7/30/2019 The Difference Ups & Inver

1/5

The difference's between an inverter and a UPS are as follows

1) CHANGE OVER TIME: An off-line ups (the standard) switches to the batteries in 3 to

8 milliseconds, after the main power has been lost.

The typical Inverter changes over in about 500 milliseconds

2) SIZE: Off-line UPS's go up to about 2kVA

Inverters go to 16kVA, 3 phase(what i could find browsing)

3)VOLTAGE REGULATION: UPS's have automatic voltage regulation (AVR) set on

average at 220v

Inverters output voltage is the same as the mains input voltage (South Africa = 230V)

An inverter can transform a voltage from say 12volts dc and up to 230v AC.

UPS means Uninteruptable Power Supply. If you use an UPS between your computer,

and your socket in the wall, and experience a power failure, the UPS will act as a batteryand give you some extra minutes work time to save your work, and turn of the machine

properly. Without the UPS your machine would die immediately.

*note: the UPS is NOT a normal battery, so you cant put a battery between your

computer and the mains.

The difference's between an inverter and a UPS are as follows

An inverter simply takes a DC voltage, usually from a battery, and converts it to AC foruse by standard appliances.

A UPS does the same thing, but has added circuitry to charge the battery when AC utility

power is available, and to automatically switch the inverter on when utility power fails.

Inverter Tutorial and Frequently Asked Questions:

Q: What is an inverter?

7/30/2019 The Difference Ups & Inver

2/5

A: An inverter takes DC power (battery or solar, for example) and converts it into AC

"household" power for running electronic equipment and appliances.

Q: How is an inverter different than a UPS?

A: A UPS typically includes the battery and battery charger in one stand alone unit.

However, there are UPSs that use external batteries, and PowerStream makes inverters

with battery chargers, so the differences blurr as features proliferate.

UPSs also can have communication with the equipment that it is powering letting the

equipment know that it is operating on standby, giving it shutdown warning, or

communicating with the human in the loop. Inverters typically don't have thiscommunication.

Q: Why are they called inverters?

A: Originally converters were large rotating electromechanical devices. Essentially theycombined a synchronous ac motor with a commutator so that the commutator reversed its

connections to the ac line exactly twice per cycle. The results is ac-in dc-out. If you invert

the connections to a converter you put dc in and get ac out. Hence an inverter is aninverted converter. For more information about such converters see

http://www.nycsubway.org/tech/power/rotary.html (thanks to Karl W.Berger, PE for this

answer).

Q: What if I want a DC output to run such things as a laptop from a car cigarette lighter,

or telephone equipment at -48 volts?A: Then you want a DC/DC converter. PowerStream has some DC/DC converters just for

those purposes. http://www.powerstream.com/dcdc.htm

Q: What is the difference between sine wave and modified sine wave?

A: Alternating current (AC) has a continuously varying voltage that swings from positive

to negative. This has great advantages in power transmission over long distances. Power

from your power company is carefully regulated to be a perfect sine wave, because that iswhat naturally comes out of a generator, and also because sine waves radiate the least

amount of radio power during long distance transmission.

On the other hand, a sine wave is expensive to make in an inverter, and many sine wavetechniques use heavy, inefficient transformers. The most inexpensive way to make AC is

to switch the DC on and off--a square wave. A modified sine wave is scientifically

designed to simulate a sine wave in the most important respects so that it will work formost appliances. It consists of a flat plateau of postive voltage, dropping abruptly to zero

for a while, then dropping again to a flat plateau of negative voltage, back to zero for a

while, then returning to the positive voltage. This pause at zero volts puts more power

7/30/2019 The Difference Ups & Inver

3/5

into the 60HZ fundamental than a simple square wave does, so it is called "modified sine

wave" instead of "square wave."

Q: Can I use a modified sine wave inverter for my medical equipment?

A: For Medical equipment, oxygen generators, etc. talk to the manufacturer of theequipment. PowerStream inverters are never tested or rated with medical equipment, and

we don't guarantee that they will work to save your life. For such applications please find

inverters that are rated and tested for such applications.

Q: What about square wave inverters?

A: These old-fashioned inverters are the cheapest to make, but the hardest to use. They

just flip the voltage from plus to minus creating a square waveform. They are not veryefficient because the square wave has a lot of power in higher harmonics that cannot be

used by many appliances. The modified sine wave is designed to minimize the power in

the harmonics while still being cheap to make.

Q: How do I know if I need a sine wave, or if I can live with a modified sine wave?

A: The following gadgets work well with a modified sine wave: computers, motor-drivenappliances, toasters, coffee makers, most stereos, ink jet printers, refrigerators, TVs,

VCRs, many microwave ovens, etc.

Appliances that are known to have problems with the modified sine wave are some

digital clocks, some battery chargers, light dimmers, some battery operated gadgets that

recharge in an AC recepticle, some chargers for hand tools (Makita is known to have this

problem). In the case of hand tools, the problem chargers usually have a warning labelstating that dangerous voltages are present at the battery terminals when charging. We

would like to add to this FAQ any appliances that you have had trouble with, or had

success with, using modified sine wave inverters.

Q: Why do I hear buzzing on my stereo when using a modified sine wave inverter?

A: Some inexpensive stereos use power supplies that cannot eliminate common-modenoise. These would require a sine wave inverter to operate noise-free.

Q: Why don't I measure rated voltages when using a multimeter on my modified sine

wave inverter?A. The rated voltage is an RMS (root mean square--they square the value to make sure it

is always positive, then average it, then take the square root of the average to make up for

having squared it in the first place) measurement. Most multimeters are designed to givecorrect RMS readings when applied to sine waves, but not when they are applied to other

waveforms. They will read from 2% to 20% low in voltage. Look for a voltmeter that

braggs about "True RMS" readings.

Q: How should I select the right size inverter?

A: First add up the power ratings of all the appliances, then buy the next larger inverter!

At least that is the simple answer. Note, however, that some appliances, such as table

7/30/2019 The Difference Ups & Inver

4/5

saws, refrigerators, and microwaves have a surge requirement. PowerStream inverters are

designed to supply such surges, but since every appliance has its own requirements

sometimes you will need to get a bigger inverter than you would otherwise think. Notethat the inverter isn't the only consideration when you are pondering the mysteries of

startup surges. The battery must also be able to supply the surge power, and the cables

must be able to supply the increased current without dropping the voltage too much.

Q: How is a microwave rated for wattage?

A: When you buy a microwave oven you want to know how intense the microwave fieldis, not how much the oven draws from the wall. So a microwave oven that boasts 600

watts on the box, will have 1200 watts on the boilerplate in the back. Don't be fooled!

Q: Are stereo amplifiers rated the same way?A: Stereo manufacturers are bigger liars than politicians. Some times they use peak

output power (milliseconds), sometimes they use power drawn from the wall, but often

they just look at the competition's carton front and add 10%. However the truth is

available: look at the boilerplate sticker, which has been evaluated by UL.

Q: Why do I need such humongous cables to the battery when a small cord takes the ACoutput fine?

A: Power is volts times amps (Watts = V x A). So if you have a lot of voltage you don't

need many amps. Roughly you need 12 times as much current from the 12 volt battery asyou need from the 110 volt AC outlet. Current is what causes cables to heat up, not

voltage. That is why they use thousands of volts in power transmission grids. The thing to

do when you have lots of current is to lower the resistance of the cable. The larger the

wire the lower the resistance. Think of the cable as a water pipe. A big pipe (wire) cancarry more water (current or amperage) with less pressure (voltage), and will present less

pressure (voltage) drop from one end of the pipe to the other.

Another consideration is how far the cable has to run from the battery to the inverter.Long cable runs are expensive, either in copper or efficiency, or both.

Q: Why would you use a 24 volt inverter instead of a 12 volt inverter?A. At a given power rating a 24 volt inverter will need half the current as a 12 volt

inverter. This makes the entire system more efficient, and since high current transistors

are expensive, the inverter will be cheaper.

Q: Should I use aluminum wire, or must I use copper?

A: Aluminum is cheaper and lighter, but it also has higher resistance for a given guage,

and is more difficult to connect to. If you are an expert in such things, or know one, andneed the advantages that aluminum gives, go ahead. If not, why not use the best

conductor, copper? (Silver is slightly better, but it is cheaper to use a larger diameter

copper). To compare the two look at our web pagehttp://www.powerstream.com/Wire_Size.htm .

Make sure to use good insulation, 90C rated or better. Also, running two sets of parallel

wires instead of one can cut down on the wire heating due to more surface area.

7/30/2019 The Difference Ups & Inver

5/5

Make sure to follow all applicable electrical codes. Inverters must be grounded properly,

and treated with respect, since they put out potentially lethal voltage. A lot of smartpeople have worked for 100 years to develop rules which will keep you out of trouble if

followed. These rules are called the national electrical code, and your friend the

electrician has it memorized (or knows where to look it up).

Q: Should I use a laser printer with an inverter?

A: Only if you must. Laser printers use up a surprising amount of power (due to theheated rollers), and will discharge your battery faster than you expect, even on standby. If

you do, make sure the inverter is rated for the power of the printer plus computer plus

monitor. It doesn't do any good to have your computer brown out as soon as the the

printer starts to print. Ink jet printers, on the other hand, use a surprsingly low amount ofpower.