpoints. 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.
 
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 http://home.comcast.net/~rabarber/rv.htm for a good collection of articles.
 
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.