MEP Generator Output Waveforms and THD

[DD58]

So let me be the “dumb” one in the room. Would a power conditioner correct some of the issues with “dirty power”? Or is there somthing else I can do either at the genset or at the end device. Say my tv or my ductless ac units?


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[Farmitall]

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".

This^^^^^^^^^^^ all the way.

 

[Icesythe7]

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".

Except we are discussing swapping the MEP-831a from an inverter running an extremely clean ~1.1% THD to a normal genhead which increased THD to 11.8% which is a 1000% increase in dirty power lol especially when the IEEE 519 recommends not using sensitive devices on anything higher than ~5% THD, obv what anyone does is up to them and the odds any damage caused would even be noticeable is low it is nice to at a minimum be aware and each person can make their own decisions.

In my particular case I have a nice clean producing 803a but was contemplating getting an 831a for shorter (few hours) power outages just to power lights, tv, router, pc etc and not furnace/ac so I don't waste the fuel/wet stack the 803a, I was just curious when the inverter inevitably dies and a swap is required how much of a loss of clean power would occur given the swap as to me personally I try to keep nice clean "fuel" to all my devices haha

 

[kloppk]

I re-ran the generators all with 3 Kw loads. I'll update the first post with the pics at 3 Kw and THD values at 3 Kw for each.
Time for a

 

[Guyfang]

Prost!

You have never lived, until a Spezial has passed down the Trap! I have a cold one in front of me now!

 

[Dewie38]

Spec for 802 and 803 is not for THD the mil spec is "Any single frequency harmonic shall not exceed 3 percent in the single phase
connections or 2 percent in the 3-phase, 120/208-volt connection." up to the 50th harmonic.

 

[Jeepadict]

Except we are discussing swapping the MEP-831a from an inverter running an extremely clean ~1.1% THD to a normal genhead which increased THD to 11.8% which is a 1000% increase in dirty power lol especially when the IEEE 519 recommends not using sensitive devices on anything higher than ~5% THD, obv what anyone does is up to them and the odds any damage caused would even be noticeable is low it is nice to at a minimum be aware and each person can make their own decisions.

In my particular case I have a nice clean producing 803a but was contemplating getting an 831a for shorter (few hours) power outages just to power lights, tv, router, pc etc and not furnace/ac so I don't waste the fuel/wet stack the 803a, I was just curious when the inverter inevitably dies and a swap is required how much of a loss of clean power would occur given the swap as to me personally I try to keep nice clean "fuel" to all my devices haha

I've known some folks and read many threads where the house load is less than what would keep the 803 from wet stacking. Many have chimed in before to say that for purposes of back-up/stand-by power, short-term light loads are not anything to lose sleep about...these are "prime power" sets, and the wet stacking problems come from prolonged use (not hours, but weeks and months) at a light load. Any concerns about wet stacking from a temporary light load would be easily remedied by adding an additional parasitical load like an electric stove/range during emergency use or by doing a full-load maintenance run after the emergency has passed...this is also taking into consideration that the set has been ran and well maintained before an emergency arises. This thought process (tho some may disagree) is what has kept a few of my friends from downsizing their sets. YMMV

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[Icesythe7]

I've known some folks and read many threads where the house load is less than what would keep the 803 from wet stacking. Many have chimed in before to say that for purposes of back-up/stand-by power, short-term light loads are not anything to lose sleep about...these are "prime power" sets, and the wet stacking problems come from prolonged use (not hours, but weeks and months) at a light load. Any concerns about wet stacking from a temporary light load would be easily remedied by adding an additional parasitical load like an electric stove/range during emergency use or by doing a full-load maintenance run after the emergency has passed...this is also taking into consideration that the set has been ran and well maintained before an emergency arises. This thought process (tho some may disagree) is what has kept a few of my friends from downsizing their sets. YMMV

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I'm trying to talk myself into buying another set and you are ruining it lol

 

[Jeepadict]

I'm trying to talk myself into buying another set and you are ruining it lol

My bad, sorry coach! Hahaha

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[Digger556]

I'm trying to talk myself into buying another set and you are ruining it lol

Just do it.

 

[FarmingSmallKubota]

I'm trying to talk myself into buying another set and you are ruining it lol

You have already made up your mind to buy another one don't try to fool us. most of us know the sickness that is Generators. My wife asks all the time is that one for sale or for the personal collection?

 

[kloppk]

Original post updated with waveform pics and THD for all generators with 3 KW load.

 

[Icesythe7]

Original post updated with waveform pics and THD for all generators with 3 KW load.

No surprises all pretty clean except 831 with gen head I don't think I've ever seen a single cylinder non inverter generator ever under 9% THD, all the crappy throw away portables (by this i mean the typical tube cage honda clone engine with an "insert name of place you bought it from here" sticker on it) I collect for no reason have the same issue.

 

[Digger556]

No surprises all pretty clean except 831 with gen head I don't think I've ever seen a single cylinder non inverter generator ever under 9% THD, all the crappy throw away portables (by this i mean the typical tube cage honda clone engine with an "insert name of place you bought it from here" sticker on it) I collect for no reason have the same issue.

3600 rpm, open frame, box store generators are all terrible. This was a Honda-built unit I tested. I doubt off-brand is better.

 

[Icesythe7]

3600 rpm, open frame, box store generators are all terrible. This was a Honda-built unit I tested. I doubt off-brand is better.
View attachment 904645

they are indeed terrible but easy to buy for like $50 bucks a pop repair them (generally just lack of maintenance) and flip for $200 after a good wash, oil change, re adjustment of governor and avr pot and load test.

 

[nextalcupfan]

I find the timing of this post ironic since I just bought an oscilloscope to test my 803a.

For Reference my Street power waveform.

Generator no load (Red L1 Yellow L3)

50% load (about 6000w)

100% load (about 12000w)

125% load (about 15000w)

All loads above are resistive heaters with a small fan (3000-5000w garage heaters)

And here is the waveform running my house with my 3ton Air Conditioner running.
Approx 35% load


Defiantly a little dirtier with the house load.

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.

 

[nextalcupfan]

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.
1

2

3

4

5

6

7

8


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.

 

[2Pbfeet]

These are great baseline data.

To the point that I think @nextalcupfan's images make, is what the generator is connected to can have a significant impact.

At the end of the day, it is the whole system, generator, wiring, load, that work together or not to give the final power quality under use. A generator by itself, or driving a load bank of resistive load is a baseline for THD in my book. Depending on the wiring and devices making up the power quality may be worse (e.g bad brushed fan motor), or better (due to EMI reducing equipment and circuits). I have seen both. Sometimes the judicious application of EMI filters on noisy equipment can make a big difference to the power quality of the whole system. But it isn't the grid with large numbers of loads averaging out the noise, together with large numbers of transformers, and phase compensators to keep the power quality and impedance within tight limits.

Some of the screamer generators can put out significantly better power with a some adjustment, and perhaps the addition of some EMI snubbers, but many have cheap, in all senses of the word, voltage regulation systems that don't keep tight limits on voltage, harmonics, or response to load changes. In my book, it depends on what you need the power for. 120V to run a $40 electric polesaw in the back 40, pretty much anything will do.

If you really, really need clean power, I think inverters are good, and so is an oversized isolation transformer. $$$

Horses for courses.

All the best,

2Pbfeet

 

[DD58]

These are great baseline data.

To the point that I think @nextalcupfan's images make, is what the generator is connected to can have a significant impact.

At the end of the day, it is the whole system, generator, wiring, load, that work together or not to give the final power quality under use. A generator by itself, or driving a load bank of resistive load is a baseline for THD in my book. Depending on the wiring and devices making up the power quality may be worse (e.g bad brushed fan motor), or better (due to EMI reducing equipment and circuits). I have seen both. Sometimes the judicious application of EMI filters on noisy equipment can make a big difference to the power quality of the whole system. But it isn't the grid with large numbers of loads averaging out the noise, together with large numbers of transformers, and phase compensators to keep the power quality and impedance within tight limits.

Some of the screamer generators can put out significantly better power with a some adjustment, and perhaps the addition of some EMI snubbers, but many have cheap, in all senses of the word, voltage regulation systems that don't keep tight limits on voltage, harmonics, or response to load changes. In my book, it depends on what you need the power for. 120V to run a $40 electric polesaw in the back 40, pretty much anything will do.

If you really, really need clean power, I think inverters are good, and so is an oversized isolation transformer. $$$

Horses for courses.

All the best,

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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[Icesythe7]

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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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.