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Author Topic: Portable emergency generators and total harmonic distortion (THD).  (Read 659 times)

N8OXQ

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Our radio club is in the process of looking for a new generator for our emergency communications trailer. I found specs ranging from under 5% to 20% THD! We are looking at around 7000 watts rated. All of our radios are run off 12 volt power supplies. Does THD matter? If so, what is an acceptable level? We will also be running laptop computers, printers, monitors, TV and the always important coffee pot.
Thanks for your input.
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KF4HR

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #1 on: October 25, 2020, 08:25:09 AM »

I suspect the THD spec may be referring to distortion of the generators sine wave output (or modified sine wave output).  If that's the case, the lower the THD the better.
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KG4RUL

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #2 on: October 25, 2020, 09:09:09 AM »

Honda EU7000IS Portable Inverter Generator — 7000 Surge Watts, 5500 Rated Watts, Electric Start, CARB-Compliant, Model# EU7000IS

Pricey but quiet and dead reliable.
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K6AER

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #3 on: October 25, 2020, 09:17:16 AM »

THD of the generator output will have little effect on switch mode power supplies and restive  heat devices such as your coffee maker. On transformer power supplies, depending on how the transformer is wound, the frequency output and distortion could make some hum noise. Today's inverter generators this is not much a problem. Inverter generators are quiet for camping but limited to about 3 KW with a few models that are 5 KW but will not be cheap.

Sinusoidal generators have a very low THD for the windings and magnetics can only produce a pure sine wave. The generator output voltage and frequency will vary with RPM. The higher the RPM the higher the frequency output and voltage. Keeping the machine speed regulator clean and lightly lubed is essential.

You mentioned you needed 7 KW. Harbor freight has a nice line of generators in that power range with excellent warranty process. I have one of their Predator series that is about 4 years old and is a backup to the home 15 KW generator. I love the ability to move it with the wheel attchment.

Some things to consider in buying a generator is parts availability, weight and portability, noise level, electrical cable attachment and the ability to fill the unit with gas and oh...Price.

« Last Edit: October 25, 2020, 09:42:01 AM by K6AER »
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VE3HIX

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #4 on: December 08, 2020, 09:19:04 AM »

Sinusoidal generators have a very low THD for the windings and magnetics can only produce a pure sine wave.

This is true as far as it goes, but the common sinusoidal generator also has a voltage regulator that distorts the sine wave badly, less so under load. An oscilloscope will show you either spikes in the waveform as the sine wave rises or falls from the baseline, or an acorn shaped wave.

Although there are some electronics that will not run unless the THD is under 5% such as some new furnaces or almost all uninterruptable power supply (UPS) charging circuits, we have found that a distorted waveform does not seem to affect any ham equipment run continuously on field days.

As an aside, the modified sine wave output of most UPS devices is really a modified square wave, and everything plugged into them still runs properly.

Cheers and good luck,
Bob
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #5 on: February 06, 2021, 07:48:18 AM »

Sinusoidal generators have a very low THD for the windings and magnetics can only produce a pure sine wave.

This is true as far as it goes, but the common sinusoidal generator also has a voltage regulator that distorts the sine wave badly, less so under load. An oscilloscope will show you either spikes in the waveform as the sine wave rises or falls from the baseline, or an acorn shaped wave.

Although there are some electronics that will not run unless the THD is under 5% such as some new furnaces or almost all uninterruptable power supply (UPS) charging circuits, we have found that a distorted waveform does not seem to affect any ham equipment run continuously on field days.

As an aside, the modified sine wave output of most UPS devices is really a modified square wave, and everything plugged into them still runs properly.

Cheers and good luck,
Bob
While that is true to a point, an independent voltage reg supply source ie static or PMG style will not induce load influenced issues into the exciter circuits. 2 small isolation transformers used down stream of a static or PMG excited machine will provide an almost perfect sine wave if that is deemed required.
The major issue with THD & Harmonics is when the natural harmonics of both load & gen aligned. This is where short sighted excitation & voltage reg design rear their ugly heads. The main issue in the walk-in box store EPG world, is the consumer is provided just enough information to make a totally uninformed, improper purchase, for the task at hand. Price point EPG gear is just that.
Cheers
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K6BRN

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #6 on: February 21, 2021, 02:51:35 PM »

"Honda EU7000IS Portable Inverter Generator — 7000 Surge Watts, 5500 Rated Watts, Electric Start, CARB-Compliant, Model# EU7000IS

Pricey but quiet and dead reliable."

And less THD than mains power, to boot.  I use the older, carburated EU6500IS, and it's a gem.

Brian - K6BRN
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #7 on: February 26, 2021, 05:14:27 AM »

And less THD than mains power, to boot.  I use the older, carburated EU6500IS, and it's a gem.
Whose testing gear were you using to see/read THD?
Also do you have an industrial plant w/robots on your Feed line?
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KF5LJW

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #8 on: February 26, 2021, 08:19:00 AM »

Non issue, generator power will be cleaner than utility. Only thing to look out for is make sure the generator is not using an Inverter to generate AC. Stay far away from them.

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KG4RUL

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #9 on: February 26, 2021, 08:36:31 AM »

Non issue, generator power will be cleaner than utility. Only thing to look out for is make sure the generator is not using an Inverter to generate AC. Stay far away from them.

Could you give your reasoning for that statement?  My experience with inverter generators (Honda) is they are electrically quit and dead reliable.
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K6BRN

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #10 on: February 26, 2021, 05:31:40 PM »

And less THD than mains power, to boot.  I use the older, carburated EU6500IS, and it's a gem.
Whose testing gear were you using to see/read THD?
Also do you have an industrial plant w/robots on your Feed line?

Ken:

An oscilloscope with FFT - I have few.   Very handy for checking mains power quality.   

On mains power, flat-topping of the AC wavefore is visually  obvious and quite a few interesting spurs show up.  This varies a little bit with home loads and AC outlet choice - but not a lot.  I've watched this problem develop quite a bit over the last decade.

Plenty of neighborhood switch mode power supplies and inverters out here, both drawing from the mains power grid (like variable speed A/C units and electric car chargers - both very popular out here) and feeding into it - like solar installations.  Use of this technology has expanded geometrically, and as it has, power quality has dropped.

I currently have four generators ( and have had more over the years) at three homes.  Three generators are Honda inverters and one is a mechanically governed, electronically regulated "traditional" generator (Generac 4000XL).

The Honda inverter generators simply work, every time and produce visually perfect waveforms.  There are some higher frequency spurs visible in the FFT, but these have never been a problem.  When I switch (most) of the CA home over to the Honda EU6500is, all of the office loads, computers, lights (LED - very non-linear) and ham station come back on line.  Inverter EMI/RFI noise does not seem to be an issue for radio operations, perhaps because my Astron linear supplies make pretty good low pass AC line filters.  And at the house outlets, the waveform is very clean.

When operating the radio on portable ops, I've run off of the tiny EU1000is and sometimes attach a compact IEPS 12A line filter when operating below 40M.  Noise has never been an issue - electronic or audio.

The Generac 4000XL - an older model from before their breakup/sale and reconstitution, is a pretty good little unit, too, with an OHC engine, full pressure lubrication, a Toyota Corolla compatible spin-on automotive oil filter, adjustable electronic voltage control and a mechanical governor.  THAT pupply is 20+ years old, has given very good service but has plenty of visible distortion in its waveform - always has - nowhere as clean as the Honda inverters.  And the generator head exciter is brush-fed  rather than induction driven (which has even more distortion).  The Generac also burns a lot more gas, though it was quite good for its day.

Out here and in Hollywood, the EU6500is generators have been standard fare for powering Kino lighting (VERY demanding VERY non-linear loads) for MANY years and tests show less than 3% THD.  See link below.  They usually have a pallet of them (and the Kino lights) on a flatbed just over at Manhattan Studios (AKA Marvel) just down the block from me and trundle them over to whatever local on-location shoot they're doing for the day.

http://www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html

 BUT....   CHEAP inverter generators are like anything else.  The Hondas (and I hear the Yamahas, too) work very, very well and provide exceptionally clean power, use little fuel and are RELIABLE.  So... PLEASE do not come back with a reply that says:  "My Harbor freight POS let me down (or works better)", or that a Coleman or other late to the game inverter generator with Chinese electronics ... is not so good because its an inverter, or is better at 1/4 the price, etc. 

I've used generators for years, and the survivors are the Hondas and one (very old) Generac.  Tried the cheapo brands and know just how BAD they can be, when you really need them.  During the recent winter storms in CT, my cousin just walked over to my place and borrowed the little Honda EU2200is to power his fridge, lights and a gas heater blower after his Brand X POS died within two hours of use.  The Honda ran just fine for three days.

I don't know what Dereck's (KF5LJW) bad experience with inverter genertors has been, if any.  I'm going to bet that his site backup needs, if portable at all, are more in the MQ Power class of big diesel generators, that BEGIN at 8KW and go up, far beyond where the EU6500is leaves off.

But I'd like to hear his story, too.

Brian - K6BRN
« Last Edit: February 26, 2021, 05:35:02 PM by K6BRN »
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #11 on: February 27, 2021, 03:35:51 AM »

Brian,
All EPG unit's, have THD & TIF numbers, the question is when/where do these numbers effect the total end product? When there is an alignment of the end products natural harmonics with the EPG gears, mostly only then does this become a end product issue.

During all my years of field work I've seen this issue many times, mostly when many a SCR was on line. However when the load changed via a different on coming PF load, even this small change negated the alignment to the point the end product was no longer effected. 

As you're aware just looking at a EPG's product with an O scope only shows transients. Question is do these effect the end product, or will they combine to produce EPG heating?  Also depending upon the excitation systems design (External or closed) load transients may or may not be reintroduced into the equation. Closed excitation systems are the most prevalent do to cost, and I know of no external  style (battery or PMG style) on small (<12KW) EPG units.

Remember all EPG gear has a KW & KVA rating & unless you have military set all single phase gear is rated at a unity PF (1.0) When small EPG units are used on any load other than a 1.0 PF the KVA rating drops like a rock. When you combine that with a closed loop system, it goes down hill rapidly.

The small EPG industry does a very poor job of educating the consumer, then combine that with box store sales policy's and confusion is the order of the day. My old saying "In confusion there is opportunity" (seems to rule many things these days, laughing).   

Inverter EPG units are good to a point, depending end product requirement. However they are not the be all, many say they are. Their main selling point is dB @ XX distance.

Kenneth
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K6BRN

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #12 on: February 27, 2021, 08:51:28 AM »

Ken:

You can use whatever you like to perform a technical/academic evaluation of any generator to any degree you wish.  Live it up.   But in the end, utility, reliability and affordability is what makes the difference.  And the best determination of this is direct experience.

At 7 KW, the selection of usable, reliable and (cheap) generators is vanishingly small.  Plus, larger units are generally less fuel efficent for loads that are small, relative to their capacity - important in an emergency where fuel is scarce.

I belong to three ham clubs.  All have EmComm capability, two have extensive capability.  They (we) started out using 3.5 -5.5 KW economy generators.  They were severely limited by noise (surrounding areas - parks, swapmeet lots, etc, would not tolerate their presence and we did everything we could to quiet them - bigger muffler, sound enclosures, etc).  This made them unwieldy and caused at least one to continually overheat.  They also burned a LOT of gas.  And their relaibility was flat out poor.  So we "bit the bullet".   All three clubs went to Hondas, and the noise, portability and reliability problems were solved.  Period.  The units still need normal maintenance.  Some have thousands of hours on them - quite a bit for consumer grade units.  All still  are working well.

One member just dumped his economy/Costco generator.  Too big, too noisy, to hard to use, so never saw any "game time".

BTW - my Generac 4000XL is a survivor of those early experiments.  It actually held up well, but needed a noise containment enclosure that weighed as much as the generator and was difficult to transport.

So the question of which generator to get for a ham club EmComm setup?  Here's a few tips.

1.  Rather than buying one large, heavy unit and relying on it for ALL needs, buy two smaller units that are more physically agile and redundant (this IS EmComm, after all).

2.  Start with ONE EU2200is and add a second as needed and as funds are available- they can be paralleled - or used separately for split operating locations.  Plus they are REDUNDANT, pretty much a "must have" for emergency services.

3.  Once a club has this base capability, THEN investigate the luxury of ONE, very heavy, very powerful 7KW generator.  ONE club has a EU6500is and uses it - but it's mostly fixed in place on their very large EmComm trailer - it weighs 276 lbs.  The next step up in reliable power would be a MultiQuip trailered diesel generator, IMHO.

4.  Power quality on cheap generators can be truely BAD.  If I can SEE obvious waveform distortions on an oscilloscope trace and large amplitude broadband noise "shoulders" close to 60 Hz (3-600 Hz) on the FFT, that's a warning, and more than sufficient to say:  "Be Careful!".  Check out the $100, 2-cycle (and popular) Harbor Freight "capacitor voltage regulator" portable generator that was all the rage not too long ago, and tell the forum what you find.  I already know.

5.  Invest in a few, high quality in-line AC noise filters.  They can be relatively small and light (5 lbs) are easy to plug in if there is a problem and reduce conducted/cord radiated EMI/RFI that can impact ops on 160M and 80M, if it happens.

6.  Invest in a few industrial grade, heavy gauge extension cords of 100 feet length (total) minimum.  Many local, public parks frown on generators directly IN the parks and prefer they be placed in the parking lots, usually in a corner away from people.  And any EmComm setup will eventually be leveraged for Field dDay and other public uses.  So get ready.

As always, opinions vary - do what you like.  But this strategy has been evolved over the past two decades and works well for me and my clubs.  We are happy and fully prepared - this has been proven many times.

And I've already given you an example of professional use that contains in-depth analyses of this area, should you actually follow the links in it.

If this were a military/logistics operation, the answer would be very different.  MQ power and similar would be the way to go.  But hams vary in physical ability, means and in application needs and environment.  Think about it.

Best Regards,

Brian - K6BRN
« Last Edit: February 27, 2021, 09:11:54 AM by K6BRN »
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #13 on: February 27, 2021, 11:46:51 AM »

Brain,
Our views seem to be different, as all I have to base mine on are 50+ years of EPG field/Desk experience on small units not sold in box stores, to much, much, larger base load units.

Have a nice day,
Kenneth
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K6BRN

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #14 on: February 27, 2021, 03:55:45 PM »

Hi Ken:

Yes, our views are different (which is just fine) and I suspect our experiences and applications are as well.

Sounds like yours might have been military (or commercial).

As always, do what works for you.

Best Regards,

Brian - K6BRN
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