Home » Public Forums » GMCnet » [GMCnet] Power Inverters
| [GMCnet] Power Inverters [message #34631] |
Fri, 06 February 2009 15:43  |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Does anyone know what the sine wave looks like from an Onan Power Drawer?
Carl S.
'75 ex Palm Beach
Tucson, AZ.
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Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Power Inverters [message #34639 is a reply to message #34631] |
Fri, 06 February 2009 16:29  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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""Does anyone know what the sine wave looks like from an Onan Power Drawer?""
For some reason I really got a chuckle out of that one 
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Power Inverters [message #67148 is a reply to message #34647] |
Thu, 10 December 2009 23:40 |
bukzin
Messages: 840
Registered: April 2004
Location: North California
Karma: 0
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[quote title=Oldrvguybcg wrote on Fri, 06 February 2009 15:40]I'm sure you are already aware of this but I wanted to put my two cents in.
Be sure to measure both with a sufficient load. Unloaded and loaded may look
very different. Does anyone have capability to get a trace image or a scope
camera.
Brian Gleissner
74 Sequoia
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
If you have a scope, get a look at the sine wave and
just take a photo and post it to us.
But I'm sure you thought of that!
Bukzin
1977 Palm Beach
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| Re: [GMCnet] Power Inverters [message #67171 is a reply to message #67148] |
Fri, 11 December 2009 08:34 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Richard,
Don't know if your email refers to mine or not but I will respond. I am in
Sydney and Double Trouble is in Houston.
I don't own an oscilloscope.
Next time I visit Ken Henderson we'll throw his on the Pro Watt SW-2000.
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Richard
Sent: Friday, 11 December 2009 4:41 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Power Inverters
[quote title=Oldrvguybcg wrote on Fri, 06 February 2009 15:40]I'm sure you
are already aware of this but I wanted to put my two cents in.
Be sure to measure both with a sufficient load. Unloaded and loaded may look
very different. Does anyone have capability to get a trace image or a scope
camera.
Brian Gleissner
74 Sequoia
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
If you have a scope, get a look at the sine wave and
just take a photo and post it to us.
But I'm sure you thought of that!
--
Bukzin
1977 Palm Beach
Chico California
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Power Inverters [message #67174 is a reply to message #67171] |
Fri, 11 December 2009 10:02 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Done.
Since we're on the subject, perhaps an explanation of the wave forms we're
discussing is in order:
I presume everyone knows what a standard "line power" 120 vac 60 Hz sine
wave looks like on a Cartesian coordinate graph of time versus voltage -- a
smooth, approximately parabolic, curve starting at (0,0), climbing to
(1/240th sec,170 v), flowing back down to (1/120,0), down to (3/240,-170),
and ending at (1/60,0). The area inside that curve (including the "loops"
above and below the horizontal axis) is the ENERGY represented by that
curve. Notice that the actual voltage, in reference to the horizontal axis,
is at 120 only as it transits 4 points on the curve! By convention, the 120
vac is actually the Root Mean Square (RMS) voltage, a representation of the
ENERGY, NOT the actual voltage, which is continuously varying. The actual
peak voltage in the standard sine wave is 1.414 times the 120 vac RMS
voltage -- the 170 volts mentioned in the curve description.
Because of the physics involved in the conversion of mechanical energy to
electrical energy by rotating a conductor in a magnetic field (or
vice-versa), rotating generators naturally produce the described sine wave.
But when generating an alternating current by electronic means, it's not
easy to create a sine wave; it's far easier to generate a SQUARE wave. That
is, a wave which starts at (0,0), rises immediately to (0,120), holds that
voltage to (1/120,120), then drops to (1/120,-120), holds that to (1/60,
120), and rises back to (1/60,0). As far as ENERGY is concerned, that
square wave curve encompasses the same area as the 120 vac RMS curve and is
there therefore equivalent to that standard "line power" curve.
There's an immediately obvious problem with a square wave vs a sine wave:
The voltage never gets as high -- only 120 vs 170. Since most of our line
powered equipment is to some extent frequency dependent, an inverter
designer dare not change the frequency to affect the encompassed area and
yield a higher peak voltage; he's left only with the wave shape. So, what
he does is the next easiest thing to creating a simple square wave: Create
one which "momentarily hesitates" at zero voltage. That is, instead of
transitioning from (1/120,120) to (1/120,0), the voltage will rise to,
hypothetically, (0,170), hold it to only (1/240,170) before dropping to
(1/240,0) which it might hold until (3/240,0), the drop to (3/240,-170), and
hold that to (1/60,-170), when it would return to (1/60,0). While those are
nominal, not calculated, values, they illustrate that the "modified sine
wave" bears almost no similarity to a sine wave, it does provide the same
ENERGY. I'd call this a "modified square wave" or at best, a "one-step
modified sine wave"
A more sophisticated (and expensive) "modified sine wave" design would
provide additional voltage steps, typically 4 steps. I've personally used
as many as 16 steps in low power circuits. At that level of modification
the sine wave approximation is pretty good. You are not likely to find a
commercial high power inverter with that resolution.
If the "modified sine wave" is equivalent, energy-wise to the standard sine
wave, why is it not "good enough"? All of the ins & outs of that would take
far more space than anyone wants to study, but heres' a brief explanation:
Every waveform can by created by combining sine waves of different
frequencies. Hard to visualize without graphics, but it's true -- just
trust me. :-)
To generate a square wave from sine waves takes a LOT of sine waves of MANY
frequencies. A perfectly square wave (no rounded off corners) would require
an infinite number of sine waves of infinitely high frequencies and every
sine wave of every frequency below that down to the fundamental frequency of
concern (60 Hz). Guess what: all those frequencies except that fundamental
are NOISE. Switching inverters inevitably generate RF frequency noise.
That RF noise is usually somewhat filtered, but it's physically impossible
to remove all of it -- if one did succeed, the only remaining signal would
be that fundamental sine wave, which we wanted but couldn't easily achieve
in the first place. Here, as everywhere, there is no free lunch.
Sorry 'bout all that! I guess I'm spending time on something I understand
instead of getting back to work trying to fix my EFI. :-)
Ken H.
On Fri, Dec 11, 2009 at 9:34 AM, Rob Mueller <robmueller@iinet.net.au>wrote:
> Richard,
> ...
> I don't own an oscilloscope.
>
> Next time I visit Ken Henderson we'll throw his on the Pro Watt SW-2000.
>
>
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| Re: [GMCnet] Power Inverters [message #67222 is a reply to message #67219] |
Fri, 11 December 2009 18:55 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Thanks Matt. During about paragraph 2, it occurred to me that it's simply
not possible to cover all the details completely, with absolute accuracy, in
simple terms, for an audience as broad as ours. So if anyone has quibbles,
they're welcome to revise and improve it. :-)
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
On Fri, Dec 11, 2009 at 7:13 PM, Matt Colie <mcolie@chartermi.net> wrote:
>
>
> You do not really understand something unless you can explain it to your
> grandmother. - Albert Einstein
>
> I think you came about as close as anybody could hope.
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumiere (say show-me-air)
> SE Michigan
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Power Inverters [message #67224 is a reply to message #67222] |
Fri, 11 December 2009 19:48 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Well, Professor, I for one love this kind of explanation.
Larry Davick
The Mystery Machine
----- Original Message -----
From: "Ken Henderson" <ken0henderson@gmail.com>
To: "gmclist" <gmclist@temp.gmcnet.org>
Sent: Friday, December 11, 2009 4:55:06 PM GMT -08:00 US/Canada Pacific
Subject: Re: [GMCnet] Power Inverters
Thanks Matt. During about paragraph 2, it occurred to me that it's simply
not possible to cover all the details completely, with absolute accuracy, in
simple terms, for an audience as broad as ours. So if anyone has quibbles,
they're welcome to revise and improve it. :-)
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
On Fri, Dec 11, 2009 at 7:13 PM, Matt Colie <mcolie@chartermi.net> wrote:
>
>
> You do not really understand something unless you can explain it to your
> grandmother. - Albert Einstein
>
> I think you came about as close as anybody could hope.
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumiere (say show-me-air)
> SE Michigan
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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