3 phase converter using a transformer?

There is a guy selling a book on ebay to use a 3 phase transformer to
run as a converter from single phase using capacitors to help start the
motors. Any thoughts on this? Advantages / Disadvantages? I want to run
a 7.5 hp 3 phase compressor motor but the cost to run a 15 hp converter
continually is too much.
Reply to
premier_pgh
Loading thread data ...
If you want to say that you do not want to pay the cost of running the phase converter when the compressor is not running, it is not too hard to rig a system involving one (I think) time delay relay that would start the phase converter, and then start the compressor after, say, 10 seconds, when the pressure switch decides it needs to run the compressor.
Then your phase converter runs only as needed. You can also buy a 5 HP single phase motor and use a smaller pulley.
i
Reply to
Ignoramus16356
The way it works would be that you would use one pole of your compressor's starter to send a signal to the main contactor of the phase converter to start it.
There would also be a contactor on the output side of the phase converter (RPC).
That contactor would be actuated by a time delay on relay, wired to close 10 seconds after the phase converter starts.
This way, the compressor would come up 10 seconds after the phase converter starts. The above assumes that your compressor is the only load. If it is not, it would need another contactor near the compressor motor, turned on by another pole of the pressure switch.
Your expense would be a time delay relay $30, and a pair of contactors -- also $30. A simple solution.
i
Reply to
Ignoramus16356
You don't really understand how rotary converters work. A 15 hp idler motor will consume about 600 watts of power, which is small compared to the 7.5 hp load motor draw.
Jim
Reply to
jim rozen
do not forget that the compressor runs intermittently, but the phase converter would need to run continuously -- unless it is switched on on demand. (which is what I suggested, to run a regular RPC but switch it on demand based on pressure switch, see my another post).
So, 600 watt continuous could even exceed the draw of the compressor on a daily basis.
sosc
i
Reply to
Ignoramus16356
Ah, but based on the comment that his compressor would be running continously, that's not an issue.
Did he make that comment? Nope. But I've found that the quickest way to get a poster to provide more information about the project is to simply make wild guesses about what he's doing. Then everyone including him, every other contributor on this board, and their brothers-in-law, chime in to say I'm wrong.
But at least the details come out that way.
Jim
Reply to
jim rozen
I wonder why the OP is not coming back with more details... Like the planned use of the compressor.
i
Reply to
Ignoramus29795
I have been following the responses here, thanks. But I was more interested in the use of the Transformer to get a 3 phase voltage.
Reply to
premier_pgh
It won't work.
Jim
Reply to
jim rozen
Do you have the item number of that ebay auction that you mentioned?
i
Reply to
Ignoramus29795
I am curious if anyone tried to build a homemade VFD (perhaps without the "V" part), using a rectifier, some way of smoothing the DC, a PWM, and a bunch of mosfets or IGBTs that would create 3 phase output. It seems doable in principle, although I cannot see how it would be superior to a regular rotary phase converter. The only advantages I see is less noise and less idle opwer consumption.
i
Reply to
Ignoramus29795
If someone did there would be another name for it, A welder =)
Reply to
Brent Philion
Iggy-troll sez:
"> I am curious if anyone tried to build a homemade VFD (perhaps without
So Iggy, it seems you must have gotten a new electronic dictionary for Christmas! As usual, you are brimming with buzzwords in new combinations that support the totally inane questions you impose on the good readers of RCM.
And rather than being "curious" (the entree to many of your troll-posts) why don't you try to recall some of the answers you've already gotten from well meaning members of RCM. How many times do you have to be told you aren't going to be able to build a VFD? And, I don't care how sophisticated you'd have us believe you've become as an accomplished "e-bayer", you aren't liable to find the components and instructions (those you could understand) on the construction of a VFD.
Give it up, Iggy-troll. Why don't you go back to your idea of using a a variable frequency square wave generator as the driver/trigger for a VFD of your own design? Give us a rest, already! Why not experiment on that idea, and keep quiet until you have something of substance to report.
Bob Swinney
Reply to
Robert Swinney
Give him a break Bob. At least his ramblings keep him out of hospital dumpsters (:
Reply to
Jim Stewart
I am not sure what made you fume at the mouth so much, Bob.
My inverter was working, until I miswired the snubber circuit and fried the IGBTs. I posted pictures to that effect. I am going to get some parts this week and put it back together in a little bit more compact form (because I will use 400 amp IGBTs instead of paralleling 200 amp ones).
i
Reply to
Ignoramus29795
Actually, as it turns out, VFDs are implemented using pulse width modulation (if you do not know what it is, it is your problem and not mine).
formatting link
``The latest method used for adjusting the motor voltage is called pulse width modulation PWM. With PWM voltage control, the inverter switches are used to divide the quasi-sinusoidal output waveform into a series of narrow voltage pulses and modulate the width of the pulses.''
i
Reply to
Ignoramus29795
Iggy-troll goes:
"> I am not sure what made you fume at the mouth so much, Bob."
Aw Jeeze, Iggy-troll. I just wanted to give you another chance to come back with one of your half-baked retorts; you know, collect one more appearance of seeing your name in print on RCM. That is what you are doing, isn't it?
Bob Swinney
PS: I think you meant "foam" not fume at the mouth. Grammar, spelling and good use of the English language is not the hallmark of an accomplished troll. See, you scored again, when you weren't even trying.
Reply to
Robert Swinney
You are right. It is foam at the mouth. Do you have anything of substance to say?
i
Reply to
Ignoramus29795
I had a lengthy discussion about this several years ago with a professor of electrical engineering (a guy who really knows his stuff when it comes to power electronics). His view was that it was entirely possible, but not a simple project. Areas of concern were acquiring semiconductors and heatsinks which would cope with the power required, minimising the losses, and also the design and calibration of the control system, which is not as simple as it seems because it must reduce the voltage as the frequency is reduced. I decided to build a static phase convertor instead, partly because of the cost of the semiconductors and the doubtful reliability of a home made VFD, and also because I was busy with other things at the time.
Best wishes,
Chris
Reply to
Christopher Tidy
Thanks Christopher. That was interesting. Semiconductors and heatsinks are available these days, but your point on control is a very good one.
i
Reply to
Ignoramus29795

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.