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Author Topic: Portable emergency generators and total harmonic distortion (THD).  (Read 660 times)

RADIOPHONE

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #15 on: February 27, 2021, 04:32:42 PM »

In La-La Land, when Adam 12 and Squad 51 can't quench cancel culture riots/looting...who you gonna call ?

Ghostbusters ?
Naw.  HAM Emergency Command Radio Club will save the day.  Code 3.

Activate! Activate! Roll out the extension cords.  Fire up the generators.

Vroooom!  Vrooooom!  HAM to the rescue.
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KBKZ2105

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #16 on: February 27, 2021, 04:47:12 PM »

Hi Ken.  It's good to have a generator but if it's sitting on concrete, or around it, with re-bar, it, will have (THD).     
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #17 on: February 28, 2021, 03:13:24 AM »

Hi Ken.  It's good to have a generator but if it's sitting on concrete, or around it, with re-bar, it, will have (THD).     
Am I understanding your question correctly? Will THD be present with a generator near rebar? If that's your question then yes it will.  Or are you asking about a shielding question?


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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #18 on: February 28, 2021, 05:49:05 AM »

One question I have concerning this threads topic, why do people use a EPG unit that produces A/C then convert that to DC, instead of using one that produces DC only?
 
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RADIOPHONE

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #19 on: February 28, 2021, 07:09:32 AM »

One question I have concerning this threads topic, why do people use a EPG unit that produces A/C then convert that to DC, instead of using one that produces DC only?

Good question.

Probably because suitable 12v DC generators are not readily available on the market ?

Weight factor ?

Not enough demand to produce/market them ?
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #20 on: February 28, 2021, 09:49:30 AM »

They are simple to build, depending db level at XX distance.  Many belt drive set up's are out there as well.
Or if one is really concerned about THD, just transform a 120Vac unit to 15-19 Vac & build or buy a full wave bridge.  You can use the voltage reg on the AC side to control output.

I built one using a Honda, driving a 100 GM single wire. Depending load demand you can engineer engine speed vs load so as not to over heat the engine. 

 
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KBKZ2105

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #21 on: February 28, 2021, 12:12:17 PM »

Hi Ken.  It's good to have a generator but if it's sitting on concrete, or around it, with re-bar, it, will have (THD).     
Am I understanding your question correctly? Will THD be present with a generator near rebar? If that's your question then yes it will.  Or are you asking about a shielding question?

No sorry my spelling isn't very good.  That was my statement.  A generator sitting on concrete with re-bar will have (THD).
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N8AUC

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #22 on: February 28, 2021, 06:54:40 PM »

I don't think it matters if the generator is sitting on concrete or not. It's an electrical parameter that is in large part, governed by what kind of generator it is, and what its internal circuit configuration is. If you've somehow got a generator whose THD is dependent on what it's sitting on, I'm afraid you have much bigger issues to worry about.

THD is total harmonic distortion. It is a measurement that tells you how much of the distortion of a voltage or current is due to harmonics in the signal.

The simplest way to view THD is as the ratio of the RMS voltage of the total signal less the RMS voltage at the fundamental frequency, divided by the RMS voltage at the fundamental frequency alone.

The reason you want to minimize THD in the output of a generator, is most important if you're driving a load that has a power transformer as its input. Transformers that are wound on a magnetic core, all have a magnetic resonance frequency that is governed by the dimensions of its core, the type of material from which the core is made, and the construction method used to build the core. Transformers designed for use at lower frequencies (like 60 Hz) are much larger and heavier than transformers designed for use at higher frequencies (like 400Hz). Weight minimization is why many aircraft have 400Hz AC electrical systems, because the transformers are lighter in weight. If you feed the transformer with a signal that contains frequency components (harmonics) that deviate significantly from its design frequency, the harmonic energy is lost as heat in the transformer core. This is in addition to I2R losses caused by the wire in the windings itself. The higher the harmonic content, the higher the energy that heats the transformer core. Done to excess, this excess heat can damage the transformer prematurely.

Inverter generators typically have a higher THD than non-inverter generators, although this isn't always true. This is caused by the switching circuits in the inverter itself. Some inverter generators (like the Honda) have a pretty low THD, because there are extra components in the output network of the inverter to smooth and filter the output waveform, which reduces harmonic content. Cheap inverter generators are often cheap because they omit those extra components to save on parts and manufacturing cost.

« Last Edit: February 28, 2021, 07:07:20 PM by N8AUC »
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K6BRN

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #23 on: February 28, 2021, 09:59:14 PM »

What an AC generator is sitting on has nothing to do with its THD.

As I've said before - ANY cheap generator is liable to a variety of problems, inverter or otherwise, and this includes high THD.

Ironically, THD is fairly easy to control in an AC inverter design, whether its a battery driven inverter or generator driven one.  Honda and Yamaha both have high quality, very low distortion inverter designs.  See the following link for a description of this and comparison to a traditional generator:

http://www.screenlightandgrip.com/html/hdfilmstrip4lg.html

Cheap generators are cheap for a reason - you really do get what you pay for.

Brian - K6BRN
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K6BRN

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #24 on: February 28, 2021, 10:10:27 PM »

OK - I just HAD to share this video of a spectacular (cheap) diesel generator melt down....

https://youtu.be/gwNfhEUqfuY

Skip to 1:30 if you are impatient.  Wonder what it's THD ... was...?

Brian - K6BRN
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KF5LJW

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #25 on: March 01, 2021, 08:05:00 AM »

One question I have concerning this threads topic, why do people use a EPG unit that produces A/C then convert that to DC, instead of using one that produces DC only?

Very simple low voltage 12 volts = low efficiency, low power toys. Imagine if your home used 12 volt DC. That 1500 watt toaster oven would need cables the size of your wrist from your breaker to the wall outlet. That electric water heater or cook-top would need cables the size of your leg. Forget air conditioning. Don't even ask about the cables from the utility transformer to your home, there is not enough copper in the world to do that.

So now you have a small gas generator say 5 Kva, At 12-volts the minimum size cable would be 750 MCM, the size of your arm weighing 8-pounds per foot. Need to extend that more than 20-feet requires even a larger cable. Simple 5th grade math.
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KF5LJW

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #26 on: March 01, 2021, 08:08:45 AM »

No sorry my spelling isn't very good.  That was my statement.  A generator sitting on concrete with re-bar will have (THD).

No problem. Anyone who thinks a generator sitting on concrete generates THD is too stupid to be expected to spell.
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NQ3M

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #27 on: March 01, 2021, 09:07:03 AM »

I had often wondered how long it would take some of the forums of eHam to degrade to the level this thread has. People now respond w/o at least trying to understand where the other party is coming from or the subject they are referring to.
Glad I was educated on 12 Vdc wire size, in 50 years of EPG work I never knew how to size DC wiring

Color me gone from here.
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W1RKW

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #28 on: March 01, 2021, 11:57:53 AM »

No sorry my spelling isn't very good.  That was my statement.  A generator sitting on concrete with re-bar will have (THD).

No problem. Anyone who thinks a generator sitting on concrete generates THD is too stupid to be expected to spell.

That's from sitting on concrete with rebar.

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KF5LJW

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Re: Portable emergency generators and total harmonic distortion (THD).
« Reply #29 on: March 01, 2021, 06:40:01 PM »

That's from sitting on concrete with rebar.

You do realize every pad mounted generator in the world sits a concrete pad with rebar right? About as silly as sitting a battery on concrete will discharge a battery.
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