Let's address the AC generator first. Most of us know it is a noisy, expensive and inefficient source of power. Unless one needs to run air conditioning and/or other heavy users of electricity, the generator is spinning its wheels just to produce what little electrical power we need. In relatively high power AC load ranges generators are most efficient and actually last longer. Light loads cause them to build up carbon in the cylinder(s) and exhaust system. The carbon ends up adding its abrasive material to the oil, further reducing the life of the generator. Actually, a generator is happiest and lives longest when providing electrical loads of 75% to 80% of its capability.

Many people with standard tower or desktop computers buy a small Uninterruptable Power Supply (UPS) system to insure that clean AC power is supplied to the computer regardless of what happens to the normal AC power source. RVers should have some rudimentary knowledge of what an UPS system is made of for reasons that will become obvious shortly. First, the UPS is plugged into the regular AC power source, whether provided by generator or power company. The sensitive electrical appliances (computer equipment) are in turn plugged into the UPS system. If you are going to run a computer off of a generator, such a system is very appropriate because generators are renowned for shutting down or surging for any number of reasons. Some campground power is not much better, sometimes worse.

So what is inside an UPS system? The input AC power cord first meets up to a power converter. The power converter turns AC into DC. The DC is supplied to an internal battery that gets charged. The output of the battery feeds electronics called an inverter that turns the DC battery power back into AC power. Since it is the DC battery source that is feeding the inverter anyway, when the AC input power goes South the battery continues to provide the DC power to run the inverter that provides AC power to your computer or whatever else you have plugged into it. That may sound confusing when first read. Stated briefly, the AC input gets converted to DC and that feeds the internal battery which feeds an inverter that provides AC output power. Obviously the bigger the internal battery the longer it can provide AC power for your computer without the power company or a generator feeding the whole thing. This works to provide one with good steady power through brown outs, surges and temporary power outages. Should a temporary power outage become a longer lasting inconvenience, it gives you time to shut down your computer in an organized manner before the UPS goes down due to lack of battery power.

Actually, a typical RV already has the first two highly important components of an UPS system. It has a converter that turns AC into DC and charges the house batteries. Those batteries are many times bigger than what a home UPS has. Should we lose AC power or not have it in the boondocks, the house batteries continue to provide DC power for our RV lighting, DC television, radio, propane heater ignition and fan, water pump, as well as providing the electrical controls and automatic ignition for the refrigerator and hot water heater in relatively new RV appliances.

All that is needed to provide UPS capability to an RV then is an inverter to turn the house battery DC into AC. Voila! UPS is created in a big way. My UPS power requirements are very simple. I only need to provide power to a laptop computer and portable printer and/or to charge their internal batteries (their own UPS system of sorts). Sometimes we will use our DC television and power the satellite receiver with the inverter. Our little inverter was purchased at Radio Shack for just a little over $100. It provides continuous AC power up to 220 watts and 300 watts for up to 5 minutes. It came with a cigarette lighter type connection that we plug into the TV signal amplifier that also has a cigarette lighter auxiliary outlet. We only plug the little inverter in when we need it in the boondocks or under way in the RV to use our GPS mapping system for hours at a time. With short trips of a little over an hour we simply let the internal laptop PC batteries handle the job.

When underway, the RV engine alternator provides power directly to the engine starting battery and house batteries thus bypassing the converter and directly charging the batteries. It is the house batteries we are using, through an inverter, underway to provide the input AC to the laptop, which in turn provides DC power to our DelorMe GPS. We could provide the AC by firing up the generator while running a computer and little else. We would definitely be using a lot of fuel relative to the electrical product produced while making much noise and not doing the generator any good either. Enough said?

I hope it is now obvious that getting and keeping the house batteries charged for most
power needs is the challenge. Many RVers don't know the main RV engine will charge the
batteries much faster than most RV converters will using the generator, and I certainly am
not advocating doing that. The problem is that the typical MagneTek converter can and
does provide 40 to 50 amps of DC power to the RV appliances and lights, but provides
very little to charge the batteries. Most have a simple resistor in the charging circuit to
control the charge rate. Typically, about 12.4 volts is supplied to the batteries for
charging. This will not cut it. The RV engine initially provides about 13.2 volts but it
drops down quickly to a much lesser voltage. These engine alternators and their regulators
were designed to replace the power used during starting the engine and then taper off
quickly. Some newer RV power converters have more sophisticated circuitry and can
provide almost the entire rating current from the converter to the batteries (up to 40 or 50
amps). They do this by deploying circuitry that knows how much the batteries have been
discharged and provides as much as 13.8 volts to the battery. They automatically drop the
voltage down when the batteries start to become fully charged.

The MagneTek 6500 series converters are popular with RV manufacturers. They are
relatively inexpensive and almost insure the batteries are never overcharged or dry up.
This is a severe detriment to RVers who like boondocking.. However, they do sell an
upgrade called a 7300U that is fairly easy to install for about $200. If you remove the
cover of your converter, you will see DC fuses and AC circuit breakers on the top chassis.
The bottom half houses the converter while the top half is for the distribution of DC and
AC. Almost any RVer with a screwdriver and pliers can upgrade their converter to the
7300U. The instructions are excellent. Wires connecting the top and bottom half are
removed after disconnecting the house batteries and insuring that there is no AC input to
the RV. The bottom half simply slides out and the new converter is slid in. Wires are
reconnected per the instructions and you now have at least 40 amps DC available to
charge the house batteries. Also, the original converter probably had only a few fuses and
circuits rated as filtered, because devices such as DC lighting and fans are not sensitive to
electrical noise in the DC circuit. The new converter upgrade comes with all circuits
filtered and electrically noise free. This makes a big difference in TV reception because
turning on fans no longer provides the on screen "snow storm".

If you go this route, be advised that some RV manufacturers (Winnebago) lace the wires
feeding out from the top half of the chassis together and then secure them at the point
where the two chassis meet in the middle with a nylon strap screwed to the chassis. If this
is the case, the bottom half will not simply slide out without getting your hand in back,
taking the screw(s) out and disconnecting the lace from the chassis. After that, it is a
breeze. With this new found battery charging system you will need to pay more attention
to the acid level in the batteries. At least once a month top them off with distilled water
and they should last a long time. In our case we have only two class 27 deep cycle marine
batteries which are in excellent shape after 4 years of almost continuous use. Maintenance
is everything in the life of these deep cycle batteries.

Yes, there are other ways to recharge batteries. Solar panels and their regulating circuits
can provide noiseless and essentially maintenance free charging power. However, I think it
is appropriate to understand that even the large, modern solar panel probably will produce
the equivalent of 15 ampere hours of charge to the batteries per day. That is why it is
generally accepted that one large panel should be used with each house battery. With two
batteries and two solar panels you can expect to have about 30 ampere hours of charge,
which is very significant. However, one would need two solar panels and regulator circuit
having a maximum sunshine converting capacity of about 50 watts each. Good solar panel
systems cost about $10.00 per watt of capacity. Remember, they won't be producing at
all at night and will seldom have the direct sunlight to produce their maximum rated
output. Between the sun rising and falling one can expect about 10 hours of effective
sunlight which will probably produce an average of about half the rated output. Thus one
solar panel would produce, on average, about 1.5 amps for 10 hours or 15 ampere hours
of DC power stored in the batteries. Solar, generator, engine alternator under way and
shore power at campgrounds are all tools to provide electrical collection and storage for
our precious batteries. Any and all of them have their place, use and time in our power
finding and battery storing toolbox.

Inverters come in all sizes with many options. First make sure that it produces a good
clean AC output. Many are made to power heavy tools such as drills, vacuum cleaners,
and high power electrical motors only. Those that are capable of powering sensitive
electronics such as a television, VCR, satellite receiver or PC have extra circuitry to more
closely match the AC provided by a generator or power company. Those appropriate for
an RV, can be purchased to provide as high as 5000 watts or as little as 100 watts of
power. Some RV maintenance shops and retailers will tell you the only way to get a fast
high charge in the batteries is to purchase and install an inverter that also has a very high
rate battery charger in it. That is true, but as talked about earlier it is not the only way.
Often these larger inverters are installed permanently in the AC line and always provide
the AC power to selected outlets in the RV. When shore power is available they also
provide very high charge rates to the batteries, typically between 40 to 60 amps.
Obviously, when the shore power is interrupted or not available, the batteries become the
source of power for both DC and AC through the large inverter. Installation of such an
inverter is complex, always takes up space and must be well ventilated. It should be
installed by a qualified RV electrician or someone very familiar with inverters, and DC/AC
distribution systems.

Before you go out and buy a big inverter consider that Inverters are not 100% efficient.
What this means is that the power consumed from the batteries is not totally reproduced in
equal, relative AC output power. Many lose about 20% of that power, but some are as
efficient as 90%. Also, remember that the DC and AC power are not equal. DC power is
12 volts and AC is around 120 volts. Not considering the efficiency loss with inverters, to
get 10 amps of AC power out of an inverter 100 amps of DC will have to come out of
those precious batteries. That is a lot of current. Most of us are using at least 2 type 27
batteries. At full charge they have about 110 ampere hours in each of them. This means
that a 1 ampere load could theoretically be pulled out of each battery for 110 hours. With
2 such batteries in parallel we have 220 ampere hours available. Even though deep cycle
batteries can be discharged lower than regular starting batteries without hurting them, they
should not be discharged much below 50% or it will rapidly decrease their life. This means
we really have only 110 amp hours available between the two batteries, unless we want to
be replacing them every year or so. Considering inverter inefficiency loss, let us assume
you want to run your color 19î television for 5 hours. A typical RV color TV consumes
about 220 watts of AC power. That means it is drawing 2 amps of AC out of the inverter
(amps = watts divided by volts or 220 watts divided by 120 volts = about 2 AC amps after
inverter inefficiency). Since the battery is providing the real source of the power it will be
drawing 20 amps during that time (remember the 12 to 120 or 10 times as much rule).
After 5 hours the batteries will have been depleted by 100 amp hours. You now have only
10 ampere safe hours left in the batteries and they need to be recharged right now. Those
10 amp hours would probably have been used up from the DC house lights, water pump
and other devices that need DC power to function.

If you really needed a 5000 watt inverter it would be drawing (5000 watts divided 120
volts times 10 for DC input) 416 amps from the batteries. You would need a heck of a set
of wires from the batteries to the inverter to handle that and the 2 batteries would reach
50% strength in less than 15 minutes if they didn't melt down or explode first, which is a
very real possibility. Recharging them from a 40 amp converter/charger would take more
than 3 hours of generator running time. At least for us, we don't think we want or need
that!!!!!!!! Realistically, air conditioning is out of the question for inverter/battery use.
Probably the highest powered device that would receive consideration by Susan & me for
connection to an inverter would probably be our 700 watt microwave oven and that would
need to be used sparingly. Subsequently, I think any inverter having over about 1200 watts
AC output is probably a waste and over-kill for most RVers.

In a boondocking situation, we would rather run our black and white little 9 inch TV that
uses 50 watts of DC 12 volt power. In 5 hours, we would have consumed 250 watts or
about 20 amp hours verses 100 with the inverter and the color TV. Doing that we can
afford to access our satellite receiver on our little converter. The satellite receiver draws
about the same power as the B/W DC television so we would have used up 40 amps if we
needed satellite reception. That can be replaced in a hour of generator time and it can be
timed with the microwave baking a couple of potatoes, running the computer/charger and
vacuuming the RV. We are then ready for another day minus the RV lights and so on.
Don't unnecessarily use DC appliances during this AC power rich time, it will detract from
the DC available for charging batteries.

A laptop computer, being used while charging from an inverter, takes less than 10 watts. I
could use it that way for 12 hours and only consume 120 watts or 10 amp hours from the
battery and still have 3 hours of PC battery left when it is unplugged from the inverter.
One needs to add up all the wattage requirements of devices they use and multiply them by
the hours or parts of an hour they are to be in use and calculate the amount of battery
power that needs to be replaced regularly. Once done you will have a better idea of your
power needs. If they are excessive for your battery storage, more batteries and more
charging capacity needs to be added. The charging can consist of any and all of the ways
discussed above.

This article was designed to assist you in determining what kind(s) of power sources are
appropriate for your needs. Only as much technical data needed to convey the concepts of
the different technologies, costs, limitations and capabilities were included. After you have
decided on what type(s) of power source technologies you want and how much power
you need there are excellent, more detailed information sources from specialists in those
given technologies. The best, most easily readable book I have found is "RVers' Guide to
Solar Battery Charging" by Noel & Barbara Kirkby covering batteries, wiring and
inverters as well as solar. There are excellent Online Advisors available here at this WEB
site to assist in each of the areas discussed in this somewhat generalization of the subjects
and technologies at hand.

.Mel Chaney

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