MEP Generator Output Waveforms and THD

[kloppk]

In another thread people were interested in how clean the AC output was from various generators as compared to utility power.
Below is a compilation of various AC power source waveforms and Total Harmonic Distortion (THD) calculation results.


Function generator set at 60 Hz. "Ideal" AC waveform.



Utility Power - 2.4% THD





MEP-831A with factory Inverter. No Load- THD 1.1%



MEP-831A with factory Inverter. 100% Load- THD 1.0%






802A No Load - THD 2.7%



802A - 3 KW Load - THD 3.5%





MEP-1030 No Load - THD 2.6%



MEP-1030 3 KW Load - THD 3.0%





MEP-831A with PMA & Inverter Swapped out and using a convention generator head in place of them.
No Load THD 4.1%



MEP-831A with PMA & Inverter Swapped out and using a convention generator head in place of them.
Under full load. THD 11.9%
Strange as the waveform looks cleaner...

 

[Icesythe7]

In another thread people were interested in how clean the AC output was from various generators as compared to utility power.
Below is a compilation of various AC power source waveforms and Total Harmonic Distortion (THD) calculation results.
All tests done with generators unloaded.

Function generator set at 60 Hz. "Ideal" AC waveform.
View attachment 904567


Utility Power - 2.4% THD
View attachment 904573




MEP-831A with factory Inverter - THD 1.1%
View attachment 904575



802A - THD 2.7%
View attachment 904577





MEP-1030 - THD 2.6%
View attachment 904579




MEP-831A with PMA & Inverter Swapped out and using a convention generator head in place of them.
THD 4.1%
View attachment 904581

Perfect and thanks for the results, I figured the 831a would be the cleanest with an inverter and the dirtiest without one since single cylinder engine, however when you get time can you post the 831a under a load aswell as that is obviously when the distortion matters, 3-4% is pretty typical on unloaded single cylinder non inverter generators but under a load where it is harder to maintain a constant engine rpm will show how good/bad it can really perform.

 

[WWRD99]

That's nice to know! Is the 803 about the same sine as the 802?

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[Icesythe7]

That's nice to know! Is the 803 about the same sine as the 802?

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The 803 should be a bit better than the 802(probaly only noticeable under a load as no counter magnetism slowing down motor under no load), what causes the distortion is the engine slowdown/speedup inbetween powerstrokes of each cylinder so generally the less downtime of a powerstroke the more smooth the engine runs and therefore rotor spins xd, hopefully when klopp has time he can put some side by side comparisons up of loaded gensets as that is where it obviously matters since under no load nothing is plugged in anyways.

anything ~5% or higher is generally unsafe to anything sensitive but obv anything near that will probably start taking a little life from the device, so 1-2% under a load would be crazy good and that is why inverters are the best!

 

[kloppk]

... when you get time can you post the 831a under a load as well as that is obviously when the distortion matters,

Added to the original post

 

[Icesythe7]

Added to the original post

11.8%!!! oh lord thats worse than my harbor freight predator 9000 at full load (9.6%), we now know what not to plug sensitive devices into haha...very much appreciate you taking the time to do this I wanted alot of this info for awhile now but only have an 803!

 

[Digger556]

Thanks for the data points! I've been wanting to revisit this and quantify the THD, so you are saving me a lot of effort.

Here a comparison to some other generators and inverters I did previously:

MEP-802a Power Quality (With oscilloscope pics)

Most folks know the MEP units with brushless genheads make clean power. However, I've always wondered how clean. I used a Rigol DS1054Z scope with a Micsig differential probe to do the measuring and screen captures. (So I don't blow up the scope) For baseline reference, here is incoming...

www.steelsoldiers.com

 

[kloppk]

11.8%!!! oh lord thats worse than my harbor freight predator 9000 at full load (9.6%), we now know what not to plug sensitive devices into haha...very much appreciate you taking the time to do this I wanted alot of this info for awhile now but only have an 803!

I'm redoing that test. Will revise original post when I can today.

 

[Digger556]

How did you calculate THD with that scope? I have a Rigol DS1054Z and I think the only good way to do it is export the raw data.

 

[Guyfang]

Historically, Military gen sets have almost always a clean waveform.

 

[kloppk]

Used the scope to do an FFT on the waveforms, measured the amplitude difference between the fundamental frequency and the harmonics. Then run that thru a spreadsheet to calculate THD.

 

[Digger556]

Used the scope to do an FFT on the waveforms, measured the amplitude difference between the fundamental frequency and the harmonics. Then run that thru a spreadsheet to calculate THD.

Okay, I can do that with mine. Thanks!

 

[Icesythe7]

Historically, Military gen sets have almost always a clean waveform.

mep-831a is the cleanest by far, since single cylinder I'm sure that's why they decided to use an inverter...its a shame they are a pita, I am looking to buy one on sunday fully working for $800 (hopefully) and was curious the THD if/when I am forced to swap out the inverter but if it is going to be that high there is no reason (for me atleast) to do the swap for what I plan to use it for.

 

[Triple Jim]

I'd be interested in knowing what devices are sensitive to harmonic distortion. I've run desktop and laptop computers on square wave inverters for many hours with no problem, and a square wave has more than 40% harmonic distortion. Motors generally don't care about a few percent, since they're so inductive that they effectively filter out higher frequencies. In general, electronic devices like computers and sound systems have a power supply to convert line voltage to the DC that actually runs them, and those power supplies are very forgiving.

 

[DD58]

Wow so not bad but not great. I’ll keep this in mind and only run it to 70% won’t run the TVs on it just the fridge and the ac units of need be. I’m going to have to get an 802 and call it a day


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[Icesythe7]

I'd be interested in knowing what devices are sensitive to harmonic distortion. I've run desktop and laptop computers on square wave inverters for many hours with no problem, and a square wave has more than 40% harmonic distortion. Motors generally don't care about a few percent, since they're so inductive that they effectively filter out higher frequencies. In general, electronic devices like computers and sound systems have a power supply to convert line voltage to the DC that actually runs them, and those power supplies are very forgiving.

There is a nice write up here https://electrical-engineering-portal.com/harmonics-influence that will explain the negative effects on multiple different types of devices like even normal motors will run hotter than normal, degradation of fuses etc

It isn't that all these devices will not run on dirty power it is just that it will cause premature wear that is generally avoidable...you can run your car for many thousand miles without an oil change even many years but it will eventually sludge up and destroy the motor earlier than with proper oil changes, like you said the power supplies in pc's/tv's etc are indeed forgiving but no reason to knowingly feed them dirty power unless it is necessary or if your don't care to replace them earlier than needed.

 

[DieselAddict]

I think most items that would be affected to the point of concern have gone out of favor (analog radio and TV being ones that come to mind). I know there are concerns with running sensitive medical equipment on low quality power. All I could say is to follow the manufacturers advice with that stuff.

Now with most things being driven from switch mode power supplies, the probability of damage is pretty much gone.

As mentioned above the main effect is some additional heating. If you aren't running the equipment at its limits there isn't much to worry about.

 

[rickf]

Has anyone ever done this test with the older 002-003 sets?

 

[Guyfang]

Much ado about nothing. If we are powering a 1.4 billion dollar Patriot Battery, or a Hospital using state of the art medical equipment, using Military gen sets, I really doubt that the power is very "Dirty".

 

[Digger556]

Much ado about nothing. If we are powering a 1.4 billion dollar Patriot Battery, or a Hospital using state of the art medical equipment, using Military gen sets, I really doubt that the power is very "Dirty".

My local utility power was more distorted than what my 802a was producing. I consider the TQGs to be "clean" power.