Practical Motor Home Inverter Applications

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Two weeks ago week we looked at the type of inverters commonly used in motor homes.  This week we will touch on applications of inverters in our home on wheels.   We will deal with integrated types only, generally these are 2,000 watt output and larger.  We will also focus only at the inverter operation, not the charger function. 

 

The inverter basically takes 12 volt direct current from the batteries and inverts it to 120 volts alternating current, similar to that in your house. 

 

 In doing this, it produces either a M.S.W. (Modified Sine Wave) or a T.S.W. (True Sine Wave) depending on the make and model.  Modified types are the cheaper of the two to produce, and are the ones found currently on the majority of motor homes today.  True sine types are becoming far more popular recently.  This is due to lower prices recently and more sine wave affected electronics that are being introduced into today’s modern coaches.

 

The inverter in a standard configured propane equipped motor home is generally wired to power the following.

• TV’s, receivers and entertainment centers
• Most duplex 120 outlets
• Microwave
• Awnings, if 120 VAC (Such as Gerard)
• Refrigerator (If 120 volt AC)
• Ice maker (If 120 volt AC)

The balance of AC powered loads such as air conditioners, hot water tank, electric stoves and of course, battery chargers only operate on shore power. 

Some microwave models can be damaged if used to cook using a modified wave inverter.  This damage can result in causing the efficiency to drop substantially after continued use.  While wiring the inverter to the microwave outlet is normal, which at least keeps the clock on time, it may be wise to run the generator for any microwave cooking while boondocking.  This applies to M.S.W. inverters, but is not applicable to T.S.W. installations.  Additionally, some models of modern residential refrigerators may be susceptible to modified sine wave inverter current.  The issue is control board related.   This primarily affects newer all electric coaches.  These really require a true sine wave inverter to assure trouble free operation.

Inverters in conventional propane equipped motor coaches are generally turned off when not required, particularly if dry camping.  This is due to a continuing draw, albeit light, of electric current, even if all loads are off.  First, there is a search mode that essentially searches for a load, even in stand-by mode.  Secondly, TV’s, microwave readouts and many modern receivers use power in the “off” mode.  The TV’s and receivers remain on stand-by to be instant “on”.

Inverters in all electric coaches are generally always left on.  This is required as the refrigerator, if it is a residential type, is 120 volt AC only.  Inverters can be left on even when connected to shore power.  Once connected, the unit shuts down the inverter and operates as a charger and will automatically take over in the event of a power disruption.

Now, as if the inverter/charger didn’t do enough, there are models available with a built-in automatic generator starting board.   These will automatically start and stop the generator as required to keep the batteries within operating voltage range.  Additionally, the auto start can be wired to the air conditioning thermostat and provide instant start should the temperature within the coach rise above a user preset value.  Once the temperature is within the set temperature range, it will automatically shut the generator down until the next event.

If you have never had a coach with an inverter/charger, you don’t know what you are missing.  The convenience of having household power without the need for continually running the genset, is well worth the costs involved.  If you already have an inverter equipped coach, you probably wouldn’t have a coach without one again.

 With A Current Alternate View      -       Lug_Nut

 

Solar Power - Pt-2 Inverters

Howdy !

OK, now I know that everyone completed their power requirements worksheets so now we can talk about the size and type of power support system we are going to need to operate all that equipment. First let’s figure out the operating cycle of the inverter. All the duty cycle means is how long the inverter system is expected to operate. For example, if we want to run all our loads for 12-hours out of 24-hours the duty cycle will be 50%. Now let’s look at typical loads.

For example, if the load includes a small television and VCR or DVD , the power requirements are relatively small and the usage is usually short-term (i.e. the duty cycle is low). The support system may consist of the engine battery, whether from a tow vehicle or a motorhome, with one auxiliary deep-cycle battery, the existing engine alternator, and the necessary fuses and cables. With such limited power usage the batteries alone may be able to power the loads without running the vehicle engine and recharging them from the alternator. Ah, one thing to remember here, if you lump the starting battery into the power supply bank you may not have enough “Umph” to get the dang engine to start !

Now, if the loads are larger, such as lights, heater elements for a refrigerator or water heater , or even a standard RV microwave, the power supply system will require a larger battery bank and may necessitate a high output engine alternator, solar panels or even a stinky ol’ generator. The batteries alone cannot supply long-term power to loads like these. Ultimately, the energy must come from someplace other then just the batteries.

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Innovations in Generator Slides

 Front generator slide outs were a great innovation and made maintenance to the genset and surrounding components much easier.  The first one I remember seeing was on an early ‘90’s Newmar, London Aire.  It was a manually slid unit slightly larger than the generator set.  These have become more popular and are now used on a number of makes and models.           Read more

Cleaning Generator Slip Rings and Brushes - Part 19

The majority of modern RV generators utilize slip rings and carbon/graphite brushes to transmit magnetizing power to the generator rotor coils. This current/voltage signal comes from the control circuit during starting and the voltage regulator during operation. Read more

Battery Connections - How Shocking!

Howdy !!

I had a reader ask how to connect two 6-volt golf cart batteries to replace an RV marine 12-volt unit. Tell the truth I thought about just sending him a private letter but then got to thinking that if one person had the question then likely more folks had the same question so here is the answer.

The little diagram here shows the connections for serial and parallel connections.

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Troubleshooting Generator Controls Part 18b

Troubleshooting the control system in your RV generator looks and sounds complicated. It can be if you look at the total system concept. It is fairly simple if you look at the board and the system as a collection of simple circuits. Read more

Troubleshooting - RV Generators - Part 18a

Troubleshooting an RV generator set requires that you think like Sherlock Holmes and ‘deduce’ things so, get your hat, curved pipe (and maybe a beer) and we’ll see what we can do. First, your generator has to have a problem. The first great rule is “If it ain’t broke, don’t fix it”. If it is broke, then we get to play around and scatter parts all over the lawn. Use your senses to help with the problem. Sight, smell, hearing, touching, etc: Troubleshooting is greatly facilitated if you have the service/overhaul manual for your generator. They are available from the manufacturer, a local dealer or on the internet. The second great rule is “Read (and understand) the book”.

The third rule of T-shooting is “determining what type of problem you have”. Ie: Don’t replace the fuel pump if you have forgotten to install the battery. You will troubleshoot differently for operational, mechanical, electrical, or fuel problems. That being said, the majority of T-shooting should be done on a Go/No Go basis. That means picking a point in a system and determining if you have the correct parameter or not.

Lets take a common problem and see if we can troubleshoot it. The engine cranks but won’t start. It ran yesterday at the wilderness campsite, so there is a problem. Remove one spark plug and reconnect the plug to its wire. Crank the genset – SEE sparks?? Yes/No – YES. So it is probably something else. Sniff the spark plug area – SMELL gas?? Yes/No – NO. Aha, a possible fuel problem. Lets go to the middle of the fuel system and test there. Disconnect the fuel pump wire and get a jumper wire and connect it from battery positive to the fuel pump hot wire. Do you get any pumping sounds?? Yes/No — YES, but it’s really NOISY. OK, the pump is probably good so let’s get a gallon jug of gas and connect it to the input side of the fuel pump. Try the jumper wire again. Hey, the pump ran and then got quieter and seemed to run slower. Before you drop that 70 gallon gas tank to change the rubber fuel lines, turn on your ignition switch and see if you have over ¼ tank of fuel -Yes/No — NO. SOF (Statement Of Fact) — RV genset fuel lines go in the top of the fuel tank but stop a few inches (1/4 tank) from the bottom. This lets you run the generator for wilderness camping and still drive back to a service station (RV’s are hard to push). You have just troubleshot for about an hour and finally found it. You have also ADDED to your knowledge of the generator system so all is not lost and I know it won’t happen to you again, don’t I? You will notice that we didn’t disconnect any pressurized fuel lines and test them. If you have to open a pressurized fuel line just make sure an extinguisher is very close and the wife has paid up your insurance policy.

Next week – genset control T-shooting, get your multi-meters ready. — You don’t have one?? Why not?

Generator Jim

RV Generator Charging Systems – Part 17

Most built-in RV generators don’t have much of a battery charging system. They normally output only enough DC to run their own subsystems with an amp or two left over. In the 1980’s, most built-in generators had a 5 amp nominal charging system. With coaches having converters and “Smart Chargers’ in them, the generator manufacturers have dropped the genset internal charging systems. ONAN’s Quiet Diesel series has an option of the installation of a 10 amp charging system but it must be ordered with the generator set or it costs $$$ to get it installed later. The larger motor coaches with constant speed diesel generators usually have an automotive type alternator as part of the genset. This alternator will charge any battery/s connected to the genset.

The inverter generators normally have charging systems built into them but, if connected to an RV, the ‘Smart’ converter/charger in the coach will charge batteries at a much faster and safer rate. I would only use the inverter chargers for an emergency charging of the truck, car or lawn mower batteries.

The contractor type gensets have the capability of running a household or light commercial level battery charger. They don’t normally have separate charging regulators and DC power windings.

For those of you with dual battery systems. If you’re driving down the road and the main engine alternator goes out. Start the generator (on its batteries) and then turn on the ‘emergency start switch’ (or whatever your coach manufacturer calls it) and continue on your way with the generator and the ‘Smart’ charger feeding the chassis DC systems.

Generator Jim

Engine oil systems - Part 16

RV generator engines are built with one of two oil systems. The smaller ones generally have splash systems and the larger engines will have pressurized systems.

The splash system works by whipping the oil with some sort of an agitator and splashing it all over the inside of the engine. Sooner or later all parts of the engine will get lubricated. Most agitators (dipper rods) are built onto the connecting rod as it is the one part of the engine that moves around the most. As the con rod rotates the agitator dips into the oil and throws it around. Splash doesn’t work well with vertical overhead valve engines as it is difficult to get the upper end of the engine lubricated with any degree of reliability. Most of the side valve (flathead) one cylinder generator engines will have the splash system and it has worked well in them for generations. Some of the horizontal overhead valve engines such as the ONAN KV and KY series are working well with a splash system due to careful design and having the crankcase ventilation system built into the valve cover area.

The pressurized system utilizes some type of gear pump to force oil into all critical bearing surfaces of an engine. Just about all of the vertical overhead valve engines are using pressurized systems. The pump usually has a screen on its intake side to stop large particles of dirt, metallic shavings and miscellaneous loose engine parts from getting into the pump. The more expensive engines then pass the oil through a filter and then through drilled oil passages to the bearings in the engine. As an example, the older ONANs came with the oil filter as an option. Without the filter, the oil change interval was 50 hours. With the filter, the oil change interval was 150 hours. A pressurized system can allow an engine to develop more horsepower for a given cubic inch displacement due to the positive oil input to the bearing surfaces and their ability to be loaded to a higher degree with safety.

The oil that goes into RV generator engines has changed in the last 20 years. Until the multi-viscosity oil proved themselves reliable, the major manufacturers were careful about recommending them. 30 SAE heavy duty, high detergent oil is still the old standby for these engines. As these engines (air cooled) run hotter than a liquid cooled engine, the manufacturers have gone to the heavier grades of multi-viscosity oil. 15-40 diesel engine oil is the factory shipped oil for some manufacturers. They don’t know where the unit is going and this oil is good anywhere in the country. It’s also better for the engine as the additive package in the oil is made for heavy use, dirty conditions, and high temperatures. Synthetics have been around since the advent of turbine (jet) engines. The oil has come into wider use in recent years due to its ability to sustain high temperature conditions. Whether a synthetic is good for your particular unit depends on the type of operation you normally put it to. Running the genset at the rest stop for lunch 5 or 6 times a year is not a reason to use synthetic. A good high detergent 30 SAE will suffice. If you are boondocking for a week or so, and want the air conditioner, then consider synthetic. If your motor coach has its generator running whenever you’re in it, on the road or not, then synthetic is the oil for you. One thing to think about – The purpose of oil is to cool, seal, lubricate and CLEAN the internal parts of an engine. DO NOT use non-detergent oil in your genset.

You may now start the heated discussion as to which oil is better.

Generator Jim

RV Generator Starting systems, Part 15

RV generators have either rope or electric starting systems.

The rope is the old standby and is a carry over from lawn mower engines. Most modern rope systems incorporate a spring loaded compression release mechanism in the engine to ease starting of the larger engines and to help keep from breaking your arm if they kick back. The only thing you can do to a rope system is to possibly carry an extra rope and enough tools to change it out. A broken rope can ruin an otherwise good boondocking trip. Please don’t use plastic coated braided wire as a replacement. If the engine kicks back, it will twist/rip the entire front sheet metal housing off the engine. Don’t ask me how I know. Read more

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