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The Sink, Faucet and Water Tank

Vanagon camper sinks are set up to use city water from a hose connection in the front hookup box. Vanagons also have a 13 gallon water tank located in the rear cabinet next to the lower bed which is filled through the rear-most outside hookup box. Underneath the van are two drain caps, a white cap on the rear pipe drains the water tank, and the grey cap with a lanyard on the front pipe which allows the sink to drain grey water. There is no grey water holding tank. Before the first camping trip, we suggest that one tests the faucet and electric water pump, then drains and perhaps cleans out the water system. There is a cap on top of the water tank that can be removed to check for debris and algae.

The original sink faucet has a switch on top that twists clockwise to turn on the water pump. The switches do sometimes get corroded or break over time. But be advised that if the water tank red LED is on because the tank is empty, the LED panel will not give power to the switch, as a fail safe for the water pump. Occasionally the LED panel will not work the water indicators, same result, no water pump action.

One does not necessarily need to consider the water tank as a source for potable water, but it is best not to fill the tank with contaminated or highly mineralized water. Water such as Sacramento city water will eventually coat your system with hard water deposits which cannot be removed. Some water from bad wells or other questionable sources can cause algae growth or contain dangerous biological or chemical contaminants.

For cleaning and disinfecting a water tank, we highly suggest using chlorine dioxide (ClO²). It is entirely safe when used in proper dilutions, and is used by many cities to treat local water. One of the hallmarks of being highly bioactive as a disinfectant is that chlorine dioxide is quite unstable. So it is generally generated as needed for immediate use. One part of a liquid dilution of sodium chlorite is mixed with another part of a liquid composed of a suitable acid. The reaction between the two liquids forms chlorine dioxide in just 2 to 3 minutes. The reaction also creates some free chlorine gas, so do not get your eyes or nose close to it.

Once the reaction is complete, the liquid can be poured into the water tank through the top, then the tank filled. If one wants to put the chlorine dioxide solution into the tank through the fill cap in the outside hookup box, we suggest that one pre dilutes the liquid in a quart or so of water, then pour in that solution using a funnel or an adapter. GoWesty makes a Water Tank Filler Nozzle that can be used for this purpose.

We suggest that one turns on the faucet to get the solution in the pipes, then fills the tank completely and drives for a while with the ClO² cleaning solution in the tank to get the tank ceiling cleaned well. If there was algae in your tank, the ClO² solution should be made at least double strength and left at least overnight. Then the tank should be drained, scrubbed and rinsed, then repeat the chlorine dioxide cleaning cycle with normal strength solution. Check the plastic water hoses, as they may need to be replaced.

There are online sources for the chemicals kits to make chlorine dioxide. Many campers are familiar with Aquamira Water Treatment Drops as a backpacking standard. The small bottle kit of 1 oz each will treat your tank twice. At this strength, the water is drinkable, as this is a normal procedure for water purification.

For a very informed article about chlorine dioxide useful to laypersons, check out this webpage from Lenntech in the Netherlands.

Vanagon Camper Refrigerator Operation

Gear case (3)Vanagon camper refrigerator operation is not particularly difficult. But there are a number of factoids in the three categories of AC, DC and propane operation modes. The fridge will run on AC, but of course only when connected to shore power with an extension cord. We normally use the AC mode to check that the refrigerator works before we perform any cleaning or repairs. Pretty much all fridges we check run on AC, although occasionally we have seen a bad fan or clogged condenser cooling fins.

The DC power mode is available originally from the factory only when the engine is running. Some think it can just be fed by an auxiliary battery, but it is soon obvious that the current draw is so high that a large battery lasts just one day, maybe less. Better fridges, like the Engel, draw far less power and present a viable option for those who really want DC fridge capability. Plan on using a large auxiliary battery with at least an 80 Amp-Hour (AH) rating, or two batteries if you are a hard-core week-at-a-time camper.

Propane is really the best option for the average camper on the average trip. Getting it running on the propane is not difficult when they are working correctly. Be advised that as these fridges got older, the burner section often gets excessive dust and debris inside, making lighting up difficult or impossible. And some of the air pumps go bad as the O rings get hard or broken. The electronics for the flame mechanism are much like a wall furnace. There is a pilot light, a piezoelectric igniter and a thermocouple that checks for the pilot light flame. We include the following video to clarify the process.

Vanagon Camper Refrigerator Operation

Vanagon Camper Refrigerator Operation

A YouTube Video from Volkswagen. Intended for mechanics, it shows refrigerator operation and removal. We don’t recommend that customers try to remove the refrigerator.

Just a couple of points not covered in the video. The water drain outside the fridge at the bottom left can be used to clean out the burner box before lighting the pilot light. One can blow compressed air into the drain tube briefly. Also, especially as the air pump gets weak or inoperative, one can also blow softly through the water drain port using a 5/16″ plastic or rubber hose while lighting the pilot light. This technique can be used to get a pilot lit when the air pump is not working.

Rarely, the pilot light indicator LED on the camper panel may not work. Usually, if the LED is not lit, the pilot is not working. There is a sight glass for the pilot light at the lower left corner inside the fridge. Most people cannot see the pilot light through the sight glass unless it is very dark. One can confirm that the refrigerator has lit and is working by touching the outer flue vent VERY briefly. The flue vent will get hot enough to burn you once the fridge is going, so be very quick and careful.

To sum up about a refrigerator that won’t work, there are obviously a lot of things that can be wrong, but most fridges just need a proper cleaning of the air pump and pilot light. At Karmakanix, we normally start with a quote for just cleaning, and if the problem proves to be due to further complications, at least we have enough time to diagnose the nature of the issue and let you know. Parts are available, although some take a bit of research and patience.

Some folks help out the refrigerator a bit with a block of ice, not always a good ploy. Aside from soggy food, everything gets a bit damp and potentially messy. Remember the pilot light sight glass hole at the lower left corner of the fridge. Water should NOT be allowed to drip through, as the burner box is on the other side. If one uses ice, it should be in a sealed container. Remember that this is a vehicle, and a puddle will slosh when driven.

Dry ice is an option, since it goes straight from a solid to a gas. Dry ice is CO2, a greenhouse gas. A Vanagon doesn’t compete with a coal-fired power plant, but if you choose to use dry ice CO2, be sure there is some ventilation at night. Overall, most prefer using an ice substitute, which can be left in the fridge kind of like a coldness capacitor. We feel that a good, environmentally-friendly solution is the Tundra Series Ice Substitute by Artic Ice, because the initial freezing temperature is 5°F. Artic Ice products have a textured surface to enhance surface area, and a temperature indicator with progressive blue bars to indicate the unit’s actual internal temperature.

We find that a number of customers bail out on the factory refrigerator and get an Engel fridge to replace it. The power consumption of the Engel is a fraction of the factory fridge. We recommend Engel models that can be run on AC or DC power because eventually you are going to need to run the fridge at home or in your hotel room. The power requirements vary according to the size of the fridge and the ambient temperature, but to sum up, they all run around 1 amp or less once they are cold. That’s barely more than a dome light. Check out the Engel Website to compare models.

The Auxiliary Battery System

Many campers need an auxiliary battery to make sure they don’t inadvertently end up with a main starter battery that is too discharged to start the engine. That said, one should still have a set of jumper cables, even if they are only ever used to get some other camper started. The jumper cables should be at least made from 8 gauge wire. The smaller the gauge, the bigger the wire. A set of 8 gauge jumper cables is not going to allow a vehicle with a dead battery to get jump started right off, but they will allow the donor alternator to charge up the receiver battery and the engine will likely start after 15 to 30 minutes of charging, depending on the condition of the receiver battery.

That said, real jumper cables that can start another car without waiting a long time would be made with 4 gauge and up to 12 feet long, 2 gauge and up to 16 feet long, 1 gauge and up to 20 feet long, or 0 gauge and up to 30 feet long. The math on this quiz is actually a bit more complicated, but that synopsis of gauge size vs. length will do. Make absolutely sure the cables are connected correctly. Hooking jumper cables up backwards may kill or damage any or every computer or alternator on either or both cars. If one does not understand precisely what that last sentence means, then probably one should get someone else to jump start the dead battery.

Vanagon auxiliary batteries usually reside in one of two different locations. A relatively small deep cycle AGM battery will fit under the driver’s seat, ranging from 40 to 50 Amp Hours (AH). Originally, a flooded lead-acid Group 42 size battery was the old school choice for the auxiliary battery in that location. A much larger AGM or flooded battery can be installed in its own box under the back seat, rated 65-100 AH. Occasionally, we find a camper that uses up much of the area under the sink for a battery. We find that battery Amp-Hour (AH) ratings generally mean less than diddly and more than squat. When the batteries are brand new, a comparison by rating is very close to true. After that, all the other variables take over, and battery quality is a much larger factor. After a few camper seasons, the smaller no-name batteries will barely charge your cell phone and run a stereo for an evening. The larger, high-quality batteries are still very powerful, and can be trusted to run important equipment.

For an example, a CPAP machine seems like important equipment. A CPAP designed to work on 12 Volts which draws 2.5 amps would need 20 amp-hours for 8 hours of run time (2.5 x 8 = 20). The battery should have at least a 44 ampere hours rating left in its lifespan to guarantee one night of sleep. So an AGM battery that was born with an iffy 50 amp-hour rating, and is a few of years old, can’t be used reliably for this job. Most CPAP machines are 120 VAC only, and would require an AC inverter, and a good one of the pure sine wave inverter type. More on that later.

The idea we want to get across is that a battery’s amp-hour rating when new is one thing, the actual reliable rating during the service life can vary intensely. In the best of circumstances, an auxiliary battery is likely to lose 5% to 7% of its capacity per year, and have a 5 to 7 year service life. And if the usage and charging habits mistreat the battery, one may need a new one every year. Don’t do stingy math to calculate important ratings. Do your best estimates, then at least double them for reliability. That’s the way to be a happy camper.

The most common error in many camper battery calculations is thinking that one can use all the battery capacity. Well, you can, once or twice. The best generalization is never run a battery down below 30% to 50% discharged, or the battery won’t last very long. The standard is that a battery is good until it reaches 70% capacity, after which they usually fail completely within some months. A new starter battery can be discharged near 100% about a dozen times, then it is junk. An old starter battery won’t last even one time near completely discharged. At 50% discharged, a starter battery gets 100 reliable cycles, and a deep cycle will last 400 to 500 cycles. At 30% discharged, a starter battery will go maybe 150 cycles, but a deep cycle battery will provide 1000 to 2000 cycles reliably before it reaches 2/3 capacity.

Information varies between manufacturers about what voltage reading or electrolyte specific gravity constitutes completely discharged. A fairly accurate test is to take a steady state voltage reading several minutes after shutting off all devices. For a new battery, 12.2 Voltage means recharge soon, and 12.0 Volts is a total lower limit. Going past that is going to radically reduce battery life. Many campers buy a small digital voltmeter that just plugs into the cigarette lighter / power outlet, not super accurate but close enough.

One can also use that voltmeter to evaluate if the load on your auxiliary battery is too high. With the auxiliary battery fully charged up, and everything is turned on that is used consistently, the auxiliary battery should not drop below 12.2 volts. If one uses an appliance with a intermittent big load, then after a one second surge, the momentary voltage should not drop below 11.9 volts. These numbers are generalized estimates, but if your system runs lower voltages, maybe the battery is too old, too small or discharged. Maybe your devices are just too big or numerous. Maybe the wires you used are too small or corroded. If you are using an inverter, it could be too small. Some device or appliance could be too large for the inverter, or shorting it out. More on that inverter stuff later.

Campers that want to install two auxiliary batteries in addition to the starter battery need to understand that the original alternator will barely push enough power to keep the batteries charged and run the basic functions of the fuel and ignition systems, lights and wipers. Charging up a pair of discharged auxiliary batteries is going to be slow, and using other large electrical consumers at the same time could be a problem. One solution is to get an accurate voltmeter to check charging and steady state voltages. Another option is to get a high quality battery tender / charger that can handle the charging job later once AC power is available. We suggest that you buy at least a 20 amp, 2 bank battery tender, that’s 10 amps per battery.

Auxiliary Battery Isolator

The purpose of an isolator is to separate the main starter battery from the auxiliary camper battery so the starter battery does not go low from using camping equipment. The isolator also allows both batteries to charge with the engine running. There are three basic kinds of isolators: Relays, Diode Packs and Automatic Charging Relays (ACR).

The relay type is the original standby, and some use the original camper relay mounted in the box under the driver’s seat for battery isolation. Not such a good idea, since they are rated 30 amp, and will likely overheat if trying to charge a low battery and running the refrigerator at the same time. The 30 amp relay can be replaced with a 70 amp fan relay, or with the OE (Original Equipment) auxiliary battery relay from the Eurovan, which is round with 2 large posts and one small actuating post. Not a bad choice, but perhaps not the best choice since we replace 2 or 3 of these per year for failure. Although it should be said that they lasted generally between 10 and 15 years before failing.

Diode packs are typically blue with 3 or 4 posts. Since any diode has a .7 volt loss, the 3 post type are guaranteed to undercharge both batteries. The 4 post type require that one disables the voltage regulator inside the alternator, bends a metal tab that connects the regulator to the alternator D+ post, and solders in a wire from the regulator output to the 4th post so the alternator will charge unregulated all the time. Not a good idea. With two large batteries, the voltage is usually within specs, possibly high if one or both of the batteries is small. But if one removes the auxiliary battery, the main battery is going to overcharge radically, likely around 15.2 to 15.4 volts, or higher. Who’s going to notice, right? And the car runs faster because of the higher ignition voltages, and everything is fine until the battery fails early from positive grid corrosion, or some component goes up in smoke.

Lastly, there are Automatic Charging Relays (ACR), which are also known in some other parts of the world as Voltage Sensitive Relays (VSR). Although the word “relay” is in the name, there are no internal contacts or moving parts. One just hooks each battery to each main post, and the batteries remain isolated whenever the engine is not running and the voltage is below about 13 volts. When the voltage rises after the alternator starts charging, the 2 main posts are connected, and both batteries charge. Simple, fool-proof and reliable. And a bit expensive. But we have never seen one fail, yet. ACR’s were originally mass produced for sailboats, and are typically sold in marine supply stores.

Battery Tender: Keeping Up With The Charging

If a camper owner only drives the vehicle a few times a year, then a battery tender for each battery is essential. This does entail an extension cord. Driving for 20 to 30 minutes once a month will definitely not keep a battery in a good state of charge. Once a week would just do the job. Driving once a month for 2 to 3 hours would work to keep up a battery. One is fighting self-discharge rates, the vehicle’s normal parasitic draw and increasing battery age. And these driving recipes will likely yield a 3 to 4 year battery life at best. Let a sailor give you a clue. On our sailboat, battery charging with the engine is once a month for 20 to 30 minutes. But the high-quality battery tender run from shore power is hooked up any time the boat is in the slip. Both the batteries generally last 10 to 12 years.

Most people can’t connect up with an extension cord all the time. Mostly for this reason, the tiny .75 amp tenders are useless. They cannot recharge a large discharged battery. We recommend 1.5 amp for camper batteries that remain plugged in whenever not driving. For those who forget to plug in, or only get hooked up once a month for a few days, we recommend a tender with 3 to 4 amps per battery minimum. Once again, there is a large variance in quality. First, get the picture that a trickle charger is NOT a tender and will often damage a battery during long term usage. Tenders have the ability to perform Float Charging accurately to avoid over-charging, thus extending the life of a battery.

The good tenders do a good job of constantly evaluating the battery and adjusting the charge voltage to match, which can be important with yearly temperature changes or when discharged after camper usage. The best tenders can also perform pulse charging as an equalizing charge when needed to remove sulfate deposits and will do so once a month to help keep all the cells at the same state of charge. For further information, see the Karmakanix Knowledgebase page on Charging Systems.

Time to remind: We are talking about campers and auxiliary batteries. So we are talking about dual battery tenders with campers, as opposed to single battery tenders for single battery cars. Not to help sell anything, but we find that the Noco and the ProMariner chargers / tenders lead the field. And Noco is made in the USA.

The Solar Charging System Option

We do not suggest trying to go solar to keep up with camper battery usage. Realistically, one would need panels at least the size of the whole van to get close to accommodating the complete energy needs of an avid camper. Fixed panels mounted on top of the van are going to prove impossible. They are going to be a source of water leaks, low fuel mileage due to wind drag and an accident-waiting-to-happen for breakage.

Real solar requires buying or making a folding unit that can be aimed at the sun, moved to re-aim during the day, and folded up to transport inside the van. Moving solar panels to follow the path of the sun means getting much closer to their rating in total power over the sunlit hours. If one uses a high quality 200 Watt portable panel setup, then one is generating around 12 amps at 17 volts, given perfect sunlight and re-aiming the panels at least three times during the day. Use 3 amps to run your Engel Fridge, phone charger and some music. You have 9 amps left to charge up the low battery from the night before. Assume that the fridge takes less power at night. At 2 amps per hour for the 16 hours of no sunlight, one needs a 66 amp-hour battery which will end up at 50% discharged at the end of 16 hours.

None of this is true, because none of it is perfect. And the math is actually way more complicated. A certain amount of charging power is wasted, some simply because the battery charge tapers off, and it does not return all the power required to charge it. This 200 Watt setup would prove adequate for summer camping with a small high-efficiency refrigerator. An 80 Watt system is unlikely to provide for your personal power needs and your fridge on a 24 hour basis, even when everything is new. It only generates a bit less than 5 amps when it is looking at a full-on sunny day.

Going winter camping when the days are short and sometimes overcast? Camping in the California Desert with cold nights that lower battery capacity, or planning on staying off the grid for a couple of weeks? Then you probably should go with a much larger system. We are not trying to kill your buzz, we have seen this work. Just giving clues as to the actual nature of the project. Especially if you already bought into solar, you should know that you can just add another complete system side-by-side with the one you have now. But you must have a diode set between them to isolate them from each other.

The AC Power System: Household Appliances

The Vanagon camper has one AC outlet just behind the refrigerator, and another AC outlet inside the cabinet in front of the fridge which has the grey AC power cord for the fridge plugged into one outlet. There has a 15 amp circuit breaker built in under the outlet next to the fridge. The AC power system requires that an extension cord gets plugged into the hookup box on the left side of the van. The original hookup box is a bit of a janky design, and in some aging vans that have spent their lives outside, the electrical connections on the inside of the box might be corroded. It is a very good idea to get out and feel the box for possible heat indicating a bad connection if one is using a device that requires more than just an amp. If one is planning on using a space heater (1500 – 1800 watts) for the first time, then probably best to remove that 30 year old hookup box to check the wiring for corrosion beforehand. Gowesty makes a well designed replacement 110 Volt Electrical Hook-up Box that is way stronger than the original and user friendly.

One should know that the thickness or gauge of the wires in the extension cord need to be larger as the length gets longer. And one needs to consider the power requirements of all the devices and appliances that are to be used. Charging your shaver or toothbrush and using a laptop would require 16 gauge wire for a 25 to 40 foot cord, or 14 gauge wire for 50 to 100 foot cord. Running an electric heater at night is as big a load as one should ever have on your camper A/C circuit. That would require a 14 gauge wire for a 25 foot cord, or 12 gauge for a 50 foot cord. That’s pretty thick and a bit expensive, but should be safe. Overload is a serious issue. Remember, you are in there sleeping. One should periodically feel the ends of an extension cord to be sure that they don’t get beyond just warm, hot indicates a bad cord or insufficient wire size. It is unwise to trust the fuses or circuit breakers from some campsite. You could end up melting plastic, or starting a fire.

The AC Inverter: 3 Very Different Kinds

Like most equipment, everyone wants to know “What kind?” and “How big?”. In the case of available AC inverters, there are two basic kinds, Pure Sine Wave Inverters and Modified Sine Wave Inverters. Actually Modified Sine Wave Inverters fall into two categories: Modified Square Wave Inverters and Stepped Sine Wave Inverters, both of which are always called “Modified Sine Wave Inverters”. The differences are not obvious, but they are functionally huge. A normal AC voltage sine wave is so well known that everybody assumes every AC inverter puts out that same waveform. Until your electric blanket controller goes up in smoke. Just kidding, kinda.

Let’s start by describing the dinosaur in the room: The Square Wave Inverter. These are extinct and not sold anywhere, and for a good reason. The original AC inverter was just a square wave that oscillated between a positive and a negative voltage at 60 times per second. The big problem with this waveform is that both the voltage RMS (as measured on a meter) and the peak voltage varied up and down with the DC battery voltage. So many devices could not deal with the high AC voltage when the engine was running and charging the battery.

The amount of Total Harmonic Distortion (THD) was huge with just a square wave. We are not going to include the THD concept in this article, except to say that a pure sine wave has almost none (1% – 3%), and the coarser and choppier a waveform looks, the higher the THD (30% – 40%). A square wave has a THD of 48.3%. A further explanation is superfluous to this article. For you disappointed Techies, here is a link to Wikipedia about THD. Maybe a better link for the Concept Curious is to this page from AllAboutCircuits.com and just ignore the math.

Pure Sine Wave Inverters

A pure sine wave inverter does indeed have the same basic AC output waveform as your house, although the exact waveform varies from brand to brand as to how smooth it is. Some are actually smoother and cleaner than the power in your house from the grid, making them ideal for off-grid recording studios. Just to be clear, the information in this article refers to stationary home-sized inverters as well as inverters that are more commonly mobile and in use in campers.

A pure sine wave inverter has an output of 120 VAC RMS voltage when measured with a voltmeter. RMS means Root Mean Square, which is the effective averaged voltage that determines the available power. The waveforms of a pure sine wave inverter voltage and of your house AC voltage both have a peak voltage of 170 VAC Peak and a measured voltage of 120 VAC RMS, which is a constant ratio of .707, which is the square root of 2. End of math quiz.

Pure sine wave inverters involve sophisticated circuitry and filters, making them much more expensive than modified sine wave inverters. They are also quite a bit more efficient. Inverter conversion efficiency varies over a large range as the load changes. They are typically very inefficient at lower loads below 1/5th of their rated output wattage. They reach peak efficiency at around 2/3 to 3/4 of its rated wattage load, then decrease slowly above that. When manufacturers give efficiency ratings, they are referring to peak efficiency without regard to output. A pure sine wave inverter with a peak efficiency of 93% may be less efficient at lower, more normal working loads than another inverter rated at 85%. The key point to the higher efficiency is that the battery will last longer than if one was using a cheaper modified sine wave inverter where the efficiency when you are using it could be as low as 60%, and never higher than 80%.

The vast majority of pure sine wave inverters work by making a small 60 hertz (cycles per second) sine wave out of the 12 volt source, then amplifying it and maybe filtering it. In theory, one could take the signal from a stepped sine wave type inverter and just keep filtering until it smoothed out. This is just not done, as it would generate a lot of heat and lose a lot of efficiency.

The obvious advantage of buying a pure sine wave inverter is that it is compatible with every sort of device and appliance. Lithium batteries charge better and last longer. Devices with electric motors run way more efficiently, at the right speed, and don’t overheat. Stereos and radios don’t make annoying noises. Microwave ovens are quiet and cook faster. Florescent and HID lights work. Computers don’t have mystery glitches and crashes. And printers work more accurately.

Modified Sine Wave Inverters: The Square Modified Sine Wave Inverter Kind

The majority of the inverters on the market are Modified Sine Wave Inverters. There are two very different kinds of modified sine wave inverters, and we would like to differentiate by calling them square and stepped, referring to the huge difference in waveforms. Most modified sine wave inverters basically have an AC voltage output that is just a square wave with some time spent at 0 volts. A very good idea, as that makes the measured RMS voltage stay the same at different battery voltages, even though the peak voltage goes up and down with the battery voltage. Somewhere below about 10 Volts, depending on the model, the AC output voltage will turn into just a square wave. This goes back to the Root Mean Square notion, the area under the wave. As the peak voltage goes up, the wave gets shorter so the measured voltage, and hence the power, stays the same.

Almost all modified sine wave inverters are this single square wave plus zero type, which are referred to as Square Modified Sine Wave Inverters on this page. The voltage rises and falls abruptly, the phase angle changes abruptly and it sits at 0 Volts for some time before changing its polarity. Consider that AC voltage is making electrons shiver back and forth at 60 times per second, changing direction every 8 milliseconds. The 120 VAC in your house has a smooth transition between the positive and negative peaks. The direction of the current, which is the flow of electrons, follows the voltage as it rises and falls smoothly. A square modified sine wave inverter has big steps in the voltage and that makes those electrons around jerk back and forth. Basically, the more a device requires that the voltage ramps up and down smoothly, the more inefficiently that device runs on a square modified sine wave inverter, creating heat and noise with the wasted energy.

The graph of a waveform using a square modified sine wave inverter at a normal battery voltage of 12.6 Volts shows that the peak voltage is at 160 VAC and the square pulse width is about 75%, so 25% of the time the voltage is at 0 VAC. A voltmeter would measure 120 VAC RMS voltage. At higher voltages, such as when the alternator is charging, the peak voltage increases as high as 200 VAC. The square pulse width reduces to about 55%, so 45% of the voltage is at 0 VAC, still yielding a measured 120 VAC RMS. At lower voltages, like when the battery is getting discharged, the peak voltage decreases to as low as 120 VAC. The square pulse width gets closer to 100%, and the pattern is pretty much a square wave with no time at 0 VAC. A voltmeter will still measure 120 VAC RMS voltage. The reason for explaining all this is that when using a less expensive square modified sine wave inverter, the lower the battery voltage, the greater the loss of efficiency and the greater the problem with the function of certain devices, especially brushless motors. It should be mentioned that all these waveforms and voltages are given without regard to the wattage requirements, meaning the power used by devices. As a refresher, power is measured in Watts, which is Volts times Amps.

Modified Sine Wave Inverters: The Stepped Modified Sine Wave Inverter Kind

More expensive stepped modified sine wave inverters, which are more likely to be found in a house off the grid, use a set of stacked up square waves that better imitate an actual alternating current sine wave. These are referred to as Stepped Modified Sine Wave Inverters on this page. The stacks are made by combining stepped sine waves with odd harmonic frequencies of 1st (60 Hz), 3rd (180 Hz), 5th (300 Hz.), 7th (420 Hz.) and so on. The overall voltage trace on an oscilloscope resembles a stepped shape known as the Mayan Temple. Although always sold as modified sine wave inverters, technically these can be called stepped sine wave inverters or stepped modified sine wave inverters, as the wave form actual closely resembles a jagged pure sine wave.

Many of the better inverters with stepped sine waves show the voltage waveforms in their literature and user guides. At a normal battery voltage of 12.6 Volts, there are 9 steps in the waveform. At higher voltages, such as when the alternator is charging, there are less steps. At lower voltages, like when the battery is getting discharged, there are more steps. At all battery voltages, the output is the same peak voltage of 170 VAC Peak and a voltmeter will read 120 VAC RMS, the same as with a pure sine wave inverter. The efficiency can be as high as 90% or slightly more, which is approximately the same as a pure sine wave inverter, and most devices function well. The nutshell is that a stepped sine wave inverter is really close to a pure sine wave inverter in the look of the waveform and the functional compatibility with devices.

Modified Sine Wave Inverters: The Devices and Appliances

There are some devices that can use cheaper square modified sine wave inverters, some that may function OK but not necessarily well, and some that will not function well and/or may get damaged. There is always a loss of efficiency with a modified sine wave. The loss is the largest with devices that have motors. Lots of these devices are not likely to be out on the road camping with you. The following types of devices may not work properly and may get damaged from using a square modified sine wave inverter. Some devices, but not all, may run perfectly well on a stepped modified sine wave inverter.

  • Laser printers and photocopiers, anything with a thyristor that controls heat.

  • Transformer-less capacitive input powered devices. These are low voltage DC output power supplies / chargers that work by chopping off the top of an AC sine wave to make a DC voltage and current, then lowering the voltage. A square sine wave does not work well for this process. Devices included: Razors, some electric toothbrushes, smoke detectors, night lights, chargers for hand tools or flashlights.

  • Clocks and devices with timers like coffee makers, etc, may lose the correct time.

  • Output voltage control devices like dimmers and motor speed controllers may not function, lighting and fans for instance.

  • Devices that use radio frequency signals carried by the AC distribution wiring.

  • Devices that use microprocessor controls or silicon-controlled rectifiers (SCR).

  • Some fluorescent lights, the ballast will not generate the signal to start the light and may overload the inverter while trying.

  • High intensity discharge (HID) lamps like Metal Halide lamps.

  • Some cell phones become unusable when charging through an AC adaptor. Apps may crash or refuse to function.

  • Appliances like refrigerators, microwaves, and compressors that use AC motors don’t run efficiently and may overheat.

  • Any device that incorporates a brushless motor will require up to 30% more power and may overheat.

  • Some battery chargers for portable tools may not work at all.

  • DON’T RISK expensive medical equipment like a CPAP machine or an oxygen concentrator.

  • There will likely be a background scream / whining noise through the stereo when a square modified sine wave inverter is in use.

Most devices that use a rectifier to change the AC into DC are fine on a square modified sine wave inverter, like a laptop charger. Still, some laptop manufacturers claim the square wave will cut the lifespan of the charging device. We advise that one should read the literature that comes with the computer. Running some laptops on a square modified sine wave inverter will void any warranty.

Many appliances are available either in a 12 Volt DC version or with a proprietary 12 VDC adapter, which are definitely more power efficient and sometimes safer than using an inverter. One is going to lose a minimum of 10% power going from DC to AC, much more with a cheaper square modified sine wave inverter.

Choosing The Correct Inverter: The Right Size

We advocate that one calculates their likely maximum total power requirement for everything one will use in watts, then double that to pick out an inverter. Most importantly, if one is planning to use a tool or appliance that has an electric motor in it, then triple the wattage rating of that tool or appliance to pick out an inverter. And that may not be enough.

This would seem excessive at first glance since most review sites recommend a 20% margin. But the biggest reason is the peak power spike. Doubling ones power requirement will usually cover peak power requirements. One should know that any device with a motor will need 2 to 5 times the stated rated wattage power requirement to start up, then it drops to the rated wattage. Some other devices have a startup spike, but not like an induction motor. Most campers are not traveling with drills, electric chainsaws, microwave ovens or laser printers, but any appliance makes it important to know the peak power rating of the inverter. If the peak wattage ratings of the devices and appliances are available, definitely use the 20% cushion in the peak power calculation. Remember that usually only one device has to start at any given moment.

Most devices do not list their peak power rating. Sometimes peak power rating is also called a surge rating. Charts and information can vary wildly about peak power ratings, some with a few obvious errors. Most inverters have a peak power or surge rating that is about double the maximum rating. Remember that when the 120 VAC device has a high peak power during startup, the 12 volt battery will have a power spike as well, and the DC power spike will be 15% to 30% higher than the AC wattage surge spike. So both the battery and the wiring will need to be of a size and rating that is up to the task.

We have seen a few camper vans that would better be described as a rolling home office, and the power requirements of the devices added up quickly. A 1000 watt AC load translates into about 10 amps of DC current after losses with the best of inverters. That’s more than your headlights. Now double that to cover your average peak spike. One can see that a smaller 44 AH deep cycle battery may not last a full day of that sort of office use, especially if the auxiliary battery is already a few years old.

For you mobile office fans, a laser printer has perhaps the most wicked peak power surge of all devices. According to a study by Ken Schwantje of Samlex America, an inverter manufacturer, a 450 watt laser printer had a 4668 watt surge on cold start and a 2880 watt surge on a warm start. That would require the mother of all inverters to power that in your average camper van. In contrast, inkjet printers have peak power requirements barely larger than the rated wattage.

One should know that many cheaper inverters with two AC outlets only send half the rated power to each outlet. Many times, this fact is not covered in the literature or manual, and one finds out when the inverter fails to operate and maybe squeals an alarm when a device close to the maximum rating tries to start up. If one has a tool that needs 400 watts to run, like a small drill which needs 3.5 amps, with a peak power requirement of 1000 watts to start the tool, then a minimum of a 1000 watt inverter with a 2000 watt peak power rating is needed just for the one tool. The same thing applies to the peak power or surge rating, one outlet can only provide half of the peak power rating.

Another reason for planning ones power usage with a large cushion is that eventually one may take a passenger who also has devices with power needs. It can be surprising how much AC power a bunch of kids can use at night while camping.

The power for the load of AC devices used through an inverter when driving is provided by the alternator. One can consider running the engine for a short period when a large device is being started or used, especially if the vehicle has a small or very old auxiliary battery.

As mentioned, inverters vary in their zone of peak efficiency. As a bald-faced generality which is not always true, most inverters have their best efficiency range somewhere around 40% to 75% of their rated AC voltage output capacity. Models vary in how much and how fast the efficiency curve drops above that range. To better conserve the available battery charge, it pays to have a power usage plan and the right sized inverter that will spend much of its time within the range of its highest efficiency.

Just a thought, many off-the-grid homes use two inverters. One modified sine wave inverter as the work horse to run most of their devices. Most savvy home owners pick a stepped sine wave inverter without even knowing it, just based on the reviews for reliability and quality of life. Then they run a separate circuit with their pure sine wave inverter for audio and medical equipment.

Choosing The Best Inverter: The Best Features

Better inverters also have a multistage fan so they are quiet when the load is low, but can dissipate the extra heat that comes with higher loads. Perhaps the best reason for buying a larger inverter is to avoid having a large amount of heat generated on a hot summer day. Because square modified sine wave inverters are less efficient than pure sine wave inverters, they generate far more heat. And if one depends on your power inverter to heat your van in the winter, there is something wrong with your tactics.

Inverters vary a lot in noise levels while operating at different power levels. Especially if you are going to run a device or two while you are sleeping, the noise level can be a big deal. Also remember that a square modified sine wave inverter is very likely to cause a noise through a stereo that can vary from a whine to a scream. That can make it hard to fall asleep to your favorite tunes.

GFI outlets are a good idea if you camp in the rain. Really, GFI outlets are a good idea anytime power is being used outdoors. Ground is ground, and if you are standing on it, you are connected to it. A shorted device is going to hurt, and maybe worse. They put GFI outlets in a bathroom for a really good reason. If you are dry, you generally have an iffy connection to ground, and a 110 VAC shock is going to hurt and surprise you badly. If you are wet, you are well connected to ground, and a 110 VAC shock might be fatal.

USB ports may be important depending on the User. More and more, USB has become the standard for powering and charging most small devices. It is way more power efficient to have the inverter provide USB power than to convert battery 12 VDC to household 110 VAC, then go back to USB 5 VDC with a charger in the AC outlet. Remember, conserving battery power is paramount. Why waste it with another conversion?

Check on the overload protections and alarms. Many inverters have an audible alarm for overload, which is safer than just depending on looking at some LED panel. Better to have a unit that notifies you before it cuts the power or starts smoking. Inverters use power anytime they are turned on, even when nothing is plugged in. Remember to shut it off when it’s not in use.

Some smaller inverters come with just alligator clips on the 12 volt cables. Given that the Vanagon battery box crowds the positive terminal, this may not be safe, especially if one is connected while sleeping or traveling. The alligator clips should be changed to eyelet connectors using a professional grade wire crimper tool. The wires then need to be permanently connected to the battery terminals. Always reinstall the red plastic shield over the battery positive terminal.

Pure sine wave inverters have come down in price since last century relative to their equivalent wattage modified sine wave inverter prices. Modified sine wave inverters are often reviewed as unreliable, among other complaints about heat and noise. Some of these experiences may have been at least in part due to the types and power requirements of the devices the client may have been using, and whether the inverter had a square or stepped sine wave. Certainly pure sine wave inverters have a better overall reputation for quality and reliability. And a stepped modified sine wave inverter is the next best thing. It would seem that a cheap square modified sine wave inverter is like having a car with square tires.

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