DIY VFD Update

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Just in case anyone is intrested, here are some pix of  my 100 amp DIY VFD
being
assembled. As soon as time permits i will post a video of the VFD in
opperation.
I still have to make a remote control pannel.

http://members.cox.net/azotic/inv1.jpg
http://members.cox.net/azotic/inv2.jpg
http://members.cox.net/azotic/inv3.jpg
http://members.cox.net/azotic/inv4.jpg
http://members.cox.net/azotic/inv5.jpg
http://members.cox.net/azotic/inv6.jpg
http://members.cox.net/azotic/inv7.jpg

Best Regards
Tom.




Re: DIY VFD Update


On Fri, 15 Aug 2008 03:19:17 -0700, with neither quill nor qualm,

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Cool!  It looks like the project is really coming together, Tom.

--
Challenges are gifts that force us to search for a new center of gravity.
Don't fight them. Just find a different way to stand.
                                                       -- Oprah Winfrey

Re: DIY VFD Update



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The big power modules mounted on the heatsink - what are they and what
did they cost?

Thanks,

Joe Gwinn

Re: DIY VFD Update



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They are dual IGBT transistors also known as a GTR module. Basicly
they are 2 NPN transistors conected in series to form a half bridge which
means the are capable of switching both + and - DC power back and forth.
You get AC output in the form of a square wave as a result. You can achive
the same result by using 2 individual IGBTs.

The GTRs i am using have the capacity to switch 100 amps at 1200 volts,
they have built in free wheeling diodes which cuts down on the component
count. I bought these GTRs on ebay for $8.00 each, shipping was $7.55.

Best Regards
Tom.






Re: DIY VFD Update



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So each module is a a half-bridge containing two IGBTs plus some
frewheeling diodes.  What make and model?


The reason I ask is I'm designing a homebrew impulse magnetizer, to be
built around three 2900 microfarad 350 volt computer electrolytics I got
surplus somewhere (no longer recall when or where).  In this case, the
current is all surge and no continuous, and the modules I'm considering
are Diode-SCR half-bridges.  (IGBTs don't seem suitable.)  The circuit
protects the electrolytics from reverse voltage by returning the
inductive kick to the capacitor with the correct polarity to charge it.

The surge current will be something like 3000 amps for 10 milliseconds.  
I'm still working out the details, such as how big a surge current is
needed.  Even if the SCRs and diodes are happy, the capacitors have a
limit as well.

I got the circuit idea from an expired US patent, 4,258,405 to
Steingroever.  Steingroever uses Mercury-pool ignitrons, as nothing else
will withstand the currents necessary to use pulsed magnetic fields to
form metal.  <http://en.wikipedia.org/wiki/Ignitron

For more information on metalforming, see US patents 5,586,460;
5,684,341; 5,813,264; and 5,953,805.  Also see the website of Dr
Steingroever's company: <http://www.magnet-physik.de/ .

They use very high voltages and small inductances, to yield very short
pulses, the better to create the eddy currents against which they push
to apply force to the metal being formed.

For our purposes, and with some care, the ignitrons may be replaced with
big SCRs.  But even the biggest of SCRs is a wimp compared to a big
ignitron.  

Richardson Electronics still offers ignitrons and hydrogen thyatrons:

<http://industrial.rell.com/et_ignitrons.asp

<http://industrial.rell.com/et_Hthyratrons.asp

But they tend to be expensive.


Joe Gwinn

Re: DIY VFD Update



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I am using Toshiba MG100Q2Y51A GTR modules.

Intresting project your working on, there are IGBTs that might work
for your application but there going to be pricey. I did see some 600 amp
IGBTs on ebay this week that were reasonably priced. If your going to
buy some on ebay make shure you ask the seller if you can return them
should they be blown. Some sellers are selling units they claim are tested
but they are not. I had to return some that had blown gates and would not
fully turn off.

Best Regards
Tom.




Re: DIY VFD Update



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I'll look these up.

 
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My original instinct was that SCRs were better suited than IGBTs for
this application, but I have not really dug into the issue.  I'll get
the datasheet for the Toshiba IGBT and think about it.


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Good point.  The price differential probably makes it worthwhile to eat
the expense of a few bad devices, if it comes to that.  But I would buy
more units than strictly needed.  And to cover lab accidents.

Joe Gwinn

Re: DIY VFD Update


azotic wrote:
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Joe is right, IGBTs are not well suited to high current pulses.
    You have to keep them fully saturated, or the current hogs
to the hottest part of the die, in a positive-feedback death
spiral.  The design of the FET to BJT drive scheme built into
the transistor only allows so much base drive.  SCRs are better
at this, as increasing current increases drive to the internal
transistor-like structures it is built from.  You could also use
a bank of parallel MOSFETs, although the 350 V supply requires
using more of them.  MOSFETs are so cheap, you might be able to
buy a couple dozen new for what a used monster SCR or BJT would
run you surplus.  MOSFETs are quite tolerant of pulse overloads,
too.

Jon

Re: DIY VFD Update



Don't you want a 3 phase sine wave output?
SE

azotic wrote:
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Re: DIY VFD Update



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A sine is not nessesary to run a 3 phase motor.

Best Regards
Tom.




Re: DIY VFD Update


azotic wrote:
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Does that mean that you just use a variable freq square wave, or is it
like the commercial VFDs & use PWM on a carrier?

Bob

--
Nota for President

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Any progress on drawing up a circuit diagram?

RWL


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Thanks, i plan on adding a jog and brake feature to the design
which i think will be handy to have.

Best Regards
Tom.




Re: DIY VFD Update


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http://members.cox.net/azotic/inv1.jpghttp://members.cox.net/azotic/inv2.jpghttp://members.cox.net/azotic/inv3.jpghttp://members.cox.net/azotic/inv4.jpghttp://members.cox.net/azotic/inv5.jpghttp://members.cox.net/azotic/inv6.jpghttp://members.cox.net/azotic/inv7.jpg
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Just wondering, does the little bridge rectifier on the lower right of
picture inv6 provide the power to the much larger switching elements
on the heat sink.  Is the large white cylinder in the last couple of
pics the rectified DC filter cap?  What do you calculate the ripple
current in the DC filter cap to be?

Carl

Re: DIY VFD Update


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Are you planning on making and selling the PC board?
Components?

Wolfgang

Re: DIY VFD Update



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The thought had crossed my mind. If i do decide to sell circuit
boards for this project there will be a parts placement printed on
patern on the top side. I am thinking that building a board will work
like painting by the numbers, you would place the parts U-1, D-3 etc.
into the board with the locations marked U-1, D3, etc. then just
solder them in place.

Best Regards
Tom.




Re: DIY VFD Update


On Fri, 15 Aug 2008 19:07:53 -0700, with neither quill nor qualm,

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Au contraire, mon ami!  I strongly suggest using sockets as you did.

--
Challenges are gifts that force us to search for a new center of gravity.
Don't fight them. Just find a different way to stand.
                                                       -- Oprah Winfrey

Re: DIY VFD Update



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Oops, all the ICs will be socketed.

Best Regards
Tom.




Re: DIY VFD Update



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The output of the bridge rectifier is connected directley to the large white
filter cap ( 2700uF @ 420Vdc ). I didnt do any ripple calculations for
the HV dc buss since motors and transformers dont seem to have problem
with ripple. However there are seperate regulated power supplies for the
logic and gate drivers where ripple would be a huge problem. The large
white filter capacitor at the end of the buss just happened to have the
same center to center hole spacing as the GTRs which makes it possible
to mount it right on the buss bars and eliminate the additional wiring that
would be needed if i had to mount it elsewhere.

Best Regards
Tom.




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