MEP Generator Output Waveforms and THD

[DD58]

Unless you are running it maxed out + the sensitive electronics I wouldn't worry about it, the harmonics as you see with no load is about ~4% which is fine, it probably doesn't start distorting alot until under a 60%+ load, if you want to condition it tho obv will not hurt anything and everyone will have their own opinion so I'd just read each and do what you feel is best.

Ok I’ll have to do some reading. Thanks for this.


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[2Pbfeet]

So for the 831 with the conversion done, put an isolation transformer after gen set and then a line conditioner for each hot leg. Would that be worth it for sensitive electronics?


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I'm not familiar with "the conversion" in a MEP-831A; could you elaborate on what got converted on your unit? New generator head?

In the interim...
If it were me, I would probably start with a pair of these 20A for 240V;
https://www.amazon.com/Suppressor-Single-Phase-Line-Conditioner-JREle-CW4L2-20A-S/dp/B073MCGBP5
one on each side of the hots, connected to neutral and ground.
If you are running the MEP-831A IN just 120V, I would use its big 30A brother;

https://www.amazon.com/gp/product/B08L6QX1RK

They are available from lots of sources and are a good general purpose item to take the edge off of less than perfect power supplies, and they aren't too expensive.

After that, I think it gets into what your electronics are sensitive to / about. If they strongly prefer glitch free power, at 117-123V I might fork out for a true UPS (a pure sign wave version that always runs the load off of the internal batteries) like this one;

https://www.amazon.com/gp/product/B00ESZJ8ME

Again there are lots of choices of brands and vendors, and this is just for illustration, though I have lots of experience with Eaton and they have always stood behind their products, at least for me.

If it is more that your sensitive electronics don't tolerate voltage fluctuations under load switching, I would look at an autotransformer, or ferroresonant transformer, but the latter tend to be real power hogs. I would run the autotransformer as 240V input, either 120 or 240/120 output. They have the real advantage for small generators for always matching the two hots to neutral at a defined voltage (120V), so you don't have to worry about balancing the two legs, or neutral drifting due to imperfections in the neutral.

https://www.victronenergy.com/upload/documents/Datasheet-Autotransformer-32A-and-100A-EN.pdf

If you go the transformer route, I would look at commercial surplus and Craigslist. I see lots coming up for sale pretty cheaply. Given the amount copper in a transformer it is never going to be inexpensive.

Does that help?

All the best,

2Pbfeet

 

[kloppk]

...Unfortunately I read the earlier post about calculating THD but don't really understand, if someone could gently walk me though it that would be appreciated so I can get those numbers too.

Here is a YouTube video on how to do it.
THD

 

[WWRD99]

Here is another test I did where I recorded the waveform while my AC kicked on.

Results are interesting, here are the still images which I believe are in 100ms intervals.
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I'm a little surprised with how much the voltages sags and spikes.
Min was 188v and Max was 270v.
That's quite a shift IMO.

I wonder with the ac compressor your seeing the pulse of the compression in the compressor? Changes in load constantly from it? Curious if a soft start would help some but probably just when it turns on. I don't think there's a way to relieve the pulse of a compressor even a radial one. Then again if it doesn't vary more than what I've read here of 5% it's ok. Great info!!

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[nextalcupfan]

I wonder with the ac compressor your seeing the pulse of the compression in the compressor? Changes in load constantly from it? Curious if a soft start would help some but probably just when it turns on. I don't think there's a way to relieve the pulse of a compressor even a radial one. Then again if it doesn't vary more than what I've read here of 5% it's ok. Great info!!

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Actually I just had a hard start kit installed right before I did the tests.
Compressor is a Scroll type.

 

[WWRD99]

Actually I just had a hard start kit installed right before I did the tests.
Compressor is a Scroll type.

Interesting!! I really don't know much about the electrics of how they are made but I know ac pretty good. Curious if it would make a difference once running but not sure. I have been looking at one for mine but so far the 803 has run it fine but thought it would make it easier for it to get it going! Great info.

 

[nextalcupfan]

Interesting!! I really don't know much about the electrics of how they are made but I know ac pretty good. Curious if it would make a difference once running but not sure. I have been looking at one for mine but so far the 803 has run it fine but thought it would make it easier for it to get it going! Great info.

The hard start kit only helps on startup, once running the draw is normal.
Unfortunately the UEI inrush amp clamp the AC guys brought wasnt up to the task.

However a friend of mine did a hard start install on an Amana 3-ton heatpump and measured the inrush for me.
90 amps without 49 amps with.
Thats a huge difference when you are hooked up to a generator.

 

[WWRD99]

The hard start kit only helps on startup, once running the draw is normal.
Unfortunately the UEI inrush amp clamp the AC guys brought wasnt up to the task.

However a friend of mine did a hard start install on an Amana 3-ton heatpump and measured the inrush for me.
90 amps without 49 amps with.
Thats a huge difference when you are hooked up to a generator.

Thanks for the info!! That is a huge drop too.

 

[2Pbfeet]

Thanks for the info!! That is a huge drop too.

FWIW: Switching to a fully variable speed "inverter" type AC/heatpump practically eliminates in-rush currents making them much more generator friendly.

 

[2Pbfeet]

So for the 831 with the conversion done, put an isolation transformer after gen set and then a line conditioner for each hot leg. Would that be worth it for sensitive electronics?


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Ok, did some more reading on the 831 conversion, and yes, I think that the line conditioners would help with the EMI noise, but the you would need some device that stores energy (e.g. an autotransformer) to help with voltage variations due to load shifts. To get completely clean power, I think that you would need one of the pure sine wave inverter type UPSes that are always on battery.

I don't have a CRT TV or anything that I think is particularly sensitive to power quality, at least that I know of.

FWIW: I have an open frame electric start 5kW/6+kW surge single cylinder diesel Yanmar clone brushless generator that produces power that is acceptable to all of my electronics, though the most sensitive are behind an inverter style battery based UPS. The frequency variation is about 1Hz no load to full load, with only a three to four Hz momentary drop when dumping a 5kW load on it. Even with a secondary muffler, it is loud, loud, loud, but it always starts, and it can be manually started via decompression quite easily.

I guess if I were you, I would get the Mecc generator head up and running and then see if any of my electronics had an issue with it, but I wouldn't be starting a well pump or HVAC with the electronics online without some monitoring.

All the best,

2Pbfeet

 

[2Pbfeet]

Here is a YouTube video on how to do it.
THD

That's a really nicely done video. Thanks for sharing it.

 

[nextalcupfan]

That's a really nicely done video. Thanks for sharing it.

Now if only I could make heads or tails of it....