Anybody else have yucky "sinusoidal" wave forms from their Chinese ST head?

[solarguy]

Yeah, intro says it all pretty much.

I put the oscilloscope on the output of the ST head, just out of curiosity, and it looked like crap, not smooth at all.  Analysis of the timing indicated that this had nothing to do with the 6 impulse per second powerstroke which causes flicker (whole separate deal).  It was jagged, peaky and "messy" for lack of a better term.

I had the (apparently naive and incorrect) impression that rotating generating machinery normally produces pretty smooth wave forms.

Please note that I have not had any problems from this "messy" wave form.  I am just intellectually curious.

Finest regards,

troy

[mobile_bob]

while i own a couple of st heads i havent checked the waveform or taken one apart yet,but

i wonder if part of the problem is lack of skew in the stator

many years ago i built an old delco generator as a 3600 rpm alternator, complete with slip rings, as the fields were in the case i took the power off
the slip rings from the converted armature/rotor.  The unit had no skew and when checked produced a ragged waveform, basically there was spikes/dips in the waveform everytime the slots went thru the field.

as opposed to:

later i converted an old delco truck alternator, this one had a 4 pole rotor and a skewed stator, i rewound the stator and took single phase ac off of it
when connected to the scope it produced a very clean and properly formed waveform without all the glitches of the early machine.

in operation i couldnt tell the difference in the two, exept the ragged own had a higher surge capacity, easily starting a 3/4hp bench grinder

i suspect that most loads would not be effected by the power of an ST head, especially intermittent loads such as most household appliances.

most modern electronic devices have their own switching power supplies and are well filtered and shouldn't care much about the ST power
quality i would think.

bob g

[GuyFawkes]

You've just touched on an example that I picked in another thread. So...

1/ I'm not a sparky, but I have put my scope on the mains power many a time and never seen anything approaching a clean sine wave.

2/ Don't let your "impression" of what you think things should be lead you into a "decsion" that something is wrong, ten seconds before you hooked the scope up I bet you were happy... 

3/ Take a pic and let those members who work with AC have a look and offer a professional opinion. Then go by what they say, not what

[GuyFawkes]

This reminds me

here in the UK we have 220 VAC mains @ 50 Hz

my old hitachi scope (with standard probes) will max out the display on mains, so I thought "aha" and used a small transformer (lazy or what) and mentioned this later that night to a sparky who came around to visit, "so" he says "were you displaying the ac waveform, or the ac waveform after a transformer has altered it?"

oops

tried it again with a resistor and got a noticeably different, but still not pure sine, ac waveform.

so it ain't what you measure so much as how and where, get the how and where wrong and you ain't measuring what you think you are measuring

[BruceM]

Another thought- make sure you are looking at the waveform with only a resistive load (lights, heaters w/o fan, etc).  I'm very interested in your findings!

Best Wishes,
Bruce M

[Doug]

This actualy normal for a small machine like this. That much said it could be better....
I haven't scoped an ST head but I have a fairly good idea what people who do are seeing.
The wave form tends to have jagged saw tooth like features, and is a little peaky.

Causes:
Differences in the magnetic flux in the air gap as the rotor pole faces cross over sections of copper and air where the density is lower and high density areas at the teeth.
Some machining tolerences aren't as tight as they could be causing higher leakage of flux in the air gap between poles in the rotor.

There's not much you can do about this but then again its not a realy big deal. When its loaded with resistive and reactive loads it actulay smooths out a bit...

Doug

[europachris]

Martin has scoped his R195/7.5kW setup at 5kW resistive load.  Not a very pretty wave at all.  Here 'tis:  http://martin.nile.googlepages.com/  Scroll down a ways and you'll find the pic.

I'll scope my R185/3.2kW Markon 2-pole setup next time I fire it up and see how a high quality 'consumer grade' brushless head does by comparison.

We can certainly do better, but it will take a $1500 Marathon Lima MAC series 5kW head to do it, but these babies have a separate brushless exciter built in and skewed rotors.  Very nice.

Chris

[Doug]

Thats actualy better than I was expecting....
I scoped a couple of motors and alternators (other assorted machines as well ) in college. Most of these were about on par with the photo posted. I do recall one alternator on what was called a "Universal machine" for lab work used a one coil per slot layout and I could actualy count the slots perpole on the scope trace.

Small, cheap, ugly, but simple!

Doug

[listeroidsusa]

I ran a waveform on my tektronix scope and even on commercial power there is distortion, probably because I have some neighboring plants with tig welders, vfd's, and other devices. I've also got some lighting circuits, well pump and refrigerator runing single phase off of my 208 3 phase. I've got all kinds of power in my shop, 5, 6, 12, 24, 90, 180, and 300 vdc, as well as 115, 208, 240, 380, 480, and 575 3 phase.  In a time past I wound motors and repaired industrial electronic boards.

Mike

[solarguy]

Martin's website was a fascinating read.  Amazing how many hobby casters are involved in this whole alt. energy thing.

Back on topic, Martin's oscilloscope trace looks twice as "neat" as mine did. 

Note to Guy, I was never really dissatisfied with the ST head, before or after the o'scope, but was curious what makes for a pretty sine wave and what screws it up.

Finest regards,

troy

[mjn]

Here is the image that Chris was referring to:


My scope is a pretty poor 25 year old portable 10Mhz scope, which adds its own 'flavor' to the waveform. (a 10 mhz square wave looks like a sine wave) In theory this is slow enough that the scope should not be distorting the waveform that much).

I have another picture of the waveform taken with no load. The picture is a lot more jagged with little bumps.   I'm away from home right now.  I'll post the picture when I get home this weekend.  When I originally hooked up the scope, I did just as Guy did and looked at the output from a 12V step down transformer.  Later I hooked directly to the line to take this picture.

The only problem that I have noticed with the power is that the ceiling fan in my house makes more noise when I'm on generator power. 

[mjn]

Here is the picture I took with no load on the generator. 

Sorry for the blurry picture.  Now I remember why I didn't upload it earlier.

Martin

[fattywagonman]

Maybe you're already considered this but you could always clean it up with a CVT...

[BruceM]

I"ve never seen a small (3-5 KW) CVT.  Do you know of a source?

[solarguy]

Mine doesn't actually cause any obvious problems, so it is unlikely that I will do anything about it.  Just out of curiosity, how efficient is a transformer of the type mentioned, assuming that it is appropriately sized, etc.?

Finest regards,

troy