Installed 8/30/95 . . . . .Undated 6/20/97 & 2/3/99
Difference in Inverters Multi Stepped vs.Sine Wave Format
Is It Possible To Upgrade An Invertor?
Difference in Inverters Multi Stepped vs.Sine Wave Format
By Charlie Collins > June 1997 (Backhome magazine 2/98) - Mr Solar Newsletter (updated 6/25/97 & 9/1/97)
Stand-Alone Inverters
Stand-Alone inverters convert DC power stored in batteries to AC power that can be
used as needed. Selecting an inverter for your power system based on the maximum load
you will be powering, the maximum surge required, output voltage required, input
battery voltage and optional features needed. High quality stand-alone inverters
are available in sizes from 100 watts, for powering notebook computers and fax
machines from your car to 8000 watts, for powering an entire house or small
commercial operation.
The size of an inverter is measured by its maximum continuous output in watts.
This rating must be larger than the total wattage of all of the AC loads you plan to run
at one time. The size of the inverter can be minimized if the number and size of the
AC loads is kept under control. Wattage of most AC loads can be determined from a
tag or label on the appliance, usually located near where the power cord enters,
or from the owner's manual. If the inverter is expected to run induction motors,
like the ones found in automatic washers, dryers, dishwashers and large power tools,
it must be designed to surge, or deliver power many times its rating for short periods
of time while these motors start.
Synchronous Inverters
The synchronous inverter has one function, which is to change DC power to AC power that
will be fed into the utility grid. A power system with this type of inverter uses the
utility company as a storage battery. When the sun is shining, your electricity comes
from the PV array, via the inverter. If the PV array is making more power than you are
using, the excess is sold to the utility power company through a second electric meter.
If you use more power than the PV array can supply, the utility makes up the difference.
This type of system makes the most sense if you have utility power, because there are
no batteries to maintain or replace, but it has a very long payback period and may not
be cost-effective at today's electric rates. In the past, synchronous inverters required
utility power to operate and could not be used in a remote site, away from utility lines.
Synchronous & Stand-Alone
In 1994 Trace Engineering introduced the SW4024 inverter, a true sine wave inverter that
can operate as a Stand-Alone inverter and a Synchronous inverter at the same time! In a
typical installation, the SW4024 is connected to a 24 volt battery bank, the utility power
lines, a standby generator and the house load center. When batteries are in a charged
condition, the SW4024 supplies AC power to the house from the batteries. If the batteries
become discharged, the inverter supplies the house loads from the utility lines, while
charging the batteries. If the batteries become fully charged by another power source,
such as photovoltaic modules or a wind or hydroelectric generator, excess power may be
sold back to the utility. If utility power fails, the inverter can still operate,
supplying critical loads. If a standby generator is started, it can also supply power to
loads, and the SW4024 will synchronize to the generator and allow loads to be powered
that are too large for either the generator or inverter to supply alone.
Wave Form
Another factor in the choice of an inverter is the output waveform. Inverters deliver
power in one of three basic waveforms: square wave, modified square wave (sometimes
called modified sine wave) and pure sine wave. Utility power is delivered as a pure
sine wave.
Square wave inverters have the lowest cost and efficiency and are not sold
however we do not sell them. The price of
the better quality inverters is low enough to make square wave inverters an unattractive
choice.
Trace 800, 1500 and 2500 series inverters and all Powerstar inverters have modified
square wave output with harmonic distortion of around 40%. They are a popular choice
for a "whole house" inverter because their high surge capacity allows them to start
large motors while their high efficiency makes them economical with power when running
small loads like a stereo or a small light. Unfortunately, this type of inverter may
destroy some low cost rechargeable tools and flashlights, and their waveform will not
allow many laser printers, copiers, light dimmers and some variable speed tools to
operate. Some audio equipment will have a background buzz that may be annoying to music
connoisseurs.
Sine wave inverters
Sine wave inverters have finally become more economical. Exeltech inverters are an
excellent choice for power systems running audio equipment and other electronics
that are waveform-sensitive. Many people have installed large modified sine wave
inverters to run common household loads and an Exeltech inverter to power circuits
running stereos, televisions and computers.
The new Trace SW4024 inverter has a pure sine wave output, plenty of surge capacity
to run large induction motors, and high efficiency to economically run small loads.
All of our inverters supply standard 120 Volt 60 HZ AC power, such as one gets from
utility companies and fuel-powered generators. Most of them can be special ordered
with other output voltages and frequencies for use anywhere in the world. Please
contact us with any special requirement that you have.
Inverter problems
The electronic circuitry in inverters may, in some cases, cause problems with radio
and television reception, noise on telephones and buzz in audio equipment. Sine wave
inverters cause the least amount of interference. Interference can be minimized by
locating the inverter very close to the batteries, twisting together the cables
that connect the inverter to the battery and locating the inverter away from appliances
that are susceptible to interference. All inverters cause interference on AM radio!
Inverters Question: I recently moved to southern Utah from California. I am planning on
building a home west of Cedar City and would like to incorporate solar electricity in it.
I have a couple of questions and would appreciate your input. One of the real problems as
I see it is the conversion of DC to AC electricity. I understand there is a device called a
rotary inverter. however these devices have a very poor efficiency. Is there another method
to change the direct current over to alternating current?
Eric B. , Cedar City
Mr. Solar: Eric, You are correct in your understanding of rotor inverters having a
very
poor efficiency. There has been a tremendous improvement in inverters in the past 15 years.
Todays inverters are made using solid state circuitry. When you operate a inverter and light
a 50 watt AC light bulb then it uses only a small amount of DC power from your batteries.
However when you use the same inverter and operate a 800 watt load then the inverter uses
much more DC power. This is all controlled automatically and the end result is that the
inverter efficiency of power conversion is above 90%.
Todays inverters take direct current from the storage batteries and increase the voltage to
110 DC. Then through pulsation it creates a modified square wave that simulates the sign
wave that your local power company sells you. You can operate electric motors on the modified
sign wave, however you may find a hum on your stereo equipment. Therefore I recommend that
if you desire a 100% clean sound that you connect your sound system to a true sign wave
inverter.
There are several inverter manufactures on the market, however I usually only consider two.
The Trace inverter is the top of the line, and is considered by many to be the work horse
of the industry. They offer inverters from 700 watts to 4000 watts. Their new 4000 watt true
sign inverter is stackable and therefore now you can get 8,000 watts of continues power.
This new one has several built in features that are standard such as an automatic generator
starter, complete digital metering and a built in battery charger. Trace has been offering
a stackable inverter for a number of years and this means that if you want to increase your
power usage you marly add another inverter in line thus doubling your power.
Powerstar inverters are the other one that I recommend. They have a small inverter especially
designed for stand by or cabin usages. These inverters are upgradable. This means you can
start with their small inverter for under $500.00. Then at a later time if you find that
you need more power then you can increase your inverter size by returning it to the factory
and they will increase its' capacity. They make inverters from 400 watts to 1300 watts.
Eric, I realize that this is a brief explanation. If you would let me know of your power
requirements I will be happy to recommend the proper inverter for your new home.
Question:Our Cabin is wired for 110 AC power. We are wondering how we can start
on solar with an economical unit that can be expanded at a later date.
Bill C., St George Utah
Mr. Solar: Bill, now there is a very economical way to start with a small economical
upgrade-able inverter in your system that is completely expandable. You can start with a small
expandable set of nicad batteries and use your generator to charge them. This will give you
ample lights to enjoy your cabin with out the expense of a large battery bank and a very
large inverter. There is a new inverter manufacture making such an upgrade-able inverter
to change your stored DC power to user friendly AC. This inverter comes in various sizes,
400, 700 and 1300 watts of AC power. This means that you are now able to buy a 400 watt
inverter for less than $500.00 and at a later time if you decide that you want more power
all you have to do is return your inverter to the factory and they will increase the power
of your unit to the next size. In other words if at a later date you decide you want to use
more than four 100 watt light bulbs at one time then all you have to do is return the unit
and pay the difference between your invertor and a larger one.
This is an ideal way to start with solar. You will also need a small set of ni-cads
which
are also completely upgrade-able and at any time when you want you can upgrade them to a
larger set by adding to them. You should always consult a solar professional so that you
only buy building blocks that will be compatible in the future with your overall plan. As
you know we feel that it is only wise to use ni-cads as they are the only battery that you
can increase your size at any time as well as being maintenance free. However the original
cost is higher, and perhaps you may wish to save a couple of hundred dollars and install
lead acid batteries.
Bill, now you can have power for lights in your AC wired cabin and when you use your generator
then your cost for this type of set up is approximately $1600.00 using ni-cads. This price is
less than the cost of a large inverter with all the extras on it. Then as the need arises and
you feel that you want to increase your usage you merely upgrade your inverter. If you want
more storage then you add more batteries, or if your want to charge your batteries with solar
then you just add UL approved solar electric panels. As you know we only recommend that you
use UL approved panels which will give you less problems with your insurance.
Bill we have helped install several of these small systems here in Southern Utah and the
owners will be more than happy to show them to you, should you be interested in seeing them
operate please contact me and we will be happy to arrange a visit with a local satisfied
customer.
Hi folks,
There has been quite a bit of talk lately about charge controllers that use
"maximum power point tracking." Home Power Magazine just did an article on one
unit available, and from it I have received a number of requests for info on such
units. So I turned to a friend of ours at Solar Converters, Dan Pringle, and he
gave me a quick tutorial.
Maximum power point tracking is actually a very cool technology. In its simplest
use, it allows you to realize the true potential of your panels.
Your 75 watt solar panel in full sun is delivering 4.4 amps into your 12 volt
battery. This is only, at best, 58 watts (13.2 volts X 4.4 amps) and you paid for
75 watts.
The answer lies in an industry tradition of rating solar panels at their peak
voltage, usually around 17 volts. Thus 4.4 amps at 17 volts gives you 75 watts.
Once you hook up the panels to your 12 volt batteries, the panels match the
voltage, but the amperage stays approximately the same.
A Maximum power point tracking charge controller acts something like a
transformer. It takes power from the panel at 17 volts and feeds it to the
battery at 12 volts. As power in must equal power out (less a little for
efficiency @ about 96%) the 4.4 amps at 17 volts is 6.3 amps at 12 volts.
Note that the above happens ideally under spec sheet conditions, where maximum
output is at about 25 degrees, which is pretty rare for most of our applications.
But there have been reports from one of our vendors showing a 75 watt panel
delivering between 5.0 and 5.9 amps into discharged batteries, depending on
temperature and panel quality. As temperature increases, the process yields a bit
less, but when the panels are cool, like in the winter when we need every amp we
can get, these devices show great promise.
Temperature is the nemesis of a MPPT charge controller. If you are in the hotter
states you may see no benefit in the afternoon, perhaps even a decrease, say 5%,
in charging. But in the off-peak hours, when the panels are cool and the sun is
not direct, your net annualized gain will still be 5 -10 percent higher, but not
as great as in a cooler climate. If you are in the mountains or in a northern
area, gains will be substantial. In Canada, Dan Pringle's test unit at home
routinely gets 30 - 40 % more than a PWM.
There are also some other interesting uses for MPPT devices. Here are a few
ideas.
1) High voltage panel use. If you have to run your array cable a long distance,
it might be more economical to run some of the higher voltage panels available to
keep the wire size down. Or you could wire your panels in serial to get high
voltage and then have the MPPT charge transform it to 12 or 24 volts at your
batteries.
In some cases the higher voltage panels (like the Solarex MST-43MV "Millennia"
series which are 72 volts peak) could be more economical for battery charging
than a number of 12 volt modules. And you can use smaller gauge wire from the
array.
2) Oddball Module collections - Another use for the MPPT controller is using a
number of different modules on one array. Rather than using multiple charge
controllers, the MPPT controller can accumulate all the varying amperages and
provide the batteries with a steady charge.
**NOTE: In discussing this with Dan Pringle of Solar Converters, he points out
that this is a tricky setup. As some panels may have a sort of mini amount of
maximum power point tracking, and the charger could latch onto the wrong amount
and end up charging at less than best rate. Some experimentation will be required
in a setup like this.
3) Better Winter Production - Looking at the specs, it appears that the highest
increase in production will be when the panels are cooler. And in the winter they
tend to be cooler, and we all know that we can always use a little more output in
the shorter days of winter!
So, you ask, where can I get one of these neat new chargers. Well of course, the
first place I'm going to suggest is from us, here at the Do It Homestead.
We are carrying the Solar Converters Inc. Power Tracker controllers. They are now
on the controls page of the on line catalog
(http://www.mrsolar.com/catalogue7.html#pt )
They come in various configurations, and we will have them as part of our
Newsletter sale this month as well.
Right now the Solar Converters product is the only product on the market that
handles voltage converting MPPT. Other units may MPPT but run say, 12 V panels
to 12 Volt battery. Solar Converters Power Tracker can charge 12 V batteries
from 12, 24, 26, 48, 52(Golden Photon), 40(EPV), 52(ASC), 65(Solar Cells Inc.,)
and 72(Millennia) volt panels and they have these units in the field.
I'm going to be installing a Solar Converters Power Tracker here in New England
and will report back over the next couple of months on how it goes. But if you
want to do nothing more than improve your winter production, I'd grab one now as
well.
I want to thank Dan Pringle again for all his help.
As I recall when I was in science class (some 50 years ago) the teacher explained to us the
difference in AC (Alternating Current) and DC (Direct Current). DC has a current flow in
only one direction, while AC rapidly changes the direction of current flow back and forth.
Typical AC in the United States is 60 cycles per second (60 Hz) in other countries it is 50
cycles per second (50 Hz). Each cycle includes the movement of current first one way, then
the other.
The AC wave form delivered by a utility company or a diesel or gasoline generator is that of a
true sine wave. AC is generated as well as motors that use the current - in the case of
generators the armature or rotating coil is forced though the N and S poles and electricity is
generated. The changes in current flow direction are gradual, so a graph of the voltage
through the cycles is a "sine" wave. Sometimes it is referred to as "sinusoidal." This is done
with wind, a hydro turbine, steam turbine or atomic turbine. The motor works on the same
principle - but opposite - the electricity is used to turn the armature and then the motor moves
through pulleys or gears what ever it is required to operate.
To better understand the difference between inverters we are giving you a short comparison of each type.
Sine wave inverters produce an AC output wave form like power produced by the electric utility companies and rotating generators. The sine wave inverter's wave form is characterized by the highest peak voltage and smooth voltage transitions (no square wave components). Such inverters are the most costly of the three inverter types because they contain additional electronics to produce the required wave form.
Modified sine wave inverters are sometimes called "quasi sine wave inverters" or "modified square wave inverters." Modified sine wave inverters generally cost more than square wave inverters because they contain additional electronic circuitry to produce true RMS regulated AC output. Modified sine wave inverters have higher AC peak voltages than square wave inverters, and automatically control the width of the AC output wave form to regulate the output voltage (pulse-width modulation). The shape of the modified sine wave inverter's wave form includes a square wave component. It is stepped in such a way, however, to closely approximate the true sine wave produced by the electric utility companies.
The square wave inverter is a low cost device that produces a pure square wave AC power output. This AC power can be an accurate 60 Hz frequency if it crystal controlled. It does not have the necessary peak voltage to properly operate many AC appliances that contain electronic power supplies (e.g., computers, TVs, and VCRs). The square wave is appropriate when operating AC loads such as resistive heating devices.
We did get some interesting comments from our readers about this however to better
understand why our scanner brunt up an why others are having trouble with certain "so called
sine wave inverters" we decided to run some tests.
We have tested a Beta unit from Heart - this is their new sine wave one. This
is similar to the one that we tested for them some 6 months ago and I must say that it is a pure
pleasure to test such a fine inverter, so quite and clean :-). This inverter is available now for sale in
and am sure that you will enjoy using it as we have during the past months. I
must say that Heart does NOT want to mislead their customers by telling them that it is a sine
wave if it is not and therefore I was VERY happy when our Friend Don Harris of Harris
Hydro came by recently with his FLUKE 95 scope meter and we tested 3 inverters for their
wave format.
We have now tested the following inverters:
As I see it these inverters fall into two main categories:
the High Frequency Switch Mode Design (HFSMD), and the Multi Stepped Design (MSD) inverter with many steps.
The Heart and Exeltech inverters use the high frequency switch mode design which produces a wave consistent with one generated with an armature .
The Trace SW series (up to 52 steps / cycle) and the BP / Vanner ( up to 400 steps / cycle) are both very good inverters for most electrical equipment.
You will note that the following:
high frequency switch mode design inverters.
As you can see it goes without saying that there is a difference in the two basic types of inverter wave forms. Some say that theirs are a true, real, full, even sine wave inverter and NOT a stepped one. Looking at the pictures I am sure that you will see the difference. I am sure you know your equipment will be much happier using the smother type of wave format - as you know this is what your motors designed to use - correct?
Also please note the chart on the inverter comparison which shows the THD along with other valuable information. The Total Harmonic Distortion (THD) is a measure of the sine wave quality and is expressed in a percentage. The lower the THD the higher the quality of the sine wave power.
Warranty
BP - TruSine YES No Yes - 400 <1.75% Constant 36 Months
HEART PSW YES Yes No <5% None 12 Months
EXELTECH No YES No 1.5 - 2% None 12 Months
TRACE SW No No Yes -52 3 to 5% Taper 24 Months
*HFSM High Frequency Switch Mode
**MSD Multi Stepped Design
+ TDH Total Harmonic Distortion (stand alone operation)
It is our feeling and experience that this modern "high tech" equipment is designed for the wave form that the
grid produces and not the bumpy sine wave. We know that their inverter is excellent for many
applications, however you must decide what is the best for you and act accordingly.
DC to AC Inverter Information
By Dave Katz
Written 1995
Inverters
© Copyright 1993 By Charlie Collins From
"Ask Mr. Solar" Column Published November 28, 1993 Daily Spectrum
What is an Inverter(Backhome Magazine)
© Copyright 1993 By Charlie Collins From
"Ask Mr. Solar" Column Published November 28, 1993 Daily Spectrum
Is It Possible To Upgrade An Invertor?
© Copyright 1992 By Charlie Collins From
"Ask Mr. Solar" Column Published 8/6/92 Daily Spectrum
Maximum Power Point Tracking
© Copyright 1999 By Harry Brown From
"Ask Mr. Solar" Column published 11/99 52nd Mr Solar Newsletter