Home brew 3 phase VFD ?

I think that most people wanting to build 3 phase sources build the rotary converters.

If you were going to build a 3 phase VFD I would suggest taking a look at the Freescale DSP56F807 microcontroller. It has a great PWM generator designed for stuff like this. I have used (underused?) the PWM generator for DC motor drives, and it is really capable.

Good Luck, Bob

Thanks for the tip, the rotary phase converters don't have the flexability i want and are to noisy for me. I was thinking about using one of my old note book computers interfaced to some power semiconductors and hopefully end up with a user programable vfd.

Best Regards Tom.

Do not underestimate the cost of this project, and you will end up with something rather substandard. But it is fun.

For example, single phase input rated, 1 horsepower VFDs can be bought on eBay for about $47 plus $12 shipping. It is hard to beat that.

i

Got an example of that price point, Igor?

Can he put several of them in series to up the HP?

Do not underestimate the cost of this project, and you will end up with something rather substandard. But it is fun.

For example, single phase input rated, 1 horsepower VFDs can be bought on eBay for about $47 plus $12 shipping. It is hard to beat that.

i

Back when I was working as an electronics engineer in San Jose, California (heart of Silicon Valley) I came up with a design for this. It was a chip which produced variable PWM waveforms. I planned to use power Darlington transistors to go between the CMOS logic chip and the gates of beefy SCRs. I got as far as simulating the whole design in a mixed signal simulator.

Then I found out what the failure mode of SCRs is. About the same as hand grenades. Did I want this in my house? No.

I scrapped the design, never looked back.

Start with your output phase, your "power semiconductors". If you can find some of those that meet your spec at a price point you can live with, that's one thing. I'm guessing that buying a small handful of them will get you a price much higher than an entire VFD made by TECO or someone else.

Igor, I'm still waiting for that $47 1hp VFD new on ebay ..

Grant

Now the power devices will probably be Insulated Gate Bipolar Transistors, but the failure mode is the same. 240VAC Rectifies to over

300VDC and a multi-horsepower drive will need many amps of DC supply capability. I have built some smaller drives and from that my advice is: A) keep a CO2 fire bottle handy. B) always wear safety glasses. C) never leave the room with a prototype energized. D) buy lots of spare transistors and drivers. E) don't try to build with point to point wiring, parasitics will kill it. F) keep a CO2 fire bottle handy.

In the few commercial VFD's I have played with programmability was never in short supply. Figuring out all the programability they gave you was tough enough.

That said, doing it is still one of the best ways to learn about a new area of technology. I have been kicking around the idea of designing and building an inverter welding machine for a while. It would not replace my commercial machine for a long time, but it would be a heck of a project. I wonder if argon puts out fires as well as CO2? (grin)

Bob

Probably better, but it sure costs a heck of a lot more. It costs me $13 to refill a 20 pound CO2 cylinder but it costs me about $42 to refill a 150 cf argon cylinder, about twice as tall.

Grant

Well, check out eBay item 180144202452, "ALLEN BRADLEY AC DRIVE".

Allen Bradley VFD CAT NO. : 160S-AA04NSF1P1

The manual for it is here:

Check page 14 of it to see that it is a Bulletin 160, single phase input, 240v, 1 HP, open enclosure, analog signal follower, P1 (includes programmer keypad).

It went for $47, the seller charged me $12 for shipping. It would sell for less, if I had ability to snipe at the last second, which I did not because I was with my 1.5 year old after he took a bath. So I placed my last bid 3 minutes before auction end.

Beware that 160-B* drives are 380-460 volts only. You need 160-A*. The letter S after 160 denotes single phase input.

i

Forgot to say, my snipe program did not work at the time due to ebay changes.

i

Some of these drives are for only digital control rather than an analog input. Some come without the programming contol pad on the front. Dont buy the B type drives, thats the ones I use. :)

John

I thought that analog signal means potentiometer? No?

i

Agreed the power stage is the heart of a vfd, i have a variety of mosfets, igbt and scrs to play with. This will be a learning experience, been reading all the available information from the semiconductor manufactures and online textbooks, now i would like to experiment with some of designs i studied and test some of my own ideas.

Best Regards Tom.

Saftey is a main concern, so i will be expermenting at reduced power levels and gradualy step up the power. I did download some schematics from esab for thier inverter welders. Learned a lot from studing thier schematics.

Heres a link to esabs document library:

Best Regards Tom.

They sell special inverter semiconductor blocks for VFDs, with six transistors on one block packaged exactly for this application. They show up regularly on ebay.

I think that microcontroller really is the heart of a VFD, it would not be easy to program.

i

Tom, without any doubt, you should buy a VFD, and a three phase motor, to play with, in order to make your own. Your cost for a very small combo should be negligible compared to the time wasted making guesses that could be easily clarified with an existing drive.

i

Rather than using a microcontroller for experimenting i intend to use one of my old notebook computers, interface it to the power block and write some sofware to controll the power block thru one of computers I/O ports.

Best Regards Tom.

I do have some comercial VFD"s and a couple of 3-Phase motors, and your right comparison is always a good idea. At this time i want to learn thru doing, time and cost are not a factor when have fun.

Best Regards Tom.

Definitely check out International Rectifier. They have a bunch of reference designs and kits for making VFDs in a variety of sizes. These are for both PM and induction motors. The reference designs can be bought with PC boards, but the published data sheets on them have not only schematics but PC board layouts for you to study.

Jon