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Registered Member #1749
Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497
I have been planning to build an inverter for a wial now I have several IGBT's from VFD's and I was going to use a rewound MOT but the local hospital called me to recycle an old xray film viewer this thing was huge and heavy but I removed a large 1223VA 117V terroidal issolation transformer would that be more efficient than a MOT? ]img_20141013_125930.jpg[/file] ]img_20141013_125723.jpg[/file] ]img_20141013_125830.jpg[/file]
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Very likely, if the original transformer is designed to be used without active cooling, it will be more efficient - MOTs are awful for efficiency; I use 2 in series to double the area and increase the efficiency.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
1223VA minus abit, works out to be about 1kW transfomer, a MOT is about that, but since it was free, all go. Scrapping microwave ovens give some good thing that might be useful, apart from the transfomer. The transfomer you got, is at USA volatge but is deisgned for low contious use, but it should be a good stepup if xray, but saying that 500mA can kill you, and all you need is the voltage to breakdown the skin layer, so I would be VERY CARFUL WITH THAT TRANSFOMER.
Registered Member #1749
Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497
The ratings are primary 117v 60hz and the secondary is 117v at 10A I am planning on using a 555 timer or better with some way to drive the IGBT's I want to use two fuji electric 25A 1200V IGBT's with 2mfd 1200v snubbers Im not sure if it will be OK to switch semiconductors at 240hz+- ? But I will find out. I want my input Voltage to be 12-48v it is undecided at this time.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
usually the iron core transformers will tolerate higher stress if you switch them at a higher harmonic like 150Hz
why don't you use a class D amplifier design with the transformer as load? I think it should be easily made to get a sinusoid at the transformer input and make the transformer part of the output filter...
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Just a point to note, IGBT's have a fairly high VCEsat, which will hammer your efficiiency, especially at only 12v supply. IGBTs only win out against FETs as the voltage gets well into 3 figures.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
I'd personally choose the toroidal transformer over the MOT. You could wind a third coil onto the toroidal using very thick gauge wire for your primary, then you could place the 2 117V windings in parallel for 20A, or in series for 240V 10A (maybe build it so you can switch between the two).
MOT cores are fairly terrible, there's high losses due to the welds. They draw a large magnetizing current, and when I rewound one for high current and reassembled the core I found that the magnetizing current was even bigger (almost 2A) due to some careless welding. The only benefit is that it's slightly easier to rewind an EI core than a toroidal, but due to the low turns count required for a 12-48V input this may not be an issue.
Both cores should work fine for the application, so the final decision is yours.
Registered Member #1749
Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497
Dr. Slack wrote ...
Just a point to note, IGBT's have a fairly high VCEsat, which will hammer your efficiiency, especially at only 12v supply. IGBTs only win out against FETs as the voltage gets well into 3 figures.
That makes sence I did not think of that I guess I will use a bunch of my to220 IRFZ's that's OK I was looking for ruggedness but efficiency comes first.
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IGBT based 12 to 120v inverter
