Dirty Power vs. Clean Power

[kkwong]

The other day I had a chance to look at a hydrogen fuel cell. The rep for the company was telling me that the Air Force is using his fuel cells to power medical equipment which tells me that the sine wave on the AC side (power inverter built in) is very good.

Now for the question: What constitutes clean/dirty power from an inverter? Is it just the shape of the sine wave after the inverter?

 

[zbang]

Now for the question: What constitutes clean/dirty power from an inverter? Is it just the shape of the sine wave after the inverter?

Hmm, just saying "low distortion" might cover it. You could expand that to low or no harmonics from the inverter and good regulation (voltage, freq.) under load. Further expanded to include no zero-crossing notches, no impulse noise or transients, etc. I'm sure I'm missing something important, though.

 

[brian john]

AS stated before I AM NO ENGINEER, But IMO

An acceptable sine wave that allows all equipment supplied by the source to operate with out "issues" and is not damaging to the equipment or distribution system.

But there are standards, just to lazy to go upstairs (I am in the warehouse checking equipment) to check post and I am sure the more diligent members will beat me to the punch from their memories before I could do the research. Happens all the time.

 

[dereckbc]

Now for the question: What constitutes clean/dirty power from an inverter? Is it just the shape of the sine wave after the inverter?

The simple answer is there are two types of inverters:

• Modified Sine Wave (square wave)
• True Sine Wave.

Modified Sine wave inverters are the cheap units you find at box stores for your home PC, DC-AC for RV and some solar applications. As stated they are square wave and things like motors, medical equipment, laser printers, and sensitive electronic equipment with switch-mode power supplies don't get along well with them. This is your dirty power inverter.

True sine wave inverters memic utility power, and in some extremely expensive units like those found in commercial dual conversion UPS units, exceed the commercial utility PQ.

 

[kkwong]

Thank you all for the info...but it also begs the question, if you have a modified sine wave and you run a computer on it, don't you risk the equipment you are using?

Also, most inverters (cheap ones) are not listed for battery charging; is this because of the modified wave as well?

 

[Rampage_Rick]

The simple answer is there are two types of inverters:

• Modified Sine Wave (square wave)
• True Sine Wave.

Isn't modified sine wave a stepped wave?
Square would be no steps (+120, -120, +120, -120)
Modified Square has a delay at the zero-crossing (+120, 0, -120, 0)

What happens if you put stepped wave through a 1:1 isolation transformer?

 

[brian john]

Thank you all for the info...but it also begs the question, if you have a modified sine wave and you run a computer on it, don't you risk the equipment you are using?

A PC? You'd be surprised what a PC runs on....Not as sensitive as most people claim.

 

[kkwong]

I dunno....I guess I thought that if I'm running a computer, the sine wave would have to be fairly regular...like running medical equipment.

 

[haskindm]

I believe that a computer actually operates on DC current. If that is the case, as long as the incoming sine wave is "clean enough" that the transformer/inverter in the PC can create the DC current that the PC will use, it should work fine. It appears that a PC can deal with some fairly nasty power and still work fine.

 

[brian john]

I believe that a computer actually operates on DC current.

Which came first the AC to convert to DC or.......