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Author Topic: What can be run with a square wave?  (Read 3650 times)
boogiethecat
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« Reply #15 on: February 23, 2008, 01:33:42 PM »

Hey Richard,
You're totally right about square wave AC motor drives, they work really well.

The big difference is, as you mentioned, is "high frequency".

Truth is, even pure sine inverters are square wave inverters at heart. But as opposed to simply making a square wave (or modified one) at 60 hz, pure sine inverters AND the big motor controllers create square waves at very high frequencies, usually 50khz up to sometimes even into the megahertz range, and then those frequencies are pulse width (or similar) modulated so that their energy content is a 60 hz sine wave; the high frequency portion is then filtered out either by LC elements in an inverter or in the case of your big AC motors, by their inherent inductance, and the final result is that the load (motor etc that needs to see a pure sine wave)  actually does see a pure sine wave at 60hz, even though the reality is that the sine wave is actually being created by high frequency square waves.  Make any sense?

Heck, it's all in the smoke.  Keep the stuff inside the wires and anything goes... let it out however it happens, and stuff quits working....
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TomCat
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« Reply #16 on: February 23, 2008, 01:39:38 PM »

Jay, I heard you couldn't get that inverter till Jun or Jul because of the imported parts backlog from China


If you need one quick, here's one on the  E place... http://cgi.ebay.com/XANTREX-RS3000-3kw-Sine-Wave-Inverter-Charger_W0QQitemZ250217253616QQihZ015QQcategoryZ41980QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Jay
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luvrbus
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« Reply #17 on: February 23, 2008, 01:47:06 PM »

Jay, my daughter wants one for her S&S and Dan Rowe will have the better price as they have every thing included in the price so she is going to wait till June she said    thanks
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Sean
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« Reply #18 on: February 23, 2008, 02:04:51 PM »

[Comments deleted by author.]

(I misread the post I was commenting on -- my apologies, everyone.)

-Sean
http://OurOdyssey.BlogSpot.com
« Last Edit: February 23, 2008, 02:21:45 PM by Sean » Logged

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DrivingMissLazy
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« Reply #19 on: February 23, 2008, 02:09:18 PM »

Hey Richard,
You're totally right about square wave AC motor drives, they work really well.

The big difference is, as you mentioned, is "high frequency".

Truth is, even pure sine inverters are square wave inverters at heart. But as opposed to simply making a square wave (or modified one) at 60 hz, pure sine inverters AND the big motor controllers create square waves at very high frequencies, usually 50khz up to sometimes even into the megahertz range, and then those frequencies are pulse width (or similar) modulated so that their energy content is a 60 hz sine wave; the high frequency portion is then filtered out either by LC elements in an inverter or in the case of your big AC motors, by their inherent inductance, and the final result is that the load (motor etc that needs to see a pure sine wave)  actually does see a pure sine wave at 60hz, even though the reality is that the sine wave is actually being created by high frequency square waves.  Make any sense?

Heck, it's all in the smoke.  Keep the stuff inside the wires and anything goes... let it out however it happens, and stuff quits working....

Thanks for the technical explanation Boogie. 

Some of the equipment I used to manufacture used the three phase PWM motor drives to convert the 300 or 600 volt DC from a battery bank to sine wave AC for computer systems. I utilized a pi type LC filter to remove the harmonics and get a pure 60 hertz sine wave. Just never really knew all the technical details. The fun we used to have. LOL

Richard
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luvrbus
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« Reply #20 on: February 23, 2008, 02:22:58 PM »

Sean, I have 2- 2012 stacked and I posted they were modified sine replacing them with 1 new Magnum pure sine when Dick can get it for me
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Sean
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« Reply #21 on: February 23, 2008, 02:29:19 PM »

Sean, I have 2- 2012 stacked and I posted they were modified sine replacing them with 1 new Magnum pure sine when Dick can get it for me


Yes, sorry -- I missed the word "modified" when I read your original post.  I went back and deleted my comments after I realized my mistake.  Not soon enough, I see  Smiley

FWIW, I would definitely not try to run an induction cooktop on anything other than a pure sine unit.  For that matter, I wouldn't run any inductive loads on anything but pure sine.  As Gary said, it's just not worth the worry, or even the performance penalty.

-Sean
http://OurOdyssey.BlogSpot.com
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