[OP]
Member
Anyone out there built a transformer system three phase converter? I got the videos from the bay and got a bit overwhelmed at first, but I think it would work for me. I got an old welder I thought I might use, but it wound with aluminum which I wasn't sure of. Right now I'm using a rotary that I made for running my table saw, PM90 lathe and PM87 bandsaw. It's just noisy and a bit of a pain. Any experience?
Contributor
I don't know any way to generate three phase from single phase by using a transformer. If there is some way, I'd appreciate an explanation of how it works from someone who's looked into it.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Member
Paul,
Probably cheaper and much less pain to go the VFD route rather than trying the transformer route even if it is possible.
I agree with Mike let us know if there is a way to generate three phase with a transformer.
David B
[OP]
Member
Basically you are creating a high leg with the transformer and phase shifting with capacitors as I understand. Look up the guys website and try to figure it out from there without getting the dvds. Very scattered presentation, but my brain says it will work like he shows.
Contributor
In an absolute ideal world, the most you could shift with capacitors is 90 degrees - and in the real world it will be much less than that. Three phase has three voltages at 120 degrees to each other.
Also, with capacitors, you'd only get two phases, not three.
It might be possible to get a three phase motor to run on two phases, and two phases that are less than 120 degrees apart, but you're going to sacrifice a substantial amount of power.
As David suggested, why not get a VFD and be done with it. You'll also get speed control. And you know it will work.
Mike
[Your description is very similar to the way a capacitor start single phase motor works. And maybe that's what he's doing - using one winding as the power winding, converting a second winding to a starting winding to get the motor turning, then running on the single winding. You can do that with a three phase motor but what you've done it convert it to a single phase motor. You will lose a substantial amount of power when you do that but I don't remember the mathematics. Maybe one of the other engineers will know. I think it has something to do with the square root of three (divide rated power by square root of three??? or is that only for losing one phase, not two???). Motors never were my strong suit.]
Last edited by Mike Henderson; 02-17-2009 at 6:51 PM.
Go into the world and do well. But more importantly, go into the world and do good.
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Oh come on Mike, I am sure you have heard of this before....it is called "voodoo electronics", and for a limited time, you can get two dolls and an extra set of pins for only $19.95...but we can't do this all day.Originally Posted by Mike Henderson
I apologize to Paul, but I couldn't resist the humor. I am truly sorry, but if you bought this video, you were just fleeced. If it helps, you could report the poster to eBay as being fraudulent.
If you could actually achieve the 90 degrees in the real world (which you can't) you could build an Open Delta, but that is not going to happen anytime soon.
Shame, Shame, Mike.If you have only 2 nodes, then that is just single-phase. If you had two phases of a 3-phase system, then you actually have all three nodes necessary to create 3-phase (which is what an Open Delta is).
It is a common misstatement that people make about static phase converters, and I am just teasing, OK?
[OP]
Member
Don't need speed control - both bandsaw and lathe have variable speed pulleys and the bandsaw also a 2 speed box - not sure what to do with speed control on the tablesaw either. What is the efficiency of the VFD anyway? The rotary should have more than the static system. Can't afford to lose power on a 1.5 hp TS which comes up to speed right now with current system. I just wanted to see if any one really has tried this besides the inventor and the 'testimonials' .
I can't call it a hoax if I haven't tried it yet - right? I'll get on my x-ray glasses and aluminum foil hat and get to work on it right away. (Now if I could get that perpetual motion machine going too --------)
Contributor
I think getting up to speed and having full power are different things, no?
jim
Contributor
You have the BEST solution to running multiple 3ph machines on 1ph power Now! RPC! VFD's must be dedicated to each machine. Build a sound-proof box for your RPC instead of wasting time on untried technology. Finding the *perfect* transformer might be an expensive PITA! Like I always like to say... If it ain't broke, don't fix it.!
[/SIGPIC]Necessisity is the Mother of Invention, But If it Ain't Broke don't Fix It !!
[OP]
Member
More flies in the ointment here==Isn't 220v two hot lines 180 degrees out of phase? If they were in phase I'd think you'd get 0 volts between them. If that is true (now that is an assumption) what phase is the high (208) leg? Meaning if each is 120 out, are the two low legs only 120 out on the 220 circuit? If so, isn't that unbalanced? What is two phase? I'm wondering if my thinking is out of phase here. I'd think you would have to only move two legs 60 degrees off each way.
Where would we be if we didn't 'waste time' on untried technology? Plus I don't want to have that thing running when I'm not using it. Switching on with relays would be the next step I suppose.
Has anyone else looked at Doug Arndt's site?
Contributor
220 is no more multi-phase than 110 is multi-phase (or "out of phase" as you put it). With both (110 and 220), you have two wires that provide the voltage and there's a single sinusoidal voltage across them.
Many people have proposed the canard that 220 is two phase - it absolutely, positively, most definitely, is not. It's just single phase. It's impossible to have more than one phase on two wires (and please don't tell me about the center wire (neutral) - that's just a center tap on the secondary of the transformer and it's not even connected to a 220V load).
Most of us wish we had something other than single phase in our home shops. Alas, it's not to be.
Mike
Last edited by Mike Henderson; 02-18-2009 at 1:41 PM.
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The problem is the use of the word PHASE when talking about the type of power coming into most residences and the type of power a commercial or industry might have (3 PHASE).
I honestly don't know if it is proper to say that either leg of the 240 V signal coming into our homes is "two phase" or not. Certainly, the two signals coming in are 180 degrees out of phase with each other but calling that 2-phase doesn't seem right to my ears.
I suggest this:
(1) 3-wire Single Phase and
(2) 4-wire 3-Phase
...are pretty typical configurations.
In the past, there have been 2-phase systems. But like a 3-phase system, whose coils are 120 degrees out of phase with each other, the 2-phase system had coils 90 degrees out of phase with each other.
There is some great reading here with many links that will carry you elsewhere for deeper understanding.
Paul, I believe this section talks a little bit about why what you are trying to do cannot work. Read the second paragraph, Splitting out.
Contributor
I think some of the confusion is that people only view the "hot" wires as carrying power. Voltage is always in reference to something. That is, in standard single phase house current, the two "hot" wires are 120V in reference to neutral and 240 volts in reference to each other.
Suppose we didn't ground the center tap (the neutral). Maybe then, people would be able to visualize things better. We'd say that the voltage between either of the "outside" wires (outside meaning the two ends of the secondary transformer winding) and the center tap is 120 volts. And the voltage between the two outside wires is 240 volts. All of the wires (and voltages) would be floating referenced to ground. If you measured the voltage from ground to any of the wires, you'd measure zero (if everything was ideal and there was no leakage).
The fact that the center tap is grounded means absolutely nothing as far as voltage and phase is concerned. It's just a safety device.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
[OP]
Member
Yeah 2 phase isn't really right - it just came up and I had to push a button or two. So if I can never get three phase from single phase 220, what are the VFDs doing to the three phase motors they are running? And aren't they just static phase converters? Also I figured that Doug Arndt isn't too concerned about the phase of the setup just balancing the voltages and amps. I need to measure the third leg of my rotary and see how low it is. (yeah, not my third leg-----) The transformer just boosts the voltage where the rotary will not get to. I'm not adverse to winding my own either.
Contributor
A VFD is an electronic device that puts square wave pulses across the three supply wires. The pulses are adjusted so that they give a decent approximation of a sinusoidal wave across each two wires and those sinusoidal waves are 120 degrees apart.
The problem a VFD has when converting from single phase to three phase is that there's always power output in three phase, but the input is oscillating from zero to 240V - so there are times when there's zero voltage in the supply but the VFD has to output power. To do that, the VFD has some large capacitors that store energy. That stored energy is used when the input voltage goes to zero or is less than the output required.
So a VFD converts single phase AC to DC, then creates three phase AC.
An advantage of a VFD for industrial users is that a VFD can have a unity power factor (or really close to it). Industrial users get charged a surcharge if their power factor falls too low so they're starting to use VFDs on their large motors to improve the power factor. Of course, that's a three phase to three phase VFD.
A VFD essentially shields the motor power factor from the line.
You can get three phase from single phase. One way is to do it they way you are now - you use a single phase motor to drive a three phase generator. You convert the single phase power to mechanical power, then convert that mechanical power to three phase AC power. You can use a VFD, which converts single phase AC power to direct current (DC) power, then converts that DC to three phase AC power. There are some other techniques which do not produce clean, balanced three phase power but are good enough to run a three phase motor.
Mike
Last edited by Mike Henderson; 02-19-2009 at 12:07 AM.
Go into the world and do well. But more importantly, go into the world and do good.
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