Genset question on THD

[aarolar]

Where do you go to find out what the THD is on a certain generator? I have one of the troy built 6500 watt generators from lowes and I want to know.

Power Generator | The 625 Watt Portable Gas Generator by Troy-Bilt

 

[Larry Caldwell]

A rotating field generator is pretty close to a sine wave. THD will be minimal. Inverter generators can be more problematic, and their power is often dirtier.

 

[aarolar]

A rotating field generator is pretty close to a sine wave. THD will be minimal. Inverter generators can be more problematic, and their power is often dirtier.

Funny I thought it was exactly the opposite hence the reason why the inverter generators cost 4x as much.

 

[Gunny]

Yeah, I think Larry just accidentally typed the exact opposite of what he meant. Inverter generators do output a purer sine wave.

There a few rotating field generators that put out 5% or less THD, but from what I've seen, they always state it in their ad and in the literature.

You might call Troy Bilt and be able to get an answer

 

[Larry Caldwell]

No, I posted accurate information instead of advertising designed to get you to pay 2x as much for a generator. The advantage of an inverter generator is that it can throttle back the engine while maintaining frequency and voltage, which can give you much better fuel economy. The trade-off is that they tend to be smaller and more expensive. Building a true regulated sine wave output from an inverter is hard. Put a computer UPS on an oscilloscope sometime. You will be horrified. Fortunately, a rotating field generator naturally produces an almost pure sine wave. Any harmonic distortion is usually cause by clipping the wave peak to avoid over-voltage, but once you load the generator that goes away.

If you stick with the expensive inverter gensets no bigger than about 1600 watts, you will get good output for about $1k. If you go to 7 kw it's going to cost you north of $4k, and most of the cost is the inverter. If you go any cheaper, the output is going to be hash and trash. Any cheap rotating field genset will give perfectly adequate power for less than half the cost.

 

[LittleBill21]

No, I posted accurate information instead of advertising designed to get you to pay 2x as much for a generator. The advantage of an inverter generator is that it can throttle back the engine while maintaining frequency and voltage, which can give you much better fuel economy. The trade-off is that they tend to be smaller and more expensive. Building a true regulated sine wave output from an inverter is hard. Put a computer UPS on an oscilloscope sometime. You will be horrified. Fortunately, a rotating field generator naturally produces an almost pure sine wave. Any harmonic distortion is usually cause by clipping the wave peak to avoid over-voltage, but once you load the generator that goes away.




If you stick with the expensive inverter gensets no bigger than about 1600 watts, you will get good output for about $1k. If you go to 7 kw it's going to cost you north of $4k, and most of the cost is the inverter. If you go any cheaper, the output is going to be hash and trash. Any cheap rotating field genset will give perfectly adequate power for less than half the cost.

hasn't been my experience, my WEN sine wave is perfect at 400 dollars, and comparing it to a UPS without indicating what type of UPS it is, is useless alot are modified sine wave.

link to the sine wave, WEN 562��i 2��� Watt Inverter Generator - YouTube

my harbor freight 7000 watt genny is close but not as good in regards, also doesn't hold close to hz like the wen more like 1.5 +/-.
THD on my HF generator is "< 23%" per the manufacturer.

 

[LittleBill21]

this is the HF at 2000 watt load

 

[liberty2701]

View attachment 465120

this is the HF at 2000 watt load

Looks pretty bad.

 

[techman]

Building a true regulated sine wave output from an inverter is hard. Put a computer UPS on an oscilloscope sometime. You will be horrified. Fortunately, a rotating field generator naturally produces an almost pure sine wave. Any harmonic distortion is usually cause by clipping the wave peak to avoid over-voltage, but once you load the generator that goes away.

This is not quite true. harmonic distortion in a small generator is in large part due to cost savings. The geometry of the magnetics plays a large part, and is a cost driver. Things like skewed rotor magnetics can improve distortion, but are more expensive to produce. As stated by others, 3%-5% is typical in these units, and load is not a determining factor. Some loads will improve the distortion and others will make it worse.

Luckily most motors don't care much about harmonic distortion. usually the worst effect is a slight increase in heating, but not enough to worry about. Also most of our modern electronics rectify the AC to DC and convert the voltage and run off a lower voltage. The conversion to DC makes them almost entirely immune to harmonic distortion, so no ill effects. The biggest issue is with devices that might use the AC as a timing signal, like some older digital clocks. They might run faster (like twice as fast or more) if the distortion is bad enough.

The biggest issue with gensets harming consumer products is voltage regulation. Low cost gensets have low cost methods and components for voltage regulation. When a large load is removed (thing refrigerator compressor switching off), the genset voltage can spike up before the voltage regulator adjusts it. This voltage spike can last hundreds of milliseconds, which can kill some devices. A good power conditioner can prevent this, but they are expensive.

Paul

 

[LittleBill21]

Looks pretty bad.

its pretty good compared to several i have viewed