Phase Converter Good Or Bad

[randyc]

It creates unbalanced three-phase: the third leg is not necessarily at the same voltage, and it will have different degrees of phasing to the other two legs (hard to explain without vector diagrams). The phase and voltage of this third leg will also vary with load.

Now this I can understand rather than the concept of a 3-phase motor running on single phase.

This would allow the motor to instantly reverse (and brake, if you reverse, then quickly switch to neutral). despite the phase/voltage imbalance. The imbalance in the artificially created third phase also explains the inefficiency of the conversion process. I'm guessing that phase error is on the order of thirty degrees nominal and that the phase error is mostly responsible for the voltage difference, is that correct ?

Thanks Alan.

 

[Brain Coral]

Thanks Brian.
That looks to actually be affordable.
Do they send good instructions with those kits?

I just can't see why all of the other places want so much for the same thing. They don't even include the motor for the high prices they are charging.

The wiring is really simple and they do send a sheet describing what to do. It's a simple matter of running a new circuit from your panel to the converter... single phase 220v and ground, sizing the wire and breaker according to the instructions. Then, the motor gets wired to the panel with a 3 wire and ground. If you go that route, there's plenty of guys here to help.

Brian

 

[Andre]

Have a kit from WNY supply and a 3ph 5hp motor from C-list. Just waiting to put it together to fire up my surface grinder

Picked up a air compressor form the side of the road, needs a TOTAL rebuild, but I will set it up with a disconnect so when not using the grinder I can use it as a small (and much quieter) air compressor. Then disconnect it when using it as a phase converter, or at least that's the plan anyway.

 

[randyc]

Here is a circuit simulation of what Alan explained. A single phase generator is driving a three-phase load through a phase shift network consisting of two capacitors (the starting capacitor is not shown).




As is apparent from the waveforms, the output IS three-phase, not single phase. As Alan noted, there is a phase and amplitude imbalance. I have no idea if the amount of imbalance shown is typical. The circuit values selected for the simulation were fairly arbitrary and I saw no point in trying to optimize them.

 

[Cactus Farmer]

Please excuse the wordiness (if that's a word at all) , that said, I have an 8-12HP Add-a-phase that is wired to a 10HP very heavy motor(picture two guys lifting it with a tommy bar to the taigate of a 4X4 Dodge PU). This powers all my 3 phase motors in the shop. I was always curious about the wave forms of this "made" third phase. I understand some about how the third phase is generated in the extra windings of the idler motor by the changing magnetic fields of the two other windings. As I looked at this wave diagram they are not in perfect phase but the idler sure allows more work to be done by the 3 phase motor being operated this way. Idid expect them the b chopped up saw tooth wave forms.
My intro to Add-a phase operation was at a shared shop where there was a 3 phase motor on a mill, 1HP as I remember, and the other fellow bought a "phase converter". The mill was weak and spun up to speed slowly. Now ,this fellow was sometimes secetrative and "hid" the instructions to the Add-a-phase. I found them one day and as I read the small pamphlet is implied adding an idler might help the mill run better with an increase in power/work done. There was a 3600rpm 2 HP 3 phase motor laying around so I took it upon myself to wire it in the works. Old whistle britches came in as this was being done and started to complain. I sugested he be quite and help me try something. We put an old wafer switch to work controling the 220 to the Add-a-phase and then rewired the 2HP motor between the mill and AAF. As I turned the switch on the 3600 motor screamed like a banshee as it should running that fast. I then turned the milll on. It ran backwards! Confused I shut it down and began calling electrical pros. Voilla! Two wires were swapped and all was normal again. Now as for increasing power, I was sharpening end mills with a new to me grinder and thought this was the perfect time to test the newly sharpened mills and the power of the old Bridgeport. A 3/4" mill plunged down 3/4" into some mystery metal, probably A-36 plate , and it cut like a cheese. Happy camper,even old fuddy duddy was thrilled. I was building my shop at that time and asked about these Add-a-phase contraptions. Well, an old friend sold his to a fellow I knew and he was moving him operation to a new three phase wired building and no longer needed the 8-12 and the 10HP monster motor. I aquired it and as I was wiring my shop with the help of an experienced elec. helper (he could bend pipe pretty) we wired the lights and 220 around the shop. I then had him do one more run of EMT around the first girt on the building and every 15 feet or so added a "T" with a blank box. We then ran 3 green wires through the EMT and looped it throught the blank boxes. I then wired it to the BIG motor and the Add-a-phase. He is telling me the whole time that this is not going to work, I just kept stripping wire. As the moment came to test, he stood well clear of the building. I flipped the breaker for the 220 and the 10HP started to hum............I then shut it down and wired in my old camelback with the old style open frame motor to the 3 green wires and restarted the 10HP rotary converter. The DP ran like a Swiss watch and I put a sharpened 1 1/2' drill in it and drilled a hole in a trailer hitch that I had built. The old DP has a back gear and power downfeed too, so I just let it work and stood back. The pipe bender was shaking his head saying that this shouldn't work......
sometimes you just have to show 'em that book learning is good but sometimes there are other ways...........life is good on days like this.

 

[randyc]

We want MORE, I love anecdotes like this one !

 

[Alan Douglas]

Yes indeed, an idler motor will help balance the phases.

To get three-phase from single-phase, something has to store energy during the AC cycle and release it out of phase. This can be a capacitor, or the magnetic field of an idler motor.

I'm guessing that phase error is on the order of thirty degrees nominal and that the phase error is mostly responsible for the voltage difference, is that correct ?

Sounds reasonable. Some of the voltage difference is also because the neutral point isn't the same.

 

[Alittlerusty]

First post phase amatic rotary phase converter on my bridgeport purrs nicely , bought mine used on Craigslist for $250 and took about 10 mins to hookup just make sure to not hookup any electronics to the wild leg (generated leg)