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What Is Clean Electricity?

Graycenphil

Registered
Last Subscription Date
02/16/2012
I know this has been touched on lots of times, but I am still not too clear on it all.

First, what exactly is bad about the electricity often produced by small generators? Just the varying frequency and voltage, or something more?

What do the power companies do that makes their power so clean, besides super stable frequency?

I had always heard that the Honda inverter genreators made some of the cleanest power, but I hear folks on this forum say the square wave is not good for some motors. Are these Honda generators not so good then?

How concerned should I be? I have also heard computers are just fine, because they make the AC back into DC for their circuits anyway. What about well pumps, washing machines, refridgertors, etc?

FWIW, my well pump failed several months after running it off my generator for two weeks during two seperate storms last year. But the pump was 25 years old, and the pump part ws pretty well shot too (the notor failed, but the pump wasn't far behind) so I'm not necessarily blaming the generator. Any chance they are related?

Thanks.
 

len k

Subscriber
Last Subscription Date
12/12/2018
Well pump ,,,,,,,maybe, although it sounds old.
Transformers, motors, and inductors don't like square waves. It heats up the windings, which if too hot and applied too long deteriorates the insulation.

I don't consider a square wave to be clean power.

Utility power has a very stable frequency. And a relatively stable voltage. Utility generators are so massive/powerful that even what we consider a large load is nothing to their generators (so the voltage barely lowers,, mostly due to the resistance of the utility wire to the transformer). Unless you live in an industrial area where companies have massive electrical loads with hi harmonic content (switching 3 phase motor controlers).

---------- Post added at 04:01 PM ---------- Previous post was at 03:54 PM ----------

Also square waves can be mathematically represented as a fundamental (60hz) and series of harmonic voltages all added to gether (120HZ,180,240, 300......).
The higher frequency components can make currents flow thru the bearings of the motors due to capacitance coupleing. This current damages the bearing, to the point of having to replace it. This is a problem in industrial motors also.

I think the overheating of motors comes from the flat top of the square wave, since the voltage is not changing in this portion of the waveform, the inductance of the motor is not helping limit the motor current (V=L di/dt). So current and heat increase.
 

Jack Hottel

Subscriber
Last Subscription Date
01/02/2020
References to dirty power usually refer to distortion of the sine wave. It may have random electrical noise as well as harmonic distortion, which can be seen on an oscilloscope. Large power generators are designed to minimize this, producing a more perfect sine wave, at the cost of more complexity and expense.
Inverter generators make DC which powers an onboard inverter to produce AC. Inverters produce a stepwise approximation of a sine wave which some loads do not like. Again more complex and expensive inverter designs can produce a more perfect sine wave.
Computers and other electronics are typically designed for the world market, in parts of which, power quality is truly abyssmal. They typically rectify to DC and work from that.
Appliances with electronic controls designed for the American market are a mixed bag.
Some refuse to run properly on generator power, though I suspect that is changing as more home standby generators proliferate. Also newer standbys often use electronic governing, which holds the frequency much tighter than mechanical governors can.
As far as your well pump was concerned, if your frequency and voltage were anywhere near what it was rated for I don't think it would have had any problem. Pump motors do go bad, one of their great enemies is lightning, since by their very nature they are ofen the best path to ground. The other is short cycling, as with a too small or water logged pressure tank. Starting is a high stress time and the oftener it happens the shorter the motor's life. At 25 years your pump didn't owe you anything and I don't think the generator had anything to do with it's failure.
Jack Hottel
 

Ed Sparks

In Memory Of
Last Subscription Date
06/28/2015
The biggest enemy of well pumps is leakage of the pump seals to the motor shaft. Out here the water can be very corrosive and when a pump fails it is 90% of the time caused by leakage from the pump seal into the motor housing eating a bearing or shorting the windings.
the other 10% is caused by short cycling or brownouts causing the motor to not run properly. We usually dissect them to try and figure out the cause of the failure.
Do you have a surge preventer on your pump wiring?

25 years is a very good long life for a submersible pump.
I change out a few every year and very few of them make it to twenty years of age.
 

len k

Subscriber
Last Subscription Date
12/12/2018
Electronics that use a switching power supply aren't fussy about using square wave power as they rectify it to DC than use it. I have seen switching power supplies in many computers, vcr, cd players, dvd players.
But I have heard there is a problem with newer switching power supplies that have a active PFC (power factor correction) circuit when they try to run on square waves.
=================

It will likely be hard to find an inverter that ouputs a true sine wave, for any reasonablely large power output.
A couple of practical ways of making true sine wave for lower power are:

1) taditional method like in an audio amp , but that results in a large power loss in output transistors (and resulting heat to get rid of). Not really practical for higher power.

2) a class D audio amp setup , but you would need big inductors (expensive chokes) and capacitors to filter out the distrotion. Not practical for higher power, for weight and cost reasons.
 

Graycenphil

Registered
Last Subscription Date
02/16/2012
Very interesting. So it sounds like you are really better off with a conventional generator than an inverter, despite the much higher price of the inverter. And it sounds like I should be just fine running the house off the MDJE or old Homelite (or the 5CW, if I get it started). Appliances are pretty much all old fashioned, conventional style washer, dryer, fridge, etc.

Ed - I never heard of a well surge protector, but a quick Google search shows they exist. I guess I'll get one.

I've had a few lightening experiences. My first house got hit when I wasn't home. Ruined the cordless phone, but I also had no water. I started poking around, and found no power at the well. So I ran a new temporary wire above the ground. Now I had water, but a big leak in the crawl space. It had cracked a copper pipe under the house. I fixed that and now had very low pressure. After letting it run for an hour or so, I had a wet spot on the ground. Dug down and found a crack in the plastic pipe. Seemed like every time I fixed one thing, there was something else wrong.

In our current house 20 years, and we haven't been hit by lightening. But there is a spot down the hill behind the house where trees have been hit at least six times.
 

len k

Subscriber
Last Subscription Date
12/12/2018
I think inverters are just high priced because they are new and the sales force is good at hyping them up. Even old Onans are a good generator, just make sure the governer is adjusted correctly and moves freely. Voltage output and frequency are proportional to rpm.(hi rpm=hi voltage).

I suspect an inverter's claim to fame is it could be better on fuel consumption. When power demand is down, they can reduce rpm. But I would go with a conventional generator, everyone I talk with, and technical magazines I read, say motors and transformers run hotter on square waves. Not good for an expensive tv that likely already runs too hot.

Also alot of onan's have a twist to the laminations of the windings to further reduce sine wave distortion, the cheap China junk likely lacks this.
 

Joe Romas

Subscriber
Age
76
Last Subscription Date
10/03/2019
Inverter generators have several advantages that may or may not be of concern. They are good for things like camping because the motor speed is controled to be only fast enough to meet the demand instead of the 3600 rpms a common 2 pole unit needs to produce 60 cycles. They are also light weight and small that are additional virtues for camping. They are expensive because of the inverters that are needed to control the voltage and frequency.

Regarding "clean" power. Before it died I used a old dual Tectronics scope to set govenor speed on generators. One probe on commercial power and the second on the generator output and adjusted untill they matched.
On commercial power the wave form was a very slim line and the generator output was a "fat fuzzy" line even though they both had the correct wave form. I would think the shear size of the commercial power grid smooths out the power;)
 

armandh

Sponsor
Last Subscription Date
09/02/2010
SIZE MATTERS

the electrical grid of generators and loads acts as a huge flywheel
to even out small distortions in the wave form.

but since they are not all happening at the same place it is not perfect

a lightning hit will put one hell of a spike in the line [near by]

a well designed generator will produce generally clean power
but a load switching off can produce a spike because the system is small

ferroresonant regulators can smooth the spikes but waste power

a generator large enough to pull the start up load
should run the well pump without damage

be sure the well pump run cap are in good shape

several years ago our local utility company was embarrassed by straight line winds that
showed-up their slack tree trimming efforts with over week long outages for a large number
of very vocal customers.

my mother stayed home with her helper and kept cool with my 7.2 KW generator
lots of heavy extension cords and a good window air conditioner.

at over 3 HP per KW and an over built generator I would put it up against any residential well pump in its power rating

http://www.smokstak.com/forum/attachment.php?attachmentid=10828&d=1156252963
http://www.smokstak.com/forum/attachment.php?attachmentid=19060&d=1179334731
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Last edited:

Power

Registered
Running a square wave thru a transformer will provide a sine wave output.
Transformer has to be derated because of extra heat generated by square wave.
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
...FWIW, my well pump failed several months after running it off my generator for two weeks ... Any chance they are related?
Sure, the generator could have stressed the well pump motor. First question I'd have is what the rating of the generator and well pump motor are? An undersized generator will have too much voltage droop when starting a motor, and this tends to cause an extended start interval during which the motor and its start circuit (capacitor or start winding) are stressed. A 25 year old well pump motor, if 2-wire, is likely a split phase motor as opposed to a capacitor start. Split phase motors draw an alarming amount of starting current - more than a capacitor start motor of equivalent size.

BTW, an inverted based generator doesn't necessarily output a square wave. In fact, I'd be really surprised if it did...

I have an Honda 1000i, and a scope... Maybe I'll check it out...

---------- Post added at 07:38 PM ---------- Previous post was at 07:34 PM ----------

Running a square wave thru a transformer will provide a sine wave output.
Only if the transformer, for some unexplained reason, can't pass the 3rd and higher harmonic content of the square wave...

There are plenty of transformers that work perfectly well on 60 Hz as well as 400 Hz. Or, back in the day, there were plenty of transformers that would work over the 20 Hz to 20 kHz range. So transformers don't necessarily turn square waves to sine waves.
 

len k

Subscriber
Last Subscription Date
12/12/2018
To a square wave input voltage a transformer is basically an inductor that doesn't like to let higher frequencies pass. So the higher frequencies don't get through as much and the waveform looks more sine like , than square like. (Remember it's the higher frequencies that make it look square vs sine.)

Square waves can be mathematically represented as a fundamental (w=60hz) and series of harmonic voltages all added together (120HZ,180,240, 300, 360......).
V=Asin(wt)+ Bsin(2wt)+ Csin(3wt)+ Dsin(4wt)+ Esin(5wt)+ Fsin(6wt).......

The current can be analized as the sum of the individual current at each frequency.
Higher freqencies don't get thru the transformer/inductor as much as the fundamental (60hz). How much just depends on the physical design and materials used in the transformer.

---------- Post added at 08:08 PM ---------- Previous post was at 08:00 PM ----------

Would have to look at it with a scope, but I would supect if you input a square wave to a transformer the output would look square-ish , with just the corners rounded off somewhat.

It also depends on what transformer you are using, audio transformers can pass 15Khz.
Power Xfmers no where close.
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
Square waves can be mathematically represented as a fundamental (w=60hz) and series of harmonic voltages all added together (120HZ,180,240, 300, 360......).
V=Asin(wt)+ Bsin(2wt)+ Csin(3wt)+ Dsin(4wt)+ Esin(5wt)+ Fsin(6wt).......

The current can be analized as the sum of the individual current at each frequency.
Higher freqencies don't get thru the transformer/inductor as much as the fundamental (60hz). How much just depends on the physical design and materials used in the transformer.
Exactly, although a square wave has no even harmonics - only odd.
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
So, here's a surprise - the output of my Honda EU 1000i (Inverter) generator looks pretty sine-like to me...

The picture is no-load. At 1000W there was NO discernable change in waveform.
 

Attachments

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
This double trace shot is Onan JB vs. Mains power.

Onan (YD regulator) gen output (7.5 JB) with a 20% load (top trace)

Mains power (bottom trace).

Inverter waveform above beats them both, IMO.
 

Attachments

len k

Subscriber
Last Subscription Date
12/12/2018
Jim.......Just wanted to show the (almost) general case.
Forgot the exact details (even harmonics)....It's been awhile since I had to calculate the coeficients.

Nice sinewave for the Honda inverter.......thats no squarewave!!!
Would be interesting to see it with 1 or 10 watt load.

The Onan sinewave is a little peaky.

Nice scope.!!

why does the scope make the peaks white?
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
Hmm. Good question. It's an old Tek digital scope - I'm guessing the sample points are closer together on the screen near the peaks, and the camera got overexposed? :shrug:
 
B

BergmanJ

Guest
Jim,

Your Tek 'scope still uses a CRT, which has a parameter of the phosphor called "writing speed": Cameras usually do get "overexposed" on some part of the sine peaks because the electron beam is on the phosphor in that immediate area longer due to the transition through "zero" of the "Y' axis (it's traveling at a relatively slower speed [actually goes from "positive" through "zero" increasing to "negative" - that's why it's called a "sine" function] across that area of the screen, thus able to provide more exitation to a given area of phosphor = makes it brighter).

There's some more to it; but, I've already been long-winded enough!!:brows:

Hope this helps someone to learn something "new".

Regards, JLB
 

len k

Subscriber
Last Subscription Date
12/12/2018
Figured exposure, but since it was a fancy scope thought it might be an option to change colors at a threashold voltage level. Abrupt color change in small pics.

Guess the inverter generators are just like the UPS inverters ,,,,,,, some have sinewave output and the cheaper ones have square.
 

Phil P

Registered
Last Subscription Date
11/24/2013
Hi

That “sine” wave for the Honda is why it is expensive.

The inverters approved for uploading power to the grid are expensive and have a sine wave like the Honda. I have a friend that sells the power from his solar panels back to FPL. Those inverters were quite costly.

Phil P
 
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